Trg Manual For Avr With Maxdna Plc.pdf

OPERATING INSTRUCTIONS FOR DIGITAL AUTOMATIC VOLTAGE REGULATOR

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TABLE OF CONTENTS 1. General Information

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1.1 Purpose of the Operating Instructions

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1.2 Mechanical Structure

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1.3 Design and Schematic Representation

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1.4 Explanatory Notes on the Schematic Diagram

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1.5 Brief description of Excitation Sysem

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2. Power Supply System

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2.1 Principle of primary power supply (/YU101)

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2.2 Power Supply Distribution System

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3. Digital Voltage Regulator, DVR

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3.1 Principle of Operation of the Regulator AVR

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3.2 Basic Structure of the Regulation Processor

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3.3 Operation of AUTOMATIC Channel

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3.4 The MANUAL Channel

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4. Pulse Section

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4.1 Pulse Generation and Amplification

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5. Converter

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5.1 Final Pulse Stages

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5.2 Converter Power Section

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6. Field Current Circuit

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6.1 Exciter Field Circuit-Breaker

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6.2 De-excitation

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7. Monitoring

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7.1 Excitation Monitoring

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8. Binary Controls

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8.1 EXCITER FIELD CIRCUIT-BREAKER ON/OFF

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8.2 EXCITATION ON/OFF

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8.3 CHANNEL-1 ON / CHANNEL-2 ON / CHANNEL-3 ON

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8.4 MANUAL CHANNEL (CHANNEL-3) “RAISE “/”LOWER”

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Warning signals light up whenever the field current set-point is at its minimum or maximum value. If both “RAISE” and “LOWER” commands are issued simultaneously, no adjustment is made in EDN 48-0673-11

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the set point. The field current set-point is preset automatically at the value for no load excitation current (Ifo) whenever the excitation is switched on or generator breaker opens. 39 8.5 AUTO CHANNEL (CHANNEL-1 / CHANNEL-2) “RAISE “/”LOWER”

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8.6 Display of Analog Values

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8.7 Alarms40 8.8 Check-List for Operating Staff

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8.9 Local Operator’s Panel, Exciter Cubicle

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8.10 Micro-Terminal

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9. Preventive Maintenance and Operational Malfunctions

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9.1 Overview

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9.2 Preventive Maintenance and Care

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9.3 Operational Malfunctions and Functional Tests

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10. Installation and Commissioning

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10.1 Installation Site

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10.2 Ambient Air

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10.3 Commissioning

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1. General Information 1.1 Purpose of the Operating Instructions Operating Instructions (OI) for the excitation system describe the most essential functions of the excitation system and provide instructions for its correct operation, installation, and preventive maintenance. They are directed at trained operating staff who have a basic familiarity with electronics. The description basically describes the specific principle of operation of the system supplied. In case of malfunctions, the Operating Instructions aid in quick and directed pinpointing of the fault. Whenever the fault lies within a printed electronic circuit board or another interchangeable module, remove the defective component and replace it with a spare. Troubleshooting and repair within the module itself requires special know-how and the use of special procedures that can only be ensured by the manufacturer. The Operating Instructions also contain suggestions and recommendations for the installation and operation of the unit. They provide recommendations for the basic procedures and the rough scope of testing for initial commissioning. These instructions are, however, not a commissioning manual and are based on the assumption that the commissioning staff possesses special know-how and experience.

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1.2 Mechanical Structure The excitation equipment comprises of Regulation cubicles- REG-1 and REG-2, Thyristor cubicle-TY, Field Suppression cubicle-FS and Transformer cubicle-TR (Refer overall General Arrangement drg.) The Field Suppression cubicle-FS contains components of the Exciter field circuit including the Exciter field circuit-breaker, the De- excitation resistor and Shunts. The converter units TY contain the thyristor bridges and their auxiliary components, firing pulse transformers, thyristor fuses etc. The transformer cubicle TR contains Excitation transformer and PMG (Permanent Magnet Generator) supply isolator. The racks R1 to R5 for binary controls have been placed in REG-1 (Refer scheme sheet YD102 for layout of modules). Rack R6 for binary controls has been placed at the bottom in REG-2. On the back of REG-1 are placed the Terminal blocks for interconnection to these racks R1 to R5. This panel also contains the Power supplies for Binary controls. Input / Output modules provided in Racks R1 to R4 are normally used for binary signal exchange between Regulation circuits and Binary controls. The binary control and signal connections between Regulation & FB / Thyristor cubicles or Regulation to other plant Equipment are made mainly via the input and output modules placed in R5 and R6. Auxiliary relays are provided for driving the breaker / contactor coils and for providing remote potential free contacts where required. An Industrial computer mounted in REG-1 provides the local operator’s control, display and alarm signaling panel. The swing frame containing the electronic tiers (refer to Appendix: /YD101) is mounted on the front of the regulation cubicle REG-2. Other components of the open and closed-loop controls are mounted on the two side walls and the back wall, two UNC 4660 analog input module, transformers, relays, protective switches, signal converters, etc. The view of swing frame (refer to the scheme drg sheet no. arrangement of the electronic equipment.

/YD101) shows the physical

CHANNEL 1 is on the right in tier AA. The left half of the tier AA comprises of modules for Adaptive PSS (Power System Stabiliser) of Channel -1. CHANNEL 2 is on the right in tier AB. The left half of the tier AB comprises of modules for Adaptive PSS (Power System Stabiliser) of Channel -2. Tier AC in Regulation cubicle-2 has a Micro-Terminal useful for communicating with Regulator CPU, for analog values and parameters. Firing pulses are processed in Tier AG and AP which include Pulse intermediate stage, final pulse (amplifier) stages, and the power supply for the Final Pulse Stages. On the back of tiers AA and AB there are bus circuit boards in the upper portion for the standard connections for DVR modules (power supply units, data bus, etc.). Other signal connections specific to the given application are installed in the lower portion of these tiers, using WIREEDN 48-0673-11

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WRAP technology. 9- or 21-conductor (plug-in) system cables are used to interconnect the tiers. 96 pin Harting connectors are provided at DVR racks for signal exchange to and from racks provided for Binary Controls. Tiers AH & AJ have MAXI-TERMI-POINT connections.

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1.3 Design and Schematic Representation

1.3.1 Type Designations for DVR Equipment All apparatuses in swing frame of REG-2 have a type designation that has been shown on the schematic diagram for the excitation equipment and marked on the module itself. Always use this designation when ordering or making inquiries. The following example (Micro-Terminal UNS 2660) will explain the coding system:

DVR (Name: Equipment System) Type of Module

A: Cubicle C: Chassis K: Tier L: Power part S: Special Unit None: Plugs into tier

Series of Numerals Revision Status IMPORTANT: “b,c,...” supersedes “a”, but not vice-versa(=upward compatibility) Sub-classification, Type of Unit: E: Electronic Unit in general G: Casing without Circuit Boards installed P: Plug-in Module Z: Casing with Boards installed Variable Equipment i.e., special equipment of the module for a given standard function (“Spec.” -> adaptation as described in the test/commissioning report IMPORTANT: The variant number on the module used must always be the same as the variant number in the schematic diagram

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Components other than modules such as switches, relays, transformers, etc., have designations and data of their own. The data for ordering these components can be obtained from the list of components for the schematic diagram (/YL001 ...). 1.4 Explanatory Notes on the Schematic Diagram The schematic diagram shows all essential functions of the hardware and software and all electrical connections of the components, including the interconnections for the given excitation system. For purposes of clarity for practical use, all unessential information has been deliberately omitted from the schematic diagram. Such details, generally needed only in special cases, can be obtained from the data sheets for the modules in question. Plantspecific hardware and software settings can be obtained from the test / commissioning report. The schematic diagram comprises the following sections: List of symbols used

/YA006,/YA007

Cable list

/YD003…

Views of the swing frame, Layout of modules

/YD101,2, /YD115

Lists of components

/YL001…

Block diagrams for the system hardware

/YU101…

Block diagrams for the system software

/YU105 AU010…,AU020…etc.

Lists of connections Measurement circuits in general

CE...

Hardware and software for the regulator channels

DE...

Hardware and software for the alarm circuits / operator commands and operation messages

EG...

Hardware and software for monitoring the electronics

EW…

Hardware excitation

the

EY...

Hardware and software for Exciter field circuit breaker

GS...

Hardware and software for power supply in general

GW...

Hardware and software for excitation monitoring and for the converters, including converter controls

GX...

and

software

for protection of

The view of the swing frame /YD101 shows not only the names of the modules but also, usually, a cross-reference to the page of the schematic diagram on which the pertinent connections for the module are to be found. Locations where no entry is made for the type of module but where a cross-reference to the schematic diagram appears are locations left open for standard optional equipment.

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As seen from the examples below, every signal has a signal designation and a diagram crossreference. The signal designation gives the signal a specific and unambiguous name made up of the name of the functional group (e.g., GS020) and the signal code (e.g., XU12). The crossreference to the diagram indicates the page in the schematic diagram on which the associated signal source, or sink, can be found. The signals also form the tag names where they are referred in logic sheets. The signals are also described in plain text where that is helpful. This plain text provides the user with information on the functional characteristics of the signal in question (it is not an identification of the signal!). Different text can be used to designate the same signal at the output and the input. There are often different texts at the signal branching points as well, to explain their specific functions at the signal sinks.

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Signal output from Binary controls

(1)

Schematic diagram number For identification, filing, and reordering the schematic diagrams pertinent to this installation

set

of

(2)

Name of the functional group All the components and functioning parts shown on the given page of the Schematic Diagram are functional components of this group. The listing for a “functional group” can be comprised of one page or several pages.

(3)

Page Number The pages for a given functional group are numbered in ascending order, starting with /YS.... Sheets showing functions of the binary controls start with /YS5.. .

(4)

Processing priority Processing cycle in the processor for the functional block inquestion. Functions with the 1st priority (“1.”)are processed at intervals of 20 ms. Functions with the 2nd and 3rd priorities (“2.”, “3.”) at programmable multiples of this 20 ms interval.

(5)

Block number

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Each block is assigned a number, for unique identification. This also guides the processor for order of execution, within a group and within the priority assigned. (6)

Designation for the signal(Also called as tag) This consists of the functional group name (e.g.,GS020) and the signal code (e.g., XU12). For output signals, the functional group name is normally identical to the designation in the page heading (2). There is a different signal code for each signal within any given functional group. Naturally, the outputs for signal branching (as in the present example) have identical signal codes. In certain cases for convenience of understanding while trouble shooting short forms of texts are also given as tag names.

(7)

Signal cross-reference Designation of the sheet for the signal sink

(8)

Plain text Optional description of the function of the signal.

Signal Input for the Binary controls(Example):

(1)

Plain text Optional description of the origin and signal meanings.

(2)

Signal designation. Consists of the name of the functional group which the signal is coming from or the signal name (tag name) EDN 48-0673-11

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(3)

Signal cross-reference Designation of the sheet for the signal sources. Direct hardware signals on modules (Example): (1)

Location of the module Together with the designation of location in the page heading (in this example, “AA”), this tells where the module is placed (In this example, “AA-29” means swing frame A, Tier A, Location 29).

(2)

WIRE-WRAP Connection The connections marked with a “w” are WIRE-WRAP connections. All connections in Tiers AA, AB without a “w” are connections made via system cables. (refer to the Cable List, Schematic Diagram /YD003…). Note: Connections to and from binary controls are grouped on to free rack connector and connected to the terminals behind racks R1 to R3(maximum up to R6 using Harting connectors.

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1.5 Brief description of Excitation Sysem

The Digital Automatic Voltage Regulator regulates the terminal voltage (and/or the flow of reactive power during parallel operation with other machines or the grid) of the synchronous machine (generator) by direct control of the Main Exciter field current using (static) Thyristor Converter. The Voltage Regulator is intended for the excitation control of generator equipped with Alternator Exciter employing rotating non-controlled rectifiers. The excitation equipment of the Generator and its interconnections with the voltage regulator is shown in the block schematic diagram sheet - YU101. The PMG (Permanent Magnet Generator) as applicable for the project and indicated in block diagram normally provides supply to the thyristor sets. The Excitation system consists of Logic Sequence panel, Regulation panel, Thyristor panel, Field suppression panel and Transformer panel. Regulation part consists of two independent Automatic voltage Regulation channels along with its limiters and PSS for controlling Generator terminal voltage and one independent manual channel for controlling the Exciter field current. Each channel has independent sensing unit, power supply unit, gate control unit and pulse intermediate stage. Excitation of the generator is started by closing the field circuit breaker Q2 and by switching ON Excitation, which leads to releasing of pulses to Thyristor Bridge for the channel in operation. The redundancies provided in the system assure good operating reliability (availability) of the excitation equipment. In case of failure of operating channel automatic transfer of excitation control to standby channel is ensured.

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The Thyristor converter consists of two independent parallel rectifier bridges, both of which are always in service. Even if one block fails the other bridge takes over the full design current of the excitation circuit. Each converter block is provided with its dedicated Pulse Final Stage and conductionmonitoring unit for necessary control and logical operation. In medium rating Thyristor Bridge, each of the arms in the bridge is fitted with a thyristor and a branch fuse. Each device is protected with suitable RC snubber circuit for dV/dt protection of device. The Thyristors are generously dimensioned with respect to voltage and current, thus ensuring a very low failure rate. Redundancy in the regulator section is ensured by means of three independent channels. Channel-1 and Channel-2 are Automatic Channels and Channel-3 is manual channel. Each channel has independent measuring inputs. Auto Channels have limiters & power system stabiliser. Channel 1 and Channel 2 (the AUTOMATIC channels) are built as voltage regulators and either of them can be ON during normal operation. In addition to the voltage regulator, which has a PID control algorithm, these AUTOMATIC channels also contain various limiters and power system stabilisers and corrective control circuits to ensure the use and stable operation of the synchronous machine up to its operating limits. Each of these channels possesses a Gate Control Unit with pulse intermediate stage to generate the firing pulses for the thyristor converter. During normal operation, the Pulse intermediate Stage of the Channel in operation is active and transmits the firing pulses to both the Thyristor Bridge via pulse final stage amplifier and pulse transformer. Various monitoring functions of operative channel initiates an automatic switchover to hot stand by channel in case of a malfunction. When Channel -I is ON, the pulses from Pulse intermediate Stage of Channel-2 and Channel3 are blocked and so on. Under faulty conditions of both Auto channels, automatic bumpless transfer to Manual channel is initiated. Channel 3 is (the Manual channel) built as a field current Regulator. The Manual channel is very useful for the purpose of commissioning & maintenance or under extreme emergency operational requirements,. The excitation can be controlled in Manual channel both from local or remote as desired by the commissioning /operating personnel. Field discharge normally is initiated on shutdown of the generator, or in fault situations by the generator protection equipment. Field discharge commands drive the thyristors set in operation to the maximum negative output voltage (inverter operation) via the gate control sets in operation. In addition to this, a tripping command is given to the main Exciter Field Breaker. The field breaker connects a discharge resistor across the field of the main exciter for effective field suppression. Automatic follow up of channels ensures that the standby channel always generates the same control variable as the operative channel under steady-state operation. . This ensures smooth switchover from active channel to standby channel. To ensure that the stand by Channel will, in case of a switch-over initiated by a malfunction in the operating Channel, take over without disturbing the operating point of the machine as it was prior to the problem, the response of the tracking for the channels is set relatively slow.

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The sequence of Automatic changeover: CH.3 (Manual) CH.1(Auto)  CH-2 (Auto)  CH.3 (Manual) In addition to voltage regulation the Auto channel is also capable of performing the following functions and is designed and set at works as per the project specific requirement. The functions/features possible in Channel-1 / Channel-2 are: Reactive droop / drop Decreases / increases the excitation proportional to compensation the Generator reactive current. Soft start Enables gradual build up of Generator terminal voltage to preset value in both channels depending on the set time. V / Hz Limiter Reduces excitation with a delay whenever set V/Hz ratio has been exceed to prevent saturation effect in Generator or Generator Transformer. Maximum Field Current Reduces excitation with a delay whenever set Limiter. maximum excitation (exciter field / Gen rotor) current limit has been exceeded. Inductive Stator Current Reduces excitation with a delay whenever set Limiter maximum Generator Stator current limit has been exceeded in the lagging zone of the machine capability. Capacitive Stator Current Increases excitation whenever set max. Generator Limiter stator current limit has been exceeded in the leading Zone of the machine capability. Load Angle Limiter Whenever the load angle increases beyond the set value, the limiter increases the excitation to reduce the load angle. Power System Stabilizer Influences the voltage regulator to dampen low (PSS) frequency active power oscillations.

In addition to the Regulator Systems, the Digital Automatic Voltage Regulator is provided with redundant BINARY CONTROLS SYSTEMS, PLC-1and PLC-2, realised using maxDNA architecture. Each PLC unit is provided with a DPU (Distributed Processing Unit) along with its dedicated set of Analog/digital Input/ Output modules housed in Racks of Regulation cubicle-1 (REG-1) and Regulation Cubicle-2 (REG-2). Modules housed in Racks R1, R3 and R5 of REG-1 are dedicated for PLC-1 and those modules pertaining to Racks R2, R4 in REG1 and R6 in REG-2 are dedicated for PLC-2. Each PLC unit is capable of complete control processing and initiating logical operation as per the system requirement. Redundancy in PLC unit ensures that at any instant of time only one of the PLC units is in operation while the other unit is in hot stand by state. In case of failure of operating PLC (failure of DPU or I/O modules) the entire logic control is automatically transferred to the stand by PLC unit. Any one of the redundant PLC-1/PLC-2 has the capability to act as master for realising the necessary complete logical / binary controls of the Excitation System. The logical functions being performed in each PLC’s are 1. Exciter Breaker ON / OFF controls. EDN 48-0673-11

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2. Excitation ON/OFF controls. 3. Channel 1 / Channel 2 / Channel 3 change over controls. 4. Excitation Raise / Lower controls for each of the channels In addition to Binary controls, monitoring of PT voltage & Field current as well as follow-up function are also implemented in PLC-1 & PLC-2 independently. The most important monitoring inputs for the excitation system as field currents (If) & Generator voltage (Ug) are redundant (2-fold). These inputs are checked for discrepancy and plausibility. An alarm is always initiated in case of malfunction in field current if the value is below the acceptable minimum limits while in Auto channel. In case of malfunction of “If”, tripping of the unit is initiated if Manual channel is in operation. A switch over to stand by regulating channel, if permitted, is also initiated in the case of failure of PT signal to the regulator. For ease of trouble shooting/ commissioning at site a local Operator Work Station is provided in the Regulation cubicle-1 for issuing various commands to the regulator, such as -- LOCAL / REMOTE operation selection. -- EXCITER FIELD BREAKER ON / OFF. -- EXCITATION ON /OFF. -- CHANNEL-1 / CHANNEL -2 / CHANNEL -3 selection. -- CHANNEL -1 RAISE / LOWER -- CHANNEL -2 RAISE / LOWER -- CHANNEL -3 RAISE / LOWER -- ALARM ACKNOWLEDGE / RESET. -- FIELD FORCING LIMITED. --DOOR MOUNTED INDICATING LAMPS / MONITORING UNITS IN THRISTOR PANEL -- LAMP AVR FAULTY -- THY-1 CONDUCTION MONITORING UNIT. -- THY-2 CONDUCTION MONITORING UNIT. --DOOR MOUNTED INDICATING LAMPS / METERS IN FIELD SUPPRESSION PANEL -- LAMP STATION DC SUPPLY HEALTHY -- DC VOLTMETER (INDICATION EXCITER FIELD VOLTAGE) -- DC AMMETER (INDICATION EXCITER FIELD CURRENT)

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2.1 Principle of primary power supply (/YU101) In this Brushless excitation system, the PMG provides the power supply for the converter. A station battery supply is absolutely necessary for the control of the field circuit breaker. Two power supply interface units are provided. Each one is supplied from Station DC battery Feeder and from the nominal AC input, i.e., PMG supply through a transformer. The AC voltage rectified is connected to the DC battery voltage in the power supply interface units through the de-coupling diodes and noise suppression filters for forming independent DC supply bus. The paralleled output from power supply interface units, feeds the dedicated rack mounted Power supply unit of each of the regulating Channels (CH-1, CH-2 and CH-3) through miniature circuit breakers. When two feeders of Station DC battery are extended up to AVR panel, the DC input of the two, power supply interface units shall be from, two different feeders. The two synchronous voltages Usyn1 and Usyn2 are derived from the AC input supply to the thyristor bridges via transformers T3 and T4. Channel-1 is supplied from Usyn1. Channel-2 and 3 are supplied from Usyn2. The Gate Control Units need these voltages to enable them to issue the pulses at a given firing angle relative to the input voltage of the converter. For testing, the two synchronous voltages can be switched over to an auxiliary power supply while the generator is at a standstill (T3, T4) using switch –S20. The electronic equipment and the Gate Control Unit circuits can then be tested while at standstill. Normal operation of the unit using Test Supply is not permitted. Single phase AC supply required for tier fans FN -1 and FN –2, panel illumination and anti condensation heater circuits are derived from Station Illumination Supply. 2.2 Power Supply Distribution System refer to block diagram (/YU101) Regulation Channel-1 and Channel-2 are powered from the output of separate power supply interface units (UNC 4664) G01 and G02 respectively. The output from power supply interface units G01 & G02 feed the rack mounted DC /DC converter Power supply units (AA37/AB37) of regulating Channel 1 & Channel 2 respectively through miniatures circuit breakers. The electronic modules for Channel-1, Channel-2 and Channel-3 are each supplied exclusively from their own dedicated rack mounted Power supply units with electrical isolation between input and the output. These power supply units can function within a input voltage range of 75% to 140% of rated input voltage. All output voltages (+5V; 15V and +24V) are directly or indirectly monitored for under / over voltage. An event of disturbance in voltage level is signaled by a fault signal while at the same time the output current is reduced and the power supply unit shuts down. 24 VDC System Power Supply (SPS) and Field Power Supply (FPS) required for powering independent PLC-1 & PLC-2 are each derived using redundant DC/DC converters (100% redundancy) which can accept a wide range of input voltage and are powered through miniature circuit breaker from output of power supply interface units.

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System Power supply is used for powering modules in PLC (max DNA) racks. Field power supply is used as interrogation voltage for binary inputs available as potential free contacts for driving output auxiliary relays.

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3. Digital Voltage Regulator, DVR 3.1 Principle of Operation of the Regulator AVR To regulate the voltage and the reactive power of a synchronous machine, the field voltage must be adjusted quickly to the changes in the operating conditions (with a response time that does not exceed a few ms). To accomplish this, analog control systems include amplifiers, which make continuous comparison of the actual values against the reference values and vary the control variable to the converter with almost no delay. Most of the delay that occurs originates in the converter, since the firing pulses for changing the rectifier phase angle are only issued periodically (every 2.8 or 3.3 ms). The DVR Digital Voltage Regulator calculates the control variable from the measured and reference data in very short time intervals. This results outwardly in a quasi-continuous behavior with a negligible delay time (as in an analog regulator). The calculations are made in the binary number system. Analog measurement signals, such as those for generator voltage and generator current, are converted into binary signals in analog/digital converters. The set-points and limit values have already been defined in digital (binary) form. An understanding of the actual computation processes in the digital voltage regulator is not necessary for operation, preventive maintenance or troubleshooting. Like the operator of a pocket calculator or a personal computer, all the operator needs is to know how to operate the instrument and the programming for this working tool. For that reason, we will explain below only the principle division of work among the various modules and the flow of data processing. The purpose is, above all, to make clear how the processor system has been integrated into the rest of the power electronics system. 3.2 Basic Structure of the Regulation Processor refer to block diagram (/YD101) There are 3 channels for performing the regulation function. Channel-1 and Channel-2 are auto channels and function as a closed loop generator voltage regulator. Channel-3, acts as manual channel and functions as an open loop field current regulator. Acquisition of Input signals: The actual values Generator Voltage, Generator current, Field Current and Synchronizing Voltage measured are processed in a separate UNC 4660 peripheral unit for each channel. These peripheral units are used for preprocessing signals from external measurement circuits, i.e., for galvanic isolation and adaptation to the electronics level. The binary input signals required (For example, FB is ON/OFF, GCB is ON/OFF, Pulse block ON/OFF etc.) for the Regulation processor is provided by the Digital Output modules in Binary Control system in Regulation cubicle REG-1. Similarly, the binary output signals (For example, Various limiters in operation, Ref value Max/Min, DC short circuit etc.) from the

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Regulation processor are passed on to the Digital Input modules in Binary Control system in Regulation cubicle REG-1. Auto mode of operation: The most important input parameters to the AUTOMATIC mode are the generator voltage Ug, the generator current Ig, the field current If, and the synchronous voltage Usyn. From the UNC 4660 peripheral unit, Ug, Ig, and Usyn are sent to the UN 0661 Interrupt Generator (plugin module on the processor bus) for filtering and further processing. The UN 0661 Interrupt Generator also uses the 3-phase Ug signal to generate the 12 interrupts per period to trigger the cycles for processing actual values in the processor while in Auto mode. Synchronized with these interrupts (i.e., with the phase positions of generator voltage Ug) this processor measures the generator current Ig, and then calculates the reactive current (I. sin) and the active current (I. cos). With these two results, the processor is then able to derive further operating parameters, such as the load angle, the active power, etc. The processed analog signals are converted to Digital Signals (by UN0610) for processing by CPU module (UN0660) using software (firmware). The functions of Voltage Regulation, Limiters, Power System Stabiliser etc. have been accomplished in firmware. The non-varying standard software function modules can be configured to the design desired, for plant-specific purposes, using software switches (KFlags). Thus, for example, the stored status of a K-Flag determines whether or not a limiter is active, and whether the de-excitation or the excitation limiters take precedence. Because these K-flags determine the software Scope of Supply for the installation, they cannot be changed permanently via the Micro-Terminal. In this way, they differ from such setting data as the values of the parameters for the PID filter of the voltage regulator or the set points for the limiters. These values can be permanently changed using the Micro-Terminal. Communication is possible, with each of the UN 0660 processor systems, via the MicroTerminal by plugging on the connecting cable. In this way, signals within the processor, set parameters, analog signals can be viewed and the set parameters can be altered temporarily (F... range) or permanently (C... range). The control voltage output from the voltage regulator (in the AUTOMATIC channel) is processed in UN 0663 Gate Control Unit and formed into a chain of pulses at the appropriate firing angle. The pulses of the active channel are directed to the pulse bus via the associated UN 0096 Intermediate Pulse Stage. The pulses for each converter block are routed through UN 0809 Final Pulse Stage, to fire the thyristors. 3.3 Operation of AUTOMATIC Channel refer to block diagram (/YU105)

3.3.1 General Information The functions of the automatic voltage regulator AVR are: 

to regulate the generator voltage



to regulate the effect of reactive and/or active current on the voltage (droops) EDN 48-0673-11

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

to limit Volt/Hz



to limit max. field current



to limit inductive stator current



to limit capacitive stator current



to limit the load angle



to stabilize the power system

Block Diagram /YU105 shows the software structure of the AUTOMATIC channel (Channel-1 or Channel-2). The generator limiters not provided for the installation in question (optional equipment) are identified in this overview as “Not Supplied.” The parameter values, signal values, and software switches (flags) marked with addresses (hexadecimal numbers) can be viewed and altered via the Micro-Terminal (refer also to Sect. The values selected are displayed in %, sec, p.u., Hz, etc. and can, where necessary, be changed directly in these formats. The plant-specific settings of the variables and the flags can be obtained from the Test and Commissioning Report. This block diagram provides the information about the important functions and possible settings of the AUTOMATIC channel. For the sake of clarity, no detailed presentation has been given of special functions such as tracking circuits, initializations, etc. Binary signals are shown in broken lines, analog signals in solid lines. The corresponding text designations in the schematic diagram can be used for identification of the input signals (hardware inputs). The only analog output signal from the automatic voltage regulator, control variable Ucontr, is sent via the data bus (CRU bus) to the Gate Control Unit (refer to Data Sheet). Most of the binary messages (outputs) from the AVR are of no interest functionally and they have been omitted for the sake of clarity. The basic structure of the digital voltage regulator and the limiters is simple. This is necessary in order that the behavior of the regulators/limiters will remain calculable and understandable in all operating situations and that there will be no problem in adjusting and optimizing them. The central PID filter in the digital voltage regulator defines the dynamic response of the closed-loop controls both in the voltage regulator mode and after limiters have intervened. The “control deviation” at the input to the PID filter is the control deviation for voltage, the control deviation of a de-excitation limiter (the value determined by minimum value selection), or the control deviation of an excitation limiter (the value determined by maximum value selection). Flag F730 (“PRIOR”) is used to determine whether the exciting (Min. value) or the de-exciting signal takes precedence on the min/max value limiter (normally: F730 = 1111, i.e., the de-exciting signal takes precedence). With the exception of the Minimum Field Current Limiter, all other limiters have variable factoring multipliers of the signal outputs so that they can be adjusted individually together with the common PID filter, which has been optimized for voltage regulation. The setting parameters for this PID filter are as follows: Vo

=

KR

Static amplification

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Ta

1 = ---Tc1

Vp Tb

Integration time constant Proportional amplification

=

1 ----

Differential time constant

Tc2 V

Amplification of high frequencies

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The BODE diagram below shows the assignment of settings in accordance with DIN/IEC standards based on a typical example:

The PID filter amplifications Vo, Vp, and V can be adjusted in p.u. values. But the “ceiling factor” Vp1 must be adjusted correctly with parameter F310 if the total amplification (circuit amplification) of the control circuit is actually to conform to this p.u. setting. This factor must agree with the “external” amplification, i.e., with the ceiling value of the transformer / converter circuit: Ufmax Vp1 = ------Ufo in which

Ufmax = ceiling field voltage Ufo = no-load field voltage

To attain a suitable response of the AVR when starting excitation (“EXCITATION ON”), it may be necessary to change the proportional amplification of the regulator during this phase. Vp2 (transiently activated) and Vp1 (permanently activated) can be adjusted for this purpose. For example, the value of Vp2 takes effect immediately once the excitation is switched on and remains effective for a period as set at F30C. Once the period F30C (e.g., 5 sec) has expired, Vp shifts over to Vp1 (becomes the steady-state Vp) at the rate of change set on F30E.

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The standard operating mode for the PID filter is voltage regulation, for which the discrepancy between the voltage set-point (F270) and the current value for generator voltage Ug (F90A) (the control deviation) is supplied at the input. To compensate for the voltage drop in the Generator transformer, or whenever several generators are operating to the same distributing bus, the generator voltage must be varied in proportion to the measured generator current (droop influence). To accomplish this, the voltage set-point is varied as a function of the measured reactive current IX and/or active current IR. Flag F712 enables the IX droop, Flag F710 the IR droop. The desired compensation is set in F282 and F286 respectively. Flags F284 and F288 are used to select whether this droop influence is to increase the voltage or to reduce it (compensation). Combined influence of the active and reactive currents is attained by enabling both droops, IX and IR. Flag F716 activates a so-called “Soft-Start” at the starting of excitation. This “Soft-Start” ensures that the voltage set-point integrates from 0% to 100% within the time set on F290 when the excitation is switched on (“EXCITATION ON”). A “smooth” excitation of the generator can be achieved in this way whenever there is no demand for a quick excitation.

3.3.2 Switch-Off Criterion for Field Flashing / Ug > X% & / or If > Y% The Firmware of the channels supplies the criterion for switching off the field flashing. Whether this criterion is activated based on the actual value for generator voltage Ug or for field current If, or both, depends on the settings of the two threshold values F2A0 / F2A2 (0% setting means that the output is always “logical 1”). Whenever Flag F72A is not activated, the binary output is fixed at “logical 1”. This criterion is used basically for Field flashing switch OFF in Static Excitation Equipment (Direct Excitation), the signal can be used for any other application like, permission of Conduction monitoring or permission to Auto synchroniser etc.

3.3.3 Voltage Set-Point Various signals and settings control and limit the voltage set-point F270. For example, the values of F254 and F252 define the normal operating range possible for set-point adjustment (e.g., 90 ... 110%) using external control commands (control room, local operator’s panel, superposed control system). The effective set-point adjustment rate is governed by parameters F258/F25A. The set-point can be set at the values of F250 and F256 by activating appropriate control commands (“SET” input). Enabling Flag F71A and activating a binary input prior to switching on the excitation (“EXCITATION OFF”) sets the Ug set-point at the value of UAUX. This makes it possible, for example, to ensure that the generator voltage will agree exactly with the network voltage after the voltage build-up. An external value with variable amplification (F520) can be added to the Ug set-point by enabling F724 (for example, for stability tests).

3.3.4 Regulator Tracking in MANUAL Operation Whenever the AUTOMATIC channels are not in operation (the MANUAL channel is ON), “follow-up” equipment ensues a smooth switch-back to the AUTOMATIC channel will always be possible. To track, the voltage set-point is shifted by means of RAISE/LOWER pulses, from the UN0663 Gate Control Unit (refer to data sheet of UN0663), so that control variable EDN 48-0673-11

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Ucontr at the output from the PID filter, is held steady and identical to the control variable Ucontr from the MANUAL channel.The tracking must react slowly. But, the resultant transient control deviations, resulting from the amplification in the PID filter might cause severe interference with control variable Ucontr. To prevent this, the follow up equipment intervenes on the regulator’s mixing point with a corresponding compensation signal.

3.3.5 Ug/f Limiter At under frequency, the Ug/f Limiter reduces the generator voltage so as to prevent saturation effects in the supply and measuring transformers. To adjust this limiter, the max. permissible generator voltage at rated frequency is defined and set using parameter F280. When any under-frequency occurs, the generator voltage is thus reduced in proportion to that setting. An appropriate adjustment on parameter F28E is used to achieve a delayed intervention of the Ug/f Limiter.

3.3.6 Field Current Minimum Limiter The Field Current Minimum Limiter maintains the field current at a preset minimum level. Normally the minimum level is defined by the minimum current of the converter (Holding current of thyristors). Parameter F410 defines the adjusted minimum value. F758 is the enable flag for this limiter function.

3.3.7 Field Current Maximum Limiter The Field Current Maximum Limiter is provided to protect the generator rotor from over currents occurring in steady-state and transient operation. High field currents are normally the result of a sharp drop in network voltage, or of an improper raising of the voltage set-point by the operating staff. The field current is held steady at the value TH1, i.e., at the maximum thermal value permissible for the excitation circuit and the rotor. In order that the generator can support the power network with its transient overload capacity during brief collapses in voltage, a temporary switch-over is made to the transient over current limit MAX1 (a higher setting). When the generator or the converter is operating at a reduced capacity, these limits TH1/MAX1 can be switched over to the lower settings TH2/MAX2 by activating the corresponding binary signals. The switch-over from the thermal limit TH1/2 to the transient over current limit MAX1/2 can be configured in one of three ways:

a) Depending on the overcurrent, with -dU/dt ENABLE Flag programming: F418 = any setting desired ; F41A = 0000. This variant enables the transient overcurrent value MAX1/2 whenever a collapse of voltage in the network is detected. The ENABLE time is fixed, and can be set using parameter F408. Parameter F40C defines the limiting gradient for detection of the collapse -dU/dt. The example below shows the typical behavior of the limiter configured in this way:

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b) Dependent on the over current time integral, with -dU/dt ENABLE: Flag programming: F418 = inactive; F41A = 1111. This variant likewise enables the transient over current value only when a collapse of network voltage has been detected. However, the switch-back to the thermal limit is not made dependent upon the time itself, but on the calculated time integral i²dt of the over current. Parameter F416 can be used to set the maximum i²dt for the overcurrent in p.u. The setting on Parameter F414 in s/p.u., takes into account the time the rotor needs to cool down, i.e., the rate of temperature change in the case of intermittent over current operation. The example below shows how the timing of the switch-back to the thermal limit depends on the present value for over current i²dt: The overcurrent time integral is based on the formula:

=  i2 dt =

If ------------0.9 IfTh

2

-1

.t

Example: The setting of i²dt equivalent to Version a (F416) at a constant 1.6 times the nominal field current for 10 seconds (with TH1/2 = 105%) is:

(1.6 / (0.9 * 1.05)

2

- 1)

* 10 = 18.7 p.u.

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c) Dependent on the overcurrent time integral, without any preconditions Flag programming :F418 = 1111 ; F41A = 1111 In this variant, the transient over current becomes available without any prior conditions (without a -dU/dt ENABLE) with the time integral i²dt.

3.3.8 Inductive Stator Current Limiter The Inductive Stator Current Limiter holds the stator current Ig within permissible limits while the generator is in the “over-excited” operating range by reducing the field current accordingly. The setting TH (thermal limit) provides the limit against stationary over currents that might occur. To take advantage of the generator’s transient overload capacity, a switch-over is made to the higher setting MAX. The principle of operation of this switch-over to the value MAX, permissible only transiently, is identical to that employed for the field current limiter (refer to the description above). When the drive output from the turbine is very high, stator current may exceed permissible limits even while inductive loading of the generator is low. In this case, if the stator current limiter is not kept from influencing the field current, the control circuit will oscillate back and forth between the Inductive Stator Current Limiter (de-exciting) and the Capacitive Stator Current Limiter (exciting). Parameter F43C is used to set a function, which will block the stator

current limiter when the reactive current I is low. The output signal of that function then dominates the control variable of the Ig-dependent limiter via a maximum value selection.

3.3.9 Capacitive Stator Current Limiter The Capacitive Stator Current Limiter holds the stator current Ig within permissible limits while the generator is in the “under-excited” operating range by increasing the field current as required. The positive behavior of this limiter (build-up of excitation) is due to the way in which EDN 48-0673-11

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the synchronous generator behaves in the under-excited operating range. In order to reduce the generator current Ig (less -Ix), the generator calls for an increase in the field current (refer also below: “Power Chart”). To prevent fluctuations when the reactive current Ix is low (as described above with regard to the Inductive Stator Current Limiter), this limiter also possesses a function that can influence the Ig-dependent control variable. This adjusted value for this function (F43C) is the same as that for the inductive stator current limiter.

3.3.10 Load Angle Limiter The Load Angle Limiter prevents the synchronous machine from slipping out of phase due to slippage of the rotor. The load angle , the difference in phase between the rotor and the stator rotating field, results mainly from the driving torque (active power P) acting on the generator and the level of rotor current (field current). If the driving torque remains constant, an increase in the field current reduces the load angle ‘’. The current load angle  at any moment is obtained from the generator current and generator voltage based on a simplified model of the generator. Whenever this calculated load angle  (F886) exceeds the preset limit angle (F4A0), the limiter increases the field current until the load angle has dropped back to its permissible value. The quadrature reactance, Xq of the generator (F4A4) and the network reactance, Xe (F4A6) during normal operation must be adjusted on the regulator in order to obtain the load angle ‘’. The graph below shows the Power Chart for a salient-pole machine with typical limiter characteristics:

3.3.11 Power System Stabilizer The purpose of a Power System Stabilizer is to use the generator excitation to damp electromechanical oscillations between the network and the generator. Depending on the

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design of the generator and the requirements imposed for network stability, its main function will be either to damp the oscillations originating in the machine or those from the network. A synchronous generator working in a combined power network is, in principle, an oscillating structure. In order to produce a torque, the magnetic field of the rotor and the stator must form a given angle (referred to as the rotor displacement or load angle ‘’). The electrical torque ME increases as the angle  increases, just as with a torsion spring. Because the ME of the generator and the mechanical driving torque MA from the turbine are in equilibrium during steady-state operation, the angle  remains in a given position. Whenever this state of equilibrium between MA and ME is disturbed, the load angle slips of this rest position, and changes thereby the electrical torque ME. The torque attempts to restore the load angle to a stationary position. Due to the mass inertia of the turbine/generator rotor, however, this can only take place aperiodically. It does so in the form of more or less effectively damped oscillations (again similar to the effect of mass inertia on a torsion spring). In order to damp the oscillations, there must be a damping torque produced depending not on the electrical torque ME associated with the angle, but on the difference in frequency (f) between the rotor and the stator rotating field, i.e., on the slippage. This torque is produced, mainly by the so-called damper winding in the rotor, but the dimensioning of damper winding is subject to limits imposed by considerations of design and economy. Some further action is therefore needed to increase the damping effect. The following drastically simplified formula shows the parameters upon which the amount of active power PE supplied by the generator depends: PE = active power . U f g --------- . sin  I

PE =

Xd

I

f

= field current

U

= terminal voltage g Xd = direct-axis reactance  = load angle

It can be seen from the above relationship that the active power that the generator transfers depends not only on the load angle , but also on the field current If. This means that, a transient change can be made in the active power PE and with that in the effective electrical torque ME by varying the field current. The principle of operation of the DVR Power System Stabilizer becomes clear from a consideration of the oscillations in power output and frequency (PE, f) and the vector diagram:

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If it is assumed, that oscillations in the network frequency generates load oscillations with the mass inertia of the rotor, then the active load of the generator (e.g. MW-measured) is influenced with a sinusoidal value -PE (ME-MA = -PE). By inversion of -PE, one obtains the fluctuation in power provided by the rotor, +PE. As is known, the slip signal f follows +PE with a phase delayed by 90°. The +ME produced by the periodic changes in the load angle  is in phase with +PE. A good damping is attained if ME is varied in phase with the slip f. However, this signal must also be advanced somewhat to compensate for the time constants in the excitation circuit and the generator. As mentioned above, the electrical torque ME can be influenced by varying the field current. To accomplish this, a suitable control signal, referred to as variable disturbance compensation, must be imposed upon the voltage set-point or the converter control variable Ucontr. As can be seen from the vector diagram, by applying proper weighting factors (K1, K2), and then adding together the signals -PE and f, an overall stabilization signal can be produced that rotates in advance of the f signal by any angle desired between 0° and 90°. Because the amplitude of -PE remains proportional to the amplitude of f, a constant angle in advance of f results for the compensation of the time constants referred to above. The optimum weighting factors K1 and K2 for a synchronous generator working to a power network depend on its operating point at any moment and the external reactance of the network. Normally, the selection of a compromise setting is good enough to attain stability in all operating points and for all external reactance. For special demands, these settings must be parameterized as a function of the external reactance (which means, optional equipment: Xe-Identification). The BHEL-EDN computer program HE038 is used to calculate optimum values for K1 and K2 based on the generator data and the network reactance. The Power System Stabilizer PSS is a section of the AVR computer program (see Block Diagram /YU105) and is processed once per network cycle. The voltage at the generator terminals and the generator current are measured in order to define the signals PE and f. The calculated signals for P (=PE) and f are then sent across DC filters “D” (real

differentiators) that transmit only the dynamic portion of the signals. The PE and f signals obtained in this way are then weighted (multiplied by) with the factors K1 (F330) and K2 (F332) and sent to the summing point of the voltage regulator.

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To satisfy BHEL-EDN computer program HE038 for calculating the parameters K1 and K2, the polarity of the f signal is selected automatically according to the status of Flag F732 (The digital voltage regulator has a non-inverting PID filter instead of inverting PID filter of analog controllers). The PSS stabilization signal is imposed on the automatic voltage regulator only if the following prerequisites are met: 

Generator on line



Generator power output > the value F338



Generator voltage in a range between F33C and F33A

The stabilization signal is limited at the output from the PSS to the lower and upper limits of F336/F334. Flag F732 defines whether the stabilization signal is introduced before or after the PID filter (usually before the filter). Because the PID filter, as noted above (refer to Sect. 3.3 ) already takes the ceiling factor Vp1 into account, the PSS signal needs to be multiplied by Vp1 if it is added to the voltage regulator following the PID filter (divider at the input to the min/max limiter). If the signal “MECH LOAD” (from the turbine) is available, this parameter can be imposed on the electrical load signal P by activating Flag F736. This precaution prevents the DC filter “D” in the P-channel from producing an unnecessary “stabilization” effect in the case of rapid changes in turbine load. As an alternative for the AVR’s Power System Stabilizer, a stabilization signal from an outside system can be imposed by activating the binary input “PSS-SIGN.EXT.” Flag F340 can be used to select between an analog and a 12-bit signal, and F33E to select the polarity desired for that signal.

3.3.12 Slip- stabilizing adapter The memory subdivisions in the PSS adapter are similar to those in the voltage regulator. Block I contains the operating program for the PSS adapter. Block II contains an EPROM with the configuration. Block III is not occupied. Block IV has an EEPROM where the precalculated weighting factors are tabulated. The addresses for these factors are given in the attached Report of settings. Finally, Block V contains the RAM. The following will be a brief description of the function of the PSS Adapter. As we already know, the slip stabilizing signal is formed from the sum of two other signals namely the generator active–power signal and the generator frequency signal. The amplification and the mixing ration for the two signals are referred to as the weighting. The stability of a synchronous machine operating on a network depends on the operating point of the machine and on the external reactance. Usually a compromise weighting can be selected to cover all operating points, together with the expected external reactances. This value is set in the slip stabilizing system, and results in satisfactory damping at all operating points.

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If, however, the network conditions do not permit the use of a compromise setting, the PSS adapter provides a solution. The complete operating range (power chart) of the machine is divided into six operating sub – ranges. Then, using computer program HE 038, the weighting factors are determined for the six sub – ranges and for three different (expected) external reactances Xe. Thus we have a total of 18 operating sub – ranges under consideration. For each of these

sub-ranges, the optimum weighting factors are determined and are stored in a table of parameters in the EEPROM. The power and frequency signals, of course, have to be weighted separately, so a total of 36 values are stored. From there, the values are issued to the voltage regulator as 2 x 6 – bit signals which are next multiplied by the basic weighting factors which have been set. The basic weighting factors in the voltage regulator can be modified, in 64 steps ( 6 bit ), by a factor between 0 and 4. The task of the PSS adapter is now to assess the operating point of the machine and the instantaneous value of the external reactance. Once this has been done, the corresponding weighting factors are read from the stored table and are transferred to the voltage regulator. The operating point of the machine is determined from the measurement of Iactive and Ireactive. Measurement of the external reactance Xe is more complicated. When determining Xe, it is assumed that the voltage at the network center is constant. If there is now an oscillation in the active power, then the value of angle also oscillates. As UN

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is constant, the phase angle of the generator voltage will thus oscillate about the value e. From this brief consideration, it can already be seen that identification of Xe can be made only during transient processes. The value e is measured by comparing the generator phase angle with a constant –frequency signal. Finally, the system calculates how large the e for the oscillation which is present most be in order to yield the three preset values of Xe. After this, a comparison is made to see which of the three calculated values of e comes closest to the measured value. The “best” value is selected, and this determines the corresponding weightings to be used. When the transient dynamics have decayed, and after a subsequent delay time which is stored at address C3C0, the weighting is reduced by one step. If the maximum Xe has already been identified, then after another delay period there is another reduction of one step. In other words: in steady-state operation, the slip stabilizing works with the lowest weighting, and thus the maintenance of constant voltage takes priority. If, in steady-state operation, the oscillations exceed the value set at address C3C4, the weighting is raised one step. During the time delay which is set at address C3C2, there is no further monitoring of the oscillation at steady state. This is to prevent automatic switching to the maximum weighting when there is oscillation in steady-state operation. As with the voltage regulator, the WRITEFLAG is set whenever a parameter is changed with the microterminal. During execution of the program, there is a cyclic comparison of the parameters filed in the EEPROM with those in the RAM, and a comparison of the configuration flag in the user program with the corresponding values in the RAM. When a deviation occurs, the WRITEFLAG is set. Depending on which comparison has detected the fault, either a parameter fail flag is set at address FF00 or a K-PROM-fail flag at address FF04. Address

Description

Meaning of status

FF00

Parameter Fail Falg

FFFF=fault 0000= No fault

FF02

Address at which fault found

FF04

K-PROM-fail flag

FFFF = fault 0000=No fault

FF06

Address at which fault found

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3.4 The MANUAL Channel

3.4.1 Summary The independent MANUAL channel (Channel 3) has been built as a simple field current regulator without additional limiters. Its main function is to maintain the excitation of the generator even if the AUTOMATIC channel becomes non-operational. The MANUAL channel also performs valuable service for purposes of testing, commissioning, and preventive maintenance. In a Manual channel, measurements, regulator, generation of firing pulses, and power supply are physically separate from those on the AUTOMATIC channel.

3.4.2 Principle of operation All the functions of the MANUAL channel including Reference value Generation, PI regulation and generation of firing pulses, have been implemented in single electronic module, the UN 0663 Gate Control Unit. When Manual channel is selected, the control variable Ucontr of Field current regulator, which is implemented in UN0663 Gate Control Unit is used as the reference value for generating firing pulses on the principle, known as “ramp control” (Comparison of Ucontr with Usynsynchronous saw tooth signal). For further processing in the UN 0096 Intermediate Pulse Stage, the Gate Control Unit supplies six firing pulses at its output whose phase position with respect to the synchronous voltage Usyn is in accordance with control variable Ucontr. An internal linearization ensures that the field voltage produced via the firing pulses remains proportional to the control variable Ucontr throughout the entire range. As a result, the circuit amplification of the control remains constant over the entire range. Whenever excitation is switched ON or Generator breaker is opened, the set-point for Field current is set automatically at the preset - ref. Value. This provision ensures that the generator voltage always attains approximately its nominal value after the Voltage build up. The UN 0663 Gate Control Unit can be re-functioned (by pre-selection with a switch ) for purposes of testing to act as a purely firing pulse control. In this case, the control variable Ucontr is adjusted directly using the RAISE / LOWER push buttons on the front of the module. In this way, for example, the relationship between the phase position of the firing pulses and the control variable Ucontr can be checked easily.

4. Pulse Section 4.1 Pulse Generation and Amplification refer to block diagram (/YU101) The UN 0663 Gate Control Units of every channel each supplies six firing pulses for operating the 6-pulse thyristor bridges. The low-power pulse signals from these Gate Control Units are amplified in the UN 0096 Intermediate Pulse Stage, galvanically isolated, and then sent to the common pulse bus. On the output end, the Intermediate Pulse Stage of the stand by channel is always blocked.

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The Gate Control Units generate the pulses based on microprocessor control. The reference voltage used for the firing pulse phase location is the output voltage from the excitation transformer (Usyn1 and Usyn2). The commutation spikes of the synchronous voltage caused by the converter are calculated prior to use of the voltage as a reference value and are deliberately filtered out. The lower limit for the firing pulses (double pulses), which are offset from one another by 60°, is defined by the limit rectifier position (min) and the upper limit by the limit inverter position (max) for the firing angle. min and max can be adjusted on the Gate Control Units using DIL(Dual In Line) switches. min ensures that the firing pulses will not be issued (premature firing) until there is sufficient positive phase voltage on the thyristor involved. max prevents a dangerous “tipping” of the thyristor bridge into the rectifier mode if the firing angle  is too large (“late firing”). The critical factors determining max are the overlap time ümax (max. commutation time) and  the “recovery time” of the thyristors (max < 180° - ümax -  ). An external control signal can force the firing pulses into their inverter limit position. Other binary inputs can block or direct the firing pulses of the Gate Control Units so as to produce freewheeling on the Thyristor Bridge. During freewheeling, the firing pulses for the thyristor pair R and S are blocked and the pulse signals T+/T- are engaged with chains of pulses. All Gate Control Units contain a field current monitor that blocks the firing pulses immediately whenever the current exceeds a preset threshold level. In this case, the field circuit-breaker is also tripped via an output contact. The purpose of these provisions is to prevent damage to thyristors and thyristor fuses in case of a slip-ring short-circuit, or to keep any damage that does occur to a minimum. The pulse signals are galvanically separated at the outputs from the UN 0096 Intermediate Pulse Stage (with pulse transmitters) and are then directed to the common pulse bus. This transmission of the pulse signals to the pulse bus via passive transmitters ensures a high degree of active channel autonomy. Practically no possible malfunctions on the standby channel (including, for example, sustained pulses) affect the active channel.

5. Converter 5.1 Final Pulse Stages refer to block diagram (/YU101) The UN 0809 Final Pulse Stages adapt the output pulses from the UN 0096 Intermediate Pulse Stage (pulses on the pulse bus) to the gate currents needed for the thyristors. Each thyristor bridge is equipped with its own Final Pulse Stage. Each Final Pulse Stages is provided with a power supply module UN 0901. The module generates a high initial pulse amplitude in order to reach the necessary gate current gradient. The Final Pulse Stages and their associated thyristor bridges form single units. All six pulse outputs from a Final Pulse Stage can be blocked by an external control signal, so that all thyristors in the associated thyristor bridge will block the current. A blocking of the pulses is initiated whenever there is a malfunction in the associated thyristor bridge.

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5.2 Converter Power Section refer to block diagram (/YU101) Fully controlled thyristor sets in three-phase bridge connection are used. Each of the 6 bridge arms is fitted with a thyristor and an arm fuse. The thyristors are generously dimensioned with respect to voltage and current so that the failure rate is very low. Each thyristor bridge arm is equipped with current flow monitoring CT’s. The absence of conduction in any arm is identified by a Current flow monitoring module and alarm is given.

6. Field Current Circuit 6.1 Exciter Field Circuit-Breaker refer to block diagram (/YU101) The circuit breaker in the Exciter field circuit is used to isolate the field circuit from the converter. It is capable of switching off the synchronous machine from full load under the worst conditions of a 3-phase short-circuit. In addition to its main contacts, the Exciter field circuit breaker also has a de-excitation contact with which the stored magnetic energy in the Exciter field can be dissipated across the de-excitation resistor. The de-excitation contact closes shortly before the main contacts open so as to ensure proper commutation of the field current from the main contacts to the de-excitation contact when the breaker is switched off. The stored energy in Generator field winding is dissipated with natural time constant of the generator field and Exciter armature circuit. The Exciter field circuit-breaker is switched on by electromagnetic force and is kept switched on by a mechanical latch. When the latch is released by trip coil, the circuit breaker is thrown open. The circuit breaker also has auxiliary contacts that report its status. 6.2 De-excitation refer to block diagram (/YU101) When malfunctions occur, the stored field energy must be dissipated as quickly and safely as possible to protect the generator. This is done by the converter, the field circuit breaker and the de-excitation (discharge) resistor. De-excitation (with opening of the Exciter field circuit-breaker) takes place in the following stages: 

The converter, driven to its inverter limit position (negative ceiling voltage), recovers a portion of the field energy in to the network. A trip command is given to the field circuit breaker.



The de-excitation contact closes, diverting the field voltage to the de-excitation resistor.



Then, immediately, the main contacts open, building voltage. The field voltage commutates to the de-excitation resistor.

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

The current diminishes at a given time constant TE: Lf (with linear resistance:

TE = -----------) Rf + Re

Due to the reversal of the field voltage by the converter, the Exciter field current commutates from the main contacts of the Exciter field circuit breaker to the de-excitation resistor in a very early phase. This reversal of the field voltage prevents burn-off on the main contacts and provides effective protection for the field circuit breaker. Depending on the operating policy, an operational shutdown of the excitation can also be effected with the field circuit breaker closed. This method is useful mainly when the excitation is switched on and off frequently. In this case, the converter is merely driven into the inverter limit position so that the field energy is recovered into the network. The converter then blocks since it is supplying positive current only.

7. Monitoring 7.1 Excitation Monitoring

7.1.1 General Information refer to scheme sheets GX000-YS501… The main goal of Excitation Monitoring is to make optimum use of the redundancies provided in the excitation system and to give alarm whenever a malfunction makes these redundancies unavailable. The Excitation Monitoring is implemented in Programmable Logic Controls. The field current is monitored to see that it does not exceed a maximum level and, if necessary, a switch-over to the hot Stand by channel is initiated.

7.1.2 Actual Value Monitoring refer to scheme sheets GX000-YS501… The actual values for generator voltage Ug and field current If are monitored for malfunctions (plausibility). This monitoring is active regardless of whether or not the Generator Breaker is closed. Essentially, when Excitation is ON, the measurements are monitored by comparing the signals (the smaller signal reading is detected as incorrect). If the stand by channel is not faulty, “Active channel Ug fault” derived by comparison with stand by channel Ug is permitted to initiate change over action. If Ug is not between 90 to 110% and if difference is > 10% then also Ug is considered as faulty. The measurement channel malfunctions are enabled operationally whenever, after excitation has been switched on.

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If (Field current) is also monitored by comparing If1 and If2 and which ever is less is declared as faulty. In addition “If” is monitored for value greater than Ifo when Generator Circuit Breaker is OFF and for a value less than Ifo when the Generator Circuit breaker is ON.

8.

Binary Controls

8.1 EXCITER FIELD CIRCUIT-BREAKER ON/OFF Commands with Status Pressing the ON button / issuing command through HMI interface closes the Exciter field circuit breaker when all conditions to PERMIT breaker closing, shown in the functional representation in schematic diagram GS020-YS501 are satisfied. Whenever this command is wired parallel to the command “EXCITATION ON” (refer to schematic diagram AU020YB001), excitation is switched on, at the same time as the Exciter field circuit-breaker (refer to the next section). Pressing the OFF button / issuing command through HMI interface, switches off the field circuit breaker and the excitation, which de-energizes the generator through the converter and the de-excitation resistor. Provided all PERMIT criteria for Exciter Field Breaker OFF are present as shown in functional representations on schematic diagram GS020-YS501, pressing the “FIELD BREAKER OFF” button / issuing command through HMI interface, switches the Exciter Field breaker OFF. 8.2 EXCITATION ON/OFF Commands with Status Depending on the operating control philosophy for the installation in question, these commands can be issued together with the commands FIELD CIRCUIT-BREAKER ON/OFF as described above (refer to the input wiring in schematic diagram AU020/YB001). If the commands FIELD CIRCUIT-BREAKER ON/OFF and EXCITATION ON/OFF can be operated separately, the excitation can be switched on and off without having to activate the field circuit breaker every time. This prevents undue stressing of the field circuit breaker in cases where the excitation must be switched on and off frequently. If the logic is so designed then the field circuit breaker must be in the ON position before the excitation can be switched on. Provided all PERMIT criteria for Excitation ON are present as shown in functional representations on schematic diagram GS021-YS501, pressing the “EXCITATION ON” button switches the Excitation system on, i.e., the enable is given for the firing pulses to the converter. Pressing the OFF button / issuing Excitation OFF command through HMI, switches off the excitation, i.e., the converter is directed to inverter operation, de-energizing the generator, if Excitation OFF PERMIT is available.

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8.3 CHANNEL-1 ON / CHANNEL-2 ON / CHANNEL-3 ON Commands with Status Basically, a shift can be made from one channel to the other at any time because the stand by channel is always matched automatically to the active channel. Whenever a malfunction is detected on channel-1, a switch-over to the channel-2 is forced, and it is no longer possible to switch back to the channel-1, while the malfunction is not removed. A switch-over to a faulty channel is not possible. Similarly, whenever a malfunction is detected on the channel-2, a switch-over to the channel-1 is forced, and it is no longer possible to switch back to the channel-2, while the malfunction is not removed. When both Channel-1 and Channel-2 are faulty automatic switch over to Channel-3 is initiated. The control room has Balance voltmeter to monitor the difference between the Control Voltage of “channel in operation” and a “stand by channel”. As there are totally three channels a switch is provided in control desk to select a channel for balance indication. If Channel-3 fails while in operation, tripping of Excitation is initiated. 8.4 MANUAL CHANNEL (CHANNEL-3) “RAISE “/”LOWER” Commands with Status MIN/MAX, These “RAISE “/”LOWER” push buttons or the commands from HMI are used to adjust the setpoint for field current. When the generator is under no load, this adjustment changes the generator voltage; in operation under load, it changes the reactive power output. Because there is no limiter available on the MANUAL channel, care is needed when issuing “RAISE” or “LOWER” commands to see that the operating limits for the rotor and the generator (as defined in the Power Chart) are not exceeded. Warning signals light up whenever the field current set-point is at its minimum or maximum value. If both “RAISE” and “LOWER” commands are issued simultaneously, no adjustment is made in the set point. The field current set-point is preset automatically at the value for no load excitation current (Ifo) whenever the excitation is switched on or generator breaker opens. 8.5 AUTO CHANNEL (CHANNEL-1 / CHANNEL-2) “RAISE “/”LOWER” Commands with Status MIN/MAX, The “RAISE “/”LOWER” push buttons or the commands from HMI are used to adjust the set point of the generator voltage. When the generator is under no load, adjustment to reference, changes the generator voltage; in operation under load, it changes the reactive power output. When the operating limits of the rotor and the generator are being exploited to the full, appropriate limiters intervene and disable the “RAISE”/”LOWER” commands in the direction limited (refer to Sect. 3.3 for the limiters). Warning signals light up whenever the generator voltage set-point is at its minimum or maximum value. If both “RAISE” and “LOWER” commands are issued simultaneously, no adjustment is made in the set point.

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When Excitation ON command is issued, Generator Voltage Reference is PRESET to its nominal value. 8.6 Display of Analog Values Field Voltage (Uf), Field Current (If) and Balance Voltage V between the control variables of the regulator channels are displayed in the control room. The displays for If and Ug are particularly useful whenever one is operating in the Manual mode. The V indicator shows the voltage by which control variable of the selected mode of the stand by channel differs from that of the selected mode of the Operating channel. The selected mode of the stand by channel is matched automatically to the selected mode of the Operating channel. This tracking implemented in Binary controls processor is set to be relatively slow acting: any switch-over from one channel to the other necessitated by a malfunction will be made to the steady-state value present prior to the malfunction. The generator can be operated in the AUTOMATIC mode up to the limits set in generator capability diagram. The permissible operating range for the AUTO mode are outside the operating range permissible (and set) for the MANUAL mode. Because the MANUAL channel cannot, in such cases, track the AUTOMATIC channel, the V indicator steadily reports a difference. During “normal” steady-state operation of the generator, the V Balance meter must always be at null position. UNLESS THERE IS ANY SPECIFIC REASON, IT IS ADVANTAGEOUS TO SELECT AUTO CHANNEL FOR OPERATION. 8.7 Alarms The alarm messages in the control room are general messages grouped according to the information needed by the operating staff. The cause of the malfunction can be seen in detail on the ALARM INDICATIONS page of the HMI PICTURE in the Regulation cubicle. A detailed analysis of the malfunction can be undertaken using LOCAL HMI, by FOLLOW ing the tagname. In addition a provision has been made to list the, possible causes, Immediate action by Excitation system and Further procedure to be carried out by maintenance staff, on LOCAL HMI itself. UNDER-EXCITATION LIMITER IN ACTION is displayed whenever an “exciting” limiter has intervened (refer to Sect.3.3.9 ) to increase the field current. Response: If permissible in view of the generator’s reactive power output at the moment, raise the voltage set-point. OVER-EXCITATION LIMITER IN ACTION is displayed whenever a “de-exciting” limiter has intervened (refer to Sect. 3.3.7 ) to reduce the field current so as to dominate the voltage regulator. Response: If permissible in view of the generator’s reactive power output at the moment, lower the voltage set-point. COMMON ALARM / AVR FAULTY is displayed whenever an alarm (either high or low priority) is ON. Response: Do not start the unit. If it is in operation, find out the cause of the malfunction from LOCAL HMI alarm indications at the excitation cubicle and proceed as called for in the support instructions for Trouble shooting.

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COMMON ALARM STAGE-II is displayed whenever a channel failure occurs. The defective channel can be in operation or in stand by while the malfunction occurred. Thus common alarm stage-II indicates that redundancy is not available. Find out the cause of the malfunction from LOCAL HMI alarm indications at the excitation cubicle and proceed as called for in the support instructions for Trouble shooting. EXCITATION TRIP is displayed whenever the excitation and the generator have been tripped by a critical malfunction of the excitation system. Response: Find out the exact cause at the local HMI alarm indication on the excitation cubicle. In the case of a system malfunction, call for Service. In the case of a justifiable protective operating trip, acknowledge the malfunction signal and restart the unit. 8.8 Check-List for Operating Staff Check for the following periodically during operation:

a) In the control room: 

Neither an “over-excitation” nor an “under-excitation” limiter has intervened.



Set-points for the channels are not in their limit positions.



The reading for channel tracking (V) is steady in the middle of the dial.



The field current, generator voltage, and reactive power output are stable.



Test the indication / alarm LED’s. Various monitors check the stand by channels continuously to ensure that they are functional. Nevertheless, we recommend that a brief switch-over to the other channel be made periodically, e.g., after a start-up, to test its functional readiness.

b) On the exciter cubicles: 

Regulator cubicle REG-1 does not contain any active alarms (red coloured LED symbols, on the alarm indications, pages of picture).



The cooling system for the converter cubicles is working properly, air inlets and outlets are open and free of dirt.



There are no unusual noises.

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8.9 Local Operator’s Panel, Exciter Cubicle refer to block diagram (/YD115) A LOCAL HMI (Human Machine Interface) PC has been provided in Regulation cubicle REG-1. PRECAUTION: IT IS ESSENTIAL THAT NO OTHER ADDITIONAL SOFTWARE IS LOADED ON TO THIS PC OR THE PC IS NOT ACCESSED USING PEN DRIVES / OTHER REMOVABLE DEVICES WHICH ARE DETRIMENTAL TO THE PROPER FUNCTIONING OF THE PC BY VIRUS INFECTIONS. This Industrial PC has been loaded with maxDNA software, with which Binary controls and HMI based operation have been implemented. User shall login as OPERATOR and run “max VUE Runtime”. To log on as operator: 1. The computer shall be switched on if it is not already on. When the computer is turned on, it goes through normal boot up routines. When the computer finishes start up procedure, the Windows XP Auto Logon dialog appears. 2. Alternatively you may press keys to open the logon dialog. 3. Enter your user name(operator) and password to logon as operator. 4. max STATION shall automatically start up. If not click on the maxStation icon. max STATION start up window appears and automatically startsup the underlying system and software backplane logic. 5. Click on the “maxVUE Run time” icon. 6. Click anywhere on the display away from any animation area to open the next display, usually the MAIN MENU display. For further details on “Working in maxVUE” please refer chapter max station operator’s guide available in the path C:\Mcs\maxDOCS\_Release 4.2 Manuals\278610 Volume 1 7. Further operator can navigate to the desired control / display by the buttons provided for the purpose. Typically a click on control button / soft push button provided for controlling the unit (say UNIT-1), shall open the screen containing the block diagram of Excitation system.

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Various control commands provided using soft push buttons are as identified in the Picture-1 above. 1. Field Breaker ON / OFF control 2. Excitation ON / OFF control 3. Channel-1 / Channel-2 / Channel-3 selection 4. Reference Raise / Lower for Channel-1 5. Reference Raise / Lower for Channel-2 6. Reference Raise / Lower for Channel-3 7. Local / Remote selection (Not available at REMOTE control room) 8. Acknowledge / Reset (Not normally provided at REMOTE control room) The corresponding status displays are available near the push button controls as well as on the pop-ups which open when the button controls are operated.

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Display of the following analog signals have been provided on the block diagram picture. A. Exciter Field Voltage B. Exciter Field Current C. Channel Balance Voltage D. Generator Voltage E. Generator current F. Active Power G. Reactive Power H. Power factor I. Generator Field current It may be noted that first five in the above list are required for the operator to know the machine parameters while controlling / operating from LOCAL of Excitation panels. Others though provided are not essential for LOCAL operation. Excepting Exciter Field voltage, Exciter Field current and Channel balance voltage, all other displays are indicative in nature, considering the high conversion factors used for display purposes. Fault indications have been shown as grouped display in the block diagram picture. This display shall be GREEN under healthy condition and turns RED whenever there is a fault. A click on this display enables operator to navigate through the detailed alarms list page. In the detailed alarms list page, the LEDs corresponding to the fault indications are displayed in RED, when there is a fault. A left click on the LED enables operator to view the quick trouble shooting support text. The system is in fact user friendly and enables operator to follow the signal to locate the cause of fault indication. Pressing the button LAST enables operator to go to the previous display. Pressing enables operator close maxVUE Runtime. Pressing MAIN takes the control to Main Menu. Micro terminal In addition, to the above operator work station, a portable Micro-Terminal has been provided on the AC rack of Regulation cubicle REG-2 (refer to the next Section).

Note :- Malfunctions of the UN 0660 processor units, require acknowledgment with the RESET button on the front of the module. Acknowledgment of the UN 0660 processor module restarts the processing programs involved, e.g., stored values, processing information, and temporary changes made in the RAM storage (via the Micro-Terminal) are overwritten.

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8.10 Micro-Terminal refer to block diagram (/YD115)

8.10.1 Summary The Micro-Terminal can be used to view parameters and signal values of the processor system (UN 0660) and to change stored values within certain address ranges. To do this, the Micro-Terminal must be connected to the UN 0660 processor in question by plugging a system cable in on its front side. This system cable also supplies the power to the Micro-Terminal. The Micro-Terminal has a 4-line LCD display in which 4 addresses (lines) appear simultaneously. The address appears at the left of these lines and the value for these addresses at the right. The four values displayed can be measured or recorded at the four measurement sockets provided below the LCD display.

8.10.2 Selection of Addresses To select a given address on the display, the cursor must first be moved to the beginning of the line desired. Then the new address must be typed on the keyboard, and this address entered using the “RETURN” key. This causes the value for the newly selected address to be displayed at the right. The Micro-Terminal automatically translates a number of the addresses into easily interpreted alphanumeric values. For example, the actual value for generator voltage is at address F90A in the processor system for the AUTOMATIC mode / channel. Whenever this address is selected, the term “Uact” appears in the address column, and the signal value, for example, 102.3% appears in alphanumeric form. A new address can also be selected by moving the cursor to a given address in the address column and “paging through” the addresses with incremental commands (push buttons: INC / DEC). Because the addresses that can be selected via the MicroTerminal are always even-numbered, the Micro-Terminal rounds up to the next evennumbered address.

8.10.3 Addresses with Variable Value (Parameters) The Regulator processor systems contain EEPROMs and RAMs as storage spaces for variable parameters. When the processor is initialized, the RAM storages take over the content from the EEPROM storages. The values stored in the RAM are used for processing the functions in the processor. The Micro-Terminal can make changes in either the RAM storage or in the EEPROM storage. Changes in the RAM storage are temporary: they are canceled again the next time the process is initialized (The value in the EEPROM storage is taken over again). Changes in the RAM storage are therefore suitable mainly for test purposes. Changes in the EEPROM storage, on the other hand, are permanent. The address range for the EEPROM storage is from HEX C000 to HEX C7FE. The corresponding addresses in the RAM range are exactly HEX 3000 higher. For example, the RAM address F250 corresponds to the EEPROM address C250. Changes in value in the RAM range are made by moving the cursor under the value to be changed, typing in the new value, and entering it with the “RET” key. As an EDN 48-0673-11

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alternative, a steady change in value can also be made by pressing the “INC”/”DEC” keys while the cursor is located under the value that is to be changed. Changes in value in the EEPROM range are made by pressing not the “RET” key alone, but the keys “SHIFT”, “WRITE”, and “RET”, in that sequence. The changed value in the EEPROM range then appears on the display, but is not yet functionally effective: The processor is still performing calculations using the “old” RAM storage value. The new value is not taken over into the RAM storage until the RAM storage is reinitialized, for example, by pressing the RESET button on the front of the UN 0660 processor involved. The alarm, “PARAMETERS CHANGED,” is issued whenever values in the RAM or the EEPROM range have been changed. This alarm can only be acknowledged by pressing the RESET button on the front of the processor involved.

Note:- The address which generates the indication of the difference can be found via the micro-terminal: Add. FB00 : 1111 - k-flag difference Add. FB02 : XXXX - corresponding address Add. FB04 : 1111 - EEPROM-RAM Add. FB06 : XXXX - corresponding address

8.10.4 Processor Systems with Fixed Functional Modules The processor systems of the Channels-1 and 2 contain software in the form of unalterable standard functional modules (firmware). The plant-specific overall function depends on the settings of the software switches, referred to as “configuration flags” (KFlags). Because these K-Flags define the Scope of Supply for the plant software, they cannot be changed in the EEPROM range. The range of addresses for the K Flags in the RAM storage includes the addresses from F702 to F7FF. The parameters of these processor systems as reference values, limit values, amplification factors, etc. can be altered and adjusted using the Micro-Terminal. There are usually max. permissible ranges of adjustment assigned to these parameter values. Whenever settings are selected beyond this range of adjustments, they are limited in the RAM range (functionally relevant) to the maximum value permitted for the range of adjustment. The values in the EEPROM range (C...) are marked with an asterisk (*) on the display as a reference for the individual using the Micro-Terminal. In the processor system for the AUTOMATIC mode / channel, the values of 12 signals can be selected directly using specific keys on the Micro-Terminal (without typing in an address). The list below shows these signal values and their essential characteristics:

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Display micro terminal Uref Uact Ifac

Designation

HEX Add.

Value Voltage in on Mic-terminal Dec

%

Ug set point (without

F270

2866

+ 7V

%

droop) Actual generator voltage

F90A

2866

+ 7V

Actual rotor current

F910

1228

+ 3V

%

IGac

%

Actual stator current (Apparent current)

F91C

2866

+ 7V

IR

%

Actual active current

F906

±1433

± 7V

IX

%

Actual reactive current

F902

±1433

± 7V

P

%

Active power output

FA80

±1002

± 5V

Q

%

Reactive power output

FA82

±1002

± 5V

Dact Deg

Actual load angle (1p.u.= F886 1 rad = 360°/2p = 57.3°)

1024

+ 3V

CPhi ind

Power factor (-1024 ..0.. F842

±1024

±10V

0 ...

±10V

\cap Ucontr

+1024 = 0 cap...1...0ind)

Deg Control variable

F992

(input gate control unit) (0:=180°;4095: =0°) Uaux

%

Auxiliary voltage

4095

F91A

2866

+ 7V

8.10.5 Binary Controls Binary controls have been implemented using the DCS (Distributed Control System) platform maxDNA. The system has a wide variety of features, facilities and configurations. The details referred below describe the configuration adopted for Excitation application. Hardware resources: Refer sheet YU102 of scheme for an overall block diagram showing the interfacing between Regulation channels and the Binary Controls. For the purpose of Binary controls two Distributed Processing Units (DPU), One of which is Primary and other Secondary(stand by) are used. The two DPUs are connected to form a back up pair. Process control can be transferred Automatically (fail Over) or operator can press the “take over” button on the DPU front panel or access the soft “Take over” button appearing on the maxTOOLS 4F down load dialog box. The Binary Input (IOP 330) / Output modules (IOP 351) provide the physical connection point, for the input / output wiring of signals to and from the process. EDN 48-0673-11

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Each Input / Output module has 16 channels. The analog inputs required in Binary controls are acquired through the Analog Input Module(IOP 305), which also has 16 channels. For interfacing maxDNA with DVR hardware Digital Input module (Type IOP 334 with 16 isolated inputs) and Digital output module (IOP 351) have been used. The Signal Flow: Potential free contacts from field  Digital Input Module  Digital Input Buffer(DIB)  Configuration logic residing inside active DPU  Digital output Buffer(DOB)  Digital Output module  Aux relay for contact multiplication and remote use. The Configuration (software file) The configuration file is built using maxDPUtools. The Input modules and Output modules are defined with the module locations. Input buffers for used channels (out of the 16 channels) of all Input modules, Output buffers for used channels (of the 16 channels) of all output modules are defined in the configuration. Each Input / Output module has 16 LEDs on its front plate which glows to indicate that the particular channel is high. The project specific Logics are built in the configuration file using maxDPUtools. To have a structured configuration, they are divided in to groups which replicate the scheme sheet drg for the logic. The system permits provision of 8 levels of groups. Inside the groups various atomic function blocks( like AND gate, OR gate, R-S flip flop, On delay timer, Off delay timer etc.) are used to construct the plant specific logic required. Unique Tagnames(DTAG-Digital Tagger) are assigned for Digital I/O signals in the buffers. Unique Tagnames can be assigned / used any where a digital signal needs to be tagged or alarmed. Similarly unique Tagnames(ATAG-Analog Tagger) are assigned for Analog I/O signals in the buffers. Unique Tagnames can be assigned / used any where an Analog signal needs to be tagged or alarmed. Each of the atomic blocks has appropriate attributes which makes the usage of these blocks versatile. The system also provides for assignment of Service / processing priority for all atomic blocks and groups. The above details are indicative of, only a very small portion of the features and facilities, to provide a brief idea. For detailed information on Configuration / atomic block function refer chapter max station operator’s guide available in the path C:\Mcs\maxDOCS\_Release 4.2 Manuals\278610 Volume 1.

Redundant Operation The system is provided with a primary DPU, a secondary DPU, and two identical sets of parallel I/O modules. The primary and secondary DPUs receive data from, and send data to, there set of I/O modules. Outputs from the inactive string of modules are inhibited until they become active. Part No. CP0309 cable installed between the two I/O strings inverts the output-enable signal so that outputs of the inactive I/O string are disabled. The IP address of the secondary DPU is always one number greater than the address of the primary DPU. The primary is always the even address while the Secondary is the EDN 48-0673-11

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odd address. The installation, preparation and adjustment procedures apply to both DPUs in a redundant configuration. Automatic Failover / Manual Takeover Logic Sequence control can be transferred automatically (Failover), or can be manually commanded to takeover. Automatic Failover can occur from either the primary DPU to the secondary DPU or from the secondary to primary based on the health of each DPU. Automatic Failover Logic Sequence control is automatically transferred from the primary DPU to the secondary DPU when the primary DPU experiences a severe diagnostic alarm or when communication between primary and secondary DPU is lost. However, if the secondary DPU is itself experiencing a severe diagnostic alarm, it will refuse control, unless the primary DPU loses power or is reset. Each DPU monitors the state of its own health as well as that of its backup. The DPU looks at things like the state of its CP, IOM and backup link. It also checks to see if it can hear good messages from the other DPU over Network A and B and over the backup link. From this information, each DPU calculates a health value for itself. This value, along with other information, is used by the DPU when it is deciding whether or not it should take control away from the currently active DPU.

8.10.6 Printer Output A printer can be connected to the plug-in connection “OUT” on the Micro-Terminal. If the Micro-Terminal is connected to control Regulation Channel-1 (AA49/AB49/AA13), the most important measured data can also be printed out on call-up. The following printer functions can be activated on the Micro-Terminal: KEYBOARD INPUT

Function

SHIFT 1 0

Print screen

SHIFT 1 1

Print out list of parameters

SHIFT 1 2

Print actual regulator

SHIFT 1 3

Not used

SHIFT 1 A

Adjust printer page length

SHIFT 1 B

Select “Elite” font

values

of

the

voltage

The special functions SHIFT 1 A and SHIFT 1 B do not normally have to be called up. SHIFT 1 0, Print Screen: The four values displayed on the screen are printed out as follows:

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1st line of display

2nd line of display

3rd line of display

4th line of display

The display format (HEX or decimal) in the print-out is the same as that on the screen. SHIFT 1 1, Print out List of Parameters: In a processor system with firmware modules, e.g., the AUTOMATIC channel, all scaled values can be printed out. These include all preset values, the settings of the software switches (K-Flags), and the actual values of the signals. SHIFT 1 2, Print Actual Values of the Voltage Regulator: The Micro-Terminal must be connected to the AUTOMATIC channel. The scaled values of all signals at the given moment are printed out. SHIFT 1 3, Spare (Not used) SHIFT 1 A, Adjust Printer Page Length: This function sets an IBM-compatible printer as follows: Page length 12 inches:

ESC C 0 12

Skip over performation:

ESC N 12

This function can be called up to print out long lists of parameters that have not already been organized accordingly in the scaling table. SHIFT 1 B, Select “Elite” font: This function sets an IBM-compatible printer as follows: Print pitch 12 characters per inch:

ESC:

(Normal pitch: 10 characters per inch) Connection of a Printer to the Micro-Terminal: Connect the UNS 2660 serial interface (OUT) of the Micro-Terminal either to the parallel Centronics interface using an interface adapter SP100, or directly to the serial interface RS232 on the printer. The following connections on the RS232 interface of the Micro-Terminal are needed:

Pin

Designation

Function

2

TXD

Transmit data (Out)

5

CTS

Clear to send (In)

7

GND

Ground

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The RS232 interface is defined as follows: 9600

Baud

8

Data bits

1

Stop bit

Even parity

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9. Preventive Maintenance and Operational Malfunctions 9.1 Overview While electronic components themselves do not suffer from aging and show only insignificant wear, the excitation equipment includes a number of such electromechanical elements as circuit-breakers contactors and fans all of which are subject to a certain amount of wear. If, even so, a malfunction should ever occur in the electronic section, there are various monitors and corresponding annunciation displays available. Certain functional parts, however, are difficult to monitor and must therefore be inspected periodically. Fouling builds up as a result of the natural draft air cooling of the electronic equipment. Some of the screw-terminal connections can work themselves loose due to vibrations. High voltages and currents (DC!) occur in the exciter circuit. Here, spots in the insulation that have become dirty present a risk of major damage from voltage flashover. Periodic preventive maintenance on the installation reduces this risk greatly. 9.2 Preventive Maintenance and Care We recommend the following preventive maintenance and care for the installation: a)

Every 3 months, with the turbine / generator group in operation



Check for blocking of the vents in the cubicles. These may be washed out using a suitable cleaning fluid, or with a blower.



Check the current distribution among the converter blocks and current conductance of the thyristors.



Compare the present distribution of thyristor device currents with that of commissioning / factory test results.



Check that the stand by channel tracks properly, the channel in service and works properly when activated. Interfere with the tracking of stand by channel with respect to the channel in operation by activating the “RAISE”/”LOWER” push buttons of stand by channels one at a time. The automatic tracking is working correctly if the stand by channel is slowly brought back equal to channel in service once the “RAISE”/”LOWER” buttons are released, so that the V-Balance Voltage indication returns to the middle. Then, check that the stand by channel is working properly by switching over briefly to that channel. If there should be a significant change in the field current If switch back immediately to the channel that was in operation and notify Service.



Check that the important measured values are correct. To do this, read the measurements on the Micro-Terminal and compare them with the values on the instruments in the control room / LOCAL HMI display. Check at least the following values on the two channels: generator voltage F90A, stator current F91C, field current F910, and active power output FA80.

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b)

Once a year, with the turbine/generator group at a standstill



Check for burn-off on the contacts of the Exciter field circuit-breaker .



Check for dust deposits in the converter. If it is severely fouled, clean it, particularly the cooling elements, using dry, oil-free compressed air.



Check for fouling of the plug-in modules (printed circuit boards and devices) in the swing frame. Only if necessary: blow the dirty components out with a dry, lowpressure air jet. In circuit boards or devices with gold-plated contacts (Tier AG, AP) clean the contacts carefully using White Spirit or a contact cleaning fluid of proven quality. If the printed circuit boards are severely blocked (cannot be cleaned out with an air jet), use special cleaning procedures and then neutralize and dry them. Be very careful in taking the circuit boards out and putting them back in, and take the “Electrostatic Discharge” precautions indicated in Sect. (9.3.2 ) below.



Check that all screw connections are firmly seated.



Check all protective equipment in the trip and the signalization circuits.



Perform a functional test on the complete electronic system as described in Sect. 9.3.3 below.

9.3 Operational Malfunctions and Functional Tests

9.3.1 General Information Basically, malfunctions in the excitation system itself can cause temporary or sustained deviations of the exciter current, i.e., can cause over-excitation or under-excitation of the synchronous machine. There are generally standby circuits available when individual circuits fail (redundancy) so as to avoid a trip due to the response of protective equipment. Malfunctions in the Binary Controls make themselves felt in a failure to respond normally to the control commands or in unintended trips or channel switch over. The operating staff must familiarize themselves with the details of how the excitation system works and with its operating controls well enough to enable them to evaluate the situation correctly in the case of a malfunction based on the readings of the displays and the malfunction signals received. Always avoid precipitous action. Most operational malfunctions in the functioning of the excitation system are detected correctly by the extensive monitoring and protection equipment and are annunciated at the alarm displays page. The various alarms are described and interpreted in more detail when a click on the LED display is made. The cause of the malfunction must be known before any general acknowledgment of the system is made. If it is not, determine and record the detailed “malfunction symptoms” as in the List of Alarms / trouble shooting support text. If an electronic circuit board should become defective, we strongly recommend against an attempt for repairing it. Replace it with a spare part, which must then be set as

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shown on the Test and Commissioning Report and handled as described in the Section below.

9.3.2 Malfunctions in the Electronic Control Cyclic self-test routines monitor, malfunctions of the digital electronics of the DVR system. A processor malfunction is announced on the front plate of the defective module by a “FAIL” LED, and is signaled to the alarm display. In case of a malfunction on the channel-I, an automatic switch over to channel-II is made. The defective module can thus be removed from the channel-I and replaced with a spare part while the generator is in operation. The various power packs have voltage monitors of their own. They switch off automatically whenever the monitor responds and signal the malfunction in the alarm display. For circuit boards in Tiers AA, AB, switch off the protective circuit-breaker at the input of the corresponding 692.03.PY2BA module before taking out and replacing the electronic modules. The voltage must be OFF before attempting to replace them! The circuit boards in tier AG, AP... may in general not be replaced while the power supply is ON. In cases the module supply cannot be switched off selectively, the module must be pulled out and inserted “decisively” (with no hesitation). Before inserting the replacement module, make all the adjustments on it, such as switch settings, bridges, special equipment, etc. as described on the Test and Commissioning Report. (Also compare it with the “old” module!). In the case of the UN 0660 microprocessor circuit boards, also make certain that the correct operating program PROM (correct HIER No.) is installed in Location A735 and the correct user’s program PROM is installed in Location A736. Whenever the parameter values on the replacement circuit board are not being entered via the Micro-Terminal (refer to Sect. 8.10.3 ), then the EEPROM in Location A738 must also be changed from the “old” module. The “old” settings of potentiometers R23 (U1), R24 (U2), R25 (UR), R26 (US), and R28 (UT) must be carried over on the UN 0661 “Interrupt generator” module.

Caution! Most of the electronics modules contain CMOS elements that are highly sensitive to electrostatic discharge (ESD). Whenever these modules have to be handled, follow the “Guidelines for Handling ESD-Sensitive Electronic Components.

9.3.3 Functional Test at Standstill Periodical functional testing is performed in order to increase the reliability of a system. It should be performed once a year, best of all during an overhaul of the turbo group, i.e., while the machine is at standstill. The main activities here involve: 

Testing the electronics equipment.



Testing the power supplies and measurement circuits.



Testing pulse generation and amplification.

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

Testing the monitors.



Checking the connections (cables, wires, connectors).



Checking for wear on the mechanical parts (e.g., relays, switches).



Checking the general condition of the installation (cleanness, oxidation, etc.).

For a functional test while the machine is at standstill, set testing switch –S20 at “TEST”, open Q3 and MCB F74 ON. The AC power supply for the electronics and the synchronous voltages Usyn are then obtained from station auxiliary supply (Refer to scheme sht. no. CE100-YS601). For normal operation, switch off F74, close Q3 and switch S20 in service. The digital control electronics have in built test routines that run cyclically and check during operation to make sure that the hardware is functional. For that reason, the functions implemented in the processor do not have to be checked in routine controls. Either all the functions of a processor system function properly, or none of them do. The latter is accompanied by an alarm signal from the processor. However, the measured data must be checked carefully. To do this, apply the associated 100% values for voltage and current at the input terminals using a 3-phase Variac or an electronic function generator. To check that the conversion in the peripheral input modules and in the A/D transducer of the processor system is correct, compare the values applied with the display on the Micro-Terminal (refer also to Sect. 9.3). The addresses for the measured data in the processor systems are as follows: Measurement

AUTOMATIC channel (AA49 / AB49)

Generator voltage

F90A

Stator current

F91C

Field current

F910

The values displayed in % on the Micro-Terminal correspond to the values in p.u. Compare them with the data in the Test and Commissioning Report. The other data measured on the AUTOMATIC channel, such as active and reactive power output, load angle, etc., are derived by calculation from Ug and Ig and do not need to be checked in routine inspections. If possible, however, check the correctness of the above-mentioned measurements, including that for effective power output FA80 (AA49) even before shutting down the group. If this checking produces proper results, no further rechecking of the actual values is necessary during the routine inspections. EDN 48-0673-11

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The power supply units have a voltage monitor built into them. To test this monitor, open the protective circuit-breaker assigned to the power supply unit. Proper functioning of the monitor is signaled on the alarm display and/or on the module itself. As a further check, measure the output voltages from the power supply units and compare them with the data in the Test and Commissioning Report. To check pulse generation, connect up a 2-channel oscilloscope or a suitable recording instrument as follows: 1st channel:

Synchronous voltage Usyn, phases UR-OV/US-OV/ UT-OV, measured

at the test sockets provided on the front plate of the UN0663 control unit 2nd channel: Pulses R+ ... S- to 0 V, measured at the test sockets provided on the front plate of the UN 0663 control unit. Triggering of Channel 1: Perform the following tests: 

Set testing switch –S20 in the cubicle at “TEST”, Q3 off and F74 ON



With regard to their phase-assigned synchronous voltage, the pulses must be in the preset limit position for inverter operation.



The double pulses must be separated by 60°el. ± 5°el.



Compare the shape of the pulses with the data on the Data Sheet for the UN 0663.



Test all the channels; the two AUTOMATIC channels (AA65, AB65) and the MANUAL channel (AE65).

To test the Intermediate Pulse Stage UN 0096, switch to Channel -1, operation and view or record all output pulses at measurement sockets R+ ... S- to 0 V. Repeat the checks for Channel –2. Then, switch to the MANUAL channel and view or record all output pulses at measurement sockets R+ ... S- on module. Compare the shape of these pulses with the data in the relevant Data Sheet. To test the Pulse Final Stages UN 0809 check all output pulses at measurement sockets R+ ...S- to 0 V. Compare the shape of these pulses with the data in the data sheet. Next measure the pulses on the thyristors themselves, i.e., downstream from the pulse transmitters. The pulse amplitude is still approx. 2 to 5 V. If there are firing pulses at all thyristors, the entire pulse path is OK. To check channel switch-over, make another comparison of the output pulses from an Intermediate Pulse Stage with the associated synchronous voltage. Set the limit position for inverter operation at 120° on one of the Gate Control Units and at 170° on the other. Then, when changing channels, a shift in the pulse location from 120° to 170°, or vice EDN 48-0673-11

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versa, must be detected. (On completion of this test, restore all inverter operation limit positions to their original settings!) During major overhauls, it is a good idea to test the inputs and outputs of the open-loop controls. To test the inputs, locate the sources of the messages using the schematic diagram / by FOLLOW ing the signals and simulate a response of the annunciation contact. The corresponding LED on the IOP330 Input module must then light up. The outputs include the commands for the field circuit-breaker and the field flashing breaker. Since the OFF commands for the field circuit- breaker are in redundant circuits, they must be tested individually. Work carefully when testing the protective equipment. To check the protective trips for over current, simulate a field current If equal to 105% Ifn at the isolating terminals. Then change the following settings temporarily, one after the other, producing an exciter trip each time: 

the UN 0663 for the channel --1 (AA65): S853 to “1”, causing an immediate trip;



the UN 0663 for the channel --2 (AB65): S853 to “1”, causing an immediate trip;



the UN 0663 for the channel --3 (AE65): S853 to “1”, causing an immediate trip;

For all trip simulations, always make certain that the trip coil of the field circuit breaker pulls in and that a generator trip is initiated.

9.3.4 Interpretation of the Alarm Displays The alarm displays on the LED indications page of the HMI picture and the other alarm and operating displays on the fronts of modules are used for quick pin-pointing of malfunctions. Refer to the appropriate Data Sheets for an interpretation of the operating and malfunction displays (LED’s) on the fronts of the various modules. The Excitation System malfunctions are signaled on the LED indications page of the HMI display using pictorial LED’s. The Plain text descriptions of these alarms also indicated by the side of pictorial alarm LEDs. When a malfunction is present, the corresponding LED flashes. The alarm can be acknowledged using the reset button “ACKNOWLEDGE/RESET” located in the same page as well as on the main picture page of Excitation controls. Brief malfunctions are stored in memory and annunciated also. The indication vanishes once these temporary malfunctions are acknowledged. List of Alarms provides instructions as to what the reasonable operational response should be once a given malfunction has occurred.

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For various disturbances, the malfunctions indication is not only lit for the source itself, but also for the secondary malfunctions. In such cases, it is often difficult to identify the actual root of the problem quickly. “Field breaker First Out”, “Excitation First Out”, “Channel-1 First Out”, “Channel-2 First Out” help to identify the actual root cause of the problem quickly. The first fault within the group will be flashing and rest of the faults will be steady. The location of non-signaled malfunctions requires a more detailed knowledge of the excitation system and a systematic procedure based on the plant documents (e.g., the schematic diagram). When an alarm occurs, cursor can be positioned on the particular LED, on LED indication page. A double click of the selected point indicates the selected point tag name in the “selected point window”. With a click on the “detail popup” at the bottom right corner of the mimic and “follow” ing the input which has caused the alarm helps in locating the fault easily. Note the following when using the List of Alarms that follows: The following general procedure always applies even though not stated in the “Trouble shooting support display”: 

Note down all alarm indications.



Press the ACKNOWLEDGE/RESET button.



Some malfunctions may still be present.



Check the symptoms listed for the malfunction indications that are still present.



“Further Procedure”:

Carry out the instructions step-by-step in the order shown. Once one step has proven successful (the malfunction has been located and/or eliminated), the steps that follow are no longer necessary.

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9.3.5 Malfunctions other than alarms Generator does not become excited

Possible Causes

Points to Check and Correct

Break in field circuit



Does the Exciter field circuit breaker close?



Check cables for interruption.

Generator becomes excited to a  partial voltage but is de-excited again shortly thereafter.

Are firing pulses present at the output from the Final Pulse Stages? Do they shift into the rectifier position after the command “EXCITATION ON”? (Refer to Sect. 4.1 5.1 5.2 )

Failure of power supply to the  electronics equipment (LED’s on the power supply units fail to light).

Has the battery supply been switched on? (Refer to over-all Schematic Diagram/YU101)

There is still a converter blockage



After “EXCITATION ON”, the following Tagnames for bridge failures shall be “false”

The set point for voltage or field  current is not at the nominal noload value

Regulator malfunction

After “EXCITATION ON,” the binary controls must issue setting commands for Channel 1and 2 to PRESET reference value. Refer to EG040-YS505.  PRESET value for Auto Channels = address F250 in respective processors (refer to /YU105).  PRESET value for Manual Channel = Switch S855 on UN 0663 of respective channel (AE65) Is the control variable Ucontr of the active UN 0663 Gate Control Unit positive after “EXCITATION ON”? If not: For Auto Channels 1 & 2 do a functional test with EDN 48-0673-11

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the Micro-Terminal based on /YU105. For Manual channel, test based on data sheet of UN0663

Overvoltage During Field Flashing

Possible Cause Points to Check and Correct Over voltage due to improper phase  sequence

Switch over to manual channel and build up the voltage. Check the phase position of UR w.r.t IR, US w.r.t. IS and UT w.r.t IT at the sockets of module UN0661 of Auto channel.

voltage 

Switch over to manual mode and build up voltage. Check the actual values of Auto channels on the Micro Terminal while exciting the generator in manual channel. If set point F270 is too high, check F250, F254 & F256. If necessary, change the “Soft-Start Time” using F290

Over Voltage due to the If regulator  in Manual mode

Switch over to Auto channel and build up voltage. Check the actual value for field current at socket “If” while exciting

Over Voltage regulator

due

to

the generator on Auto mode. Check Vp and Ta in UN0663 module as per commissioning report. Gate Control Unit malfunction



Check if the control variable Ucontr is correct (it can be measured at the socket Ucontr), check the firing pulses R+ ... Sand their phase position. Check the synchronous voltages at UR, US, and UT.

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Unstable parallel Operation with the Grid Periodic Fluctuations in Reactive / Active Power Output

Possible Causes

Points to Check and Correct

Change in the controlled system due  to changes on the grid or drive end

If the changes causing the problem cannot be cancelled, re-stabilize the control loop. Then check and/or re-stabilise the limiters as well.

Adjustments for Vo, Vp, Ta, and Tb  have shifted.

Check the settings against the Test and Commissioning Report.

Irregular Instability, i.e., Sporadic Over-excitation or Under-excitation with Origin Not in the Grid Possible Causes

Points to Check and Correct

The droop influence is causing an  irregular voltage effect.

Check active current IR and reactive current IX at Addresses F906 and F902 (refer to/YU105).



Check external current transducer circuit and actual value for current Ig against the Test and Commissioning Report.

Generator is working in an  unacceptable operating range (normally prevented by limiters).

Adjust the set-point and bring the generator back within its normal operating range. Do a functional test on the limiters.



For malfunctions that occur unsystematically, check the control voltage Ucontr on the

Repeated, short or long lasting malfunctions in the electronics.

Gate Control Unit and the field voltage Uf using a recording device or an oscilloscope. 

If the two signals are in phase during the malfunction, the

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fault is upstream from the Gate Control Unit. Do a functional test on the voltage regulator, particularly the setpoint and actual value circuits, and on the limiters. 

Over or under excitation



If the two signals are out of phase during the malfunction, the fault is downstream from the regulator, i.e., the regulator is attempting to correct the fault : Do a functional test on the Gate Control Unit, the Final Pulse Stage, and the converter as described in Sect. 5.1 . Check the set point and attentuation factor of the limiter involved against the Commissioning Report.

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10. Installation and Commissioning 10.1 Installation Site With its thyristor converters, the exciter generates heavy high-voltage DC currents in the field current circuit. If the installation is subjected to the prolonged effects of dirt and corrosive gases, there is a risk of extensive damage caused by voltage flash-over. For that reason, select the location of the exciter in the power plant carefully and, if necessary, protect it from such dangers. The converter portion should be located as close as possible to the sliprings and the exciter transformer so as to keep voltage losses to a minimum. As the excitation cubicles may be subjected to a little vibration, it should not be firmly joined to the generator platform. To counter fouling and corrosion, it is better to set the excitation cubicles up in an enclosed, ventilated room. It goes without saying that the cubicles must be protected against splashing or spraying water, falling objects, etc. 10.2 Ambient Air The air must be as dry as possible and free of pollution, aggressive gas, insects, etc. Salty vapors, e.g., due to cooling with salt water, damage the unit. As a standard rule, the ambient temperature about the exciter must not exceed 50 °C (104 °F). Make certain that the warmed cooling air can flow off. Above the air pass out area an air space of at least one meter (approx.3 feet) must be left. 10.3 Commissioning As already mentioned in Sect. 1.1 commissioning of the excitation equipment must, as a rule, be performed or supervised by staff who have special know-how and experience. Because the unit has already been extensively tested in the factory, activities during commissioning are limited mainly to functional tests on its interaction with the generator, and with equipment on the power plant end. As a result, the time required for commissioning depends to a very significant degree on the cable connections outside the cubicles and on progress of the (other) generator commissioning in accordance with the program. The steps in commissioning the excitation equipment are as follows: Preliminary testing: Generator commissioning: test runs and testing of the generator protection system Functional and stability tests during normal generator operation Preliminary testing includes testing of the measurement, control, TRIP and alarm circuits, and the functional test on the converter. The following conditions must be met before these tests are carried out: EDN 48-0673-11

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Connecting of cables must be completed and have been tested electrically. The binary input signals must have been tested as far as the LED’s on the input modules. (Switch on F56, F57, F70, F71 and F81 to F84) and S12 to test position. The binary output signals must have been tested electrically, starting from the connection terminals (Jump the output contacts on the connection terminals). There must be an external power source available for the excitation transformer or for the converter directly (Also needed for the subsequent generator test runs). A substitute resistor (> 20 A) must be available for the functional test of the converter. Normally, the test runs for the generator include the recording of the generator’s shortcircuit and open circuit characteristics and testing of the generator’s protective TRIPs. For this purpose, the excitation transformer must be supplied with power from an outside source (not in shunt connection). Functional tests and stability tests can also be performed. Note :- For subsequent installations of the same type, it is possible to a large extent to do without the stability tests since, with this digital system, there is a high degree of certainty that the later units will operate in a way identical to that of the first unit.

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Approx. time required Tests

-------------------------------------------------------------Operating Conditions n(p.u.)

Ug(p.u.)

P(p.u.)

Q(p.u.)

(h)

-

Checking voltage regulators, AUTO-1 and AUTO-2 ; Stability, range of settings (oscillograms)

1

0 to 1

0

0

2

-

Oscillograms for excitation start-up, de-excitation, AUT0-1 and AUTO-2

1

0 to 1

0

0

1

-

Checking the V/Hzlimiter

0.5 to 1

0

0

0.5

-

Effects of current on the grid

1

1

0.4 to 0.6

+0.4 to 0.6

1

-

Voltage regulators: checking stability with the grid

1

1

as desired

as desired

2*

-

Reactive load shut-down (with oscillogram)

1

1

appr. 0

+0.4

0.5 *

-

Rotor current limiting measurement, range of settings, stability (oscillograms)

1

1

0 to 0.5

± 0.5

1*

-

Load angle limiting, measurement, range of settings, stability (oscillograms)

1

1

0.5

± 0.5

1*

-

Inductive stator current limiter

1

1

0.5

+ 0.5

1*

-

Capacitive stator current limiter

1

1

0.5

- 0.5

1.5 *

-

Power system stabilizer 1 1 0.5 appr. 0 2* with sudden changes in Ug set point * During these tests, surges in reactive load of approx. 0.1 to 0.3 p.u. must be expected.

n= speed

0.5 to 1

Ug = Generator Voltage

P= MW

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