3.12 Guidelines For Monitoring Control And Protection Of Shp Stations

Draft July 10, 2008

STANDARDS / MANUALS / GUIDELINES FOR SMALL HYDRO DEVELOPMENT

SPONSOR: MINISTRY OF NEW AND RENEWABLE ENERGY GOVERNMENT OF INDIA

Electro Mechanical Works

SPECIFICATION FOR MONITORING, CONTROL AND PROTECTION OF SMALL HYDROPOWER STATION

LEAD ORGANIZATION: ALTERNATE HYDRO ENERGY CENTRE INDIAN INSTITUTE OF TECHNOLOGY, ROORKEE

CONTENTS ITEMS

PAGE NO

1.0

Objective

1

2.0

General

1

3.0

References and Codes

1

4.0

Monitoring of SHP

2

4.1

Systems for Monitoring

2

4.2

Requirements of Monitoring System

4

5.0

Levels of Monitoring

5

6.0

Control Of Units Of Small Hydropower Plant

5

6.1

General

5

6.2

Generator Connection to Systems

5

6.3

Unit Control

6

6.4

Control Functions

10

6.5

Control of Hydroelectric Power Plants

12

6.6

Modern

practice

Regarding

governor

and

Plant

15

Control 7.0

Protection of SHP Generating Units

16

7.1

General

16

7.2

Equipment Trouble

17

7.3

Devices used in a Typical Protection System

18

8.0

Generator Connected in Parallel to Grid

30

9.0

Generators Connected in Parallel on a Common Bus

30

10.0

Protection Groups

31

10.1

Controlled Action Shut Down

31

10.2

Emergency Shut Down

31

10.3

Immediate Action Shut Down

31

10.4

Electrical Shut Down

32

11.0

Protection of Power Transformers

32

12.0

Fire Protection Shut Down

32

Annexure-I

List of Generator Panel Indication and Relays

33

Annexure-II

List of Protection Elements in Micro Processor Based Relays

34

SPECIFICATIONS FOR MONITORING CONTROL AND PROTECTION OF SHP STATIONS 1.0

OBJECTIVES

This guide is intended to assist in preparation of specification for monitoring of various parameters of various operations, control and protection of main generating equipment viz turbine, generator, transformer and other associated auxiliaries. 2.0

GENERAL

The generating units of a small hydropower plant may have its shaft vertical, horizontal or inclined with the type of turbine selected to suit the site’s physical conditions. Small hydro turbines may be selected as per site conditions, head and discharge available. Small hydro-generator are of the alternating current type and may be either synchronous or induction type. Usually small hydro units upto 5 MW are expected to require minimum amount of field assembly and installation work. While machine having capacity from 5 MW to 25 MW may have slow speed, large diameter and with split generator stator that require final winding assembly in the field. Mini & micro power stations are generally provided system suiting to these being run unattended or with few attendants while bigger machines upto 5 MW capacity have more elaborate arrangement of control monitoring and protection. Machine having capacity upto 25 MW and provision of parallel operation with other systems will have more comprehensive control, monitoring & protection system. This guide, therefore, describes control, monitoring and protection requirement of SHP having capacity upto 5 MW and also 5 to 25 MW. This guide will serve as a reference document alongwith available national & international codes standards, guide & books. For the purpose of convenience this guide has been subdivided as follows • • • 3.0

Monitoring Control Protection

REFERENCES AND CODES

IEEE Std 1020

-

IEEE Std 1010 IEEE Std 60545:1976

-

IEC 61116:1992

-

IEEE std 1046

-

IEEE std. 1249

-

IEEE guide for control of small hydro electric power plants IEEE guide for control of hydro electric power plants Guide for commissioning operation and maintenance of Hydraulic Turbines Electro mechanical guide for small hydroelectric installations IEEE application guide for distributed digital control and monitoring for power plants IEEE guide for computer–based control for power

AHEC/MNRE/SHP Standards/Specification for monitoring, control and protection of SHP stations  

 1 

IEEE std. C 37101 IEEE std. C 5012

-

IEEE std 4214

-

ANSI/ IEEE std 242:1996

-

ANSI/ IEEE std C 372-1987

-

ANSI/ IEEE std C 37.95 : 1974 ANSI/ IEEE std C 37.102:1987 MASON, CR AHEC/PFC/FINAL REPORT 2002

-

4.0

plant automation IEEE guide for generator ground protection IEEE standard for salient pole 50 Hz and 60 Hz synchronous generator and generator / motors for hydraulic turbine application rated 5 MVA and above IEEE guide for preparation of excitation system specification IEEE recommended practice for protection and coordination of industrial and commercial power systems IEEE standard electrical power systems device function numbers (R1980) IEEE guide for protective relaying of utility IEEE guide for generator protection Art & science of protective relaying 1956

MONITORING OF SHP

Monitoring of operating parameters of the generating unit and their auxiliaries is very important for the life and optimum utilization of available discharge for generation. The efficient running of unit require regular monitoring. The primary input data and generation output data are monitored periodically. The details of data required for monitoring performance of a generating station is as following. 4.1 SYSTEMS FOR MONITORING 4.1.1 Water Conductor System • • • • • • • • 4.1.2 •

•

Storage level at dam / barrage / weir River discharge Headrace channel discharge Discharge at outlet of disilting basin Forebay level Discharge of spillway Penstock pressure Tail water level Hydro-mechanical Parameters Turbine and accessories o Pressure and levels in oil pressure system o Bearing temperatures (oil & pads) o Oil level in bearing sumps (if provided) o Cooling water pressure and temperatures o Clean water pressure for shaft gland o Vibration in shaft for large machines o Status of inlet and other valves. Generator and accessories o Stator winding temperature

AHEC/MNRE/SHP Standards/Specification for monitoring, control and protection of SHP stations  

 2 

•

4.1.3 •

•

•

•

•

o Rotor winding temperature o DE/NDE end bearing temperatures o Cooling water and air temperatures o Air gap monitoring Transformers o Winding temperature o Oil temperature o Oil level o Cooling water temperature and pressures Electro-mechanical Operating Parameters Turbine & accessories o Speed o Guide vane opening & limits (precent) o Runner blade opening in Kaplan Turbine (percent) o Nozzle opening in impulse turbine (percent) Generator & auxiliaries o Governor actuator balance current (Amp) o Generated power (kW or MW) o Generated hour (kWh) o Kilovolt ampere (kVA) o Kilovolt ampere reactive (kVAR) o Power factor (PF) o Frequency (Hz) o Excitation voltage (Volts) o Excitation current (Amp) o Recorder for kW, Hz, kWh etc Transformers o Tap position o HV/LV current o Primary/ secondary voltage Grid system & transmission line o Grid voltage o Grid frequency o Power export / import (kW) o Current (Amp) o Kilowatt hour (kWh) export / import Station auxiliaries o Voltage and current on LT AC system o Kilowatt hour (kWh) o Diesel generator running hour, kWh & other parameters o Drainage & dewatering system ƒ Running hours of pumps ƒ Water level in sump o Fire extinguisher – periodical testing o Battery set- Regular monitoring as per manufacturers recommendations o Battery chargers & distribution boards – voltage current etc. o Air compressors – HP /LP pressures and running hours o OPU system

AHEC/MNRE/SHP Standards/Specification for monitoring, control and protection of SHP stations  

 3 

ƒ ƒ ƒ

Running hours of pumps Level in pressure accumulators Pressure of oil

4.2 REQUIREMENTS OF MONITORING SYSTEM 4.2.1 Instrument Transformers & Sensors CTs & VTs Current and voltage transformers of rated voltage and appropriate ratio, class of accuracy is selected as per the requirement of the system. Sensors The sensors for temperatures, pressures, levels speed are installed at the proper location. 4.2.2

Indicating Meters

Analogue type of meters, separate for each parameter with selector switches etc were being used earlier installed on control panels. Now a days digital meters are being used for such parameters. Digital multifunction meters are now in use, only one meter provides several parameters an selection, as well as provides routine display. Few analogue meters like power meters (kW), voltmeters, ameters with selector switches are provided for operational facilities. 4.2.3

Temperature Scanners

Digital temperature scanners indicating the temperatures of stator winding, bearing pads, oil coolers etc. are provided and installed on the generator control panels. These scanners get the signals from the sensor installed at specific location preferably through screened cables. 4.2.4

Indicating Lamps

Indicating lamps of suitable colours as per code and practices should be provided on control panels for indication status of machine and various auxiliaries, pumps, electrical equipment like breaker, isolator, AC/DC supply system etc. Lists of such indication and relays are enclosed as Annexure-I&II. 4.2.5

Alarm & Annunciations

The protection system relays and auxiliary relays also provided signals to alarm and annunciation system. A set of annunciation windows are provided on control panels for each fault clearing relay with accept test and reset facility through push buttons. Alarm and trip annunciation indicate the fault and advise operating personnel of the changed operating conditions.

AHEC/MNRE/SHP Standards/Specification for monitoring, control and protection of SHP stations  

 4 

4.2.6

PLC Based System

Recently control of machine and auxiliaries is done through PLC based control system automatically in addition to manual systems with local and remote facilities. The data are acquired through sensors and operation of machine is achieved on present values through PC Monitors etc. The PLC will acquire data from generating units, transformers, switchgears auxiliaries through transducers / sensors/ CTs/ VTs wherever signals are week, noise level is high shielded cables should be used for carrying data / signals. For sending output signal PLC will use relays for operating breakers etc and comparators for giving ON/OFF signal. 5.0

LEVELS OF MONITORING

Normally two levels of monitoring is provided in SHP as per recommendation of IEC 1116. The levels are: • •

Alarm Tripping

In case of manned power plant ‘alarm’ comes first so as to make the operator alert if no corrective action is possible then tripping command with indication / hooter and annunciation will be there. But in case of unattended power plant direct tripping command will be initiated and shut off the facility to avert possibility of any damage to the plant. 6.0 6.1

CONTROL OF UNIS OF SMALL HYDROPOWER PLANT GENERAL

For small hydro installation simplicity of control system is advised, however, the sophistication of control should be based on the complexity and size of the installation, without compromising unit dependability and personal safety. Simplicity of control is desirable to keep total cost of installed equipment as well as cost of maintenance, repair and tests at economical level. Moreover a simpler system is more reliable as compared to complex one. 6.2 6.2.1

GENERATOR CONNECTION TO SYSTEMS Synchronous Generator

For conventional method of synchronizing the generator is started, accelerated to near synchronous speed and excitation is applied. The voltage and the frequency are matched and unit is synchronized to the system, by closing generator circuit breaker or contactor, when done perfectly no current surge will occur. Normally both manual and automatic synchronizing of generator are provided. In addition the speed of some types of turbines under no load conditions is so sensitive to small adjustments in runner blade angle or inflow as to make only automatic synchronizing practical.

AHEC/MNRE/SHP Standards/Specification for monitoring, control and protection of SHP stations  

 5 

Small hydropower plants will certainly require unattended automatic synchronizing. Manual synchronizing necessitates availability of continuous display of voltage, frequency, phase angle and devices to control voltage and speed on the control panel. Transducers or signal transmitters are provided either at the control panel or at the equipment. 6.2.2

Induction Generator

For conventional method of connecting induction generator to the grid, the generator is started and accelerated to synchronous speed. In fact, the rotor speed of generator shall be (1% slip) more than grid frequency. This is done to avoid monitoring action of generator. Once the generator frequency matches with grid frequency the generator breaker is closed. Now the generator is connected with the grid and running at no load. At this stage grid power factor is to be checked and capacitor banks are switched on as per requirement to provide necessary reactive power and further loading of unit is done upto full load. All these functions can be performed manually as well as automatically through PLC, computer, microprocessor based control system. For smaller machines which are unattended provision of integrated digital control & SCADA system is preferred. 6.2.3 • • • • • • • • • • • • • • 6.3

Status and Alarm Requirements Unit ready to start Breaker position (no alarm if manual operation only) Intrusion alarm Fire alarm Emergency status alarm (requires immediate attention0 General status alarm (response can be differed) Trash rack differential alarm Unit stopped (when not required) Unit turning (when not required) High bearing temperatures Loss of lubrication or cooling or both Low hydraulic system pressure Incomplete start or stop sequence Loss of power UNIT CONTROL

The control logic system for small hydro start stop sequencing can be provided by hardwired relay logic, programmable controllers microprocessor based systems or a combination of these. The unit control system should be designed to perform following functions:

AHEC/MNRE/SHP Standards/Specification for monitoring, control and protection of SHP stations  

 6 

• • • • • • • •

Data gathering and monitoring Start stop control sequence Annunciation & alarm conditions Temperature monitoring Metering & instrumentation Event recording Synchronizing and connecting the unit to grid Control of real & reactive power

The unit control system must be able to provide startup and shutdown sequencing under both normal and abnormal conditions. Under normal conditions, the unit is started and stopped in manner that produces minimal disturbance to the system. For instance of normal stop sequence entails a controlled unloading of machine and when completely unloaded, the generator breakers or contactor is tripped. On the other hand protective relay operation will initiate immediate tripping of the unit and complete shutdown as quickly as possible. For certain mechanical troubles the unit is unloaded as quickly as possible before tripping, in order that the potential damage from over speed is avoided. The unit control system, in order to control and monitor various control sequences, must interface with number of plant systems, including the following: • • •

Auxiliary system – pumps & valves Governor load control rollers – setters, solenoids & brake control Excitation – setters, contactors and circuit breakers

Typical startup and shutdown sequence are shown in fig. 1-3 for a Francis turbine unit, which, for the sake of illustration, are shown as including synchronous generator and governing system.

AHEC/MNRE/SHP Standards/Specification for monitoring, control and protection of SHP stations  

 7 

Fig. 1: Typical Start Sequence of Synchronous Generator

AHEC/MNRE/SHP Standards/Specification for monitoring, control and protection of SHP stations  

 8 

Fig. 2: Typical Normal Shut Down and Mechanical Trouble Stop Sequence of Synchronous Generator

AHEC/MNRE/SHP Standards/Specification for monitoring, control and protection of SHP stations  

 9 

Fig. 3: Typical Electrical Trouble Stop Sequence for Synchronous Generator 6.4

CONTROL FUNCTIONS

There are many functions to be controlled in a small hydropower system. For example turbine governor controls the speed of turbine, plant automation covers operations as auto start, auto synchronization, remote control startup or water level control and data acquisition and retrieval covers such operation as relaying plant operating status, instantaneous system efficiency or monthly plant factor. 6.4.1

Turbine Control

This is the speed / load control of turbine in which governor adjusts the flow of water through turbine to balance the input power with load.

AHEC/MNRE/SHP Standards/Specification for monitoring, control and protection of SHP stations  

 10 

In case small plants in the category of micro hydel (100 kW unit size), load controllers are used, where excess load is diverted to dummy load to maintain constant speed. With an isolated system, the governor controls the frequency of the system. In interconnected system, the governor may be used to regulate unit load and may contribute to the system frequency control. Figure 4 shows the different types of control applicable to turbines.

Fig. 4: Turbine Control 6.4.2

Generator Control

This is the excitation control of synchronous generator. The excitation is an integral part of synchronous generator which is used to regulate operation of generator. The main functions of excitation system of a synchronous generator are: • •

Voltage control in case of isolated operation and synchronizing Reactive power or power factor control in case of inter connected operation. The different generator controls are shown in fig. 5.

Fig. 5: Generator Controls 6.4.3

Plant Control

Plant control deals with the operation of plant. It includes sequential operation like startup, excitation control, synchronization, loading unit under specified conditions, normal shutdown, emergency shutdown etc. The mode of control may be manual or automatic and

AHEC/MNRE/SHP Standards/Specification for monitoring, control and protection of SHP stations  

 11 

may be controlled locally or from remote location. Plant control usually include monitoring and display of plant conditions. Different plant controls are given in fig 6.

Fig. 6: Overview of Plant Automatic Control 6.5 6.5.1

CONTROL OF HYDROELECTRIC POWER PLANTS Vertical Array of Control System

For hydroelectric power plants the components of the control system can be shown in vertical array as shown in fig 7.

Fig. 7: Hierarchy of Controls of Hydropower Plants

AHEC/MNRE/SHP Standards/Specification for monitoring, control and protection of SHP stations  

 12 

• •

•

6.5.2

At lowest level (process level) process which includes, generator exciter, turbines, switchgears, motors, pumps, valve etc is being controlled. At middle level there is control interface equipment which sends signals to the apparatus from controlling equipment and for apparatus to transmit data back to controlling equipment. Auxiliary contacts of motor starter, relays instrument transformer signal conditioner, transducers or other interface devices. At top level there is controlling system which initiate control signals and receives the data transmitted from apparatus control interface equipment. At this level itself human-machine interface is included. Categorization of Control System

The control system can further be defined by identifying following three categories of control: •

Location: a. Local b. Centralised c. Off site

•

•

6.5.3

- control is local at the controlled equipment with in the sight of the equipment - control is at other place, but with in the plant - control is at remote place which may be quite far from the plant (Remote)

Control mode: a. Manual

- Each operation requires a separate and distinct initiation. However it may be applicable for any of the three locations b. Automatic - With single initiation several operations in appropriate (PLC/ computer/ sequence are done. This system can also be applicable to any Microprocessor of the above three locations Controlled) Operation (supervision) a. Attended - Operators are all the time available at the plant to perform control action either locally or centralized control b. Unattended - Operating staff is not available at the plant. There may be occasional visits by operation & maintenance people to ensure security of plant. Information and Control Signals

Following four types of signals are provided between control board and particular equipment • • • •

Analog inputs for variable signals from CTs, VTs, RTDs, pressure, flow, level, vibration etc. Digital inputs provides digitalized values of variable quantities from the equipment Digital outputs – command signals from control boards to equipment Analog outputs – transmit variable signals from control to equipment e.g. governor, voltage regulator etc.

AHEC/MNRE/SHP Standards/Specification for monitoring, control and protection of SHP stations  

 13 

6.5.4

Communication Links

a.

Communication links with remote control • • • • • •

Following methods are available for implementing control from a remote location: Hardwired communication circuits (telephone type line, optical cables etc.) Leased telephone lines Power line carries communication system Point to point radio Microwave radio Satellite

Metallic circuit in hardwire communication circuits and leased telephone lines, requires special protection for equipments and personnels against ground potential rise (GPR) due to electric system fault, since the hydro-generator is source of fault current. GPR is also caused by lightening transmitted through power lines entering the power plant. As such suitable mitigation has to be provided. Power line carrier including insulated ground wire system can be used for communications purposes. This method couples a high frequency signal on the power line or insulated ground wire and is decoupled at an off site point. Space radio can be used, utilizing power frequencies and micro wave radio can be practical if hydro plant owner has an existing microwave system. b.

Communication with control boards

Data and control signals of following equipments will be required to be transmitted between control board & equipments. • • • • • • • • • •

Generator neutral and terminal equipment Head water and tail water level equipment Water passage shut off or bye pass valves gates etc. Turbine Unit transformer Circuits breaker and switches Generator Intake gates or main inlet valve and draft tube gates Turbine governing system Generator excitation system The communication link between control board and equipment should be reliable.

c.

Communications with Auxiliaries

Data and control signals of following auxiliaries equipments will be required to be transmitted between control board and equipments.

AHEC/MNRE/SHP Standards/Specification for monitoring, control and protection of SHP stations  

 14 

• • • • • • • 6.6 6.6.1

Fire protection AC Power supply DC Power supply Service water Service air Water level monitoring Turbine flow monitoring MODERN PRACTICE REGARDING GOVERNOR AND PLANT CONTROL Previous Practice

Control of a hydro plant generating unit was typically performed from central control board located in centralize control room. The control board contained. • • • •

6.6.2

Iron vane meters Hardwired control switches A large number of auxiliary relays to perform unit start / stop operations All the sensors and controls required to operate unit or units were hardwired to control panels allowing control of power station from cotnralised control room Modern Practice

Modern digital integrated control and protection system including programmable logistic controller (PLCs), distributed computer control system or personal computer control system not only provide supervisory control and data acquisition (SCADA) but also flexibility in control, alarm, sequencing, remote communication in a cost effective manner and has been specifically recommended for SHPs in India, under UNDP – GEF projects. Control functions of small hydro plants are standardized in following US standards a. IEEE guide for control of small hydro electric plants, “ANSI/IEEE standard 1011, 1990’. b. IEEE guide for control of hydroelectric power plants “ANSI/IEEE standard 1010, 1991. Specific hardware or software to be utilized for implementation is not however addressed in these standards. Architecture and communication are two potential problem area for computerized control system. In 1990, the International Organisation for standardistion developed a model for open architecture and protocol, know as SI (open system interconnection) – ISO mode. Programmable Logic Controllers (PLC) type plant controllers combine with PC based SCADA system are used as Governors and for plant control & data acquisition. This makes the system less costly and reliable and therefore, can be used for small hydropower generation control.

AHEC/MNRE/SHP Standards/Specification for monitoring, control and protection of SHP stations  

 15 

Personal computer based dedicated digial control system can perform all functions of governing, unit control, protection and also data acquisition & storage and are more economical and reliable. These dedicated systems with back up manual control facility of turbine control in emergency by dedicated semic automatic digital controllers can be a low cost option for small hydropower station. 7.0 7.1

PROTECTION OF SHP GENERATING LIMITS GENERAL

Small hydro turbine-generators should be protected against mechanical, electrical, hydraulic and thermal damage that may occur as a result of abnormal conditions in the plant or in the utility system to which the plant is electrically connected. The abnormal operating conditions that may arise should be detected automatically and corrective action taken in a timely fashion to minimize the impact. Relays (utilizing electrical quantities), temperature sensors, pressure or liquid level sensors, and mechanical contacts operated by centrifugal force, etc., may be utilized in the detection of abnormal conditions. These devices in turn operate other electrical and mechanical devices to isolate the equipment from the system. Where programmable controllers are provided for unit control, they can also perform some of the desired protective functions. Operating problems with the turbine, generator, or associated auxiliary equipment require an orderly shutdown of the affected unit while the remaining generating units (if more than one is in the plant) continue to operate. Alarm indicators could be used to advise operating personnel of the changed operating conditions. Loss of individual items of auxiliary equipment may or may not be critical to the overall operation of the small plant, depending upon the extent of redundancy provided in the auxiliary systems. Many auxiliary equipment problems may necessitate loss of generation until the abnormal conditions has been determined and corrected by operating or maintenance staff. The type and extent of the protection provided will depend upon many considerations, some of which are: (1) the capacity, number, and type of units in the plant; (2) the type of power system; (3) interconnecting utility requirements; (4) the owner’s dependence on the plant for power; (5) manufacturer’s recommendations; (6) equipment capabilities; and (7) control location and extent of monitoring. Overall, though, the design of the protective systems and equipment is intended to detect abnormal conditions quickly and isolate the affected equipment as rapidly as possible, so as to minimize the extent of damage and yet retain the maximum amount of equipment in service. Small hydroelectric power plants generally contain less complex systems than large stations, and therefore tend to require less protective equipment. On the other hand, the very small stations should be typically unattended and under automatic control, and frequently have little control and data monitoring at an off-site location. This greater isolation tends to increase the protection demands of the smaller plants.

AHEC/MNRE/SHP Standards/Specification for monitoring, control and protection of SHP stations  

 16 

An inherent part of the power plant protection is the design of the automatic controls to recognize and act on abnormal conditions or control failures during startup. Close coordination of the unit controls and other protection is essential. 7.2 EQUIPMENT TROUBLE 7.2.1 Plant Mechanical Equipment Troubles 7.2.1.1 Turbines (a) (b) (c) (d) (e) (f)

Excessive vibration Bearing problems Over speed Insufficient water flow Shear pin failure Grease system failure

7.2.1.2 Hydraulic Control System (a) Low accumulator oil level (b) Low accumulator pressure (c) Electrical, electronic or hydraulic malfunctions within the governing or gate positioning system 7.2.1.3 Water Passage Equipment (a) (b) (c) (d)

Failure of head gate or inlet valve Head gate inoperative Trash rack blockage Water level control malfunction

7.2.2 Plant Electrical Equipment Troubles 7.2.2.1 Generator (a) (b) (c) (d) (e) (f) (g) (h) (i)

Abnormal electrical conditions Stator winding high temperature Low frequency Bearing problems Motoring Fire Excessive vibration Cooling failure Over speed

7.2.2.2 Main Transformer (a) (b) (c) (d)

Insulation failure High temperature Abnormal oil level Fire

AHEC/MNRE/SHP Standards/Specification for monitoring, control and protection of SHP stations  

 17 

7.2.2.3 Generator Switchgear and Bus (a) Electrical fault (b) Mechanical failure (c) Loss of control power 7.2.3 General Plant Troubles 7.2.3.1 Station Service (a) (b) (c) (d) (e) (f) (g) (h) (i) (j) 7.2.4

Transformer failure Unbalanced current DC System Trouble Station Air System Trouble Service Water System Trouble Flooding Fire Unauthorized Entry Protection or Control Logic System Malfunction Water level Monitoring System Malfunction Utility System Troubles

Utility line faults and other abnormal utility system conditions should be detected and the plant be disconnected from the utility system. Abnormal utility system conditions include the following situations: a. b. c. d.

Ground or phase faults Single phasing Abnormal voltage System separation (islanding)

Coordination with the utility is needed in selecting specific protective equipment, particularly for line fault detection. 7.3

DEVICES USED IN A TYPICAL PROTECTION SYSTEM

There are numerous ways of providing the functional protective requirements of the plant. While standard devices are generally available that can provide the protective functions required, however each station should have specific design suitable for protection requirements of the power plant equipment as well as the interconnection. The following section describes components of a typical protection system that might be applied to a small hydro plant. Discussions and diagrams are included to illustrate location and arrangement of relays. 7.3.1 Protective Devices 7.3.1.1 Temperature A temperature device, possibly incorporating display and contacts for alarm annunciation and tripping to monitor bearing stator and transformer winding temperatures.

AHEC/MNRE/SHP Standards/Specification for monitoring, control and protection of SHP stations  

 18 

Resistance temperature devices operating relays can also be used to detect generator stator overheating. 7.3.1.2 Pressure and Level Pressure and level switches installed in the turbine air and oil systems, to alarm, block startup, or trip, as necessary. 7.3.1.3 Over and underspeed Direct-connected or electrically driven speed switches for alarm, control, and tripping. 7.3.1.4 Vibration Vibration detectors monitoring turbine or generator shaft sections, with alarm and trip contacts. 7.3.1.5 Water level A measuring system incorporating level sensors and monitoring equipment, to alarm, trip, or control turbine output on limiting values of headwater or tail water level, or head. 7.3.1.6 Fire Sensors located in areas where fire can occur and connected to a central fire monitor for alarm. Small generators usually do not have fire sensors or suppression equipment, since they are not usually enclosed. 7.3.1.7 Miscellaneous mechanical Sensing devices are integral to the protected systems, such as automatic greasing system, wicket gate shear pins, transformer, cooling and station sump drainage system. 7.3.2

Protective Relay and Protection System

7.3.2.1 Features of relays The protective relays stand watch and in the event of failures short circuits or abnormal operating conditions help de-energize the unhealthy section of power system and restrain interference with rest of it and limit damage to equipment and ensure safety of personals. The protective relays should possess following features: • • • •

Reliability – To ensure correct action even after long period of inactivity and also to offer repeated operation under sever condition. Selectivity – To ensure that only the unhealthy part of system is disconnected Sensitivity – Detection of short circuit or abnormal operating condition. Speed – To prevent and minimize damage and risk to instability of rotating plant.

AHEC/MNRE/SHP Standards/Specification for monitoring, control and protection of SHP stations  

 19 

•

Stability – The ability to operate only under those conditions that calls for its operation and to remain either passive or biased against operation under all other conditions.

7.3.2.2 Type of relays There are several types of relays being used for protection systems -

Electromagnetic relays Static relays Numerical relays

The old conventional electromagnetic relays are now being replaced with static relays with are much faster and maintenance free. These relays are more reliable and sensitive. These microprocessor based relays have different protections elements and therefore separate relays for each protection is not required. A list of protections generally available in these microprocessor based relays is enclosed as Annexure-II. The numerical relays are having LED indications for power ON, trip status for different protection elements, time / current characteristics selected and contacts for trip signals. However, some individual electromagnetic conventional / static relays for few important protections are recommended to be provided as standby relays. •

Advantages of numerical relays

It has been a practice to use electro-mechanical / solid state relays for all above protections. The present trend is to use numerical relays which offer many advantages as follows, over the earlier technology. PARAMETER Accuracy Burden Setting Ranges Multi Functionality Size Field Programmability Parameter Display System Flexibility Co-ordination Tools Communication Remote Control Special Algorithms Special Protections Self Diagnostics

NUMERIC 1% <0.5 VA Wide Yes Small Yes Yes Yes Many Yes Yes Many Yes Yes

CONVENTIONAL 5%/7.5% >5 VA Limited No Large No No No Two No No Limited No No

The user’s worry that numerical relays are very expensive is now removed due to continuous production, improvement in techniques which have made numerical relays above all, with features listed as above. Numerical relays are more user friendly and are gaining popularity every where.

AHEC/MNRE/SHP Standards/Specification for monitoring, control and protection of SHP stations  

 20 

Following annexures are enclosed for ready reference • •

Annexure-I Annexure-II

- List of SHP Generator panel indications & relays - List of protection elements in Microprocessor based relays

7.3.2.3 Criteria of selection of protection system The designer must balance the expense of applying a particular relay against the consequences of losing a generator. The total loss of generator may not be catastrophic if it represents a small percentage of the investment in an installation. However, the impact on service reliability and upset to loads supplied must be considered. Damage to equipment and loss of product in continuous processes can be dominating concern rather than generating unit. Accordingly there is no standard solution based on MW-rating. However, it is rather expected that a 500 kW, 415 V hydro machine will have less protection as compared to 25 MW base load hydro electric machine. With increasing complications in power system, utility regulation, stress on cost reduction and trends towards automation, generating unit protection has become a high focus area. State of the art, micro controller based protection schemes offer a range of economical, efficient and reliable solution to address the basic protection and control requirements depending upon the size and specific requirement of the plant. 7.3.3

Requirements of Protection of Turbine Two level protection is recommended as per IEC 1116. Elements to be considered

are: (a) (b) (c) (d) (e) (f) (g) (h) (i) (j)

Speed rotation Oil levels in bearing Circulation of lubricants Oil level of the governing system Oil level of speed increaser (if provided) Bearing temperatures Oil temperature of governing system Oil temperatures of speed increasers Oil pressure of governing system Pressure of cooling water

Immediate tripping is required for a, c, i, and j. While for item b, d, e, f, g and h only alarm and annunciation is required to alert the operate and take corrective action, but in case corrective action is not taken, tripping will eventually follow. Applying brakes at a particular speed (30% of full speed) is done to reduce time to achieve stand still position of machine. It is recommended two independent devices must be provided for over speed shut down on larger machines. One for alarm mostly at 110% and other for tripping at 140%, specially for machines which are not designed for continuous run away speed. 7.3.4

Requirements of Protection of Generator Elements to be considered normally are

AHEC/MNRE/SHP Standards/Specification for monitoring, control and protection of SHP stations  

 21 

a. b. c. d. e. f. g. h. i.

Stator temperature Over current (stator and rotor) Earth fault with current limits (stators & rotor) Maximum and minimum voltage Power reversal Over/ under frequency Oil level in bearing sumps Pad & oil temperature of bearings Cooling air temperature

Immediate tripping is required for items b, c, d, e & f while for items a, g, h and i first alarm and annunciation is required for taking correcting measure and then tripping if correcting measure is not taken within permissible time. It is advisable to provide heating arrangement to prevent condensation in generator. 7.3.5 Generator Protection System and Relay Selection 7.3.5.1 Categorisation In view of the economy and plant requirements generator protection for small hydropower stations is categorized a follows: • • • •

Generator size less than 300 kVA Generator size 300 to 1000 kVA Generator size 1 MVA to 10 MVA Generator size above 10 MVA

7.3.5.2 Transient overvoltage and surge protection Transient over-voltages and lightning surges are controlled by lightning arrestors. Surge capacitors are provided to restrict rate of rise of surge voltages and their magnitudes. Every generator is provided with a set of lightening arrestors / surge diverter of appropriate rating and generated voltage. 7.3.5.3 Minimum protection for a small machine with low resistance grounding are proposed as follows: Device No. 51V 51GN

Description Basic Package Voltage-restrained time over current relay Neutral ground over current relay

27 32 40 46 49R 50GS

Options Under voltage relay Reverse power relay Loss of excitation relay Negative phase sequence relay Stator over temperature relay Ground sensor over current relay

AHEC/MNRE/SHP Standards/Specification for monitoring, control and protection of SHP stations  

 22 

51VC 64B 81 L/H 86G 87G 12

Voltage controlled over current relay Generator ground over voltage relay (in place of 51GN where generator is ungrounded) Under / over frequency relay Lockout auxiliary relay Self-balancing current differential relay Over speed relay

7.3.5.4 Minimum protection for a large machine with high resistance grounding

21 24 27 27TN 32 40 46 51GN 51V 59 60V 64G 64F

Basic Package Distance Over excitation Under voltage Third harmonic under voltage Reverse power Loss-of-excitation Current unbalance (negative sequence) Ground over current (backup to 64G) Voltage-restrained over current Over voltage VT fuse failure detection Stator ground Ground (field)-I

AHEC/MNRE/SHP Standards/Specification for monitoring, control and protection of SHP stations  

 23 

81L/H 87G 50/27 95 86G 12

Under/ Over frequency Percentage differential Accidental energization protection Trip circuit monitoring Lockout auxiliary relay Over speed relay

21G 49R 60V2 78

Options System backup distance relay (in place of 51V) Stator over temperature relay (RTD) Voltage ground relay-II Out-off step relay

7.3.5.5 Typical schemes With increasing complications in the power system, utility regulations, stress on cost reduction and trend towards automation, generator protection has become a high focus area. State of the art, microcontroller based protection schemes from various manufactures offer a range of solutions to customers to address the basic protection and control requirements depending upon the size and plant requirements.

AHEC/MNRE/SHP Standards/Specification for monitoring, control and protection of SHP stations  

 24 

7.3.5.6 Generators-size less than 300 kVA Normally these generators are controlled by MCCBs, which offer O/C and short circuit protections. It is advisable to have following protections in addition to MCCB. E/F protection (51 N): This will protect the generator from hazardous leakages and ensure operator safety. Many organizations have already made E/F protection as mandatory. Since these units are very remotely located and less manpower is available for operation and maintenance, the system need more automization and fool proof protections. Therefore, recently several optional protections are also being used for micro/mini units including over speed (12) protections. 7.3.5.7 Generators – size 300 to 1000 kVA There are two major differences when compared with the small machines considered above. •

IDMT over current + E/F relay will be required in addition to normal MCCB or ACB releases – since the generator may need shorter trip time for faults in the range 100% to 400% level.

AHEC/MNRE/SHP Standards/Specification for monitoring, control and protection of SHP stations  

 25 

•

•

By virtue or larger power level, any faults inside the stator or fault between the neutral of the machine and the breaker terminals can reach very high intensity. Such internal faults must be cleared instantaneously. Normal IDMT over current E/F relays are not adequate to monitor this internal fault status-otherwise the machine can circulate very high fault currents resulting in severe damage. A high impedance differential relay scheme, is the best suited for this purpose. If the neutral is formed inside the machine, the differential relay scheme will not be possible. In this case a restricted E/F scheme is the solution. Care should be taken to provide adequate number of CTs. Machine of this size are likely to have external controls for frequency and excitation – so that they can be run in parallel with other power sources (other generators on the same bus or the local grid). This necessitates voltage and frequency related protections as well.

7.3.5.8 Generators – size 1 MVA to 10 MVA •

Stator side protections o Voltage restrained over current protection (50V/51V) Normal IDMT O/C will not work here-when an over current fault occurs, due to higher current levels, there would be a drop in terminal voltage. For the same fault impedance, the fault current will reduce (with respect to terminal voltage) to a level below the pick up setting. Consequently normal IDMT may not pick up. It is necessary to have a relay whose pick up setting will automatically reduce in proportion to terminal voltage. Hence the over current protection must be voltage restrained. Two levels of over current protection are required – low set and high set (for short circuit protection). o Thermal overload (49) This protection is a must – it monitors the thermal status of machine for currents between 105% to the low set O/C level (Normally 150%) o Current unbalance (46) Generators are expected to feed unbalanced loads-whose level has to be monitored. If the unbalance exceeds 20%, it may cause over heating of the windings. This heating will not be detected by the thermal overload relaysince the phase currents will be well within limits. A two level monitoring for unbalance is preferred-first level for alarm and the second level for trip. o Loss of excitation (40) When excitation is lost in a running generator, it will draw reactive power from the bus and get over heated. This condition is detected from the stator side CT inputs – by monitoring the internal impedance level & position of the generator. o Reverse Power (32) Generators for this size may operate in parallel with other sources, which may cause reverse power flow at certain times. During synchronization PF change due to load/ grid fluctuations Prime mover failure

AHEC/MNRE/SHP Standards/Specification for monitoring, control and protection of SHP stations  

 26 

When reverse power happens, the generator along with prime mover will undergo violent mechanical shock – hence reverse power protection is necessary. o Under Power (37) It may not be economical to run generators below a certain load level. This protection will monitor the forward power delivered by the machine and give alarm when the level goes below a set point. This may however be optional. o Under/ over voltage (27/59) This will protect the machine from abnormal voltage levels, particularly during synchronization and load throw off conditions. o Under/ over frequency (81) This will protect the machine from abnormal frequency levels, particularly during synchronization and load throw off conditions. This will also help in load shedding schemes for the generator. o Breaker failure protection This protection detects the failure of breaker to open after receipt of trip signal. Another trip contact is generated under breaker fail conditions, with which more drastic measures can be taken, like opening of bus coupler or feeder breaker etc. o Stator earth fault (64F) This element tuned to the fundamental frequency can be used for the protection of stator winding from earth fault. o PT Fuse failure protection This relay will detect any blowing of PT secondary fuse and give a contact which can be used to lock the under voltage trip. This protection is very impartment since the machines of this size have to be protected for severe damages that may occur due to internal faults. Considering the large power levels, it is necessary to have a percentage biased, low impedance differential relay. These relays generally have following advantages. -

Percentage biased differential protection with dual slope characteristics REF protection element (87 N), which will monitor the generator for internal earth faults Over current protection, as a back up

AHEC/MNRE/SHP Standards/Specification for monitoring, control and protection of SHP stations  

 27 

•

Rotor side protections Generators of this size will need rotor side protections listed below: o Diode failure relay Brushless excitation systems will have rotor mounted diodes, which can become short or open during operation. Diode failure relay will monitor the condition of these diodes, for both open circuit and short, and give alarm o Rotor excitation current This is a DC current relay which will monitor the excitation current. o Rotor excitation voltage This is a DC voltage relay which will monitor rotor voltage The above three protections are normally part of the excitation system of the generator. o Rotor earth fault Relay for this protection will monitor the rotor winding status for the earth fault, it will detect the first earth fault occurred in the winding and provide an alarm. The relay employs proven DC rejection method for the detection of E/F. there are other two methods as shown in the diagram for field ground detection.

AHEC/MNRE/SHP Standards/Specification for monitoring, control and protection of SHP stations  

 28 

    FIELD

EXCITER FIELD BREAKER

BRUSH

C1

C2 AC

64F R

R

Fig. 13 Field ground detection using pilot brushes

 

7.3.5.9 Generator above 10 MVA For large generators above 10 MVA size, the philosophy of main protection and back up protection has to be followed. In addition to the protections listed above following extra protections are to be considered.

AHEC/MNRE/SHP Standards/Specification for monitoring, control and protection of SHP stations  

 29 

o 100% earth fault protection This will help in sensing earth faults close to neutral. Third harmonic content in the zero sequence voltage will be detected by the replay for the above protection. o Inadvertent breaker closure This will avoid closing of generator to bus during process to stop, or when stand still or before synchronism. o Under impedance This will be required as a back up protection for the whole system including the generator transformer and the associated transmission line. If the distance relay fails to pick for some reason, this under impedance function will pick up and save the generator. o Over excitation This will protection the generator from over fluxing conditions 8.0

GENERATOR CONNECTED IN PARALLEL TO GRID

Whenever generators are running parallel to grid, a comprehensive auto synchronizing & Grid islanding scheme will be required. This scheme will help in synchronizing the generator to the bus and opening the incomer breaker of the plant whenever there is a severe grid disturbance, thus protecting the generator from ill effects of disturbed grid. •

Grid disturbances 9 Under-voltage / Over-voltages 9 Under-frequency/Over-frequency 9 Rapid fall/ rise of frequency (df / dt), 9 Grid failure or other faults

Generator may not be able to operate below a certain power-factor. At low powerfactor, reverse reactive power flow may damage the generator. •

9.0

Grid fault detection 9 Over current and directional earth fault, 9 Rapid fall/ rise of frequency (df/dt), 9 Vector surge relay, GENERATORS CONNECTED IN PARALLEL ON A COMMON BUS

Whenever more than one generator is operating in parallel, it is necessary to see that the plant load is equally shared by the generators in parallel. If there is unequal sharing, there would be sever hunting amongst the generators and eventually this will lead to cascaded tripping of all generators, causing a total black out. Specific load sharing relays are available in the market which provide the most effective, online load sharing system for generators in parallel.

AHEC/MNRE/SHP Standards/Specification for monitoring, control and protection of SHP stations  

 30 

10.0

PROTECTION GROUPS

The protective relays and devices of generator and turbine are proposed to be grouped into following four categories for an orderly shutdown of the affected unit with the remaining generating units and auxiliaries continue to operate. 10.1

CONTROLLED ACTION SHUT DOWN Controlled action shutdown will be initiated by any of the following conditions

• • • • • 10.2 • • • • •

Generator thrust bearing pads temperature very high Generator guide bearing pads temperature very high Turbine guide bearing pads temperature very high Governor OPU oil level low stage-II Governor OPU oil pressure low stage-II EMERGENCY SHUT DOWN Emergency shutdown will be initiated by any of the following conditions. Sped 115% and deflector/ guide vanes/ runner blades apparatus not moved to closing Deflector etc. fails to close in preset time Unit over speed (electrical) > 140% Unit over speed (mechanical)>150% Stop push button on control panel in control room is pressed Emergency shut down system will perform following functions:

• • • • • • 10.3

Trip generator breaker Stop turbine by governor action Trip generator field circuit breaker Operate trip alarm in control room Energizes emergency solenoid valve in governor cubicle to stop the turbine by bypassing governor Close main inlet valve IMMEDIATE ACTION SHUT DOWN Immediate action shut down will be initiated by any of the following conditions

• • • • • •

Generator differential protection operates Generator stator earth fault protection operates Generator field failure protection operates Generator transformer stand by earth fault protection operates Over current in stator Over current instantaneous protection in the excitation circuit The immediate action shut down perform following function

AHEC/MNRE/SHP Standards/Specification for monitoring, control and protection of SHP stations  

 31 

¾ ¾ ¾ ¾ 10.4

Trip generator breaker Trip field breaker Initiates controlled action shut down stop turbine by governor action Trip annunciation in control room ELECTRICAL SHUT DOWN Electrical shutdown system will be initiated by any of the following conditions

• • • • • •

Over current in the excitation circuit Generator back up protection operates Generator over voltage protection operates Excitation failure protection operates Reverse power protection operates Generator T/F IDMT over current, over current instantaneous & earth fault protection operates Electrical shut down system will perform following functions

• • • 11.0

Trip generator breaker Trip field breaker Governor brings the unit to spin at no load PROTECTION OF POWER TRANSFORMERS Following protections are generally provided on transformers

I. II. III. IV. V. VI. VII. VIII. IX. X. XI.

12.0

Fuses Sudden pressure protection (Buchholtz Relay) Oil temperature high Winding temperature high Over current/ earth fault Over frequency Differential protection Restricted earth fault protection Over flux protection (in large grid) Over all differential protection (Gen. Trans. Both in large machines) Fire protection system 9 Fire extinguishers 9 Mulsyfire protection 9 Fire buckets-sand filled

FIRE PROTECTION SYSTEM

For large generators, fire protections system will use CO2 as the quenching medium which will operate automatically. Hot spot/ smoke detectors are provided all around the periphery of generator winding. Bank of CO2 cylinders with control panel etc. are provided common for all the generators. The individual pipes let the CO2 enter in the faulty generator and quench the fire. Generator is isolator from the bus bar and machine stopped. The system is more effective in closed cycle cooling systems of generators. AHEC/MNRE/SHP Standards/Specification for monitoring, control and protection of SHP stations  

 32 

ANNEXURE-I LIST OF GENERATOR PANEL INDICATION AND RELAYS

Sl. No. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41

Designation L1 L2 L3 L4 L5 L6 L7 L8 L9 R Y B IPB PB1 PB2 TS DMF H ANN T A R BAPB 27 32P 51V 59 60 64S 46 40 95 87G 52G KWTR BL 86G1 86G2 86G3 86G4 Aux Relays

Inscription DC Supply on AC Supply on Generator Circuit Breaker Close Generator Circuit Breaker Open Generator Circuit Breaker Trip Generator Circuit Spring Charge Trip Coil Healthy DC Supply Failed Spare R Phase Bus Healthy Y Phase Bus Healthy B Phase Bus Healthy Immediate Action Trip Push Button Controlled Action Shut Down Push Button Spare Push Button Temperature Scanner Digital Multi Function Meter Hooter Annunciator Test Push Button Accept Push Button Reset Push Button Bell Accepted Push Button Under Voltage Relay Reverse Power Relay Voltage Controlled Over Current Relay Over Voltage Relay PT Fuse Failure Relay Stator Earth Fault Relay Negative Phase Sequence Relay Loss of Field Relay Trip coil Supervision relay Generator Differential Relay Generator Circuit Breaker Kilowatt Transducer Electrical Bell Master Trip Relay Master Trip Relay Master Trip Relay Master Trip Relay As Required

Colours Yellow Red Red Green Amber Blue Yellow Red Red Red Yellow Blue Red Green Red

Black Black Black Yellow

AHEC/MNRE/SHP Standards/Specification for monitoring, control and protection of SHP stations  

 33 

ANNEXURE-II LIST OF PROTECTION ELEMENTS IN MICRO PROCESSOR BASED RELAYS Symbol 21 24 26 27 27NT 32 38 40 46 49 50BF 50P 50N 50/27 51P 51N 51N 59 59N 64R 78 81 87G CTS VTS

Description Under Impedance Over Fluxing Field Winding Temp Under Voltage 100% Stator E/F Reverse Power Bearing Temp Loss of Field Negative Phase Sequence Stator Winding Temp Breaker Failure Instantaneous Phase Over Current Instantaneous Neutral Over Current Unintentional Energisation at Stand Still Time Delayed Phase Over Current Time Delayed Neutral Over Current Voltage Controlled Over Current Over Voltage Residual Over Voltage Restricted E/F Pole Slipping Protection Over/ Under Frequency Generator Differential Current Transformer Supervision Voltage Transformer Supervision

AHEC/MNRE/SHP Standards/Specification for monitoring, control and protection of SHP stations  

 34