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Industrial Training Report

UPPCL,220KV SUBSTATION

ABSTRACT The report gives an overview of 220kv power substation. It includes electricity transmission and distribution processes at UPPCL, Lucknow substation. Its substation, an assembly of apparatus which is installed to control transmission and distribution of electric power, its two main divisions are outdoor and indoor substation. Different equipments used in substations, Bus-bar, surge arrestor, Isolator, Earth switches, Current Transformers etc. Transformer which is being used here is core and shell type transformer for stepping up and down purposes. Different Instruments transformers, voltage, Current and CV transformers are also being used. Finally the CVT rating which gives a total output overview

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1.INTRODUCTION The present day electrical power system is ac i.e. electric power is generated, transmitted and distributed in the form of Alternating current. The electric power is produce at the power station, which are located at favorable places, generally quite away from the consumers. It is delivered to the consumer through a large network of transmission and distribution. At many place in the line of power system, it may be desirable and necessary to change some characteristic (e.g. Voltage, ac to dc, frequency power factor etc.) of electric supply. This is accomplished by suitable apparatus called sub-station for example, generation voltage (11KV or 6.6KV) at the power station is stepped up to high voltage (Say 220KV to 132KV) for transmission of electric power.

Similarly near the consumer’s localities, the voltage may have to be stepped down to utilization level. This job is again accomplished by suitable apparatus called sub-station.

Fig 1; 220 KV SUBSTATION,GOMTI NAGAR

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2.ABOUT THE SUBSTATION

Fig 2:220 kv Substation

2.1. Definition of sub-station: “The assembly of apparatus used to change some characteristics (e.g. Voltage ac to dc freq. p.f. etc) of electric supply is called sub-station”

2.2 Sub-Station: A substation is a part of an electrical generation, transmission, and distribution system. Substations transform voltage from high to low, or the reverse, or perform any of several other important functions. Between the generating station and consumer, electric power may flow through several substations at different voltage levels.Substations may be owned and operated by an electrical utility, or may be owned by a large industrial or commercial customer. Generally substations are unattended, relying on SCADA for remote supervision and control.

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2.3. Types of Substation: Substations may be described by their voltage class, their applications within the power system, the method used to insulate most connections, and by the style and materials of the structures used. These categories are not disjointed; to solve a particular problem, a transmission substation may include significant distribution functions, for example.



Transmission substation 

 

Distribution substation 

 

Collector substation 



Converter substation  Transmission substation: A transmission substation connects two or more transmission lines. The simplest case is where all transmission lines have the same voltage. In such cases, substation contains high- voltage switches that allow lines to be connected or isolated for fault clearance or maintenance. A transmission station may have transformers to convert between two transmission voltages, voltage control/power factor correction devices such as capacitors, reactors or static VAR compensators and equipment such as phase shifting transformers to control power flow between two adjacent power systems.

 Distribution substation: A distribution substation in Scarborough, Ontario disguised as a house, complete with a driveway, front walk and a mown lawn and shrubs in the front yard. A warning notice can be clearly seen on the "front door". Disguises for substations are common in many cities.

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A distribution substation transfers power from the transmission system to the distribution system of an area. It is uneconomical to directly connect electric ity consumers to the main transmission network, unless they use large amounts of power, so the distribution station reduces voltage to a level suitable for local distribution.

The input for a distribution substation is typically at least two transmission o r sub transmission lines. Input voltage may be, for example, 115 kV, or whatever is common in the area. The output is a number of feeders. Distribution voltages are typically medium voltage, between 2.4 kV and 33 kV depending on the size of the area served and the practices of the local utility. The feeders run along streets overhead (or underground, in some cases) and power the distribution transformers at or near the customer premises.

 Collector substation: In distributed generation projects such as a wind farm, a collector substation may be required. It resembles a distribution substation although power flow is in the opposite direction, from many wind turbines up into the transmission grid. Usually for economy of construction the collector system operates around 35 kV, and the collector substation steps up voltage to a transmission voltage for the grid. The collector substation can also provide power factor correction if it is needed, metering and control of the wind farm. In some special cases a collector substation can also contain an HVDC converter station. Collector substations also exist where multiple thermal or hydroelectric power plants of comparable output power are in proximity. Examples for such substations are Brauweiler in Germany and Hradec in the Czech Republic, where power is collected from nearby lignite-fired power plants. If no transformers are required for increase of voltage to transmission level, the substation is a switching station.

  

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 Converter substation: Converter substations may be associated with HVDC converter plants, traction current, or interconnected non-synchronous networks. These stations contain power electronic devices to change the frequency of current, or else convert from alternating to direct current or the reverse. Formerly rotary converters changed frequency to interconnect two systems; such substations today are rare.

 Switching station: A switching station is a substation without transformers and operating only at a single voltage level. Switching stations are sometimes used as collector and distribution stations. Sometimes they are used for switching the current to back-up lines or for parallelizing circuits in case of failure. An example is the switching stations for the HVDC Inga–Shaba transmission line.

A switching station may also be known as a switchyard, and these are commonly located directly adjacent to or nearby a power station. In this case the generators from the power station supply their power into the yard onto the Generator Bus on one side of the yard, and the transmission An important function performed by a substation is switching, which is the connecting and disconnecting of transmission lines or other components to and from the system. Switching events may be "planned" or "unplanned.

2.4. 220KV Sub-station : 220KV Sub-Station forms an important link between Transmission network and Distribution network. It has a vital influence of reliability of service. Apart from ensuring efficient transmission and Distribution of power, the sub-station configuration should be such that it enables easy maintenance of equipment and minimum interruptions in power supply. Sub-Station is constructed near as possible to the load center. The voltage level of power transmission is decided on the quantum of power to be transmitted to the load center.

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3. EQUIPMENT IN A 220KV SUB-STATION The equipment required for a transformer Sub-Station depends upon the type of Sub-Station, Service requirement and the degree of protection desired.

220KV EHV Sub-Station has the following major equipments: 

            

Bus-bar  Insulators



Isolating Switches Circuit breaker Protective relay



 

Instrument Transformer Current Transformer Voltage Transformer



 

Metering and Indicating Instrument Miscellaneous equipment Transformer

Wave trap





Lightening arrestors Line isolator











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3.1Bus-bar: When a no. of lines operating at the same voltage have to be directly connected electrically, bus-bar are used, it is made up of copper or aluminum bars (generally of rectangular X-Section) and operate at constant voltage.

The bus is a line in which the incoming feeders come into and get into the instruments for further step up or step down. The first bus is used for putting the incoming feeders in LA single line. There may be double line in the bus so that if any fault occurs in the one the other can still have the current and the supply will not stop. The two lines in the bus are separated by a little distance by a Conductor having a connector between them. and the other works only if the first is

3.2Insulators: The insulator serves two purpose, they support the conductor (or bus bar) and confine the current to the conductor. The most commonly used material for the manufactures of insulators is porcelain. There are several type of insulator (i.e. pine type, suspension type etc.) and there used in Sub-Station will depend upon the service requirement.

3.3Isolating Switches: In Sub-Station, it is often desired to disconnect a part of the system for general maintenance and repairs. This is accomplished by an isolating switch or isolator.

An isolator is essentially a knife Switch and is design to often open a circuit under no load, in other words, isolator Switches are operate only when the line is which they are connected carry no load. For example, consider that the isolator are connected on both side of a circuit breaker, if the isolators are to be opened, the C.B. must be opened first.

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3.4Circuit breaker: A circuit breaker is an equipment, which can open or close a circuit under normal as well as fault condition. These circuit breaker breaks for a fault which can damage other instrument in the station. It is so designed that it can be operated manually (or by remote control) under normal conditions and automatically under fault condition. There are mainly two types of circuit breakers used for any substations. They are

(a) SF6 circuit breakers

(b)Spring circuit breakers For the latter operation a relay which is used with a C.B. generally bulk oil C.B. are used for voltage up to 66 KV while for high voltage low oil & SF6 C.B. are used. For still higher voltage, air blast vacuum or SF6 cut breaker are used.

The use of SF6 circuit breaker is mainly in the substations which are having high input kv input, say above 220kv and more.

When if the gas gets decreases there is a motor connected to the circuit breaker. The motor starts operating if the gas went lower than 20.8 bar. There is a meter connected to the breaker so that it can be manually seen if the gas goes low. The circuit breaker uses the SF6 gas to reduce the torque produce in it due to any fault in the line.

3.5Protective relay: A protective relay is a device that detects the fault and initiates the operation of the C.B. to isolate the defective element from the rest of the system”. The relay detects the abnormal condition in the electrical circuit by constantly measuring the electrical quantities, which are different under normal and fault

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condition. The electrical quantities which may change under fault condition are voltage, current, frequency and phase angle. Having detect the fault, the relay operate to close the trip circuit of CB.

3.6 Instrument Transformer: The line in Sub-station operate at high voltage and carry current of thousands of amperes. The measuring instrument and protective devices are designed for low voltage (generally 110V) and current (about 5A). Therefore, they will not work satisfactory if mounted directly on the power lines. This difficulty is overcome by installing Instrument transformer, on the power lines.

There are two types of instrument transformer-

1. Current Transformer: A current transformer is essentially a step-down transformer which steps-down the current in a known ratio, the primary of this transformer consist of one or more turn of thick wire connected in series with the line, the secondary consist of thick wire connected in series with line having large number of turn of fine wire and provides for measuring instrument, and relay a current which is a constant faction of the current in the line. Current transformers are basically used to take the readings of the currents entering the substation. This transformer steps down the current from 800 amps to 1amp. This is done because we have no instrument for measuring of such a large current.

The main use of his transformer is:

(a)

distance protection

(b)

backup protection

(c)

measurement

Potential Transformer It is essentially a step – down transformer and step down the voltage in EE Department, SRMGPC, Lucknow

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known ratio. The primary of these transformer consist of a secondary way consist of a few turns and provides for measuring instruments and relay a voltage which is known fraction of the line voltage.large number of turn of fine wire connected across the line.

3.8Transformer: There are four transformers in the incoming feeders so that the four lines are step down at the same time. In case of a 220KV or more KV line station auto transformers are used. While in case of lower KV line such as less than 132KV line double winding transformers are used Auto transformer.

Transformer is static equipment which converts electrical energy from one voltage to another. As the system voltage goes up, the techniques to be used for the Design, Construction, Installation, Operation and Maintenance also become more and more critical. If proper care is exercised in the installation, maintenance and condition monitoring of the transformer, it can give the user trouble free service throughout the expected life of equipment which of the order of 25-35 years. Hence, it is very essential that the personnel associated with the installation, operation or maintenance of the transformer is through with the instructions provided by the manufacture diverted around the protected insulation in most cases to earth.

3.9Auto transformer: Transformer is static equipment which converts electrical energy from one voltage to another. As the system voltage goes up, the techniques to be used for the Design, Construction, Installation, Operation and Maintenance also become more and more critical. If proper care is exercised in the installation, maintenance and condition monitoring of the transformer, it can give the user trouble free service throughout the expected life of equipment which of the order of 25-35 years. Hence, it is very essential that the personnel associated with the installation operation or maintenance of the transformer is through with the instructions provided by the manufacture.

Basic principles: The transformer is based on two principles: firstly, that an Electric current can produce a magnetic field (electromagnetism) and secondly that a changing magnetic field within a coil of wire induces a voltage

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across the ends of the coil (electromagnetic induction). Changing the current in the primary coil changes the magnetic flux that is developed. The changing magnetic flux induces a voltage in the secondary coil. It is a device that transfers electrical energy from one circuit to another through inductively coupled conductors — the transformer's coils. Except for air-core transformers, the conductors are commonly wound around a single iron-rich core, or around separate but magnetically - coupled cores. A varying current in the first or "primary" winding creates a varying magnetic field in the core (or cores) of the transformer. This varying magnetic field induces a varying electromotive force (EMF) or "voltage" in the "secondary" winding. This effect is called mutual induction. If a load is connected to the secondary, an electric current will flow in the seconda ry winding and electrical energy will flow from the primary circuit through the transformer to the load. In an ideal transformer, the induced voltage in the secondary winding (VS) is in proportion to the primary voltage (VP), and is given by the ratio of the number of turns in the secondary to the number of turns in the primary as follows: By appropriate selection of the ratio of turns, a transformer thus allows an alternating current (AC) voltage to be "stepped up" by making NS greater than NP, or "stepped down" by making NS less than EMF would always be such that it will oppose development of any such change in magnetic field.



3.10Lightening Arrester:

To discharge the switching and lightening voltage surges to earth.

3.11Wave trap: Wave trap is an instrument using for tripping of the wave. The function of this trap is that it traps the unwanted waves. Its function is of trapping wave. Its shape is like a drum. It is connected to the main incoming feeder so that it can trap the waves which may be dangerous to the instruments here in the substation.

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4. SINGLE LINE DIAGRAM (SLD) A Single Line Diagram (SLD) of an Electrical System is the Line Diagram of the concerned Electrical System which includes all the required ELECTRICAL EQUIPMENT connection sequence wise from the point of entrance of Power up to the end of the scope of the mentioned Work.

As these feeders enter the station they are to pass through various instruments. The instruments have their usual functioning.

They are as follows in the single line diagram: 

Lightening arrestors 



CVT



Wave trap 



Isolators with earth switch 



Circuit breaker 



BUS 



Potential transformer with a bus isolator 



Isolator 



Current transformer 



A capacitor bank attached to the bus 

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The line diagram of the substation:

Fig 3: Single Line Diagram of 220 KV Substation Lucknow

This substation has the capacity of 220kv and can step down to 132kv using four input lines through the incoming feeders.

The substation of 220kv/132kv has many outgoing feeders, namely:  VIJAY KHAND   VIBHUTI KHAND  ANNSAL  LOHIA   AMITY 

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 ANAND NAGAR  CHAPTER-5

5.TRANSFORMER Transformer is a static machine, which transform the potential of alternating current at same frequency. It means the transformer transforms the low voltage into high voltage and high voltage into low voltage at same frequency. It works on the principle of static induction principle. When the energy transformed into higher voltage, the transformer is called step up transformer but in case of other is known as step down transformer.

Fig 4: 220/132 KV 160 MVA Transformer at LucknowSub-Station 

5.1 TYPES OF TRANSFORMER: 

Power Transformer 



Instrument Transformer 

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UPPCL,220KV SUBSTATION

Auto Transformer 

Further, Transformer classified in two types: 

ON THE BASIS OF WORKING

 ON THE BASIS OF STRUCTURE



 5.2POWER TRANSFORMER:



Fig 5: 132/33 KV 40 MVA transformer at Lucknow Sub-Statation

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5.3INSTRUMENT TRANSFORMER:

Fig 6: Instrument Transformer at Lucknow Sub-Station

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6.CIRCUIT BREAKER 6.1CIRCUIT BREAKER: A circuit breaker is the equipment, which can open or close a circuit under normal as well as fault condition. These circuit breaker breaks for a fault which can damage other instrument in the station.

It is so designed that it can be operated manually (or by remote control) under normal conditions and automatically under fault condition.

A circuit breaker is an automatically operated electrical switch designed to protect an electrical circuit from damage caused by over current or overload or short circuit. Its basic function is to interrupt current flow after protective relays detect a fault.

Fig 15: SF6 Circuit Breaker

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WORKING PRINCIPLE OF CIRCUIT BREAKER: The Circuit Breaker mainly consist of fixed contacts and moving contacts. In normal “no” condition of circuit breaker, these two contacts are physically connected tp each other due to applied mechanical pressure on the moving contacts.

There is an arrangement stored potential energy in the operating mechanism of circuit breaker which is realized if switching signal is given to the breaker. The potential energy can be stored in the circuit breaker by different ways like by deforming metal spring, by compressed air or by hydraulic pressure.

6.2TYPES OF CIRCUIT BREAKER: According to different criteria there are different type of circuit breaker:

According to their arc quenching media the circuit breaker can be divided as: 

Oil Circuit Breaker 



Air blast circuit breaker 



SF6 circuit breaker 



Vacuum circuit breaker 



6.3OIL CIRCUIT BREAKER:



A high- voltage circuit breaker in which the arc is drawn in oil to dissipate the heat and extinguish the arc; the intense heat of arc decomposes the oil, generating a gas whose high pressure produced a flow of fresh fluid through the arc that furnishes the necessary insulation to prevent a re-strike of the arc.

The arc is then extinguished, both because of its elongation upon parting of contacts and because of intensive cooling by the gases of oil vacuum.

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Fig16: Oil Circuit Breaker

6.4AIR BLAST CIRCUIT BREAKER: Fast operations, suitability for repeated operation, auto re-closure, unit type multi break constructions, simple assembly and modest maintenance are some of the main features of air blast circuit breakers. The compressors plant necessary to maintain high air pressure in the air receiver. The air blast circuit breakers are especially suitable for railway and arc furnaces, where the breaker operates repeatedly. Air blast circuit breaker is used for interconnected lines where rapid operation is desired.

Fig17: Air Blast Circuit Breaker High pressure air at a pressure between 20 to 30 kg/cm2 stored in the air reservoir. Air is taken from the compressed air system. Three hollow insulator columns are mounted on the reservoir with valves at their

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basis. The double arc extinguished chambers are mounted on the top of the hollow insulator chambers. The current carrying parts connect the three arc extinction chamber to each other in series and the pole to the neighbouring equipment. Since there exist a very high voltage between the conductor and the air reservoir, the entire arc extinction chambers assembly is mounted on insulators.

6.5 SF6 CIRCUIT BREAKER: In such circuit breaker, sulphur hexafluoride (SF6) gas is used as the arc quenching medium. The SF6 is an electronegative gas and has a strong tendency to absorb free electrons. The SF6 circuit breakers have been found to a very effective for high power and high voltage service. SF6 circuit breakers have been developed for voltage 115 KV to 230 KV, power rating 10MVA. It consists of fixed and moving contacts. It has chamber, contains SF6 gas. Whe n the contacts are opened, the mechanism permits a high pressure SF6 gas from reservoir to flow towards the arc interruption chamber. The moving contact permits the SF6 gas to let through these holes.

A typical SF6 circuit breaker consists of interrupter units. Each unit is capable of interrupting currents up to 60 KA and voltage in the range 50-80 KV.

Fig18: SF6 circuit breaker

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.6.6

UPPCL,220KV SUBSTATION

VACUUM CIRCUIT BREAKER

Vacuum circuit breakers are the breakers which are used to protect medium and high voltage circuit from dangerous electrical situations. Like other types of circuit breakers, vacuum circuit breakers are literally break the circuit so that energy can not continue flowing through it, thereby preventing fires, power surge and other problems which may emerge. These devices have been utilized since the 1920s and several companies have introduced refinements to make the m even safer and more effective.

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7.CONTROL & RELAY ROOM The control room has various control panels which shows the information like incomming power, outgoing power, frequency, time common to all sub-stations, status of various lines(healthy, faulted, under outage or maintenance), status of various protective instruments like isolators, circuit breaker, temperature of various instruments, working tap of transformer etc.

The DAS (Data Acquisition System) is used to accumulate the data received from various sources.

The relay room is separate from the control room. All relay used here are numerical and are either from Siemens® or ABB®.

The protection system is so fast that it can detect a fault within 30 ms and hence the circuit breaker can be operated within as less as 80 ms. For 400KV side C.B., one time auto reclosure is allowed in order to clear the faults automatically.

Fig 21:Control Room

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7.1Protective Relaying: Protective relays are used to detect defective lines or apparatus and to initiate the operation of circuit interrupting devices to isolate the defective equipment. Relays are also used to detect abnormal or undesirable operating conditions other than those caused by defective equipment and either operate an alarm or initiate operation of circuit interrupting devices. Protective relays protect the electrical system by causing the defective apparatus or lines to be disconnected to minimize damage and maintain service continuity to the rest of the system.

There are different types of relays:

i. Over current relay

ii. Distance relay

iii. Differential relay

iv. Directional over current relay

7.2. Over Current Relay: The over current relay responds to a magnitude of current above a specified value. There are four basic types of construction: They are plunger, rotating disc, static, and microprocessor type. In the plunger type, a plunger is moved by magnetic attraction when the current exceeds a specified value. In the rotating induction-disc type, which is a motor, the disc rotates by electromagnetic induction when the current exceeds a specified value.

7.3 Distance Relay: has the overall effect of measuring impedance. The relay operates instantaneously (within a few cycles) on a 60-cycle basis for values of impedance below the set value. When time delay is required, the relays energizes a separate time-delay relay or function with the contacts or output of this time-delay relay or function performing the desired.

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7.4Differential Relay: The differential relay is a current-operated relay that responds to the difference between two or more device currents above a set value. The relay works on the basis of the differential principle that what goes into the device has to come out .If the current does not add to zero, the error current flows to cause the relay to operate and trip the circuit. to permit differences in the input currents as a result of current transformer mismatch and applications where the input currents come from different system voltages, such as transformers..

7.6. Directional Over current Relay: A directional over current relay operates only for excessive current flow in a given direction. Directional over current relays are available in electromechanical, static, and microprocessor constructions. An electromechanical overcorrect relay is made directional by adding a directional unit that prevents the over current relay from operating until the directional unit has operated.

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8.CONCLUSION Now from this report we can conclude that electricity plays an important role in our life. We are made aware of how the transmission the transmission of electricity is done. We too came to know about the various parts of the substation system. The three wings of electrical system viz. generation, transmission and distribution are connected to each other and that too very perfectly. Thus for effective transmission and distribution a substation must: 

Ensure steady state and transient stability 



Effective voltage control 



Prevention of loss of synchronism 

   

Relaible supply by feedimg at various points 



Fault analysis improemnt in respective field 



Establishment of economic laod distribution

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9.REFERENCES 

"Joint Consultation Paper: Western Metropolitan Melbourne Transmission Connection and Subtransmission Capacity" (PDF). Jemena. Powercor Australia, Jemena, Australian Energy Market Operator. Retrieved 4 February 2016. 

 

a b c Stockton, Blaine. "Design Guide for Rural Substations" (PDF). USDA Rural  Development. United States Department of Agriculture. Retrieved 4 February 2016.



Steinberg, Neil. "Lights On but Nobody Home: Behind the Fake Buildings that Power Chicago". Retrieved 14 December 2013. 

 "Transformer Fire Video". metacafe. User Eagle Eye. Retrieved 4 February 2016.  John, Alvin. "EE35T - Substation Design and Layout". The University Of The West Indies at St. Augustine,

Trinidad

EE Department, SRMGPC, Lucknow

And

Tobago.

Retrieved

4

February

2016.

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