EQUIPMENTS USED IN SWITCHYARD400 KV Switchyard has the following major equipments, (which are installed for the transmission of power from generating station to transmission substation) which are given as below:

Main Bus Bars:

Bus Bars generally made of conducting material like aluminium or ACSR, used to carry the current from which a no. of circuits or connections made for transmission of generated power. It is designed according to the sum of rated current & the maximum current is to be handled during a small overloading etc.

The bus bars used in TATA power plant 400kV switchyard are bare Aluminium conductor. Incoming lines from unit 1 to 5 are connected to this bus bars where as the following out going lines deliver power to the receiving substations.

Vadavai-1

Vadavai-2

Limdi-1

Limdi-2

Jetpur-1

Jetpur-2There are different bus-bar schemes available for switchyards. This switchyard uses one and half breaker bus bar scheme.

Rating of bus bar

TypeQuad MOOSE type ACSR Conductor (4 wire)

Rated Current2500A

Maximum Current Capacity50 kA for 1 sec

Current Capacity125 kA

Rated Voltage420 KV

Maximum Withstand Voltage500 KV (Peak)

Fig. Bus Bar

Isolators:

Isolators or Diverter switches are used to isolate the circuits when the current on the conductor has already interrupted. Hence these isolators are used for the open or close a circuit when there is no load current on the circuit i.e. for no-load open or close operation. Isolators also provided with Earth switches to divert the trap voltages of the line to ground if any, which are used to ensure the safety of working person to avoid the shock due to any voltage trapped on line.

To prevent Mal-operation, the isolator is provided with inter locking.

Inter locking between three poles for simultaneous operation.

Inter locking with the Circuit Breaker.

Types of Isolators

Vertical break type. Horizontal break type. Horizontal Centre break type. Double break type. Vertical pantograph type.In the 400kV switchyard we use the Horizontal centre break type isolatorRating of isolator

Manufacturing CompanySiemens limited

Year of mfg2009

TypeHCB

Voltage (kV) up420

Bil (kV)1425

Switching imp. (kV) ur1050/1250

Pf (kV)520/610

STC KA/sec50KA/2sec

WT of isolator1230kg

Motor voltage415V

Control voltage220V

Fig. Isolator

Circuit Breakers:

Circuit Breakers are used on any line or circuit to make or break the circuit for normal on load open or close operation and also used to protect the circuit from damage due to any fault occurrence on the circuit by opening or tripping its contacts.

As the name suggests, it breaks the circuit. Circuit Breaker are used to protect the circuit from the faults. Classification of circuit breaker is:

a. Air blast CB

b. Air break

c. Vacuum circuit breaker

d. Oil circuit breaker

e. SF6 (sulphur hexafluoride) beakerSF6 circuit breaker is used in CGPL.

SF6 Circuit breaker:

Sulphur hexafluoride is an inert gas having good dielectric and have extinguishing properties. The dielectric strength is increased with pressure. In SF6 circuit breaker sulphur hexafluoride gas is used as the arc quenching medium. The sulphur hexafluoride is an electronegative gas and has a strong tendency to absorb free electrons. The contacts of breaker are opened in a high pressure flow of sulphur hexafluoride gas and an arc I stuck between them. The conducting free electrons in the arc are rapidly captured by the gas from relatively immobile negative ions. This loss of conducting electrons in the arc quickly builds enough insulation strength to extinguish the arc. The SF6 circuit breakers have been found to be very effective for high power and high voltage service. Rating of circuit breaker

Year of manufacturing2009

Rated impulse voltage1425kV

Rated power frequency voltage610kV

Frequency50Hz

Rated normal current3150 amps

Rated short-circuit breaking current50k amps

Rated line charging breaking current 600 amps

Rated operating sequence0-0.3 s CO-3min-CO

Control voltage 220DC

Operating voltage 240AC

Heating Voltage 240AC

Rated voltage 420 kV

Weight of SF6 filling39kg

Weight including SF65400kg

Fig. Circuit Breaker Instrument Transformers:

The Instrument Transformers which are Current Transformers & Potential Transformers (CT & PT) are used to measure the current & voltage of the circuit up to metering range and the same also used for the protection of the circuit by measuring the fault values of current & voltage to initiate the relay to act the protection. Current transformerA current transformer (CT) is used for measurement of electric currents. Current transformer is an instrument transformer. When current in a circuit is too high to directly apply to measuring instruments, a current transformer produces a reduced current accurately proportional to the current in the circuit, which can be conveniently connected to measuring and recording instruments. A current transformer also isolates the measuring instruments from what may be very high voltage in the monitored circuit. Current transformers are commonly used in metering and protective relays in the electrical power industry.

It has two winding primary and secondary. The alternating current flowing in the primary produces a magnetic field in the core, which then induces a current in the secondary winding circuit.

The most common design of CT consists of a length of wire wrapped many times around a silicon steel ring passed over the circuit being measured. The CT's primary circuit therefore consists of a single 'turn' of conductor, with a secondary of many tens or hundreds of turns. The primary winding may be a permanent part of the current transformer, with a heavy copper bar to carry current through the magnetic core.

Shapes and sizes can vary depending on the end user or switchgear manufacturer. High-voltage current transformers are mounted on porcelain bushings to insulate them from ground. Some CT configurations slip around the bushing of a high-voltage transformer or circuit breaker, which automatically centers the conductor inside the CT window.The primary circuit is largely unaffected by the insertion of the CT. The rated secondary current is commonly standardized at 1 or 5amperes. For example, a 4000:5 CT would provide an output current of 5amperes when the primary was passing 4000 amperes. The secondary winding can be single ratio or multi ratio, with five taps being common for multi ratio CTs. The load, or burden, of the CT should be of low resistance. If the voltage time integral area is higher than the core's design rating, the core goes into saturation towards the end of each cycle, distorting the waveform and affecting accuracy.Rating of Current Transformer

Manufacturing companySiemens

TypeSAS

I (din)125KAP

Insulation level1050kV/1425kVp

Rating2500-1250/1amps

Rated cost. Current3000 A

SF6 weight36 kg

Fig. Current Transformer CVT (Capacitive voltage transformer)

A capacitor voltage transformer (CVT), or capacitance coupled voltage transformer (CCVT) is a transformer used in power systems to step down extra high voltage signals and provide a low voltage signal, for measurement or to operate a protective relay. In its most basic form the device consists of three parts: two capacitors across which the transmission line signal is split, an inductive element to tune the device to the line frequency, and a transformer to isolate and further step down the voltage for the instrumentation or protective relay. The tuning of the divider to the line frequency makes the overall division ratio less sensitive to changes in the burden of the connected metering or protection devices. [1] The device has at least four terminals: a terminal for connection to the high voltage signal, a ground terminal, and two secondary terminals which connect to the instrumentation or protective relay. CVTs are typically single-phase devices used for measuring voltages in excess of one hundred kilovolts where the use of wound primary voltage transformers would be uneconomical. In practice, capacitor C1 is often constructed as a stack of smaller capacitors connected in series. This provides a large voltage drop across C1 and a relatively small voltage drop across C2.

The CVT is also useful in communication systems. CVTs in combination with wave traps are used for filtering high frequency communication signals from power frequency. [2] This forms a carrier communication network throughout the transmission network. Single Phase & single Column type, suitable for running in Hot & Humid areas.

Fig. Internal structure of CVTRating of CVTRated Voltage

400/KV

Maximum Withstand Voltage 495 KV (Peak)

Transformation Ratio

[400/]/ [0.11/]/ [0.11/]/ [0.11/]

Accuracy Level

0.2/0.5

Fig. CVT Protective Relays: Protective Relays used to initiate the fault condition & fast action of protection to avoid the damage to equipment during faulty condition in circuit either external like lightning or internal like unbalancing/short circuits etc.

Fig. Relays Junction

Lightning Arrestors:Lightning Arrestors are used to protect the circuit, line or equipment from over-voltages which are generally occurs by the external or internal surges i.e. occurs due to switching operations or lightning strokes.Rating of lightning arrester

Rated Operating Voltage

200 KV/ Phase

Rated Frequency

50Hz

Rated discharge Current (Peak)

10 KA

Switching Impulse Current (Peak)

0.3 KA

Lighting Impulse Withstand

950 KV

Fig. Lightning Arrester Carrier Current System: This system is used in the switchyard or substations for the communication, relaying, supervisory control or telemetering purpose. This system is connected to the High Voltage power circuit for the above said purpose.For example Wave trap is used for this purpose. Wave trap:

Wave trap is trapping the high frequency communication signals sent on the line from the remote substation and diverting them to the telecom/teleprotection panel in the substation control room (through coupling capacitor and LMU).

This is relevant in Power Line Carrier Communication (PLCC) systems for communication among various substations without dependence on the telecom company network. The signals are primarily teleportation signals and in addition, voice and data communication signals. Line trap also is known as Wave trap. What it does is trapping the high frequency communication signals sent on the line from the remote substation and diverting them to the telecom/teleportation panel in the substation control room (through coupling capacitor and LMU). This is relevant in Power Line Carrier Communication (PLCC) systems for communication among various substations without dependence on the telecom company network. The signals are primarily teleportation signals and in addition, voice and data communication signals. The Line trap offers high impedance to the high frequency communication signals thus obstructs the flow of these signals in to the substation bus bars. If there were not to be there, then signal loss is more and communication will be ineffective/probably impossible.

Fig. Wave trap Earth switch:

The earth switches are connected to equipments and networks for the purpose to ground them. Since the transmission line of around 400kV is near to the equipments, voltage (about 30kV) is induced in equipment. This is very high voltage so it must be ground whenever there is any maintenance. Earth switch is shown in the figure of isolator (rode tilted at some angle). And when the equipments are washing by de mineralized water( thats conductivity is less) earth switch is used.

Fig. Earth switch Insulator: Insulators are used in electrical equipment to support and separate electrical conductors without allowing current through themselves. An insulating material used in bulk to wrap electrical cables or other equipment is called insulation. The term insulator is also used more specifically to refer to insulating supports used to attach electric power distribution or transmission lines to utility poles and transmission towers.

Fig. Insulator EMVT (Electromagnetic Voltage Transformer):

EMVT is same as the PT both are the use for the voltage measuring but accuracy of the EMVT is high. Means its used for metering of supply.

Fig. EMVT Line/Bus Reactor: Line Reactor is used to control the Line voltage i.e. it reduces the line voltage in case it is going to a high value by drawing a high reactive current/ power from circuit to which it is connected and the bus reactor is used to control the voltage and current of bus bar. Generally two types of reactors used: Series Reactor & Shunt Reactor.In general, Reactor is referred as inductor. It used to connect in parallel with the transmission line to reduce the effect of capacitance of transmission line (ferranti effect). Due the capacitance of the transmission line, at the receiver ends voltage is higher than the voltage of sending end. To reduce the capacitance, an inductor (reactor) is connected. Main difference between transformer and reactor is: reactor has only single winding (primary) and secondary is grounded, but in transformer there are two windings (primary and secondary).

(Box represents the coil)

Fig. a. bus reactor

fig. b. line reactor

The secondary of line reactor is not grounded directly. Since the current in line is much higher, for controlling the current, the inductor coil is also connected in series with the neutral point. But the bus reactor can be grounded directly.

Rating of reactorManufacturing companyCropton Greaves

TypeGapped core

Rated MVAR63

Rated voltage420kV

Rated current63 amps

Line insulation kVp1300

Neutral insulation kVp550

Switching imp. Voltage1050 kVp

P. F. level230kV

ConnectionStar

Frequency50Hz

CoolingONAN

Jumping of wire: When the wire is tapped from any point is called jumping of wire.Fig. Jumping of wire Ground wire: The wire that is used for protection by lightning effect is called ground wire. It is placed in the top of the light tower and running parallel to the conductor. Generator: The electric generator is designed in order to convert movement (mechanical energy) into electricity (electrical energy) by the electromagnetic induction. The phenomenon of induction can be summarized as follows: an electric charge experiences force in the direction perpendicular to both the direction of relative motion and of the magnetic field lines when the charge has relative motion to the magnetic field either by displacement or changing the intensity. Acting on the many charges contained in a conducting materialusually, electrons in a wirethis force becomes an electromotive force ( EMF) that produces a voltage or potential drop along the wire and thus causes an electric current (the induced current) to flow. A generator is designed to obtain an induced current in a as a result of mechanical movement, which is utilized to continually change a magnetic field near the conductor. The generator thus achieves a conversion of energy of motion into electrical energy mediated by the magnetic field that exerts forces on the electric charges.

Generator is the opposite of electric motor which converts electrical energy into mechanical energy likewise mediated by the magnetic field. As far as the physical principles are concerned, electric generators and motors are very similar devices; in fact, an actual generator can be operated as a motor and vice versa. Rating of generator:Manufacturing companyToshiba

Phase 3

Type TAKS

Excitation voltage 570kV

Max. ambient air temperature50 degree C

Inlet coolant temperature64 degree C

Stator insulation classF

Rotor insulation classF

Stator winding coolingWater

Rotor winding coolingHydrogen

Stator connection Star

Direction of rotorCounter clockwise

Speed 3000RPM

Output capacity930 MVA/ 830MW

Armature current 21318 amps

Field current 5250 amps

Armature voltage 26000V

Made in JapanYear-2009

Fig. Generator Transformer

Transformer is an equipment to step up or step down the voltage without affecting the power transfer. In the switch yard, there are some transformers used in switch yard:

1. Generator transformer

2. Station transformer Generator transformer: (Power) is just after the generator. This transformer step up the voltage to reduced the power losses. In CGPL, there are 3 transformers (single phase) are used for supply from generator. There are some reasons to used three transformers:

a. size of a single power transformer is very huge compare to 3 single phase transformer,

b. The overall cost is much less,

c. The maintenance is less,

d. In India, transformer for 830MW power is not available.

Fig. connection (delta to Y) of three single phase transformer

Fig. Generator transformer

Rating of Generator transformerManufacturing companyBHEL

Type of cooling OFAF

Phase 1

Power rating310MVA

No load voltageAt LV side26kV

At HV side 420/3kV

Line current At LV side11923 amps

At HV side1278

Frequency50 hz

CONNECTION Ynd1

Insulation At LV sideLI/AC, 170/30

At HV sideSI/LI/AC, 1050/1300/630

Station transformer:

Station transformers are installed to supply the power needed at power plant itself. In CGPL, Station transformer has one primary winding and two secondary winding Y-phases. The ratings of transformers are 26kV/11kV and 26kV/6.6kV. The connection of instruments and equipment are decided according to the need of instrument and equipment. There are three transformers are connected to one unit so that the supply to equipments will not interrupt.

Rating of station transformer

Manufacturing companyBHEL

Types of coolingONAFOFAFONAN

No load voltage

At HV side26kV

At LV side11.5kV

Line current

At HV side1398amps1119 amps891 amps

At LV side1581 amps1265 amps948 amps

Phase3

ConnectionDyn11yn11

Unit Transformer:

Unit transformer is directly coupled to the unit itself so when that unit is in running condition it supplies power to which are coupled to auxiliaries directly or through unit auxiliary transformer depending upon load. Unit auxiliaries are those which are directly associated with the generating unit such as ID and FD fans, Boiler feed pumps, coal mills, fans, circulating water pumps etc.

Fig. Unit TransformerRating of unit transformer:

Manufacturing companyBHEL

Rating of transformer310 MVA

Types of coolingONAN

High voltage11kV

Low voltage6.3kV

Line current

At HV side524.86amps

At LV side836.74 amps

Phase3

ConnectionYnd1

Outgoing Lines: Outgoing Lines are generally made of conductors same as of Bus Bar conductors & these are used to transmit the generated power to substation or load centre from generating station.CONTROLLING OF SWITCHYARD

The Controlling of switchyard equipments done by SCADA (Supervisory Control and Data Acquisition) system which is given as below:

To Charge an outgoing line from Generator by using Bus Bars (Refer attached SLD):

First of all charge Main Bus-1 & Main Bus-2 by closing Bus Sectionalizer-1 & 2 i.e. circuit breaker- GS001 & GS002 respectively with respective Isolators. It is noted before closing of Isolators the Earth switch of Bus Bars & Sectionalizer Isolators side must be opened.

When Main Bus- 1 & 2 got charged check the Bus PT ( Potential Transformer) must show both Bus voltages as it is most necessary requirement of bus voltage at the time of synchronization of generator from bus bars & then from Grid.

Now all the earth switches of all the required isolators must be opened. Now close all the isolators of GT-5 bay & Bus Coupler bay on no-load condition i.e. generator on no-load or not synchronized.

Now close the circuit breaker of Bus Coupler bay & Main Bus-2 Side i.e. GS003 respectively & circuit breaker of Main Bus-1 & Tie Breaker must be open to avoid back charging of generator from Main Bus-1 or 2 i.e. GS002 open respectively.

As synchronizing parameters matched i.e. Line Voltage, Phase Angle & Frequency close the Tie circuit breaker- GS002 & check the Active & Reactive Power flow on line, as power is start to export i.e. it start to give LDC or grid close the circuit breaker of Main Bus-1 side to maintain the generated power flow through both buses.

To Discharge an outgoing line from Generator by using Bus Bars (Refer attached SLD):

In case unit or Generator (GT) is to be taken under shut down first of all circuit breakers of Tie Breaker & Main Bus-1 side simultaneously opened i.e. GS003 & GS002 respectively to avoid back charging of generator.

Now Open the Circuit Breaker i.e. GS001 of Main Bus-2 Side opened to discharge GT-5 bay.

Now open all the isolators of GT-5 bay on no load condition i.e. after opening of all circuit breakers of the respective bay & close the earth switches to remove/ ground the trapped voltages on the circuit.

As Reactor is in charged condition from Main Bus-1 so it is not needed to give shut down the Buses, these may keep in charged condition otherwise Reactor will be tripped.

PROTECTION OF SWITCHYARD

All switchyard equipments are provided with adequate protections for their safety from various fault causing conditions, to avoid the damage.For protection here 1 & 1/2 (one and half) breaker scheme is used, the two sides breakers GS001and GS003 are used for bus bar and the middle tie breaker GS002 is used for both. Various protections for installed equipments are discussed as follows:

Bus Bars Protection: Majority of the faults occurs on bus bars are single phase in nature. The clearing of bus fault requires the opening of all the circuits branching from the faulty bus or bus section. Commonly used bus protection given as below:

1. Back Up Protection: In principle it is the simplest of all to protect the buses with the aid of backup protections of the connected supplying elements which should respond to any fault appearing on the buses. When no separate bus protection is provided but distance is provided for the feeders connected to the bus. Bus backup protection may also mean that in case the breaker fails to operate for a fault on the outgoing feeder, then it regarded as bus fault. It opens all the breakers on that bus. Backup protection with appropriate time delay through a timer of 3 sec is used.2. Differential Over Current Protection: This protection is based on simple circulating current principle that under normal operating conditions or under external fault conditions the sum of currents entering into bus bar will be equal to the sum of currents leaving the bus bar. In case the sum of these currents is not zero, it must be due to short-circuit either a ground fault or phase to phase fault. This protection scheme is used for both types of faults i.e. phase to phase faults & ground faults. The setting of differential relay for differential protection is given 1.2 times of rated current.It is based on the fact that any fault within electrical equipment would cause the current entering it to be different from the current leaving it.

By comparing the two currents either in magnitude or in phase or in both, fault can be determined. It is an attractive option if both the ends of the apparatus are located near each other.

3. Breaker Failure: This scheme protects the bus bars, by isolating the bus bars from faults generated in the any other bay of switchyard, by which fault may damage other healthy equipments which are connected from these bus bars.Line Protection: Line Protection is used to protect the transmission lines from internal or external faults. Some of important line protections given as below:

1. Distance Protection: Distance protection is the name given to the protection, whose action depends upon the distance of the feeding point to the fault. The time of operation of this protection is a function of the ratio of voltage & current i.e. impedance. This impedance between the relay & the fault depends up on the electrical distance between them. It is a non-unit type protection; the protection zone is not exact. It is the high speed protection & is simply to apply & can be employed as primary as well as back-up protection to protect a line from any external fault.

2. Over-current & Earth Fault Protection: Generally a set of two or three over-current relays employed for protection against phase to phase faults & a separate over-current relay for single line to ground faults. Separate Earth fault relays are generally preferred because they can be adjusted to provide faster & more sensitive protection for single line to ground faults than that can be provided by the phase relays. Setting for Over-current protection is given 1.8 times of full load current of the line.

3. Overvoltage Protection: Overvoltage protection of the line is given to protect the line & related equipments like CT, PTs from saturation & short circuiting between two phases due to high corona which depends on line voltage. Setting for Overvoltage protection is given 110% of rated line voltage with a delay of 3 second at first stage & instantaneous tripping of line 112% of rated line voltage.Circuit Breaker Protection: Circuit Breaker is very important & costly device, which protects the equipment from damage, which mostly presents as severe faults. Some circuit breaker protections are listed as below:

1. Loss of SF6 gas or cooling media: This protection is used to avoid the damage due to arc production b/w making or breaking contacts from overheating due to loss of cooling media.

2. Pole Discrepancy: This Protection is used to protect the separate phase contacts of circuit breaker during making or breaking operation, generally not closing of one or more contacts properly, which may further cause damage to system due to unbalanced circuit loading.3. SF6 Pressure low: This protection trips the breaker if SF6 gas pressure reduces below 0.5 MPa, as at low pressure gas may not have sufficient cooling properties as contacts may damage. 4. Anti Pumping: This protection protects the breaker & its contacts from instant closing of breaker after a trip by a number of fast commands issued by DCS or operating personal.Reactor Protection: Reactor is itself an important & costly device in a protection system & its protections are listed as below:

1. Overload Protection: An overload relay of setting 1.5 times of rated load is provided to protect reactor from overloading in cases like more reactive power supply to system.2. Overvoltage Protection: This Protection is used to protect the reactor core from saturation due to high voltage by isolating the reactor if bus voltage going 112% of rated bus bar voltage.3. Buchholz Protection: This protection protects the reactor from severe faults like winding short circuits & core faults etc. This is gas based protection, which generally evolves during a fault.4. Oil & Winding Temperature Protection: This protection is provided to protect the reactor core & windings from overheating as winding & oil temperature increases due to any external fault or atmospheric condition, which may cause a severe damage to core & windings.

5. Pressure Relief Protection: It is the only mechanical protection provided to reactor to avoid the damage to core, windings & tank from excessive gas pressures during a fault, by removing excess pressure to atmosphere & also connected to trip circuit to isolate the reactor.CONCLUSION

Summer training helped me to realize the importance of each and every subject. I realized that even thought practical knowledge is very necessary; one cannot do without the theory part which forms the base. I came to know that no matter in which department you are, you need to knowledge of each and every field & everything should me in balanced manner. This has led me to give importance to everything in life as everything has its own importance.

This power plant is Indias first Ultra Mega Power Project, based on super critical technology, Here Indias biggest oil handling plant, coal handling plant, power generation unit, cooling water arrangement is available.

This training enables me to supplement my study with a practical bias has vital orientation with industry.

For an electrical engineering student the working at the power plant is must. It was my pleasure that I got chance to be trained at the Thermal Power Station.

From the Study of Control & Protection of Switchyard we can conclude the following:-

All Bus Voltages and Loading is kept within specified limits by varying the Active & Reactive Power at Sending End.

In Case of Faults, Relays detects & senses the same & initiates the fast action for the isolation of equipments to protect them from a severe damage.

All the equipments installed have their own protection schemes which coordinate with other system also for an effective & reliable operation of switchyard. I get introduced to whole generation process of electrical power.

I got knowledge of the whole equipment used for the protection system.

I introduced the switchyard and their protection.

I understand about the latest technologies used for the controlling.

I also introduced the latest equipments in the power plant.

REFERENCETata Power

http://tatapower.com/aboutus/coastal-gujarat-power-ltd.aspxL&T Power

http://www.larsentoubro.com/lntcorporate/common/ui_templates/HtmlContainer.aspx?res=P_PWR_DSCTBooksEnergy Talk

Anjani Shakti41

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