RohitPowerGridReport

POWER GRID CORPORATION OF

INDIA LIMITED

SUBMITTED BY:

PROJECT REPORT ON PATNA 400/220KV

SUBSTATION Control, Automation & Protection Of Patna Substation

ROHIT

SCHOLAR NO: 13-1-3-043

ELECTRICAL ENGINEERING

NIT SILCHAR

ACKNOWLEDGEMENT

I wish to express my sincere thanks to Mr. A.K.Verma

(DGM Patna Substation) for allowing me for this training

program and providing me with all the necessary facilities.

I wish to express my gratitude to Mr. Jagat Ram (Manager

Patna Substation), for taking out precious time for

providing enormous knowledge on transimission lines &

for giving us the insite of the substation and various

equipments.

I would like to Mr. M.Raza Sir and Mr. Sanjeev Sir for his

proper guidance, inspiring words, discussions & support

throughout my training period.

It was really a great opportunity for me working in such a

cooperative and learning environment.

Date: 16th

JUNE, 2016 ROHIT

ELECTRICAL ENGINEERING

NATIONAL INSTITUTE OF TECHNOLOGY, SILCHAR

CERTIFICATE

This is to certify that ROHIT, NATIONAL INSTITUTE OF

TECHNOLOGY, SILCHAR has successfully completed his 4

weeks training at 400/220 KV PATNA SUBSTATION,

Power Grid Corporation Of India Ltd. during the period

of 16th

May -15th

June 2016 under the guidance of Mr.

Jagat Ram and has prepared the following report on the

topic “Control, Automation & Protection Of Patna

Substation”.

DATE: 16th

JUNE, 2016 Mr. JAGAT RAM

(Dy. Manager)

POWERGRID AT GLANCE POWER GRID CORPORATION OF INDIA LIMITED (POWERGRID), the Central

Transmission Utility (CTU) of the country under Ministry of Power is one

amongst the largest Power Transmission utilities in the world. POWERGRID is

playing a vital role in the growth of Indian power sector by developing a

robust Integrated National Grid and associating in the flagship programme

of Govt. of India to provide Power for all. Innovations in Technical &

Managerial fields has resulted in coordinated development of power

transmission network and effective operation and management of Regional

and National Grid.

Company owns and operates about 1, 01,334 ckt kms of transmission lines

at 800/765kV, 400kV, 220kV & 132kV EHVAC & +500kV HVDC levels and 168

sub-stations with transformation capacity of about 1, 64,813 MVA as

on 31st May 2013. This gigantic transmission network, spread over length

and breadth of the country, is consistently maintained at an availability of

over 99%.

POWERGRID has planned to create a strong and vibrant National Grid in the

country in a phased manner to ensure optimum utilization of generating

resources, conserve eco-sensitive right of way and accommodate uncertainty

of generation plants. Strengthening of National Grid is planned in a phased

manner through consolidation of inter-regional connection framework, so as

to support the anticipated generation capacity programme of about 88,000

MW during the XII Plan.

Recognizing the role of Powergrid in the overall development of transmission

and power sector, Gov. of India has conferred Navratna status to Powergrid

in may’08.

EVOLUTION OF NATIONAL GRID At the end of XI Plan, the Inter-regional power transfer capacity of National Grid

stands at about 28,000 MW. Four power regions of the country namely, North-

Eastern, Eastern, Western and Northern are now operating as one synchronous grid

(same frequency). Southern Regional grid is connected to this synchronous grid

through HVDC links.

ASYNCHRONOUS LINKS –Part of National Grid

3 ELECTRICAL REGIONS

RIHAND-DELHI -- 1500 MW

CHANDRAPUR-PADGE – 1500 MW

TALCHER-KOLAR – 2000 MW

SILERU-BARASORE - 100 MW

HVDC BTB VINDYACHAL – 500 MW

HVDC BTB CHANDRAPUR –1000 MW

HVDC BTB VIZAG - 500 MW

HVDC BTB SASARAM - 500 MW

SOUTHER

N REGION

WESTER

NREGIO

N

EASTERN

REGION

NORTHERN

REGION NORTH-

EASTERN

REGION

1

2

3

With the commissioning of Raipur-

Rourkela between WR and ER during

Mach 2003, Indian power system

operating in three electrical Regions.

2 ELECTRICAL REGIONS

SOUTHERN REGION

WESTE

RNREG

EASTE

RN

NORTHE

RN NORTH

-

EASTE

1

2

With the Commissioning of the Tala

Transmission system during Oct 06

the E.R ,W.R and N.R Grids were

synchronised and Indian Power

systems is operating on Two

Electrical Grids.

AN OVERVIEW OF PATNA SUB STATION The Patna Sub-Station is located on Patna-Gaya road in Gauri Chak village, in Sampat

Chak block of Patna district. The station is located at a distance of 10 km from the

state capital Patna city and 25 km from ER-I, Head Quarter. The station is located at a

distance of 15 km from Patna Railway Junction, which is well connected with different

places of India and 20 km away from Patna Airport.

. The 400/220 KV POWERGRID, Patna Sub-station has been constructed by

POWERGRID as a part of transmission system associated with “Kahalgaon Stage -II

Phase – I (2 X 500 MW) STPP”. The Patna Sub-Station has a transformation capacity of

630 MVA and caters the power supply to the state capital Patna through the BSEB

system. Further it interconnects with Northern region through D/C 400 KV Patna-Balia

(Quad) Transmission lines for supply of ISGS power to the NEW (North- North East-

Western) grid. Subsequently, the station shall also be connected with Barh Thermal

Power project, NTPC through LILO of 400 KV D/C Barh- Balia (Quad) line. Therefore, in

future this station will be connected to two super power projects, i.e. Kahalgaon and

Barh.

LAYOUT

Substation layout consists essentially in arranging a number of switchgear components

in an ordered pattern governed by their function and rules of spatial separation.

The above diagram gives the layout of the Patna substation.

To depict the status and carry out the entire monitoring a single line diagram is used.

SINGLE LINE DIAGRAM

Power systems are extremely complicated electrical networks that are geographically

spread over very large areas. For most part, they are also three phase networks – each

power circuit consists of three conductors and all devices such as generators,

transformers, breakers, disconnects etc. are installed in all three phases. In fact, the

power systems are so complex that a complete conventional diagram showing all the

connections is impractical. Yet, it is desirable, that there is some concise way of

communicating the basic arrangement of power system components. This is done by

using Single Line Diagrams (SLD). SLDs are also called One Line Diagrams.

400 KV SLD

Single Line Diagrams do not show the exact electrical connections of the circuits. As

the name suggests, SLDs use a single line to represent all three phases. They show the

relative electrical interconnections of generators, transformers, transmission and

distribution lines, loads, circuit breakers, etc., used in assembling the power system.

The amount of information included in an SLD depends on the purpose for which the

diagram is used.

220 KV SLD

INTRUDUCTION TO SUBSTATION & ITS

EQUIPMENTS The First Step in designing a Substation is to design an Earthing and

Bonding System.

The function of an earthing and bonding system is to provide an earthing system

connection to which transformer neutrals or earthing impedances may be connected

in order to pass the maximum fault current. The earthing system also ensures that no

thermal or mechanical damage occurs on the equipment within the substation,

thereby resulting in safety to operation and maintenance personnel. The earthing

system also guarantees equipotential bonding such that there are no dangerous

potential gradients developed in the substation.

In designing the substation, three voltage have to be considered.

1. Touch Voltage: This is the difference in potential between the surface potential and

the potential at an earthed equipment whilst a man is standing and touching the

earthed structure.

2. Step Voltage: This is the potential difference developed when a man bridges with

his feet while not touching any other earthed equipment.

3. Mesh Voltage: This is the maximum touch voltage that is developed in the mesh of

the earthing grid.

Calculations for earth impedances and touch and step potentials are based on site

measurements of ground resistivity and system fault levels. A grid layout with

particular conductors is then analysed to determine the effective substation earthing

resistance, from which the earthing voltage is calculated.

In practice, it is normal to take the highest fault level for substation earth grid

calculation purposes. Additionally, it is necessary to ensure a sufficient margin such

that expansion of the system is catered for.

To determine the earth resistivity, probe tests are carried out on the site. These tests

are best performed in dry weather such that conservative resistivity readings are

obtained.

The second step is the layout of the Substation

The layout of the substation is very important since there should be a Security of

Supply. In an ideal substation all circuits and equipment would be duplicated such that

following a fault, or during maintenance, a connection remains available. Practically

this is not feasible since the cost of implementing such a design is very high. Methods

have been adopted to achieve a compromise between complete security of supply and

capital investment

The different switching schemes used in the layout of a

substation:.

1) Single Bus bar: Basically used in 33 to 66kv substations. The general schematic

for such a substation is shown in the figure below

With this design, there is an ease of operation of the substation. This design also

places minimum reliance on signalling for satisfactory operation of protection.

Additionally there is the facility to support the economical operation of future feeder

bays.

Such a substation has the following characteristics.

• Each circuit is protected by its own circuit breaker and hence plant outage does

not necessarily result in loss of supply.

• A fault on the feeder or transformer circuit breaker causes loss of the

transformer and feeder circuit, one of which may be restored after isolating the

faulty circuit breaker.

• A fault on the bus section circuit breaker causes complete shutdown of the

substation. All circuits may be restored after isolating the faulty circuit breaker.

• A bus bar fault causes loss of one transformer and one feeder. Maintenance of

one bus bar section or isolator will cause the temporary outage of two circuits.

• Maintenance of a feeder or transformer circuit breaker involves loss of the

circuit.

• Introduction of bypass isolators between bus bar and circuit isolator allows

circuit breaker maintenance facilities without loss of that circuit.

2) SINGLE BUS AND TRANSFER SCHEME: It consist of a single main bus along with

a transfer bus. In case of a fault the transfer bus is used. It consist of an extra

transfer bay so that in case of a fault in a particular bay the transfer bay is used.

Basically used in 66 to 132kv substations.

3) DOUBLE BUS AND TRANFER SCHEME: It consist of two main bus and a transfer

bus. It also consist of a transfer bay and a bus coupler(used for synchronization

of the two buses).Used in 132 to 220kv substation

4) ONE AND HALF CIRCUIT BREAKER SCHEME: It is used in above 220kv substation.

The layout of a 1 1/2 circuit breaker substation is shown in the schematic below:

The reason that such a layout is known as a 1 1/2 circuit breaker is due to the fact that

in the design, there are 9 circuit breakers that are used to protect the 6 feeders. Thus,

1 1/2 circuit breakers protect 1 feeder. Some characteristics of this design are:

• There is the additional cost of the circuit breakers together with the complex

arrangement.

• It is possible to operate any one pair of circuits, or groups of pairs of circuits.

• There is a very high security against the loss of supply.

SWITCHYARD PROTECTION

1. Circuit Breaker:-

The circuit breakers are used to break the circuit if any fault occurs in any of the

instrument. These circuit breaker breaks for a fault which can damage

Other instrument in the station. For any unwanted fault over the station we need to

break the line current. This is only done automatically by the circuit

Breaker. There are mainly two types of circuit breakers used for any substations. They

are (a) SF6 circuit breakers; (b) spring circuit breakers. The use of SF6 circuit breaker is

mainly in the substations which are having high input kv input, say above 220kv and

more. The gas is put inside the circuit breaker by force i.e. under high pressure. The

spring type is used for step down side of 132kv to 33kv also in 33kv to 11kv and so on.

They are only used in low distribution side

Specifications of SF6 C.B. used in substation:-

Rated voltage:-420 kv Rated current:-3150A

Frequency:-50 Hz Lightning impulse withstand voltage:-1425kv

(peak)

1st

pole to clear factor:-1.3 Switching surge withstand voltage:-1050kv

(peak)

Duration of short current:-1s Line charging breaking current:-600A

Total mass of SF6 gas:-45.5 kg Mass of C.B.:-5439kg

Classification:-C2-M2 Short circuit making current:-100kA (peak)

2. Sulphur Hexaflouride (SF6) Circuit Breakers

In such circuit breakers, Sulphur hexafluoride (SF6) gas is used as the arc quenching

medium. The SF6 is an electro – negative gas and has a strong tendency to absorb free

electrons. The contacts of the breaker are opened in a high pressure flow of SF6 gas

and an arc is struck between them. The conducting free electrons in the arc are rapidly

captured by the gas to form relatively immobile negative ions. This loss of conducting

electrons in the arc quickly builds up enough insulation strength to extinguish the arc.

Working

In the closed position of the breaker, the contacts remain surrounded by SF6 gas at a

pressure of about 2.8 kg/cm2. When the breaker operates, the moving contact is

pulled apart and an opening of a valve which permits SF6 gas at 14 kg/cm2

pressure

from the reservoir to the arc interruption chamber. The high pressure flow of SF6

rapidly absorbs the free electrons in the arc path to form immobile negative ions

which are ineffective as charge carriers. The result is that the medium, between the

contracts quickly builds up high dielectric strength and causes the extinction of the arc.

After the breaker operation (i.e., after arc extinction), the valve is closed by the action

of a set of springs.

3. ISOLATOR:-

An isolator is a non-load-breaking switch, and is provides a visible means of isolating a

component, such as a circuit breaker, transformer, etc., from the high

whenever it is necessary to perform maintenance of that component. Normally,

isolators come in pairs, wit

Isolators are only opened

breaker, and must be closed

To work on, say, a h.v. circuit breaker, the breaker

either side must be opened and locked off, temporary earths attached to either side of

the circuit break- to-work card, detailing the maintenance work, must be issued to the

crew by the supervising engineer

Specifications of isolator used in substation

Type:-HCB

BIL(kv):-1425

Rated current:-3150 amp

Motor voltage (AC):-415

Weight of drive:-100 kg

breaking switch, and is provides a visible means of isolating a

component, such as a circuit breaker, transformer, etc., from the high

whenever it is necessary to perform maintenance of that component. Normally,

isolators come in pairs, with one on each side of the component to be isolated.

Isolators are only opened after the load current has been broken using a circuit

breaker, and must be closed before the circuit breaker is closed.

To work on, say, a h.v. circuit breaker, the breaker must be tripped, the isolators on

either side must be opened and locked off, temporary earths attached to either side of

work card, detailing the maintenance work, must be issued to the

crew by the supervising engineer

of isolator used in substation:-

Rated voltage:-420kv

Switching impedance:-1050/1245 kv

amp Type of drive:-Motor

415 Control voltage (DC):-220

breaking switch, and is provides a visible means of isolating a

component, such as a circuit breaker, transformer, etc., from the high-voltage lines,

whenever it is necessary to perform maintenance of that component. Normally,

h one on each side of the component to be isolated.

the load current has been broken using a circuit

is closed.

must be tripped, the isolators on

either side must be opened and locked off, temporary earths attached to either side of

work card, detailing the maintenance work, must be issued to the

4. LIGHTNING ARRESTOR:-

A lightning arrester is a device used on electrical power systems and systems to

protect the insulation and conductors of the system from the damaging effects of

lightning. The typical lightning arrester has a high-voltage terminal and a ground

terminal. When a lightning surge (or switching surge, which is very similar) travels

along the power line to the arrester, the current from the surge is diverted through

the arrestor, in most cases to earth.

In telegraphy and telephony, a lightning arrestor is placed where wires enter a

structure, preventing damage to electronic instruments within and ensuring the safety

of individuals near them. Smaller versions of lightning arresters, also called surge

protectors, are devices that are connected between each electrical conductor in power

and communications systems and the Earth. These prevent the flow of the normal

power or signal currents to ground, but provide a path over which high-voltage

lightning current flows, bypassing the connected equipment. Their purpose is to limit

the rise in voltage when a communications or power line is struck by lightning or is

near to a lightning strike.

If protection fails or is absent, lightning that strikes the electrical system introduces

thousands of kilovolts that may damage the transmission lines, and can also cause

severe damage to transformers and other electrical or electronic devices. Lightning-

produced extreme voltage spikes in incoming power lines can damage electrical home

appliances.

A lightning arrester may be a spark gap or may have a block of a semi-conducting

material such as silicon carbide or zinc oxide. Some spark gaps are open to the air, but

most modern varieties are filled with a precision gas mixture, and have a small amount

of radioactive material to encourage the gas to ionize when the voltage across the gap

reaches a specified level. Other designs of lightning arresters use a glow-discharge

tube (essentially like a neon glow lamp) connected between the protected conductor

and ground, or voltage-activated solid-state switches called varistors or MOVs.

Lightning arresters built for power substation use are impressive devices, consisting of

a porcelain tube several feet long and several inches in diameter, typically filled with

disks of zinc oxide. A safety port on the side of the device vents the occasional internal

explosion without shattering the porcelain cylinder.

Lightning arresters are rated by the peak current they can withstand, the amount of

energy they can absorb, and the break over voltage that they require to begin

conduction. They are applied as part of a lightning protection system, in combination

with air terminals and bonding.

5. CAPACITIVE VOLTAGE TRANSFORMER:-

A capacitor voltage transformer (CVT) is a transformer used in power systems to step-

down extra high voltage signals and provide low voltage signals either for

measurement or to operate a protective relay. In its most basic form the device

consists of three parts: two capacitors across which the voltage signal is split, an

inductive element used to tune the device to the supply frequency and a transformer

used to isolate and further step-down the voltage for the instrumentation or

protective relay. The device has at least four terminals, a high-voltage terminal for

connection to the high voltage signal, a ground terminal and at least one set of

secondary terminals for connection to the instrumentation or protective relay

Capacitive voltage transformer can be effectively employed as a potential source for

metering, protection, carrier communication and other vital functions of an electrical

network. In the case of EHV systems CVTs are always supplied in multi-

unit construction. The multi-unit construction enables ease of transportation and

storage, convenience in handling and erection etc.

The Capacitive Voltage Transformer comprises of a Capacitor Divider along with its

associated Electro-Magnetic Unit. The Divider provides an accurate proportioned

voltage, while the Electro-Magnetic Unit transforms this voltage, both in magnitude

and phase to convenient levels suitable for metering and protection. The Electro-

Magnetic Unit (EMU) comprises of the following components;

* Compensating Reactor

* Intermediate transformer

* Damping device

The compensating reactor is used for tuning CVTs to the desired rate frequency of 50

Hz. Since the CVT comprises of capacitors the compensating reactor plays the role of

nullifying the capacitive effect of reactance due to the capacitance of the CVT.

Specifications of CVT used in substation:-

Pass band:-35-50/50-90/90-500 Nom. peak envelope power:-650W

Coupling capacitor:-4400 pf Nom. line side impedance:-600 ohms

Nom. equipment side impedance:-75 ohms

6. CURRENT TRANSFORMER:-

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 1 amp. This

is done because we have no instrument for measuring of such a large current. Its main

use is of protection and measurement. A current transformer is a device for measuring

a current flowing through a power system and inputting the measured current to a

protective relay system. Electrical power distribution systems may require the use of a

variety of circuit condition monitoring devices to facilitate the detection and location

of system malfunctions. Current transformers and current sensors are well known in

the field of electronic circuit breakers, providing the general function of powering the

electronics within the circuit breaker trip unit and sensing the circuit current within the

protected circuit. Current transformers are an integral part of ground fault circuit

breakers. Current transformer assemblies are often positioned between the line side

of a trip unit of a circuit breaker and the load side in order to monitor the current

there between. Current transformers in electrical substations measure the system

currents at predetermined measuring points of the switchgear with a certain

measurement inaccuracy. The measuring points are typically located at all incoming

and outgoing lines and possibly also within the system, e.g. for the bus bar protection.

The current measurement signals are used for protective functions, for monitoring the

substation, for calculating performance data for operating purposes or for

consumption billing and for the representation on a display.

7. WAVE 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.

Wave trap is a parallel tuned inductor - capacitor 'tank' circuit made to be resonant at

the desired communication frequency. It is the effort to utilize the same transmission

line between two substations for the purpose of communications. At this

communication frequencies the tank ckt provides high impedance and does not allow

to pass through them & onto the substation bus & into transformers.

8. OTHER SWITCHYARD EQUIPMENTS:-

Sl.

No.

Equipment Function

1 Bus-bar Incoming and outgoing circuits connected to bus-bar

2 Circuit-breakers Automatic switching during normal or abnormal conditions.

3 Isolators (Disconnectors) Disconnection under no-load condition for safety, isolation and maintenance.

4 Earthing Switch To discharge the voltage on deadlines to earth.

5 Current Transformer To step-down currents for measurement, control, and protection.

6 Voltage Transformer To step-down Voltages for measurement, control, and protection.

7 Lightning Arrester (Surge Arrester)

To discharge lightning over voltage and switching over voltage to earth.

8 Shunt reactor To provide reactive power compensation during low loads.

9 Series Reactors To reduce the short-circuit current or starting currents.

10 Neutral-Grounding Reactors

To limit the earth fault current

11 Coupling capacitor To provide connection between high voltage line and power line carrier current equipment.

12 Line-trap To prevent high frequency signals from entering other zones.

13 Shunt capacitors To provide compensations to reactive loads of lagging power factors.

14 Power Transformer To step-up or step-down the voltage and transfer power from one AC voltage to another AC voltage at the same frequency.

15 Series capacitors Compensation of long lines

16 Substation Earthing (Grounding)

System

-Earth mat

-Earthing spikes

-Earthing risers

To provide an earth mat for connecting neutral points, equipment body, support structures to earth. For safety of personnel and for enabling earth fault protection. To provide the path for discharging the earth currents from Neutrals, Faults, Surge arresters, overheads shielding wires etc. with safe step-potential and touch potential.

17 Overhead earth wire shielding or Lightning Masks.

To protect the outdoor substation equipment from Lightning strokes.

18 Illumination system

(lighting)

-for switchyard

-buildings

-roads, etc.

To provide illumination for vigilance, operation and maintenance.

19 Protection System

-protection relay panels

-control cables

-circuit-breakers

-CTs, CVTs, etc.

To provide alarm or automatic tripping of faulty part from healthy part and also to minimize damage to faulty equipment and associated system.

20 Control cabling For protective circuits, control circuits, metering, circuits, communication circuits.

21 Power cables To provide supply path to various auxiliary equipment and machines.

22 PLCC system power line carrier current system

-line trap

-Coupling capacitor

For communication, telemetry, tele-control, power line carrier protection etc.

-PLCC panels

23 Fire fighting system

-sensors, detection system

-water spray system

-fire protection control panels,

alarm system

-water tank and

spray system

To sense the occurrence of fire by sensors and to initiate water spray, to disconnect power supply to affected region to pin-point location of fire by indication in control room.

24 Auxiliary standby power system

-diesel generator sets

-switchgear

-distribution system

For supplying starting power, stand by power for auxiliaries.

25 Telephone, Telex

system,

Microwave system

For internal and external communication.

Pre-Commissioning Testing of equipment :

This is done for all equipments prior to energization to know that there is no damage

during transportation, erection/assembly to such an extent that there future operation

will be at risk.

Before starting pre-commissioning tests equipment should be free from dust/ foreign

materials, all visible defects, support structures, All equipment / Marshalling box has

been provided with double earthing, erection is completed in all respect, levelling &

alignment of structure and base frame is checked, control box/ Bay Marshalling Kiosk

is free from any physical defects etc.

A. Testing of Auto Transformer

1. IR Measurement: HV, IV & LV winding with respect to each other & earth (using 5kV

megger). Control wiring, tap changer motor, cooling fan, cooling pump (500V megger).

2. Vector group test & Polarity Checking: Polarity & phase relationship can be

measured by connecting terminals 1R of HV and 2R of IV and measuring voltages

between terminals 1Y2Y, 1Y2B, 1B2Y & 1B2B and connecting LV phase & Neutral point

with earth. Connect 3 phase 415V to HV terminals.

3. Measurement of winding resistance: As resistance of Auto transformer is very low,

less than 1 ohm. A specially designed kit is available to measure this low resistance of

autotransformer & reactor.

4. Magnetic Balance Test: A low voltage test conducted by applying single phase

between phase & neutral of a winding and measuring voltage induced in other two

phases of the same winding.

5. Magnetizing Current test: By applying 3 phase 415V across primary and keeping

secondary open, current is measured for all phases of primary (it will be in mA) &

should match with factory test. If there is unbalance current in any phase it means

unhealthy condition.

6. Floating Neutral Voltage test: This determines gradual deterioration/ development

of fault in transformer, done with 415V ac supply across HV winding or IV winding

after disconnecting neutral from earth. Voltage between neutral and ground is zero/ a

negligible voltage should appear.

7. Short Circuit Test: Done by applying 3 phase low voltages to high voltage side and

measuring primary currents by short circuiting LV winding terminals.

8. Operational testing of Buchholz relay, OTI, WTI contacts.

9. Oil sample characteristics: Tank & tap changer oil sample testing as per IS 1866.

Testing of BDV (KV), Moisture content (ppm), Tan delta, Resistivity, Interfacial tension

etc.

10. Dissolve Gas Analysis (DGA) of oil: for checking gases like H2, CH4, CO, CO2, C2H4,

C2H6, etc.

11. Testing of bushing: Megger, Tan delta & capacitance.

12. All auxiliary should be thoroughly checked for healthiness.

B. Testing of Current Transformer

1. Insulation Resistance (IR) Measurement:

Insulation resistance test is the simplest and most widely used to check the

soundness of transformer insulation. This test gives the condition of insulation ( i,e

degree of dryness of paper insulation), presence of foreign contaminates in oil also

any defects in the transformer

HV+IV to LV

HV+IV to E

LV to E

IR value should be above 500 Mohms

Safety instructions

The test specimen is discharged by short circuiting for a period at least

four times as long as the test voltage was applied. Before bare hand

contact , the absence of voltage shall be confirmed by measurement.

Precautions

Clean the bushing porcelains by wiping with a piece of dry cloth.

Lead wires from the bushing line lead and tank earth to megger shall be

as short as possible without joints and shall not touch tank or each other.

Testing procedure

IR measurements shall be taken between the windings collectively i.e.

with all the windings being connected together and the earthed tank and

between each winding and the tank, the rest of the windings being

earthed. Following measurements are relevant for auto-transformers and

Reactors

Record date and time of measurement sl.no & make of megger, oil temperature

and IR values at intervals of 15 seconds, 1 minute and 10 minutes

This is done for testing the quality and degree of dryness of insulation of electrical

equipment, using MEGGER.

Megger Voltage Between Permissible value

5kV

Primary to Secondary

core, Primary to Earth

400Mohms for 400KV,

200Mohms for 220KV

500V

Secondary core to earth,

Core to Core

- Do -

2. Secondary Winding resistance:

This is to measure the resistance of secondary winding & is done for all the cores with

DIGITAL MULTIMETER.

DIGITAL

MULTIMETER

Test of CT of a reactor

3. Polarity Test: In this a galvanometer is connected across CT secondary. A 9 Volt

battery is touched to primary of CT secondary. The deflection of pointer should be

similar in case of each CT to be connected in the same protection. At any instant

current entering the primary from P1 to current should leave secondary from the

terminal marked S1. A set up shown in the fig, below.

P 2 P1

S2 S1

4. Tan Delta & Capacitance Measurement:

Tan delta also called dissipation factor is a measure of the restive losses of the

insulation. This represents the condition of insulation inside the CT and moisture

content in dielectric medium.

For this measurement an instrument called TAN DELTA KIT is used. Test voltages 2 &

10KV are applied and tan delta & capacitance is measured. Permissible value for Tan

Delta is 0.005 for new equipment and 0.007 for old equipment & capacitance to match

with factory test report.

5. Current Ratio Test

Current injection through kit at primary terminals (P1 & P2) & induced current is

measured on the secondary terminals (S1 & S2). Current injected are 20%, 40% & 80%

of rated current. Ratio will be Primary current/ Secondary current.

6. Magnetizing Curve Performance:

This to prove that the secondary turns are not short circuited anywhere, to establish

the characteristics and capability of CT. A typical magnetization curve is as below.

Curve is obtained by applying 25, 50, 75, 100 & 110% of Knee point voltage to

secondary winding and measuring current using tong tester.

Magnetizing current (mA)

% o

f K

ne

e V

olt

ag

e

~ 220V AC

1 PHASE AUTO TRANSFORMER 1 PH STEP UP TRANSFORMER

LOW RANGE TONG TESTER

VOLTMETER OR MULTIMETER

220V AC ~

LOADING

TRANSFOR

1 PH AUTO

TRANSFORMER TONG TESTER (HIGH

RANGE FOR PRI.

TONG TESTER (LOW

RANGE FOR SEC.

7. Contact Resistance Measurement:

To avoid any hot spot at joints/ connectors etc. The contact resistance should not be

more than 5µΩ per joint/ connector. Measured with CRM kit (Contact resistance

measurement kit).

C. Testing of Capacitive Voltage Transformer

1. Insulation Resistance Measurement (IR)

Meggering is done same as done in CT

2. Secondary Winding Resistance: It is normally between 0.4 to 0.5 ohms for both 220

& 400kV CVT.

3. Voltage Ratio Test: 415V applied to primary winding with the secondary winding

open and using multimeter secondary voltage is measured and then ratio is

determined.

4. Tan delta & Capacitance Measurement:

Permissible value for Tan Delta is .007 & Capacitance value for all three/ two stacks

should match with factory test report.

D. Testing of SF6 Circuit Breaker:

1. Pressure switch settings: All pressure switches of gas & air circuit.

2. Air & SF6 pressure leakage rate

3. Dew point of SF6 gas.

V

4. Coil resistance of trip & closing coil using a digital multimeter in ohms.

5. Circuitry & Operational checks: For tripping, Closing, Anti pumping feature, Pole

discrepancy, Heater circuit. Etc.

6. Operating time & Dynamic Contact resistance: this is done with an advance

microprocessor based kit with combined feature to measure opening / closing time &

the resistance of the contact (inside the interrupter chamber) during closing &

opening.

7. IR value of trip & closing coils, control circuit, compressor motor (500V megger) &

Breaker in open condition to earth & breaker in closed condition with earth (5kV

megger).

8. Tan delta & Capacitance Measurement

9. Contact Resistance Measurement.

E. Testing of Isolator and Earth Switch:

1. IR of the motor winding, control & power circuit cables (500V Megger)

2. Operational checks: Like close/ open from local & remote, operating time, auxiliary

contacts, etc.

3. Contact Resistance: Contact resistance between moving & fixed contact & also with

the different clamps & connectors, value should be less than 5micro ohms.

4. Checking of interlocks with the breaker & Earth switch

F. Testing of Lighting Arrester:

1. Operation check of LA counters.

2. Insulation resistance measurement (used 5kV magger).

3. Capacitance and Tan delta measurement of individual stacks.

4. Third harmonic resistive current measurement (to be conducted after

energisation.)

G. Testing of Relay panel:

1. Relay checked using relay test kit. Numerical relays are checked/ setting done using

special test kit through computers by simulating different types of faults.

2. Wiring Check: as per scheme.

H. Testing / Checking of Bay Feeders:

1. Details of all equipment/ panels with Sl.No. / I.D. no.

2. Checking of clearance between phase to earth& phase to phase.

3. Contact Resistance Measurement of all joints.

4. Checking of interlocks.

5. Protection Tripping test

6. Primary injection test

TRANSMISSION LINE PROTECTION & AUTO

RECLOSE SCHEME

Objective of relay protection

• Separate faulty parts from the rest of the power system to facilitate the operation of

the healthy part of the system

• Protect persons in the surrounding of the power system electrical faults in the power

system

• Transmission lines 85%

• Busbar 12%

• Transformer/ Generator 3%

Total 100 %

Fault types in Transmission lines

• Transient faults

– Are common on transmission lines, approx. 80- 85%

– Lightning are the most common reason

– can also be caused by birds, tree infringement, swinging lines due to high velocity

winds etc.– will disappear after a short dead Interval

• Persistent faults

– Broken conductor fallen down due to decapping of insulator o failure of mid span

joint etc.

– must be located and repaired before normal service

Transmission line faults –Causes

..Lightning

..Flying objects

..Contamination due to pollution of insulators

..Physical contact by birds

..Human errors

..Tree infringement or Falling trees

..Insulation aging

..Broken conductors

Recommendation of line protection

400KV lines

Two independent high speed main protection schemes called Main I and Main II with

at least one of them being carrier aided, non – switched, three zone distance

protection.

220KV lines

At least one carrier aided non-switched three zone distance protection scheme. In

addition to this another non-switched / switched distance scheme or directional

overcurrent and earth fault relays provided as back up.

Different Types & Makes of relays available in POWERGRID stations for line protection

Static relays YTG31 (Areva), RAZFE (ABB)

Microprocessor based relay Micro mho, Quadra mho (Areva)

Numerical relays EPAC (Areva), REL (ABB),

7SA 52 (Siemens)

Design of distance protection

• Switched scheme – consists of a start relay to select (switch) the measuring loop to

the single measuring relay

• Full scheme – has a measuring element for each measuring loop and for each zone

Eg. Micro Mho relay which is having 18 separate measuring elements.

Z3 Z2 Z1

80% 100+

100 + 100 + 20%

Z3R 20%

Section 1 Section 2 Section 3

Zone 1 = 80% of ZL or 70% ZL in Double Circuit lines Zone 2 = 120% of ZL Zone 3F = 220% of ZL Zone 3R = 20% of ZL

Z 1A

Z 2A

Z 3A

C

SETTING CRITERIA

Auto reclosing

Fault statistics

• Single phase to earth 80%

• Two phases to earth 10%

• Phase to phase faults 5%

• Three phase faults 5%

• Outage times will be short compared to where station personnel have to re- energize

the lines after a fault.

• In interconnected networks auto- reclosing helps in maintaining system stability

Recommendations for provisions of auto- reclosing

• Presently 1 phase high speed auto- reclosur (HSAR) at 400kV and 220kV level is

widely practiced including on lines emanating from Generating Stations and the same

is recommended for adoption.

PERMISSIVE UNDER REACH SCHEME

Fault beyond the Zone 1 reach of relay A but within the Zone 1 reach of relay B Distance relay at B will trip the breaker in Z 1 time & send carrier to end A. Fault detected in Zone 2 reach of relay A and carrier recd. Trips instantaneously without Zone 2 delay

A B

Z 1A

Z 1B Fault

• If 3- phase auto- reclosure is adopted in future the application of the same on lines

emanating from generating stations should be studied and decision taken on case to

case basis

SETTING CRITERIA

Dead Time

• Auto- reclosing requires a dead time which exceeds the de-ionizing time

• Time required for the de- ionizing of the fault path depends on: -

Arcing time, fault duration, wind conditions, circuit voltage, capacitive coupling to

adjacent conductors, etc.

• Single phase dead time of 1.0 sec is recommended for both 400kV and 220kV

system.

Reclaim Time

• The time during which a new start of the auto- reclosing equipment is blocked.

• If reclosing shot has been carried out and the line is energized and a new fault occurs

before the reclaim time has elapsed, the auto- reclosing equipment is blocked and a

signal for definite tripping of the breaker is obtained.

• After the reclaim time has elapsed, the auto- reclosing equipment returns

to the starting position and a new reclosing sequence can occur.

• Reclaim time of 25 sec is recommended.

• Breaker capability

PLCC & Tele-Protection

Power line communication (PLC), also known as power line carrier, is a system for

transmitting information on an electrical conductor used for carrying electric power

from high voltage transmission lines, distribution lines, and to lower voltage lines used

inside buildings. All PLC systems operate by applying a modulated carrier signal on the

existing electrical wiring system. There are different types of power line

communications, depending on frequency bands used.

A good example of PLC that uses high-frequency communication (MHz range) is

broadband over power lines (BPL). BPL employs PLC to provide broadband data and

voice services through the use of existing electrical power lines. Typically BPL services

operate by modulating in a carrier wave of between 1.6 and 80 MHz into electrical

power lines.

PLC has long been used, with medium-frequency modulation (kHz range), for remote

measurement and reporting purposes. The applications are for example for utilities to

control and perform telemetry of electrical equipment such as meters (AMR), SCADA,

demand side management and power quality monitoring systems.

TYPES OF COMMUNICATIONS

Vhf wireless communication : 100 – 300 mhz

Leased p&t lines

Power line carrier communication: 30-500 khz

Microwave communication : 800 mhz – 4 ghz

Satellite communication : more than 4 ghz

Optical fiber communication

PLCC

• In plcc ehv power line is used for power system communications

• The plcc hf signals (30-500khz) is coupled to the ehv power line through

coupling capacitor

• It is used for speech and data transferring

• It is also used for the line protection

• Highly reliable communication system

• Maintenance free

• Less installation cost

• No running expenditure

OUTDOOR EQUIPMENT OF PLCC

• Capacitor voltage transformer

• Wave trap

• Line matching unit

• Balancing transformer

• 3 element protection device

• Drainage coil

• Lightning arrestor

• Earth switch

• Coaxial cable

• ehv transmission line

INDOOR EQUIPMENT OF PLCC

• PLCC PANEL

ABB-ETI 21, BPL-9505,WS-WSP100 & PUNCOM

• PROTECTION COUPLER

NSD60 & NSD61 OF ABB, 6710 OF BPL

• DATA MODEM

NSK3,NSK4 & NSK5 OF ABB

• TELEPHONE EXCHANGE

EPAX-200.3 & MDX50 OF BPL

• EXPRESS TELEPHONE FOR POINT TO POINT COMMUNICATION

METHODS OF PLCC COUPLING

There are different types of plcc coupling systems

Phase to ground coupling

Phase to phase coupling

Line to line coupling

Insulated ground wire coupling

Intra bundle coupling

Power Grid is adopting mainly phase to phase coupling for all the lines

PLCC PANELS

In plcc panel the voice, telemetering / tele protection signals will be in the

range of 0-4 khz

Worldwide the allocated frequency band for plcc is 30-500 khz

In powergrid each line is having 3 plcc panels

1. one for speech & data

2. two for speech & tele protection

In Powergrid ABB,BPL,WS,PUNCOM make PLCC panels are available

TELEPROTECTION

Protection of a circuit, the ends of which are geographically separate like Lines and

Cables in which co-operation is obtained between the two relaying points by the

transmission of information over the Distance by Telecommunication Technique.

The types of tele-protections adopted in power system

1. Phase comparison

2. Distance protection (Permissive/Blocking)

3. Direct Tripping

The techniques available in Tele protection

1. Protection couplers with coding : NSD60, NSD61 and 6710

2. Protection couplers without coding: NSD40 etc.

The Typical Timings For the for Permissive/Blocking applications is 20m.sec &

for Direct Tripping Schemes 28 to 30 m.sec

SUBSTATION AUTOMATION AND REMOTE OPERATION

The Main Objective of Substation Automation:

• To solve following tasks in a more efficient and economical way, by using IT

• Control of substation from ONE Screen

• Comprehensive protection management:

1. Monitoring

2. Information/annunciation

3. Resetting

4. Diagnostics and records

• Reduction of project time and cost @control wiring economy

• On line expandability

Open system & expandable, operate on international protocol (IEC 101/103 & IEC

61850) to provide more functionality to work plant and systems harder.

Advantages of Substation Automation

1. Availability of Data as Information

2. Ease of operation from local and Remote

3. Reduction in Manpower & O&M Cost

4. Hardware and software interlocking possible

5. Ease in Disturbance recording and fault analysis

6. Low Restoration time

7. Time saving in future design & engineering.

With the advent of new era the substations now are fully automated with lesser and

lesser need of and reliability on manpower. The Patna substation is an apt example.

Earlier all the power cables from the switchyard equipment were directly taken to the

control room for monitoring. However, now Kiosks are constructed in the switchyard

itself, with each kiosk carrying equipment like Micom c264 for each bay.

Micom c264

These Kiosk are interconnected and the information from each Kiosk is carried to the

control room using optical fibres. The Kiosk are connected in ringed main structure so

as to ensure that the information is carried even in case of a broken optical fibre. Most

importance fact is that the equipment can be configured using database in the control

room.

Ringed main structure

Kiosks are connected in ring main structure through optical. Even if 1 connection fails

none of the kiosk are disconnected from the grid and the bay continue to operate.

But in star connection if the optical fibre fails the whole dia gets disconnected from

the grid.

RTU Basics

An RTU, or Remote Terminal Unit is a microprocessor controlled electronic device

which interfaces objects in the physical world to a distributed control system or

SCADA system by transmitting telemetry data to the system and/or altering the state

of connected objects based on control messages received from the system.

RTU Application in POWERSECTOR

• For Telemeter Data for Grid Monitoring

• For Remote operation of Sub stations

• Apart from the above main applications the RTU also serves the purpose of

maintaining power system data through SCADA software, which can be used for

many applications.

Micom c264 RTU function

• Mode management

• Database management

• Self-tests

• Time management

• Communication

1. Tele control bus

2. Legacy bus

3. Station bus

• Input/ Output

• Control Sequences

• Automation

• User Interface

• Records

Mode management:

The available operating modes are:

• Operational: the equipment is working correctly

• Test: computer is operational but DO are not set

• Standby: this mode links to redundancy management. In this mode there is no

communication with IED or SCADA

• Maintenance: only functions needed for database and mode management are

available

• Faulty: the computer has detected a major self-test failure

• Halt: the equipment is out of service

Database management: computer stores 2 different database

with different version

• Current database

• Standby database

Self-tests:

The computer makes self-checks:

• Hardware

• Software

• Database

Time management

Time synchronization can be done via 3 means:

• IRIG-B: external clock send synchronization signal to C264/C264C through IRIG-B

standard

• SCADA: synchronization message is acquired by C264/C264C through SCADA

links.

• The user can set Time/Date by Computer HMI or CMT tool

1. System Master Clock: in PACiS system, it is enough to synchronize one

MiCOM C264/C264C. This computer is identified as Master Clock and

synchronize other equipment on station bus

Digital inputs

• Circuit Breaker Position

• Disconnecting Switch Position

• Tap changer Position (BCD)

• Pulse accumulator

• Alarm input

• Single/double input (CB)

• 1ms acquisition cycle

Digital outputs • Direct control

• Select Before Operate control

• Settable Control Pulse duration

• For CB control board -no interposing relay required

• Trip Circuit Supervision

Analogue measurements with transducers • Current or voltage inputs

• 16 bits ADC 0.1 % accuracy

• Linear or quadratic scaling

• Cyclic or variation transmission

CONCLUSION

By doing summer training at Patna Substation, I came to

know about how the transmission and distribution of

power lines are carried out in our country. I got to know

about the construction, maintenance and different

protection in a line and substation. I was exposed to

different types of equipments like isolators, circuit

breakers, relays, etc used in a substation and I also

came to know about how the equipments kept in the

switchyard are brought in the control room and

operated from there. I was taught about how the

equipment were controlled if any fault occurs.