400 kv nelmangala

Mr. Mayur Dhanaji Rane

NPTI-PSTI Bangalore

22/03/2013

400 KV/ 220 KV Nelamangala

Report

2

National Power Training Institute

Power System Training Institute

400 /220 KV Nelamangala Station

Submitted By: -

Mr. Mayur Dhanaji Rane (1540)

Guided By:-

Mr. K. Vetrivel Mr. M. N. Murthy

Assistant Director, Director, PSTI,

PSTI, Bangalore Bangalore

3

Index

Sr. No Contents Page No.

1 Introduction 4

2 Single Line Diagram of the 400KV/220KV

Substation

5

3 Bus Bar Scheme 6

4 Substation Auxiliaries 8

5 Capacitive Voltage Transformer 10

6 Current Transformer 13

7 Circuit Breaker 15

8 Isolator 17

9 Transformer 18

10 Reactor 21

11 220V Battery Charger Room 23

12 Control Room 24

13 Earthing 25

14 Bibliography 27

4

1. Introduction:-

It is 400 \ 220 KV station at about 25 kms North West of Bangalore city in

Bangalore- Tumkur road (national high way no.4) established in a 118 acre plot.

After establishing a major power generating station at Sharavathi river fall, the

power supply was stepped up to 220 KV and 4 numbers of 220 KV lines transferred

power to Bangalore. But often the lines were tripping and sometimes a cascading effect

resulted in entire grid failure plunging whole \ parts of Karnataka into darkness. This was

very often leading to failure of Southern grid even. This grid-failure had to be minimized.

Besides the 400 KV power supply from generating stations like GOOTY (Andhra

Pradesh) was to be integrated into southern grid. All these and further system studies on

Southern grid of India by CEA (Central electricity Authority) necessitated a 400 KV

station in this zone.

These reasons resulted in this Nelamangala station established in the paths of the

existing Sharavathy-Bangalore 220 KV lines. It was constructed on TURN-KEY basis by

L&T under planning and technical supervision of PGCIL (Power Grid Corporation of

India limited). It is presently owned, operated and maintained by KPTCL (Karnataka

Power Transmission Corporation limited) After establishment of this station there has not

been any grid failures of the type described before and thus the purpose has been

effectively served.

5

2. Single Line Diagram of the 400KV/220KV Substation:-

6

3.Bus Bar Scheme:-

8

4. Substation Auxiliaries:-

160KN Anti Fog Insulator Aluminium with Dead End Jumpers

Aluminium T Clamp Fix and Sliding Clamps

T Connector Circuit Breaker Clamps

9

Spacers for Double moose rigid type Spacer for Double type sliding type

Line Spacer for Moose Twin Double Tension for Moose

Double Suspension hardware fitting Types of Jumpering

10

5. Capacitive Voltage Transformers:-

The CVT’s are also used to serve as coupling condensers for connecting PLCC

equipments. Wave traps prevent telecommunication signals getting into the station side

equipments.

There are potential transformers in the form of CVT (Capacitor Voltage

transformer) to measure the incoming line voltage. The CVT’s also serve as coupling

condensers for connecting PLCC lines in one or two phases of the lines. Wherever PLCC

lines are connected one can see Wave traps to block communication signals reaching the

220 KV bus. Wave traps are tuned inductors to allow a particular frequency (here it is 50

c\s power) the first line control is through double break isolators coupled with grounding

switch.

400 kV

1. Core 1 3P Protection (connected in star)

2. Core 2 3P Directional Earth Fault Protection (connected in open delta)

3. Core 3 0.5 Protection & Metering (connected in star)

Here Core 1 is used for Protection purpose hence connected in Star

11

Core 2 is used for Directional Earth Fault Protection hence connected in Open Delta.

The formation of the star / neutral point or open delta connections of the secondary

windings of the three phases of the VTs has been made correctly and that the neutral end

of the star connected winding and one end of the open delta connected winding have been

earthed in the Marshalling Kiosk / Junction Box.

Ratings

Make Alstom

Type CVEB:400/1425

Frequency 50 Hz

Number of cores 3

Rated Voltage HV 400KV/√3

LV 110V/ √3

HF Capacitance 8800 pF

Primary Capacitance C1 9312pF

Secondary Capacitance C2 160000pF

12

Insulation Level 630/1425 KV

HSV 420 KV

Burden 200 VA

Class 3P

Insulation Class A

13

6. Current Transformer:-

400 kV Bays

CT Ratio: 500 – 1000 – 2000.

1. Core 1= PS Differential Protection Main – 1 / Distance Protection Main - 1

2. Core 2= PS Differential Protection Main – 2 / Distance Protection Main 2,Over

current, Earth fault and LBB Protections.

3. Core 3= 0.5 Metering

4. Core 4= PS Bus Bar Protection (Main Zone) except for CTs in Tie CB Bay

5. Core 5= PS Bus Bar Protection (Check Zone) except for CTs in Tie CB Bay.

14

The secondary windings of different phases of Current Transformers are generally

star connected. A typical wiring connection for Core – 1 of Current Transformers in the

Bay Marshalling Kiosk / Junction Box.

Rating

Rated Voltage 400 KV


Rated Current 2000 A

Knee Point Voltage 1500 V

Burdon 40 KV

Number of cores 5


Frequency 50 Hz

Class Protection PS

Metering 0.5

Ratio Available 2000-1000-500/1A

Total Weight 2450Kg

15

7. Circuit Breaker:-

The breakers are of single phase double pole types i.e. an interrupter and a

capacitor circuit held in porcelain bushings and working in parallel. The interrupter is of

double break type i.e. there are two female contacts on either ends inside the interrupter

with two male contacts striking into these contacts. The circuit closing or opening is in

two stages with a few mili-seconds of time gap between the two actions. The breaking \

making zone held in porcelain bushings is filled with high pressure (here it is 6 kg \ cm²)

SF6 gas for arc quenching .The gas is hermitically sealed with a pressure indicator. The

movements of the contacts are by AIR-PRESURE-TRIP with a simultaneous SPRING-

LOADING. Later the spring loading is used for closing the contacts. For air-pressure

operation the air at a particular pressure (here it is 15 kg’s per cm²) is held in high

pressure tanks. Any fall in air pressure is taken care of by an automatically working air

compressor. For the purpose of safety of the breakers, fall of gas \ air pressure beyond

certain threshold levels results in locking up of the breaker for breaking or closing

operations. (LOCK IN: The breaker fails to obey any commands ie neither opens or

closes) This interrupter is in parallel with a suitably designed capacitor circuit to raise the

potentials of the contacts so that the potential difference between male and female

contacts is reduced considerably and so the arcing is very much reduced.. In certain

breakers (Triple pole type) a third circuit is inserted to contain the effects of surge

currents of some lengthy lines they are called PIR (Pre-inserted resistance) type. Here the

initial circuit closing action is through a resister and a little later the interrupter contacts

move. (After about 12 milli seconds) But now-a-days due to development of fast acting

breakers PIR type breakers are no longer used. Most of the breakers are of auto-reclosure

16

type. In India the reclosing is for single phase faults only. The GOS’s (Group operating

switches) have an additional grounding switch for the incoming lines. In the latter the

interlocking mechanism is such that the grounding switch can be operated only if the

isolator is open. As done in all stations load breaking or closing is through breakers and

isolators are used for no load closing \ opening.

The following typical connections are made at the circuit breaker end.

a) DC positive & DC negative for local operation.

b) DC positive for remote closing.

c) DC positive for remote tripping.

d) Remote closing signal.

e) Remote tripping signal.

f) Protection trip signal.

g) Trip circuit supervision.

h) ON / OFF indications (Lamp & Semaphore).

i) Auto Trip / Spring Charged Lamp indication.

j) Air pressure / Oil pressure / spring charging limit switch contacts for auto reclose

Blocking.

k) Contacts of pressure switches for annunciations of low SF6 gas / air / oil pressure

Alarms & lockout conditions and for loss of N2 pressure.

l) Contact for annunciation of pole discrepancy trip alarm.

m) Auxiliary contacts as required for various control circuits.

Rating

Type 400-SFM-40A

Lightning Impulse withstand voltage 1425 kVP

Rated Short Circuit breaking current 40 KA

Rated Operating pressure 15.5 Kg/cm2-g

First pole to clear factor 1.3

Rated line charging current 600 A

Gas Weight 21 Kg

Rated Voltage 420 KV

Rated Current 2000 A

Rated frequency 50 Hz

Operating Voltage 220 V DC

Total weight 9600 Kg

17

8. Isolator:-

The male and female contact arms on the polycone insulators / insulator

stacks in case of single break Isolator. In case of double break Isolator, 6 nos. fixed

contacts and 3 nos. moving contacts are fitted on the polycone insulators / insulator

stacks.

The following typical connections, as applicable, are made at the isolator and earth

switch end.

a) DC positive & DC negative for local operation.

b) Interlocking supply.

c) DC positive for remote closing.

d) DC positive for remote opening.

e) Remote closing signal.

f) Remote opening signal.

g) OPEN / CLOSE indications (Lamp / Semaphore).

h) Contact for annunciation of pole discrepancy trip alarm.

i) Auxiliary contacts as required for various control circuits.

Operation of Isolator and earth switch for following:

i) Smooth operation.

ii) Complete insertion and making of contacts in close position.

iii) Complete opening of contacts in open position.

iv) Functioning of mechanical interlock between main Isolator and earth switch.

v) Setting of end stoppers in close and open conditions.

vi) Operation of auxiliary switches.

18

9. Transformer:-

The 7 numbers of 167 MVA single phase AUTO- TRANSFORMERS. (When the

HV \ LV transformation ratio is less than two we go for an auto-transformer) Six of them

are interconnected to form two numbers of three phase 500 MVA star-star-delta

transformers – that is the reason of being called ICT-1 and ICT-2 (Interconnected

transformer N0.1 etc.). The seventh one located in between ICT-1 and ICT-2 is so wired

as to serve as an alternate transformer for any one of the 6 single phase transformers and

is used as such for maintenance purposes. Transfer-buses are constructed both on 400

and 220 KV sides for facilitating the alternate transformer insertion and is actually put

into action by operating appropriate isolators.( without physical shifting of the

transformers)

The delta (connection established externally) winding is left out for the intended

purpose of stability of the ICT’s only and remains un

TERTIARY windings of EHV

The station auxiliary distribu

(each used alternatively) transformers fed from an exclusive 11 KV feeder from the

nearby regular Nelamangala sub

alternate supply.

Rating Details

S

N Parameters

a) Type

b) i) Rating

ii) Rated Capacity (MVA)

c) Rated voltage (kV)

d) Highest system voltage (kV)

e) System frequency (Hz)

f) Type of cooling

g) Vector Group

i) System of grounding

j) Insulation Level of winding:

19

delta (connection established externally) winding is left out for the intended

purpose of stability of the ICT’s only and remains un

TERTIARY windings of EHV \ UHV transformers” by the author.

The station auxiliary distribution transformers consist of two numbers of 350 KVA


nearby regular Nelamangala sub-station. A diesel generator is also used to provide

Parameters 500 MVA, 400/220/33 kV

Type 3 phase Auto transformer with loaded

i) Rating

ii) Rated Capacity (MVA)

LV

Rated voltage (kV)

Highest system voltage (kV)

System frequency (Hz)

Type of cooling ONAN / ONAF / ODAF

Vector Group

System of grounding

Insulation Level of winding:


purpose of stability of the ICT’s only and remains un-tapped. Please read “Trends in

UHV transformers” by the author.

tion transformers consist of two numbers of 350 KVA


station. A diesel generator is also used to provide

500 MVA, 400/220/33 kV

3 phase Auto transformer with loaded

tertiary winding

HV - 500 MVA

MV - 500 MVA

LV - 167 MVA (LOADED)

ONAN - 60% of ODAF

ONAF - 80% of ODAF

ODAF - 100%

400/220/ 33

420/245/36.3

50

ONAN / ONAF / ODAF

4x33.3% Unit cooler

YNaOd11

Solidly grounded


tapped. Please read “Trends in

tion transformers consist of two numbers of 350 KVA


station. A diesel generator is also used to provide

20

i)

400 kV:

a) 1.2/50µs full wave impulse

voltage withstand level

1300 kVp

b) 1.2/50µs chopped wave

impulse voltage withstand

level

1300 kVp

c) Switching impulse withstand

voltage 1050 kVp

220 kV:



1050 kVp



level

1050 kVp

33 kV:



250 kVp



level

250 kVp

ii)

Power frequency withstand

voltage (kV)

400 kV (line-neutral)/(line-line)

220 kV

33 kV

HV neutral

570 kV rms

<460 kV rms

95 kV rms

38 kV rms

k) Impedances ( % )

HV & MV - 12.5% (Tolerance - ±10%)

HV & LV - 45% (Tolerance - ±15%)

MV & LV - 30% (Tolerance - ±15%)

l) Tapping range

Auto transformer with On Load Tap Changer for high

voltage variation of

-10 to +10 % in 16 equal steps, of

1.25% each, provided on common

end of series winding.

m) Type of tap changers ON LOAD TAP CHANGER (Resistance

Transition type).

n) Connection HV & MV: Star Auto with neutral

LV; Directly earthed delta.

o) Tap control

Full capacity - on load tap changer suitable

for group / independent, remote /local

electrical and local manual operation and

bi-directional power flow.

p) Short circuit level for the

system

Voltage,kV S C MVA S C current, kA

400 10000 40 for 3 sec

220 10000 40 for 3 sec

132 5000 40 for 3 sec

66 & below 3000 25 for 3 sec

q) Creepage distance for bushing

(mm)

Voltage,kV Total Creepage mm/kV

HV 400 10500 31

MV 220 6125 25

LV 52 1300 25

N 36 900 25

r) Service Outdoor

s) Duty Continuous

t) Overload capacity As per IS:6600 / IEC354 / IEC 60076-7

u) Partial Discharge level 100 pico-columb, Max.

21

v) HV/MV winding neutral end 36 kV porcelain without arcing horns

w)

Bushings:

Winding

Rated kV

HV

420

MV

245

LV

52

NEUTRAL

36

Mounting

P F Volt Full Chopped Switching

Rated STC,3s

DRY/WET mpulse Impulse Impulse

Amp kA

630/630 1550 1550 1050

1250 40

460/460 1050 1050 ---

2000 40

95/95 250 250 ---

3150 25

75/75 170 170 ---

2000 25

---- TANK mounted ----

The fire extinguishing is Nitrogen perching. (Earlier it used to be water quenching

called water-emulsification system) Now a day the nitrogen perching fire protection

system has been made compulsory for all 100 MVA and above capacities transformers.

(In Karnataka at least for sure) The process consists of compressed nitrogen gas held in

high-pressure tanks and connected by piping arrangements to the main transformer tank

near the top plate. The action is initiated following the actions of FOUR relays

(Buchholtz, OTI , WTI and PRV trips) acting either together or one after the other. At

this juncture arrangement is made for prevention of oil flow from the conservator)

When the transformer catches fire the high-pressure nitrogen is released into the

tank and the fires are quenched as it is cut off from oxygen supply (the oil drain valve at

the bottom of the transformer tank should be opened out at this stage before it is too hot

and un-approachable by humans. In a later improvement even this action is automated.),

In order to prevent accidental actuation of this fire quenching activity during routine

works, the controls for this action is held in a metallic enclosure with a transparent glass

cover normally and suitably labeled. One will have to break open the glass and operate

the controls when the fire extinguisher is available for manual operation. Etc The entire

fire extinguisher (piping, control box etc) is red-painted.

22

10. Reactor:-

The 11 numbers of 400 KV lines 5 of the incoming ones are provided with 50

MVA star-connected switchable shunt reactors. In the cases of some unduly lengthy lines

(in excess of 150 KM’s) shooting up of voltages due to their capacitance reactance are

found to be very harming. So the capacitance reactance harming effect is offset by

purposely introducing an inductive reactance load in the form of shunt or parallel reactors

to these lines. {The criteria here is one 50 MVA reactor for all lines exceeding 150 KM’s

in length. } As regards the neutrals (Please note that the word ‘neutral’ to an electrical

engineer is meant to indicate the junction point of a star circuit) some of the reactors are

earthed directly while some are earthed through NGR’s (Neutral Grounding Reactors—

Single phase reactors) The reactors were switched on (or switched out) and included as

an inductive load whenever a length line like GOOTY BANGALORE line is closed into

or taken out of the station bus. That is why they are called switchable reactors. Once the

purpose is over the reactors are switched off. This procedure was before synchronization

of all 400 KV lines. Now they are used as loads to control the bus voltage and included

whenever voltage increase much beyond 400 KV.

Rating

Rated MVAR 50

Rated Voltage 420KV

Rated Current 68.7A

BIL Line 1300KVp

Neutral 550KVp

Phases 3

Connection Star

Type of Construction Gaped type

Cooling ONAN

Total Mass 108700Kg

23

11. 220V Battery Charger Room:-

The station is having 220, 48 volts (lead-acid batteries) station battery

sets energizing DC bus bars of 220, and 48 volt bus bars respectively. As required by

rules all the batteries are housed in separate rooms in the ground floor. All the DC

operating equipments (all relays) of 220 KV systems are energized by 220 volts DC. The

48 volts DC energies the communication lines emanating from the station. The DC

rectifiers (working on boost, float & trickle modes) that converts AC into DC and charge

all the batteries. They draw AC power from an AC bus bar energized by the station

auxiliary distribution transformers. There are two exclusive 11 KV lines strung from a

nearby 66 \ 11 KV Nelamangala Sub-station to provide power supply to the distribution

transformers. From these AC \ DC busses control cables are run to provide required AC \

DC power supply to various AC \ DC equipments spread out in the station yard The

batteries consisting of (as per standard practice in almost all the stations of Karnataka)

two-volt cells of various ampere-hour capacities are connected in series to form the

required voltage ratings. From the past mistakes it has been found that the control room

staff should always be looking at a clearly visible signs of DC presence or absence. For

the purpose a two lamp (each lamp is connected between positive or negative and earth)

method of DC indication is provided and exhibited conspicuously. There are two sets of

220 and 48 volts batteries here. Since there are several cells, they are checked by what is

called PILOT CELLS basis. All the cells are numbered and number plates are fixed to

each of them. One day the pilot cells are (for example) cell no.1, 14, 16, 25, 36 etc.

Specific gravity of acid and voltage of each of these cells are checked and maintenance

works if necessary are done. The next day another set of pilot cells (cell no’s 2,

15,17,26,37 etc) are taken up. Thus in a specific period of say one month all the available

cells are subjected to checking and maintenance.

The DC rectifiers convert AC into DC and charge all the batteries. The silicon

based rectifiers work on boost, float & trickle charge modes. This is decided on the

current requirement of the cells at various stages of charging For example for the 220

volts charger, the three modes of charge are boost at 52 amperes, float at 50 amperes and

trickle charging is at 630 mili amperes. They draw AC power from an AC bus bar

energized by the station auxiliary distribution transformer. From these AC \ DC busses

control cables are run to provide required AC \ DC power supply to various AC \ DC

equipments spread out in the station yard The batteries consisting of (as per standard

practice in almost all the stations of Karnataka) two-volt cells of various ampere-hour

capacities are connected in series to form the required voltage ratings of 220, 48 volts

DC.

24

12. Control Room:-

All the equipments-operation can be locally controlled as well as remote controlled

from a control room and SCADA (Supervisory Control and Data Acquisition) operable.

An RTU (Remote terminal unit) is also established to convey all the relevant data to the

State load dispatch centre and can also be ON LINE controlled from there.

No

Of Operation of Check Points

1

Trip protections such as

Buchholz, OSR, etc.

provided on transformers

Operation of

relevant

auxiliary

relays

Alarm

annunciation

Operation

of Master

Trip Relay

Tripping of

HV & LV

CB’s

2

Alarm protections such as

high oil & winding

temperature, low oil level,

etc. provided on transformers

Operation of

relevant

auxiliary

relays

Alarm

annunciation

3


differential, over current,

earth fault, etc. provided in

C&R Panels for transformers

Alarm

annunciation

Operation

of Master

Trip Relay

Tripping of

HV & LV

CB’s

4


distance, over current, earth

fault, etc. provided in C&R

Panels for feeders & other

circuits

Alarm

annunciation

Operation

of Master

Trip Relay

Tripping of

relevant

CB

5 Alarms provided in circuit

breakers

Operation of

relevant

auxiliary

relays

Alarm

annunciation

6 Lockouts provided in circuit

breakers

Operation of

relevant

auxiliary

relays

Alarm

annunciation

Trip circuit

faulty

indication

CB

operation

blocked

25

13. Earthing:- Earth matt normally made out of about 70mm x 6mm GI flat is constructed at

about a metre below the ground level to which all the metallic items which do not carry \

convey electricity are connected (equipment grounding).This earth matt design (normally

consisting of welded GI flats of rectangular blocks) depend upon levels of fault currents

that come into play at time of faults. The size of GI flat, rectangles size and total area of

the earth matt is now-a-days decided by a software design in KPTCL. The design also

gives out the number of CAST IRON pipe groundings to be provided and connected to

the earth matt. Apart from the earth matt groundings certain equipments are also provided

individual groundings.

Over the entire substation stone gravel of different sizes is spread mainly to reduce

the dangerous effects of STEP-POTENTIAL and TOUCH-POTENTIAL, on humans

(operating personnel) who may be present in the station yard. These potentials, occur

during creation of EPR (Earth potential rise) zones that are created during phase to

ground faults of any feeder.

Sr.

No. Purpose

Description & Size

of Material for 400

kV Sub

Stations

1

Main Earthing Conductor

for

Earth Mat.

40 mm dia.

M.S. Rod

2

Earthing Conductor for

Risers (for equipments &

structures).

100 × 12 mm

M.S. Flat /

75 × 12 mm

G.I. Flat

3

Earthing of LT panels,

DC panel, C& R Panels,

marshalling boxes,

Compressors, MOM

boxes,

junction boxes, lighting

panels, etc.

50 × 6 mm

M.S Flat

4 Earth Electrodes

40 mm dia.

M.S. Rod,

3250 mm

long

5 Earthing conductor along

racks of cable trenches

50 × 12 mm

M.S. Flat

The neutrals of all voltage levels of transformers / reactors had earthed through

Independent earthing. All these earthing points had interconnected with the sub

Station earth mat. Each earthing lead from the neutral of the power transformer / reactor

Should be directly connected to two earth electrodes separately which, in turn, should

26

Connected to the earth mesh. The transformer / reactor tanks as well as associated

Accessories like separate cooler banks shall also be connected to the earth mat at two

points. Capacitor Voltage Transformers & Lightning Arresters shall be earthed through

two independent risers directly connected to earth electrodes which should in turn be

connected to the substation earth mat. The distance between the electrodes should not be

less than 4 meters. All other equipments such as Circuit Breakers, CTs, Isolators, Post

Insulators, etc. had earthed at two points.

27

14. Bibliography:-

1. EHV substation construction manual

2. O & M Manual of substation.

3. IS 3043: Indian Standard Code of Practice for Earthing.

4. Erection & Installation Manual for Transformers: M/s BHEL.

400 kv nelmangala

Engineering

nearby regular nelamangala

connection established externally

tion transformers consist

highest system voltage

remote closing signal

dc positive

typical connections

remote closing