220 KV Substation Details By.. Er. Mayur D Rane Engineer Kalpataru Power Transmission Limited

1. 220 KV NRS Substation Report
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National Power Training Institute
Power System Training Institute
220 /66 KV New Receiving Station (NRS) Report
Submitted By: -
Mr. Mayur Dhanaji Rane (1540)
Guided By:-
Mr. K. Vetrivel Mr. M. N. Murthy
Assistant Director, Director, PSTI,
PSTI, Bangalore Bangalore

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Index
Sr. No Contents Page No.
1 Introduction 3
2 Single line Diagram 4
3 Power flow chart of 220/66 KV Substation 5
4 Capacitive Voltage Transformer 7
5 Circuit Breaker 8
6 Current Transformer 9
7 Transformer 10
8 Capacitor Bank 12
9 220V Battery Charger Room 13
10 Control Room 14
11 Earthing 15
12 Bibliography 17

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1. Introduction:-
N.R.S, an abbreviation for New Receiving Station, is one of the oldest
substations of KPTCL (Karnataka Power Transmission Corporation) functioning
from 1951.
220 KV two lines are coming from somanahally and peenya Presently NRS
is one of the biggest station (But very compact) in Bangalore handling about 3
million units per day, with a Peak load of the station at about 176 MW’s. Out of
this about 100 mega watts are handled at 66KV side and the balance 70 megawatts
are handled at 11KV side. As regards equipments of this station, one can see
equipments manufactured about 50 years back to latest.
Two 100 MVA transformers are connected to stepped down the 220 KV
Voltage to 66 KV Voltage. Transformer 1 made of NGEF and Transformer 2 is of
ABB, to match the impedance of the transformer they are operated within 2 to 7
numbers of the taps. And 5 numbers of 66KV/ 11KV transformers are connected to
feed local feeder of 11 KV.
Two numbers are single bus arrangement is available in this substation
220 KV and 66 KV bus.

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2. Single Line Diagram of the 220KV/66KV Substation:-

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3. Power Flow Chart of the 220/66 KV New Receiving
Station (NRS)
Incoming 220 KV Supply from Somanahali & Peenya,
66KV From SRS 1&2
↓
220 KV Surge Diverter
↓
220KV CVT
↓
Line Isolator with Earth Blade
↓
245 KV SF6 Circuit Breaker
↓
220 KV Current Transformer of 0-300-600-1200/1A
↓
Bus Isolator
↓
220 KV Bus
↓
Bus Isolator

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↓
245 KV SF6 Circuit Breaker
↓
220 KV/66KV 100 MVA, 2 Transformer of NGEF & ABB
made
↓
66 KV SF6 Breaker
↓
66 KV Current Transformer
↓
66 KV Isolator
↓
10 Nos Of 66 KV Feeders

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4. Capacitive Voltage Transformer:-
Ratings
Make Crompton Greaves
Type CVE: 245/1050/50
Frequency 50 Hz
Number of cores 3
Rated Voltage HV 220KV/√3
LV 110V/ √3
Equivalent Capacitance 8800 pF
Insulation Level 460/1050 KV
HSV 245 KV
Capacity of oil 65 Kg
Total Weight 625 Kg
Then 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 cs power) the first line control is
through double break isolators coupled with grounding switch.

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5. Circuit Breaker:-
Rating
Type 200-SFM-40A
Lightning Impulse withstand voltage 1050 kVP
Rated Short Circuit breaking current 40 KA
Rated Operating pressure 16.5 Kg/cm2
-g
First pole to clear factor 1.3
Rated line charging current 125 A
Gas Weight 21 Kg
Rated Voltage 245 KV
Rated Current 1250 A
Rated frequency 50 Hz
Operating Voltage 220 V DC
Total weight 3900 Kg
It is a single pole breaker here. The breaker consist of, three numbers of
single phase SF6 circuit breakers inter connected to form a three phase item. The
arcing contacts held in a porcelain bushings containing SF6 gas at pressure of
about 6 kgs sq.cm are independent with separate seals. One male contact
movement results in engaging or disengaging with a static female contact. But the
operating mechanisms (watched by a pole disturbance relay) for all three phases is
by means of compressed air at about 15 kgs sq.cm held in high pressure tanks

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interconnected through common piping. An automatic operating air compressor
motor pump replenishes air when there is a fall in air-pressure. The opening of
breaker is pneumatically controlled and closing is by spring mechanism The
breaker is so arranged that when high pressure air opens the male and female
contacts, spring loading (for a later charging purpose) action is also initiated. The
spring load actuated by relays manual results in the breaker getting closed. The
breaker (held in three porcelain bushings) is provided with all safety devices and
indicating mechanism like SF6 gas pressure indicator, air pressure indicator etc .
The breaker trips on its own if there is a DC failure. It gets locked in (LOCK IN :
The breaker fails to obey any commands i.e. neither opens or closes) whenever the
SF6 gas and air pressure falls below the set pressures. The SF6 pressure in 66 KV
breakers is slightly less than 1 kg. sq. cm as they were installed about 50 years
back when SF6 breakers were in developing stages.
6. Current Transformer:-
Rating
Rated Voltage 220 KV
Rated Current 1250 A
Knee Point Voltage 1050 V
Burdon 40 KV
Number of cores 5
Insulation Level 220/400/1050 KV
Frequency 50 Hz
Class Protection PS
Metering 0.5
Ratio Available 300-600-1200/1A

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Live Tank Current transformer are connected in series with the given bay, the
current transformers are used for metering and protection purpose.
Each phase individual current transformer are connected and their secondary is
brought at the marshalling box and star point is created and all the secondary
terminals runs towards the control room and connected to the meters and replay
for metering and protection purpose.
7. Transformer:-
Rating Details
MVA 60/80/100
Rated Voltage HV 220000 V
LV 66000V
Ter. 11000V
Rated Current HV 140-6- 209.8-262.4
LV 524.8-699.8-874.7
Ter. 1049.7-1399.8-1749.3
Make of OLTC EASUN-MR
Short ckt current HV 2.62 KV
LV 8.75 KV
Mass/ Volume of the oil 45506 lit
Total mass 171000 Kg
Type of cooling ONAN/ONAF/OFAF

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The transformers are rated 60MVA, 80 MVA and 100 MVA
depending on the cooling system employed i.e. ONAN, ONAF and OFAF. The
switching of the transformers from ONAN to ONAF and from there on to OFAF is
done by mercury switches mounted over WTI (Winding temperature indicators)
WTI’s are provided on all the three windings (HV, LV &tertiary) of the
transformers in the case of ABB make. In the case of the NGEF make WTI’s are
provided in HV and LV windings only.
The on load tap changer (MR type) of the transformers have 17 taps
which can deliver a constant 220 KV output even if the incoming voltage varies
from over voltage 223.4 kV up to 209 kV. For the purpose of mounting the OLTC
the OLTC operation is either by an electric motor or manual and remote operable
from the control room. The main tank is interconnected to the conservator through
a Buchholtz (Gas operated) relay. The neutral is grounded through a neutral CT for
REFR (Restrict Earth Fault Relay) protection.
Apart from HV and LV winding there is tertiary winding of 11 KV output
called as stabilizer winding, and connected in delta. It mainly to stabilize the
transformer output from 3rd
harmonics since HV and LV windings are in star
connected.
Fire extinguisher :This is a recent measure introduced to protect the EHV
transformers when they catch fire even after power supply is tripped off by
concerned relay, master trip relay etc. This is based on experiences of about four
100 MVA (220 LV class) and one 400 KV class transformer catching fire and
burning up. The aim is to prevent spread of fire to other equipments and preserve
at least the salvage value of the transformer on fire. The measure speaks up the
sorry state of affairs to which our systems are sinking with regard to quality in
construction and maintenance of transformers
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

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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 (In NRS it is locked by
a separate pad lock) 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.
8. Capacitor Bank:-
Rating
Voltage 66 KV
KVAR 20000VAR
Frequency 50 Hz
Connection Double Star
Weight 3000 Kg
Current 174.43A
Insulation level 145KV/325KV
The 66 KV bus is provided with a set of 216 single phase capacitors totaling
to 20 MVAR. Each capacitor is between phase and earth. The earth terminals of
the capacitors are interconnected to form a balanced double star circuit and
grounded through a CT. To prevent shooting up of voltages during low load
conditions of night hours the capacitor bank is switched off at about 9 pm and
switched on the next day at about 6 am.

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9. 220 V DC 200 Ah Battery Charger:-
The station is having 220, 110, 48 volts (lead-acid batteries) station battery
sets energizing DC bus bars of 220, 110 and 48 volt bus bars respectively. 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. As required by rules al
the batteries are housed in separate rooms in the ground floor.
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
All the DC operating equipments of 220 KV systems are energized by 220
volts DC (with one exception- A latest 11 KV breaker is on this 220 DC) and the
rest by 110 volts DC. The 48 volts DC energies the communication lines
emanating from the station. 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, 110
and 48 volts DC.
There are three types of chargers are used in this battery room trickle
charger, float charger, boost charger as per requirement of the charging to the
batteries. When batteries are completely charged then trickle charges is use to pass
small amount of the current, at normal condition float charger is used and when
battery require emergency charging then boost charger is used.

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10. Control Room:-
Battery Room
In the Battery room 2 V lead acid batteries are placed to achieve
220V, 110V, 48V DC Supply. The set of the battery are connect in
series to get 48 V DC supply to run all the relays and control
equipments.
Control and Relay panel of the Transformer
In the panel various types of relays are placed such as,
a) Overload relay
b) Earth Fault relay
c) Restricted Earth Fault relay
d) IDmTl Overcurrent relay
e) Distance Protection
f) Numerical relay
g) Differential protection relay
h) Emergency fire extinguisher relay
And Different types of meters are located at the panel such as,
a) Ammeters
b) Voltmeter
c) Power factor meter

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d) Trivector meter ( KW, KWH, VAR)
Feeder control panel
10 Numbers of 66 kv feeders are connected and are controlled by these
panel.
RTU ( Remote terminal Unit )
RTU transmits the station parameters (V-satellite communication through
a dish antenna erected at the roof top of the control room) to the state load dispatch
centre for SCADA activities.
11. Earthing:-
Two types of Earthing are available here:-
1. Substation Earthing:-
As in the cases of all substations, an earth matt normally made
out of about 70mm x 6mm GI flat is constructed at about a meter 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.

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2. Equipment Earthing:-
In this case the entire substation auxiliary and all equipments are
earthed by the riser’s plates. And transformer is earthed at two places.

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12. Bibliography:-
1. EHV substation construction manual
2. O & M Manual of substation volume 1