This document provides specifications for various electrical equipment used in traction substations for electric rail systems. It includes ratings for isolators, current and potential transformers, circuit breakers, power transformers, lightning arrestors, and other equipment. It also provides guidelines for busbar layout and clearances, earthing arrangements, transformer characteristics, and voltage and temperature protections. The key equipment and their ratings at a sample 132kV traction substation with a 30/42MVA power transformer are also listed.

1. HV DOUBLE POLE ISOLATOR
TYPE: Manually operated single or Double break
upright mounting with the movement of blade(s)
in a horizontal plane with or without earthing
switch and suitable for outdoor installation
No. of pole Two/Three
Nominal system voltage 132kV 220kV
Highest system voltage 145kV 245kV
Rated current 1250A 1250A
Rated short time withstand
current for one second
31.5kA
(rms)
31.5kA (rms)
Isolating distance in air 1800mm 2800mm
HV CURRENT TRANSFORMER
TYPE: Single phase, Oil filled, Self cooled,
Outdoor Type
Rated system voltage 132kV 220kV
Frequency 50Hz. ±3%
Rated primary current 400-200 200-100
Rated secondary current 5A 5A
Rated burden 30VA 30VA
Class of isolation A A
HV CIRCUIT BREAKER (CB)
Rated system voltage 132kV 220kV
Rated normal current 1600A 2000A
Rated short circuit
breaking current
40kA 50kA
Rated breaking capacity 5800MVA 12250
MVA
Frequency 50Hz
TRACTION POWER TRANSFORMER
TYPE: ONAN cooled, single phase, step down Power
transformer, Double limb wound, Core Type
Outdoor installation
Winding Uniformly insulated
concentratric
Frequency 50Hz
Rated primary voltage 132kV OR 220kV
Rated secondary voltage 27kV
Rated power 21.6/30 MVA
30/42 MVA
25kV LIGHTING ARRESTER
System Single phase ac traction
Nominal system
voltage
25kV (phase to earth) possible
variation in the traction supply 22.5 to
27.5 kV sometimes touching 30kV
Rated frequency 50Hz
Type Non-linear metal oxide resistor type
without gap
Line discharge class CLASS 3
Continous operating
voltage capability
35kV (rms)
25kV POTENTIAL TRANSFORMER (PT)
Type I II
PTR 27.5Kv/100V 27.5kV/110V
Burden 30VA 100VA
1 2
25kV CURRENT TRANSFORMER (CT)
TYPE OCT – 47 AD/01
CTR 1500/750/5A
Burden 60VA
Insulation Level 35/250kV

2. DYNAMIC REACTIVE POWER COMPENSATION
EQUIPMENT ( DRPC)
System Single phase ac Traction System
Nominal system
voltages
25kV (phase to earth)
Rated frequency 50Hz
25KV AC SINGLE POLE ISOLATOR (SPI) AND DOUBLE
POLE ISOLATOR (DPI)
Type Manually operated, horizontally mounted on
pole, vertical break type and suitable for outdoor
Number of
phases
One
No’s of pole Single pole/double pole
Isolating
distance
500mm (min.) in air
Rated voltage 25kV (nominal) 30kV max.
Rated current Type –I 1250A (used at SSP & SP)
Type –II 1600A (used at FP & TSS)
AUXILARY TRANSFORMER (AT)
Type Double wound, single phase, ONAN
cooled, step down transformer for
outdoor installation.
Rated voltage of
primary winding
a) Nominal voltage 25kV
b) Minimum voltage 19kV
c) Maximum voltage 27.5kV
Rated voltage of
secondary winding
240V
Rated frequency 50Hz ±3%
Rated Power at rated
nominal voltage
5kVA, 10kVA, 25kVA and 100kVA
25kV INTERRUPTER
System Single phase ac traction system
Nominal system
voltage
25kV variation from 19kV to 27.5kV
– occasionally touching 30kV
Rated frequency 50Hz ±3%
No. of poles One
Class Outdoor
Rated voltage class 52kV
Rated normal current 800A
Rated short circuit
making current
20kA (peak)
25KV CIRCUIT BREAKER (CB)
System Single phase ac traction system
Rated system voltage 25kV
Rated normal current 1600A
Rated short circuit
breaking current
20kA
Rated breaking
capacity
550MVA
Rated Frequency 50 Hz
3 4
Voltage Regulation
The permissible variation of the bus bar voltage on the busbars at
the grid sub-station is +10% and -5% i.e., between 27,500 V. and 23,750
V. The tappings on the transformers are on the secondary winding and are
set to ensure that the voltage is maintained as high as possible but not
exceeding 27.5 kV at the feeding post at any time.

3. Rating Of Equipments At Traction Sub-Staion
with 30/42MVA Power Transformer
Sr. Name of Equipment Rating
1. 132kV Double pole Isolator 1250A
2. 132kV Current Transformer 400-200/5A
3. 132kV Circuit Breaker 1600A
4. 132kV Potential Transformer 132kV/110V
5. 132kV Lightning Arrester 120kV
6. 132kV Bushing CT 600/5A
7. Traction Transformer 132kV/25kV,
30/42MVA
8. 25kV Bushing CT 3000/5A
9. 25kV Lightning Arrester 42kV
10 25kV Current Transformer 1500-750/5A
11. 25kV Circuit Breaker 2000A
12. 25kV Single pole Isolator 3150A
13. 25kV Potential Transformer type-II 27.5kV/110V
14. Series Reactor 875 kVAR
15. Shunt Capacitor 7700kVAR
16. NCT 4/2/1A
17. 25kV Potential Transformer type-I 27.5kV/100V
18. 25kV Bi polar Isolator 1600A
19. 25kV Interruptor 2000A
Feeding and Sectioning Arrangements
 The generation and transmission systems are 3-phase systems. The single-
phase traction load causes unbalance in the supply system. This unbalance
has undesirable effects on the generators and equipment of other consumers,
if its value becomes excessive.
Voltage Unbalance (%)
Instantaneous 5
2 hours 3
Continuous 2
 To keep the unbalance on the 3-phase grid system within the above limits,
power for ac single-phase traction is tapped off the grid system across the
different phases at adjacent sub-stations in cyclic order.
TSS Bus-bar layout
 The bay widths are standardized for each primary voltage i.e. 66 kV, 110kV,
132 kV and 220 kV.
 The most generally used system voltage is 132 kV and bay widths for 132 kV
are standardized as 14.0 m for HV bay and 6.0 m for 25 kV bay.
 The stung bus on the HV side stung at a height of 9.35 m from ground level
comprises of 54/3.18 mm (28.62 mm dia) ACSR conductor (Zebra) with a
gross area of aluminium of 428 mm2.
 On the 25 kV side 50 mm outside dia. aluminium tubular bus bar is provided
at a height of 3.8 m.
 Tension of stung bus is specified as 450 kgf and the earth screen wires as 200
kgf at 4°C without wind.
 The maximum span from the last tower to sub-station gantry is generally
limited to around 75 m.
 If the distance of the incoming HV transmission line from the grid sub-station
is more than 4 km, lightning arrestors are provided on the incoming lines, at
the traction sub-station.
5 6
 The deflections of bus-bars supported on post insulators should not exceed
half the diameter of the bus bars or span/1440 whichever is less.
 The current density generally adopted for outdoor copper bus-bars is 2
A/mm2.
 The insulators, bus bars and connections should not be stressed to more than
1/4 of the breaking load or 1/3 of their elastic limit whichever is lower.
 The permissible voltage unbalance at the point of common coupling on the grid
supply system should not exceed the following limits:—

4. The minimum clearances in air for
live equipment shall be as under:
Clearance in mm
25 kV 66
kV
110
kV
132
kV
220
kV
1 Between phases NA
[ since
single
phase]
2000 3000 3000 4000
2 Between one phase and earth for
rigid connection
500 630 900 1300 2100
3 Between any point where man
may be required to stand to the
nearest
a) unsecured conductor in air
b) secured conductors in air
3000
2000
3500
3500
3500
3500
4000
4000
5000
5000
4 Minimum height of bus bar 3800 4600 4600 4600 5500
Characteristics Of Traction Transformers
 To cater for the peaks in the demands, the transformers are capable of
withstanding non-recurring over-loads of 50% for 15 minutes and 100% for 5
minutes after the transformer has reached steady temperature on continuous
operation at full load.
 Off load tap changing from + 10% to –15% in steps of 5% is provided on the
low voltage side. The maximum efficiency is specified at about 50% of full
load.
 The temperature rise over an ambient of 50oC for 100% over load for 5
minutes or 50% over load for 15 minutes after continuous full load operation
is specified not to exceed 50oC for winding (resistance measurement) and
40oC for oil by thermometer.
 The transformers of ratings of 21.6 MVA are specified as ONAN cooled and
so designed that with ONAF cooling at a later date the capacity is capable of
being increased by 40% more by provision of forced cooling (ONAF).
Winding And Oil Temperature Protection
 The life of the transformer depends upon the state of its insulation, whose rate
of deterioration is accelerated at excessively high temperatures. Therefore, the
transformers have been provided with winding and oil temperature alarm and
tripping device which operate through mercury contacts. The settings adopted
for the above are :
Winding
temperature
alarm
Winding
temperature
tripping
Oil
temperature
alarm
Oil
Temperature
tripping
100°C 105°C 85°C 90°C
Earth Resistance
 At each power supply installation, an earthing system shall be provided. The
combined resistance of the earthing system shall be not more than the
following values:-
S.N. Name of the station The limit of combined earth
resistance in Ohm
1. Traction substation 0.5
2. Switching station 2.0
3. Booster transformer station 10.0
4. Auxiliary transformer station 10.0
7 8
Earth Electrodes
 The earth electrode shall normally be of mild steel galvanised perforated pipe
of not less than 40 mm nominal bore, of about 4 m length provided with a
spike at one end and welded lug suitable for taking directly MS flat of required
size at the other end.
 The pipe shall be embedded as far as possible vertically into the ground, except
when hard rock is encountered, where it may be buried inclined to the vertical,
the inclination being limited to 30° from the vertical.
 Earth electrodes shall be embedded as far apart as possible from each other.
Mutual separation between them shall usually be not less than 6.0 m (which is
twice the length of the electrode).

5.  If the value of earth resistance can not be achieved with a reasonable number
of electrodes connected in parallel, the earth surrounding the electrodes shall
be chemically treated. The earth electrode shall be surrounded in an earth-pit
by alternate layers of finely divided coke, crushed coal or charcoal and salt at
least 150 mm all round.
 In high embankments, it may be difficult to achieve earth resistance even after
chemical treatment of electrodes. In those locations, use of electrodes longer
than 4 m so as to reach the parent soil is recommended.
Earthing Arrangement at Traction Substation
Earthing Grid.
 An earthing grid is formed by means of bare mild steel rod of appropriate size
buried at a depth of about 600-mm below the ground level and connected to
earth electrodes. The connection between the earth electrode and the grid shall
be by means of two separate and distinct connections made with 75 mm x 8
mm MS flat.
 The size of the earthing grid conductor shall be decided based on the incoming
system voltage and fault level. The fault level considered shall take into
account the anticipated increase in fault current during the life span of the
station. The size shall be as given below:
Sr. System
Voltage (kV)
Fault Level (MVA) Diameter of the grid
conductor (MS rod) in mm
1 66 Upto 4000
Above 4000 upto 5000
Above 5000 upto 6000
32
36
40
2 110 Upto 6000
Above 6000 upto 8000
Above 8000 upto 10000
32
36
40
3 132 Upto 7000
Above 7000 upto 10000
32
36
4 220 Upto 12000
Above 12000 upto 16000
Above 16000 upto 20000
32
36
40
System Earthing.
 One terminal of the secondary winding (25 kV winding) of each traction
power transformer shall be earthed directly by connecting it to the earthing
grid by means of one 75 mm x 8 mm MS flat, and to the buried rail by means
of another 75 mm x 8 mm MS flat.
 One designated terminal of the secondary of each potential, current and
auxiliary transformer shall be connected to the earthing grid by means of two
separate and distinct earth connections made with 50 mm x 6mm MS flat.
9
10
Equipment Earthing.
 The metallic frame work of all outdoor equipments such as transformers,
circuit breakers, Interrupters and Isolators, as well as steel structures shall be
connected to the earthing grid by means of two separate and distinct
connections made with MS flat of size as indicated below; one connection
shall be made with the nearest longitudinal conductor, while the other shall be
made to the nearest transverse conductor of the grid:
Buried Rail
 A steel rail of section 52 kg/m (the one used for the railway track) and
length about 13 m shall be buried near the track at the traction substation at
a depth of about one metre to form part of the earthing system.
 Two separate and distinct connections shall be made by means of 75 mm x
8 mm MS flat between the earthing grid and the buried rail. The buried rail
shall also be connected by means of two separate and distinct connections
made of 75 mm x 8 mm MS flat to the rail(s) in a single-rail track circuited
section and to the neutral point(s) of the impedance bond(s) in a double-rail
track circulated section.

6. Sr. Equipment System voltage
and fault level
Ground
conductor size
1. Equipmentson the
primary side of traction
power transformer.
66 kV, upto 3000 MVA
110 kV, upto 5000 MVA
132 kV, upto 6000 MVA
220 kV, upto 10000 MVA
50 mm x 6 mm
66 kV, above 3000 upto 6000 MVA
110 kV, above 5000 upto 10000 MVA
132 kV, above 6000 upto 12000 MVA
220 kV, above10000 upto 20000 MVA.
75 mm x 8 mm
2. Equipmentson the
secondary side of
traction power
transformer.
50 mm x 6 mm
3. Fencing uprights/steel
structures
50 mm x 6 mm
4. Doors/ fencing panels 6 SWG G.l.
Wire
This earth electrode shall be connected to the ground terminal of the LA as well
as to the main earthing grid by means of two separate and distinct connections
made with 50 mm x 6 mm MS flat for the 25 kV side LA, and with 75 mm x 8
mm MS flat for the primary side LA. For LA provided for the traction power
transformers, there shall also be a connection as direct as possible from the
ground terminal of the LA to the frame of the transformer being protected; this
connection shall also be made by means of two separate and distinct connections
made with 50 mm x 6 mm MS flat for 25 kV side, and with 75 mm x 8mm MS
flat for primary side LA.
Earth Screen.
● The area covered by outdoor substation equipments shall be shielded against
direct strokes of lightning by an overhead earth screen comprising 19/2.5 mm
galvanised steel stranded wire strung across the pinnacles of the metallic
structures. The earth screen wires shall be strung at a height as indicated in the
approved traction substation layouts (not less than 2.5 m above the live
conductors) and shall be solidly connected to the traction substation earthing grid
at each termination by means of 50 mm x 6fmm MS flat.
Earthing Of Fencing Uprights And Panels.
● Each metallic fencing upright shall be connected to the traction substation main
earthing grid by means of two separate and distinct connections made with 50 mm
x 6 mm MS flat. In addition, all the metallic fencing panels shall be connected to
the uprights by means of two separate and distinct connections made with 6 SWG
G.I. wire. All the metallic door panels shall also be connected to the supporting
uprights by means of two separate and distinct connections made with 6 SWG GI
wire.
Earthing At The Point Of 240 V Ac 50 Hz Supply For Oil Filtration Plant.
● The 240 V ac 50 Hz distribution board for power supply to oil filtration plant
shall be connected to the main earthing grid by means of two separate and distinct
connections made with 50 mm x 6 mm MS flat.
Earthing Inside Control Room.
● An earthing ring shall be provided inside the control room by means of 50 mm x
6 mm MS flat which shall be run along the wall at a height of about 300 mm from
the floor level. The earthing ring shall be connected to the main earthing grid by
means of two separate and distinct connections made with 50 mm x 6 mm MS
flat. The earthing ring shall also be connected to an independent earth electrode
by means of two separate and distinct connections made with 50 mm x 6 mm MS
flat.The metallic framework of control and relay panels, LT A.C. and D.C.
distribution boards, battery chargers, remote control equipment cabinets and such
other equipments shall be connected to the earthing ring by means of two separate
and distinct connections made with 8 SWG galvanised steel wire.
The connections shall be taken along the wall and in recesses in the floor. All
recesses shall be covered with cement plaster after finishing the work.
Connections between the MS flats shall be made by welding.
Earthing of lightning arrester (LA).
● In addition to the earth electrodes provided for the main earthing grid, an
independent earth electrode shall be provided for each LA.
Earthing Arrangement at Switching Station
● A minimum number of three earth electrodes (excluding the one to be provided
separately for the remote control cubicle earthing) shall be provided at each
switching station, and they shall be interconnected by means of 50 mm x 6 mm
MS flat forming a closed loop main earthing ring.
11 12

7. ● This ring shall be connected by two separate and distinct connections made with
50 mm x 6 mm MS flat, to the traction rail in a single-rail track circuited section
and to the neutral point of the impedance bond in a double-rail track circuited
section of the nearest track, so as to limit the potential gradient developing in the
vicinity of the switching station in the event of a fault.
System Earthing.
● One designated terminal of the secondary of each potential, current and auxiliary
transformer shall be connected to the main earthing ring by means of two separate
and distinct connections made with 50 mm x 6mm MS flat.
Equipment Earthing.
● All masts, structures, fencing uprights, and all outdoor equipment pedestals
including auxiliary transformer tank shall be connected to the earthing ring by
means of two separate and distinct connections made with 50 mm x 6 mm MS
flat. All fencing panels shall be connected to the supporting uprights by means of
two separate and distinct connections made with 6 SWG GI wire. All the metallic
door panels shall be connected to the supporting uprights by means of two
separate and distinct connections made with 6 SWG GI wire.
● The metal casing of CT’s & PT’s shall be connected to the mast/structures by
means of two separate and distinct connections made with 50 mm x 6 mm MS
flat.
● The ground terminal of lightning arrester shall be connected directly to the earth
electrode by means of two separate and distinct connections made with 50 mm x
6 mm MS flat. The earth electrode shall be so placed that the earthing leads from
the lightning arrester may be brought to the earth electrode by as short and
straight path as possible.
The metal casing of LT A.C. and D.C. distribution board, battery chargers,
terminal board, remote control equipment cabinets and other such equipments
shall be connected to the earthing ring by means of two separate and distinct
connections made with 8 SWG G.I. wire. The connections shall be taken along
the wall and in recesses in the floor. All recesses shall be covered with cement
plaster after finishing the work. Connections of earth strips to each other shall be
made by welding.
Earthing of Neutral of Local Power Supply System
● At TSS and switching stations where power supply at 415 V/ 240 V, ac, 50 Hz, is
taken from the local supply authority and having neutral earth at some distant
point in the premises 'of the supply authority, the neutral of such supply shall also
be earthed by means of two separate and distinct connections made with 6 SWG
G.I. wire by connecting to an independent earth electrode.
Earthing Arrangement at Auxiliary Transformer Station
● The combined earth resistance at an auxiliary transformer station shall be not
more than 10 ohm.
● Normally one earth electrode is sufficient for an auxiliary transformer station. The
earth electrode shall be connected to the mast on which the auxiliary transformer
is mounted by means of two separate and distinct connections made with 50 mm
x 6 mm MS flat. In addition the mast shall be connected to the nearest traction rail
or to the neutral point of the nearest impedance bond in a double rail track
circuited section by means of a 50 mm x 6 mm MS flat.
● The earthing terminal on the transformer tank shall be connected to the mast on
which the transformer is mounted by means of two separate and distinct
connections made with 50 mm x 6 mm
● MS flat. One terminal of the secondary winding of the auxiliary transformer shall
be connected to the earthing terminal on the transformer tank and as well as to the
mast by means of 50 mm x 6 mm MS flat.
Earthing Inside Remote Control Cubicle.
● An earthing ring shall be provided inside the remote control cubicle by means of
50 mm x 6 mm MS flat; the earthing ring shall be run along the wall on teak
wood blocks fixed to the wall at a height of 300 mm from the floor level. The
earthing ring shall be connected to the main earthing ring as well as to an
independent earth electrode by means of two separate and distinct connections
madel with 50 mm x 6 mm MS flat.
Crushed Rock Surface Layer
● At the TSS and switching stations, a surface layer of crushed rock shall be
provided to a thickness of about 100 mm. If considered necessary from the point
of view of containing the step and touch voltages within the acceptable limits,
higher thicknesses may be provided depending on calculation based on site
conditions.
13 14

8. It is clarified that this pamphlet does not supersede any existing provisions laid down by
RDSO, Railway Board or Zonal Railways. The pamphlet is for guidance only and it is not a
statutory document.
If you have any suggestion or comment, please write to:
Director (Electrical), CAMTECH, Maharajpur, Gwalior (M.P.) – 474 005
Ph.0751-2470740,Fax 0751-2470841
E-mail: direlcamtech@gmail.com
Disclaimer:
(For Official Use Only)
Hkkjr ljdkj GOVERNMENT OF INDIA
jsy ea=ky; MINISTRY OF RAILWAYS
CAMTECH/E/2018-19/PSI Parameter/1.0
June, 2018
egkjktiqj, Xokfy;j & 474 005
Maharajpur, GWALIOR - 474 005
सत्यमेव जयते
End User : TrD – PSI Staff
OHM IMPEDANES
The following values of OHE impedances may be used for the purpose of calculating
relay settings:
i. Single track OHE without return conductor : 0.4 l ∠70° Ohm/km
ii. Double track OHE without RC : 0.24 ∠70° Ohm/km
iii. Single track OHE with RC : 0.70 ∠70° Ohm/km
iv. Double track OHE with RC : 0.43 ∠70° Ohm/km
Lead Acid Batteries
On electrified sections batteries and battery chargers are installed at the following
locations:-
1. Traction Sub-stations -
110V, 200Ah.lead acid cells for control, protection and indication circuits.
2. Switching Stations -
110V, 40Ah lead acid batteries for operation of circuit breakers and interruptors
and motor operated isolators.
Specific Gravity
 The specific gravity of the electrolyte should be maintained at about 1.210 at 27° C
and when it drops to 1.150 the cell may be considered discharged. These values vary
with the type of battery, temperature, age and working conditions.
Cell Voltage
 The voltage of new cells at the end of a full charge will be about 2.5 to 2.75 V when
it is receiving charge at the 10 hour rate. This gradually decreases as the age of the
battery increases until it comes down to 2.4 V with normal temperature and charging
rate. No cell should ever be discharged below the point where the cell voltage
reaches 1.85 V as measured when the cell is discharging at the normal 10 hour rate.