This document provides an overview of electrical substations, including their classification, components, and specifications. It discusses the different types of substations based on voltage levels, configuration, and application. It also describes the primary functions and components of outdoor switchyards, including incoming and outgoing lines, transformers, circuit breakers, and earthing systems. Clearance requirements and specifications for indoor electrical panels, busbars, grounding, and cabling are also outlined.

1. SUBSTATION OVERVIEW
-B. Prasad
Chartered Engineer
amieclub@gmail.com

2. TYPE OF SUBSTATION
 Classification based on voltage levels, e.g. : A.C.
Substation : EHV, HV, MV, LV; HVDC Substation.
 Classification based on OutdoororIndoor: Outdoor
substation is under open sky. Indoor substation is
inside a building.
 Classification based on configuration, e.g. :
 Conventional air insulated outdoor substation or
 SF6 Gas Insulated Substation (GIS)
 Composite substations having combination of the
above two

3. Classification based on application
 Step Up Substation : Associated with generating station as
the generating voltage is low.
 Primary Grid Substation : Created at suitable load centre
along Primary transmission lines.
 Secondary Substation : Along Secondary Transmission Line.
 Distribution Substation : Created where the transmission line
voltage is Step Down to supply voltage.
 Bulksupply and industrial substation : Similar to distribution
sub-station but created separately for each consumer.
 Mining Substation precaution for safety needed in the
operation of electric supply.
 Mobile Substation: Temporary requirement

4. PROMARY/SECONDARY/DISTRIBUTION
SUBSTATION
 Primary Substations receive power from EHV
lines at 400KV, 220KV, 132KV and transform the
voltage to 66KV, 33KV or 22KV (22KV is
uncommon) to suit the local requirements in
respect of both load and distance of ultimate
consumers. These are also referred to ‘EHV’
Substations.
 Secondary Substations receive power at 66/33KV
which is stepped down usually to 11KV.
 Distribution Substations receive power at 11KV,
6.6 KV and step down to a volt suitable for LV
distribution purposes, normally at 415 volts

5. SUBSTATION PARTSANDEQUIPMENTS
 OutdoorSwitchyard
 Incoming Lines
 Outgoing Lines
 Bus bar
 Transformers
 Bus post insulator & string insulators
 Substation Equipment such as Circuit-
beakers, Isolators, Earthing Switches, Surge
Arresters, CTs, VTs, Neutral Grounding
equipment.

6. SUBSTATION PARTS
….CONTD…
 Station Earthing system comprising ground mat, risers,
auxiliary mat, earthing strips, earthing spikes & earth
electrodes.
 Overhead earth wire shielding against lightening strokes.
 Galvanised steel structures for towers, gantries, equipment
supports.
 PLCC equipment including line trap, tuning unit, coupling
capacitor, etc.
 Power cables
 Control cables for protection and control
 Roads, Railway track, cable trenches
 Station illumination system

7. SINGLE LINE DIAGRAM

8. Transformer part

9. Batteries forindustrial orsubstation applications
 Vented /
Flooded Lead
Acid batteries
 Sealed
maintenance
free
batteries/Valve
Regulated Lead
Acid
 Nickel Cadmium
(Ni-cd) batteries

10. Battery AH
 LOAD CURRENT 10A for
3 hrs.
 Cell voltage =12V DC
 CALCULATION ,
AH=10X3
 CAPACITY =30/
(0.75X0.8)=50AH
 Discharge factor=0.7
 Ageing factor =0.8
 Drain capacity =C10

11. CHARGER
 Type of charger
 Input voltage
 output voltage
 Application
 Protection
 Metering
 Indication
 Alarms
 Auto operation

12. Clearance around an Indoorelectrical panel
(NES 110.26)
Description of Clearance Distance (min)
Left to Right the minimum clearance 0.9 Meter (3 Ft)
Distance between Panel and wall 1.0 Meter
Distance between Panel and Ceiling 0.9 Meter
Clear Height in front of Panel >480V 2.0 Meter
Clear Height in front of Panel <480V 0.9 Meter (3 Ft)
Clearance When Facing Other Electrical
Panels <480V
0.9 Meter (3 Ft)
The width of the working space in front of
the Panel
The width of Panel or 0.762 Meter which is
Greater.
Headroom of working spaces for panel
boards (Up to 200Amp)
Up to 2 Meter

13. Clearance between Bare Metal Busbarin
Panel (NES 408.5)
Voltage
Opposite
Polarity
Mounted on
Same
Surface
Opposite
Polarity
Where Held
Free in Air
Live Parts to
Ground
Up to 125 V 19.1 mm 12.7 mm 12.7 mm
125 V to 250 V 31.8 mm 19.1 mm 12.7 mm
250 V to 600 V 50.8 mm 25.4 mm 25.4 mm

14. Clearance of Outdoorelectrical panel to
Fence/Wall (NES 110.31)
Voltage Distance (min)
600 V to 13.8 KV 3.05 Meter
13.8 KV to 230 KV 4.57 Meter
Above 230 KV 5.49 Meter

15. GROUNDCLEARANCE
VOLTAGE LEVEL MINIMUM GROUND CLEARANCE
less than 66kV 6.1m
66kV - 110kV 6.4m
110kV - 165kV 6.7m
greater than 165kV 7.0m

16. Earth resistance value
 Major power station= 0.5
Ohm.
 Major Sub-stations= 1.0
Ohm
 Minor Sub-station = 2 Ohm
 Neutral Bushing. =2 Ohm
 Service connection = 4
Ohm
 Medium Voltage Network
=2 Ohm
 L.T.Lightening Arrestor= 4
Ohm
 L.T.Pole= 5 Ohm


17. Measurement of Earth Resistance
(Three point method)

18. Size of earth wire for motor
Sr. Capacity Size of earth wire Size Of Earth Electrode
Cu GI Cu GI
1 01- 10 HP 8 SWG 8 SWG 60cmX60cmX3.18
mm
60cmX60c
mX6.35mm
2 10 – 15 HP 8 SWG 6 SWG 60cmX60cmX3.18
mm
60cmX60c
mX6.35mm
3 15 – 30 HP 6 SWG 4SWG 60cmX60cmX3.18
mm
90cmX90c
mX6.35mm
4 30 – 50 HP 4SWG 25mmX3 mm 90cmX90cmX6.35
mm
90cmX90c
mX6.35mm

19. IRValue of Submersible Motor
IR Value of Submersible Motor
Motor Out off Well (Without Cable) IR Value
New Motor 20 MΩ
A used motor which can be reinstalled 10 MΩ
Motor Installed in Well (With Cable)
New Motor 2 MΩ
A used motor which can be reinstalled 0.5 MΩ

20. IRValue of Transformers:
Voltage Test Voltage
(DC) LV side
Test Voltage
(DC) HV side
Min IR
Value
415V 500V 2.5KV 100MΩ
Up to 6.6KV 500V 2.5KV 200MΩ
6.6KV to 11KV 500V 2.5KV 400MΩ
11KV to 33KV 1000V 5KV 500MΩ
33KV to 66KV 1000V 5KV 600MΩ
66KV to 132KV 1000V 5KV 600MΩ
132KV to 220KV 1000V 5KV 650MΩ

21. Standard voltage
Type Voltage
EXTRA LOW
VOLTAGE
Up to 50V AC/DC
LOW VOLTAGE 50-1000V AC/DC
MEDIUM VOLTAGE ABOVE 1000V AC/DC UPTO 6.6KV
AC
HIGH VOLTAGE ABOVE 6.6KV AC TO 33 KV AC
EXTRA HIGH
VOLTAGE
ABOVE 33KV AC TO 400 KV AC
ULTRA HIGH
VOLTAGE
ABOVE 400 KV AC TO 765 KV AC

22. Cable end termination

23. Breaker ACB/VCB/SF6/OCB

24. EARTHING
 The following steps, when put into practice, will ensure a
re liable , safe and tro uble -fre e substatio n g ro unding
syste m :
 Size conductors for anticipated faults
 Use the right connections
 Ground rod selection
 Soil preparation
 Grounding using building foundations
 Grounding the substation fence
 Special attention to operating points
 Surge arrestors must be grounded properly
 Grounding of cable trays
 Temporary grounding of normally energized parts

25. Earthing .....contd

26. Cabling
 Depth of the trench 7 50
m m fo r cable s up to
1 . 1 KV
 Depth of the trench
1 20 0 m m fo r cable s up
to 1 . 1 KV
 Sand - covered with 150
mm
 Width of the trench -
350 mm minimum
 Loop –approximate -3

27. Cable laying
 Laying direct in ground
 In pipes,
 Closed or Open ducts,
 Cable trays and
 On surface of wall

28. BUILDING
 Administrative building
 Conference room etc.
 Battery Room
 Operator room
 Check and change room
 Adjacent maintenance room
 ECC room

29. Switchgearand Control Panel Building
 Low voltage AC. Switchgear
 High voltage AC. Switchgear
 Control Panels, Protection
Panels
 Capacitor panel room

30. Mechanical, Electrical and OtherAuxiliaries
 Fire fighting system
 D.G. Set
 Oil purification system

31. ACT FAST AND INITIATE
FIRST
 बड़ा सोचो
 तेजी से सोचो व
 सबसे पहले सोचो
 िवचारो पर िकसी का
 एकािधकार नही होता.
---- धीरभाई अमबानी

32. THANK YOU