1. NTPC Electric Supply Company Ltd,
NTPC, Noida.
Date: 09.02.2013

2. Presentation Layout
 GIS – Introduction
 GIS vs AIS
 Case study of typical 66/11kV S/S
 GIS Configuration
 GIS Switchgear
 GIS- Layout
2

3. GIS - GAS INSULATED SUBSTATION
 Gas Insulated Substation (GIS) is a compact, multi-
component assembly enclosed in a ground metallic
housing in which the primary insulating medium is
compressed SF6 gas.
3

4. GIS- Merits
4
• Human safety
• Earthed metal enclosuresSafe
• Fully enclosed
• guards against any impairment of the insulation system.Reliable
• Upto 70% of space required that of AISSpace Saving
• Higher initial cost is offset by
• less maintenance, reliable, safe operation
Less overall cost
• high standard of manufacturing quality assure long service
life with practically no maintenance requirement.
Maintenance
Free

5. GIS- Demerits
5
• Individual Bay cost is high when compared
with that of AIS
• Overall s/s cost including land cost is
comparable.
High initial
cost
• Procurement of SF6 gas and supply of gas to
the site is problematicSF6
• In cases of internal fault.
Long outage
period

6. 6

7. GIS – Benefits over AIS
 GIS has small ground space requirements.
 Gas insulated Substations have easy maintenance
(nearly zero Maintenance)
 Less field erection time & less erection cost.
 Non-Flammability & Non-Explosive , Oil-free & Less
Pollution
7

8. GIS – Benefits over AIS
8


9. GIS – Benefits over AIS
9


10. 10

11. 66/11kV AIS S/s (Typical)
11
66kV bays 05 no.s ( 2no.s of T/f + 2no.s of
line + 1 no. B/c)
11kV swgr 23 nos. (including APFC)
66/11kV Power T/f 2x20MVA
Total plot area 91x44 sq.mtr. (required)
Total S/s construction cost Rs. 7.77 cr.

12. SLD
12

13. Layout-AIS
13

14. Layout-
GIS
14
 Office room,
B & B/C are
provided in
First floor of
control room
bldg.

15. Land cost
15
AIS (66kV AIS + 11kV indoor swgr ) GIS (66kV GIS + 11kV indoor swgr )
Leng
th X
Brea
dth
Area
(sq.mtr.)
Leng
th X
Brea
dth
Area
(sq.mtr.)
C/R Bldg. 26x 13= 348
C/R + GIS+DG
Bldg. (Double
storeyed) 25x 9= 246
Switchyard 53x 33= 1749 Switchyard 31x 25= 775
Peripheral Area 26x 25= 1915 Peripheral Area 5x 36= 628
Total Area 91x 44= 4012.4 Total Area 40x 35= 1400

16. S/s construction cost
16
AIS (66kV AIS + 11kV indoor swgr ) GIS (66kV GIS + 11kV indoor swgr )
Ex-works
Power T/f ( 2 no.s) = 2.06Cr. Power T/f ( 2 no.s) = 2.06Cr.
66kV bay eqpt (5 bays) = 1.14Cr. GIS 66kV bays (5 no.s) = 4.5Cr.
11kV swgr. & 66kV C/R panels, S/S
aux. = 2.01Cr.
11kV swgr. & 66kV C/R panels, S/S
aux. = 2.01Cr.
Total Ex-works = 5.21 Cr. Total Ex-works = 8.57 Cr.
Civil & Erection
Power T/f ( 2 no.s) = 0.07Cr. Power T/f ( 2 no.s) = 0.07Cr.
66kV bay eqpt (5 no.s) = 0.742Cr. GIS 66kV bays (5 no.s) = 0.2Cr.
11kV swgr. & 66kV C/R panels, S/S
aux. & Fencing = 0.38Cr.
11kV swgr. & 66kV C/R panels, S/S
aux., C/R bldg. & Fencing = 0.59Cr.
C/R bldg. (350 sq.mtr.) = 0.32Cr.
GIS + C/R bldg. Double storeyed
(40+350 sq.mtr.) = 0.47Cr.
Total Civil & Erection = 1.51 Cr. Total Civil & Erection = 0.89 Cr.
Total cost including taxes & duties = 7.77 Cr. Total cost including taxes & duties= 11.50 Cr.

17. Total cost
*Considering cost of land at Rs 10,000/- per sq.mtr.
 If we consider cost savings that accrue due to reduction in manpower
& maintenance costs, outage cost etc., GIS is felt to be cost – effective.
17
AIS GIS Remarks
Cost of Land 4.01 1.40 10,000 Rs./sq.mtr.
Cost of substation 7.77 11.50
Total cost (Cr.) 11.78 12.90
Difference (1.12) Cr.

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19. 19
1. Barrier insulator
2. Busbar Gas Compartment
3. Feeder Gas Compartment
4. CB Gas compartment
5. Voltage transformer

20. GIS – Bay components
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21. GIS configuration
 Bus bar is extendable in both directions
 Modularised concept is used
 Flexible to interchange the feeders
 Feeder take-off direction can be oriented according to
the site need.
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22. 22

23. SF6
 Characteristics
 SF6 is colorlessly, odorless and a chemical neutral (inerted) gas.
 SF6 is 5x heavier than air, is not toxic and has no dangerous
components inside
 SF6 is no hazardous material
 SF6 has no eco-toxic potential
 SF6 has no impact for the ozonosphere.
 Advantages for use in GIS
 The dielectric strength of SF6 gas at atmospheric pressure is
approximately three times that of air.
 It is incombustible, non toxic, colorless and chemically inert.
 It has arc-quenching properties 3 to 4 times better than air at equal
pressure.
23

24. Circuit Breaker
 GIS uses essentially the
same dead tank SF6 puffer
circuit breakers used in
AIS.
 Each CB comprises three
single-phase metal
enclosed breaker poles.
 One grading capacitor
guarantees an equalized
voltage distribution.
24

25. Current Transformer
 CTs are inductive ring types installed either inside the
GIS enclosure or outside the GIS enclosure .
 The GIS conductor is the single turn primary for the
CT.
25

26. Voltage Transformer
 The single pole inductive voltage transformer is
connected to switchgear with the connecting flanges
with a barrier insulator.
 The primary winding is insulated with SF6 gas &
connected to high voltage terminal.
26

27. Disconnector Switch (DS)
 Disconnect switches are designed to
 continuously carry load currents and
 momentarily carry short circuit currents for a specified duration.
27

28. Earth Switch
 Two types used for GIS
 Maintenance earth
switch
 Fast earth switch
 Fast earth switch is
used to protect the
circuit-connected
instrument voltage
transformer from core
saturation caused
during isolation /
switching off the line.
28
Maint.
ES
Fast
ES
Induced current
switching
-N/A- Yes
Making capacity -N/A- Yes
Short-time current
withstand
Yes Yes

29. Lightning Arrester (ZLA)
 Zn-O element
(Zine-Oxide )
29

30. Bus
 To connect GIS modules that are not directly
connected to each other, an SF6 bus consisting of an
inner conductor and outer enclosure is used.
 Support insulators, sliding electrical contacts, and
flanged enclosure joints are usually the same as for the
GIS modules.
30

31. SF6 Terminations
 SF6 –Air Bushings
 Cable Termination (Fig -a)
 Transformer connection (SF6-Oil)(Fig -b)
31Fig(a) Fig(b)

32. Gas density Monitor
 Directly mounted on the enclosure.
 In case of gas leakage a micro-switch is actuated.
 Thresholds for refilling (first stage) or
 lock-out alarm(second stage).
32

33. Local control cabinet (LCC)
 Local control is integrated
into the switchgear.
 The local control of each
bay provides the following
functions:
 Control and monitoring of
the bays and density of the
SF6 gas inside the
compartments
 Electrical interlocking
between components
 Interface between the
remote control, local
control and the GIS
equipment.
33

34. 34

35. GIS enclosure
 3-ph enclosures used upto 170 kV system voltage, and
1-ph enclosures used above 170kV system voltage.
35
Three-phase enclosure GIS.
Single-phase enclosure GIS.

36. Bay details
 Voltage class can be increased by increasing gas density. 36
Rated voltage 145kV 175kV 245kV
Bay width, m 1.5 2.0 2.0
Bay depth, m 3.3 3.35 3.4
Bay height, m 3.2 3.4 3.4
Floor area, sq.m 4.95 6.7 6.8
Volume, cum 15.84 22.78 23.12
Weight, kg. 3800 5000 5700
Floor loading, kg/sq.m 765 750 840

37. GIS -Technical details
37

38. GIS -Technical details
38

39. 72.5 kV GIS - Single busbar scheme
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40. 72.5 kV GIS
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41. 72.5 kV GIS
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42. 145 kV GIS
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43. 145 kV GIS
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44. 170 kV GIS- Double busbar Scheme
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45. 170 kV GIS- Double busbar Scheme
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46. 170 kV GIS- Double busbar Scheme
46

47. 220kV GIS
47

48. 220/110 kV
GIS
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49. NTPC’s experience in GIS
 NTPC-TNEB JV Power plant: 400kV GIS switchyard
 NTPC-Kayamkulam : 220kV GIS switchyard
49

50. GIS -Standards
 IEC 62271-1 Common specifications for SF6-insulated
and air-insulated high-voltage switchgear and control
gear
 IEC 62271-200 Standard of medium-voltage SF6-GIS
 IEC 62271-203 High-voltage switchgear and control
gear >52 kV Revision published in 9/2011
 IEC 62271-303 Use and handling of SF6
 IEC 60376 Specification for new SF6-gas
 IEEE C37.122 Gas Insulated Substations
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