This presentation provides an overview of gas insulated substations (GIS). It discusses the limitations of conventional air insulated substations, including their large size. GIS offer a more compact alternative by using sulfur hexafluoride gas as the insulating medium. The key components of a GIS including circuit breakers, transformers, and busbars are housed in modular enclosures filled with SF6 gas. GIS provide benefits such as reduced space requirements, high reliability, and lower maintenance needs compared to conventional substations. However, their initial costs are higher and repairs can require long outages. Future trends may include more compact designs, replacement insulating gases, and increased use of GIS in urban areas.

1. A
presentation
on
An Overview
Of
Gas Insulated Substation
DEPARTMENT OF ELECTRICAL ENGINEERING
RAJKIYA ENGINEERING COLLEGE
AMBEDKAR NAGAR-224122(U.P.)
April 2018
Presented By : Guided By:
Deepak Kumar Kannaujiya
Roll No. - 1673720703
Mr. Sonu Kumar
(Assistant Professor)

2. 2
Contents:
Introduction
Conventional substations (AIS)
Limitations of AIS
The need for GIS
Introduction to GIS
Properties of SF6
GIS Equipment's
GIS assembly
Advantages of GIS
Demerits of GIS
Future trends in GIS
Conclusion
References

3. 3
Introduction
Gas Insulated Substation (GIS) is a compact, multicomponent assembly
enclosed in a ground metallic housing in which the primary insulating
medium is compressed SF6 gas.
The compactness is with the use of SF6 gas, which has high dielectric
strength.
Gas Insulated Substations (GIS) can be used for longer times without any
periodical inspections.

4. 4
AIS-Air Insulated Substation
Air used as a dielectric.
Normally used for outdoor substations.
In very few cases used for indoor substations.
Easy to expand (in case that space is not an issue)
Excellent overview, simple handling and easy access.
4

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Limitations of AIS:
Large dimensions due to statutory clearances and poor dielectric
strength of air.
Insulation deterioration with ambient conditions and
susceptibility to pollutants.
Wastage of space.
Life of steel structures degrades.
Seismic instability.
Large planning & execution time.
Regular maintenance of the substation required.

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GIS Benefits over AIS

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The need for G.I.S:
Non availability of sufficient space.
Difficult climatic and seismic conditions at site.
Urban site (high rise building).
High altitudes.
Limitations of AIS.

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Gas Insulated Substation:
Introduction:
Compact, multi-component assembly.
Enclosed in a ground metallic housing.
Sulphur Hexafluoride (SF6) gas the primary insulating medium.
(SF6) gas is superior dielectric properties used at moderate pressure for phase
to phase and phase to ground insulation
Preferred for voltage ratings of 72.5 kV, 145 kV, 300 kV and 420 kV and above.
Various equipment's like Circuit Breakers, Bus-Bars, Isolators, Load Break
Switches, Current Transformers, Voltage Transformers, Earthing Switches, etc.
housed in metal enclosed modules filled with SF6 gas.

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Properties of SF6:
Characteristics
SF6 is colorlessly, odorless and a chemical neutral (inert) 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.

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GIS Equipment's
Circuit Breaker
Current transformer
Voltage transformer
Feeder Disconnector and Earthing switch
Bus bar
Gas density Monitor

11. 72.5 kv GIS assembly
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Bus Bar
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.
The conductors made of aluminum or copper, depending on the current rating, are
supported by gas tight insulator (for standard bay bus) or individual supporting
insulators (for extended bus).
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Current Transformer
The secondary windings are designed for metering or protection purposes.
One terminal of each used secondary winding and one terminal of unused
winding have to be earthed during the transformer operation (unused short-
circuited also).

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Technical Parameters Of CT
Technical parameters of CT Value
Enclosure Single / separate phase wise
Enclosure material Aluminum Alloy
Rated voltage 72.5 KV/420 KV
Metering(66kv) 600-300 / 1A
Metering(400kv) 3000-2000-1000-500/1A

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Potential Transformer
It is used for protection and measuring.
They are based on the electromagnetic transformer principle, where primary
and secondary winding galvanically separated from one another.
Primary winding is wound on the top of the core and the secondary winding.
The letter are connected to the terminals in the external terminal box through a
gas-tight multiple bushing.
Utilization of Sf6 gas as insulating medium, together with plastic foil in the
winding.
15

16. Technical Parameters Of PT
Enclosure Single / separate phase wise
Enclosure material Aluminum Alloy
Rated voltage 72.5 KV/420 KV
Metering 66KV/110V
Metering 400KV/110V
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17. Transformer
Gas insulated transformers, using incombustible SF6 gas as a insulation and cooling
medium, enable to remove a fire fighting equipment from transformer room.
Since gas insulated transformer does not need the conservator, the height of transformer
room can be reduced.
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18. Parameters Of Transformer
Technical particulars 500 kV System 230 kV System 110 kV System
Rated Voltage 550 kV (rms) 245 kV (rms) 145 kv (rms)
Rated frequency 50 Hz 50 Hz 50 Hz
Grounding Effectively Effectively Effectively
earthed earthed earthed
Rated current 4000A 3150A 2000A
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19. Circuit Breaker
A circuit breaker is an automatically operated electrical switch designed to protect
an electrical circuit from damage caused by excess current from an overload or short
circuit.
Circuit breaker is of the single pressure type ,during interruption a compression
piston in the chamber generates the gas pressure required to extinguish the arc
between the contacts.
Maintenance free up to 2000 times load breaking. Mechanically type tested for
10000 operations.
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20. Technical Parameters Of CB
Technical parameters of CT Value
Particulars 66 kV/400 kV
Enclosure Single / separate phase wise
Enclosure material Aluminum Alloy
Rated voltage 72.5 kV/420 kV
Rated current 1600A/3150A
Rated frequency 50 Hz
Rated short-circuit breaking current 25 kA/40 kA rms
Duration 3 sec
Type of operating mechanism for CB Spring /combined
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21. Disconnectors and Earthing Switches
Disconnectors and earthing switches are often offered as a combination of both.
The disconnector has a switching capability of bus-transfer current, small capacitive
current as bus charging and small inductive current as transformer magnetizing
current, if required.
The task of an earthing switch is to earth de-energised parts of the switchgear and –
in the case of multi-pole earthing switches – to short-circuit them at the same time.
Disconnectors and earthing switches are normally motor or manual-operated.
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22. Technical parameters of Disconnectors
Particulars Parameters
Enclosure Single/separate phase wise
Enclosure material Aluminum Alloy
Rated voltage 72.5 / 420 kV
Rated current 1600 /3150 A
Rated short-time current 25/ 40 kA rms
Duration 3 sec
Rated control and operating voltage 110/220 V DC
Type of operating mechanism Motor operated
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23. Technical Parameters Of Earthing Switch
Technical parameters of E S Value
Particulars 66kV/400kV
Enclosure Single/separate phase wise
Enclosure material Aluminum Alloy
Rated voltage 72.5 /420 kV
Rated short-time current 25/ 40 kA rms, 3 sec
Rated peak withstand current 62.5 /100 kA peak
Type of operating mechanism Motor operated
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24. Gas Density Monitor
Directly mounted on the enclosure.
In case of gas leakage a micro-switch is actuated.
• Thresholds for refilling (first stage).
• lock-out alarm(second stage).
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25. Demerits of GIS
High cost compared to conventional outdoor sub-station.
Excessive damage in case of internal fault. Long outage periods as repair of
damaged part at site may be difficult.
Requirements of cleanliness are very stringent. Dust or moisture can cause
internal flashovers.
Such sub-stations generally indoor. They need a separate building. This is
generally not required for conventional outdoor sub-stations.
Procurement of gas and supply of gas to site is problematic. Adequate stock of
gas must be maintained.
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26. Advantages of GIS
Occupies very less space (1/10th) compared to ordinary substations.
Hence, most preferred where area for substation is small (e.g. Cities)
Most reliable compared to Air Insulated Substations.
Number of outages due to the fault is less.
Maintenance Free.
Can be assembled at workshop and modules can be commissioned in
the plant easily.
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Future Trends:
Compact design of switch gear by using three phase modules.
Use of vacuum circuit breaker cells in the medium high voltage GIS.
Optimization of GIS design to allow easier maintenance.
Development of DC GIS for incorporating into expanding
national/international HVDC systems.
Search for replacement gases for SF6.
The most promising - an 80%/20% N2/SF6 mixture.
Replacement of existing AIS by GIS will accelerate especially near urban
centers.

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Conclusion:
GIS – necessary for Extra HV & Ultra HV
Some important areas to be studied include:
More conservative design.
Improved gas handling.
Decomposition product management techniques.
Achieving & maintaining high levels of availability require – more integrated
approach to quality control by both users and manufactures.

29. References
E. Mikes, H. Aeschbach et al. "Innovative GIS based solutions for
substations" CIGRE SC23 Colloquium Venezuela, Paper 3.1, 2001.
Hermann Koch “Gas Insulated Substations” Library Of Congress
Cataloging-in-publication 2014
M.Bilal Latif “ Comparison of GIS substation over conventional
substation “ , IEEE
A. Edlinger, G. Mauthe, F. Pinekamp, D. Schlicht, W. Schmidt
,Disconnector switching of charging currents in metal-enclosed SF6-gas
insulated switchgear at EHV, 1984.
R. Witzman, "modelling of different GIS component", V Int.
Symp. on HV Eng., 1987-Aug.-23-28.
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