2. CONTENTS
Substation
Classifications of Substation
Air Insulated Substations
Gas insulated substations
Properties of G.I.S
Components of G.I.S
Comparison between A.I.S and G.I.S
Service conditions of G.I.S
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3. A practical view of a gas insulated substation
MANUFACTURED BY SIEMENS
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4. A SUBSTATION
An assembly of apparatus installed to control transmission
and distribution of electric power.
A substation is a place where high-voltage electricity from
power plants is converted to lower-voltage electricity
for homes or factories .
The voltage is stepped down to distribution levels and the
power is fed into the distribution grid and sent to the final
consumers.
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7. Classification based on Voltage Levels
A.C. substations
1. EHV
2. HV
3. MV
4. LV
HVDC
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8. Classification based on Outdoor or
Indoor
Outdoor substation : Under open sky
Indoor substation : Inside a building
Classification based on configuration
Conventional air insulated outdoor substation
SF6 Gas Insulated Substation (GIS)
Composite substations having combination of the above
two
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9. AIR INSULATED SUBSTATION(AIS):
Air used as a dielectric medium
Normally used for outdoor substations.
Easy to expand (in case that space is not an issue)
Excellent overview, simple handling and easy access.
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11. Major 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 takes place
Life of steel structures degrades
Seismic instability
Large planning & execution time
Regular maintenance of the substation required
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12. The need of Gas Insulated Substation
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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15. Introduction
GIS was first developed between 1968 and 1972.
Sulphur Hexafluoride (SF6) gas – the primary insulating
medium
Enclosed in a ground metallic housing.
Compact, multi-component assembly
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16. (SF6) gas- 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 components include Circuit Breakers, Bus-Bars,
Isolators, etc. housed in metal enclosed modules filled
with SF6 gas.
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17. Properties of SF6
SF6 is colour-less, odour-less and chemically inert gas
SF6 is 5 times heavier than air and non-toxic
Almost water insoluble
Lifetime – Very long (800 to 3200 years!)
The dielectric strength of SF6 is approximately 3 times
that of air.
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19. Components of G.I.S.
Circuit breaker
Disconnector (Isolator)
Ground switches
Bus-bar
Gas Density Monitor
Current Transformer
Voltage Transformer
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20. Advantages of G.I.S
Occupies very less space (1/10th) compared to ordinary
substations.
Most preferred where available area for substation is
small (e.g.: cities, hilly areas).
More 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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21. Growth of G.I.S market
According to a recent report on the GIS market, the global
gas insulated substation market is expected to grow from
an estimated $14.75 billion to $35.83 billion by 2024
Rising population, growth in infrastructure &
transportation are a few driving factors
In several countries, upgrades to the aging transmission
network are also driving the GIS market
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24. On the basis of Construction
Gas insulated
Uses SF6 for insulation
use fixed, mounted circuit
breakers
Can be indoor as well as
outdoor, compact
Air insulated
Uses air for insulation
uses three-position draw-out
circuit breakers
Mostly outdoors, covers
large area
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25. On the basis of Maintenance
Gas insulated
visually inspected every four
years or more
GIS units being sealed, are
protected from
environmental damage
Air insulated
visually inspected every year
to two years
Inspections include having a
technician torque, draw-out,
clean, lubricate and vacuum
the unit
checked for visual signs of
copper corrosion
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26. On the basis of Total Cost
Gas insulated
units tend to cost between
10% to 40% more than
their sealed technology
means lower installation and
maintenance costs AIS
Air insulated
offer upfront cost savings
lifelong
maintenance required
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27. Operating conditions of a GIS
As per IEEE 122,IEEE123 and IEC 62271
Indoor or outdoor : As per customer
Elevation above sea level : As per site location
Design ambient temperature : 40 degree Celsius
Maximum ambient temperature : 105 degree Celsius
Maximum Allowable Total Temperature in Celsius
Internal contacts/joints silver plated and 105
conductor in compact with epoxy insulator
External surface-accessible 70
External surface-inaccessible 110
External surface-normally handled by 50
an operator
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