2. Presentation Layout
GIS – Introduction
GIS vs AIS
Case study of typical 66/11kV S/S
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.
4. GIS- Merits
• 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.
5. GIS- Demerits
• Individual Bay cost is high when compared
with that of AIS
• Overall s/s cost including land cost is
• Procurement of SF6 gas and supply of gas to
the site is problematicSF6
• In cases of internal fault.
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
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.
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.
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.
SF6 is colorlessly, odorless and a chemical neutral (inerted) gas.
SF6 is 5x heavier than air, is not toxic and has no dangerous
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
24. Circuit Breaker
GIS uses essentially the
same dead tank SF6 puffer
circuit breakers used in
Each CB comprises three
enclosed breaker poles.
One grading capacitor
guarantees an equalized
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
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.
27. Disconnector Switch (DS)
Disconnect switches are designed to
continuously carry load currents and
momentarily carry short circuit currents for a speciﬁed duration.
28. Earth Switch
Two types used for GIS
Fast earth switch
Fast earth switch is
used to protect the
transformer from core
during isolation /
switching off the line.
Making capacity -N/A- Yes
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
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).
33. Local control cabinet (LCC)
Local control is integrated
into the switchgear.
The local control of each
bay provides the following
Control and monitoring of
the bays and density of the
SF6 gas inside the
Interface between the
remote control, local
control and the GIS
35. GIS enclosure
3-ph enclosures used upto 170 kV system voltage, and
1-ph enclosures used above 170kV system voltage.
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
49. NTPC’s experience in GIS
NTPC-TNEB JV Power plant: 400kV GIS switchyard
NTPC-Kayamkulam : 220kV GIS switchyard
50. GIS -Standards
IEC 62271-1 Common specifications for SF6-insulated
and air-insulated high-voltage switchgear and control
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
The introduction of SF6 gas has revolutionized not only the technology of circuit breakers but also the layout of substations.
66kV bus provided for 5 no.s of bays
Instead of SF6-to-air as connections into the substation as a whole, the nozzles on the circuit breaker enclosure are directly connected to the adjacent GIS module.
The puffer-type technique was introduced for SF6 circuit breakers, wherein the relative movement of a piston and a cylinder linked to the moving part is used to generate the pressure rise necessary to blast the arc via a nozzle made of insulating material (Figure 1). In this technique, the pressure rise is obtained mainly by gas compression.
To guarantee simultaneous interruption, the chambers are mechanically connected in series.
CTs inside the enclosure must be shielded from the electric field produced by the high voltage conductor or high transient voltages can appear on the secondary through capacitive coupling.
For CTs outside the enclosure, the enclosure itself must be provided with an insulating joint, and enclosure currents shunted around the CT. Both types of construction are in wide use.
Use of fast (High speed) earth switch provides a parallel (low resistance) path to drain the residual static charge quickly, thereby protecting the instrument voltage transformer from the damages that may otherwise be caused.
The basic construction of these earth switches is identical.
-by direct current flowing through its primary as a consequence of charge stored online
The lightning arrester protects the power utilities from overvoltage due to lightning or surges and prevents the utilities from breakdowns and blackouts.
SF6 –Air Bushings
used for connecting to open terminal equipment & Overhead transmission lines.
CABLE TERMINATION (Fig -a)
High-Voltage cables of various types are connected to SF6 switchgear via cable connection assembly & also it enables the GIS & Cables to be tested separated.
Transformer connection(Fig -b)
consists of Oil/SF6 bushing, the enclosure, the main circuit end terminal & removable connection.
For Hi-Voltage test on GIS, transformer is isolated from switchgear by dismantling the removable connection
The insulating and interrupting capability of the SF6 gas depends on the density of theSF6 gas.
The pressure of the SF6 gas varies with temperature, so a mechanical or electronic temperature compensated pressure switch is used to monitor the equivalent of gas density.
The weight and size of the GIS equipment do not change appreciably with the voltage class as the bulk of the current –carrying components and enclosures have identical dimensions for similar thermal and short time current.
The additional insulation required for the next voltage class is achieved by increased gas density.
Owing to these flexibilities, a few manufacturers offer the same equipment for two voltage classes like 170/145 kV. Even when the GIS equipment is designed for an individual voltage class, the dimensions and weights of the equipment differ marginally.
International Council on Large Electric Systems (CIGRE)
H-GIS: IEC 62271-205