1. GAS INSULATED
SWITCHGEAR
IETP
BY RAGHAV TRIPATHI

2. CONTENTS
 INTRODUCTION TO GIS
 RATINGS OF GIS
 MAIN FEARURES OF GIS
 FACTORS FOR CHOSING GIS
 SULFUR HEXAFLUORIDE [SF6]
 GIS TECHNOLOGY
 TYPICAL GIS LAYOUT
 INTERFACING OF GIS
 LOCAL CONTROL CUBICLE
 OPERATION OF GIS
 CONCLUSION

3. INTRODUCTION TO GIS
 What is GIS?
 GIS
• Compact multicomponent assembly
• Enclosed in a grounded metallic housing
• Primary insulation >>> SF6 gas
• Includes buses, switches, CB and other associated equipment.
 GIS Enclosure
• Retains the insulating gas under the prescribed conditions.
• Maintains the highest insulation level safety
• Protects the equipment against the external influences
• Provides high degree of protection to personnel

4. INTRODUCTION TO GIS
 Gas insulated components of substation are generally;
 Electrical bus bars
 Electrical isolators or disconnectors
 Circuit breakers
 Current transformers
 Voltage transformers
 Earth switches
 Surge arrestors

5. INTRODUCTION
 Terms related to GIS
 Compartment of GIS
 Gas monitoring Systems
 Gas leakage rate
 Gas Zone
 Partition
 Gas pass through insulator
 LCC
 Main circuit
 Auxiliary circuit
 Service Period

6. RATINGS
 Main Ratings are;
 Rated maximum voltage
 Rated insulation level
 Rated power frequency
 Rated continuous current
 Rated short time withstand current
 Rated peak withstand current
 Rated duration of short circuit
 Rated supply voltages

7. MAIN FEATURES OF GIS
 Factory pre-assembled and tested units (Reduces on site works)
 Operating life > 50 years (high reliability & long lifetime)
 Major inspection not before 25 years
 Motor-operated self lubricating mechanism (small motors)
 Minimal cleaning requirement (clean room)
 Corrosion-resistant (Aluminium alloy)
 Low fault probability/high availability (high reliability)
 Protected against aggressive environmental conditions
 Seismic resistance (compact; low point of gravity)
 Space requirement less than 20% of comparable AIS

8. FACTORS FOR CHOSING GIS
Atmospheric contamination
Automation
Construction
Community impact
Cost
Land size
Location
Failure rate
Reliability
Safety
Seismic
Weather

9. SULFER HEXAFLUORIDE [SF6]
 Overview
 Colourless, odourless, non-toxic & non-flammable gas
 Five times heavier than air
 Stable molecular construction
 High dielectric strength & high arc quenching properties
 A strong green house gas
 Electronegativity property
 Allows compact equipment design
 Maintenance free for 25 years
 Chemically & Thermally stable
 Excellent electric insulation
 High thermal interruption capabilities & high heat transfer

10. SULFER HEXAFLUORIDE [SF6]
 Overview
 3 times dielectric strength of air
 Does not show any ageing effect
 Standard- IEC 60376
 The leak rate- 0.5%/year per gas compartment
 Categories of SF6 gas as per contamination
 New SF6 gas
 Technical grade SF6 gas
 Non-arced SF6 gas
 Normally arced SF6 gas
 Heavily arced SF6 gas

11. GIS TECHNOLOGY
 General
 Materials – Metals for conductors, enclosure, contact materials &
Epoxy resin for insulators
 Earlier – cast steel; Now – aluminium Alloy
 Modular Design
 Three phase enclosure
1. Few parts
2. Less insulating gas
3. Less enclosure material
4. Large aluminium enclosure

12. GIS TECHNOLOGY
 CB
 Self blast type
 Parallel arrangement of interrupter
 Easy handling & maintenance
 Aluminium casting tank
 Spring type mechanism
 3PDS
 Mechanical self interlocks for DS-ES
 Inspection window
 Motor driving mechanism

13. GIS TECHNOLOGY
 HES
 Motor spring drive mechanism
 Contact system – withstand at least
two making operations with SC
rating
 Capable of grounding live
conductor if required.
 Other Equipment
1. VT
2. CT
3. 3 phase overhead line connection
module
4. 3 phase encapsulated cable
connection module
5. 3 phase encapsulated surge arrestor
module
6. 3 phase encapsulated bus bar

14. GIS TECHNOLOGY
 Single Phase enclosure
1. High level of standardized enclosure
2. Each module – only one function; (switching, measuring & connecting)
3. Main Modules are;
 CB, DS, ES
 CT, VT
 Bus bar
 SA
 Cable connection, transformer connection, outdoor connection to
OHTL or transformer

15. GIS TECHNOLOGY
 CB
1. Usually in a separate enclosure
2. Horizontal or vertical oriented
3. Higher operational pressure(0.7-0.8
MPa)
4. Basis of the bay to which DS, ES, bus
bars are connected
 DS & ES switch module
1. Usually in the same gas compartment
2. Motor operated
3. Operated only after CB has
interrupted the power flow
4. ES – electric motor operation
HES – Spring operated

16. GIS TECHNOLOGY
Instrument Transformer
Current Transformer
 Three phase insulated – 145kV
 Secondary coils – inside aluminium
enclosure the coils are connected
via pressure-tight contacts to the
secondary control cubicle
 Terminal boxes for the secondary
wiring on the bottom side
 Measuring & protection Purpose
Voltage Transformer
 Three phase or single phase
insulated
 Conical insulator at the bottom to
separate the gas compartment
 Reduce bus high voltage to lower
control levels for protective replay,
control and metering.

17. TYPICAL GIS LAYOUT
Operational requirement & Reliability, Service and maintenance considerations
SINGLE BUS
1. Reliability is not the main
request.
2. Lowest investment to
design GIS
3. Small substations
4. Relatively unimportant
sections
5. Outage in case of bus bar
failures
6. 145kV Taiyo
Double Bus
1. Operational flexibility and
reliability is higher
2. Higher investment to design
GIS
3. Coupled with Bus coupler
4. Maintenance on one bus
bar with other bus bar in
service
5. 145kV UPPTCL Sector-115
Breaker & a Half
Arrangement
1. Very high reliability
2. Even if one bus bar fails, the
power supply to feeder will
be kept in service
3. Relatively higher investment
4. 400kV Motihari

18. INTERFACING OF GIS
 SF6 Gas to Oil Bushing:
1. Directly connected to Transformer
2. Separates insulation oil from SF6 gas
3. Bellows are provided
 Gas to Air Bushing: Connected to TR/OHTL through cables
 Cable Sealing End: Directly connected to power cable

19. LOCAL CONTROL CUBICLE
Control & Monitoring
 Each CB is provided with a control cabinet
 For local control & monitoring of bay
 Generally placed in front or adjacent to bay
 Consists of control switches, local/remote switches, close open switches, position
indicators for CB, DS, ES
 Alarms, mimic diagrams, AC/DC supply terminals, control relays
 Designed as per IEC60439
 CT secondary taps – wired – LCC
 For multiratio CT – Terminal Box – LCC
 PT Secondary winding – terminated through terminal box – LCC
 Interlocking for safety & convenience

20. LOCAL CNTROL CUBICLE
Following minimum alarm is provided
1. SF6 gas pressure
2. Loss of DC supply
3. CB trip
4. VT supply fail (VT MCB fail)
5. Loss of AC supply
6. Local/remote switch
7. Trip circuit failure
8. Loss of DC supply to CB motor

21. OPERATION OF GIS
CIRCUIT BREKER
1. Main purpose – rapidly de-
energise faulty sections
2. Automatically reclosing
3. Human intervention from
LCC
4. Prevented from operating
by parameters that affect
its successful function
- Low gas density
- Low mechanism pressure
- Monitoring of proper
position of CB
Disconnect switch
1. Isolate various components
2. Do not have significant
interrupting capability
3. Motor operated or manual
hand crank override
4. Single phase operation or
three phase group
operated
Earth Switch/ High
speed earth
switch
 ES
1. Personnel protection
purpose
2. Ground – de-energised
components
3. Non-fault initiating
 HES
1. Unique to GIS
2. Primary function same as ES
3. Fault initiating
4. Motor operated
mechanism with spring
assists for rapid opening or
closing

22. CONCLUSION
Gas insulated switchgear or substations have been successfully in use for
almost 40 years with an increasing use world wide.
High reliability and higher efficiency has been reached over the last four
decades.
GIS can operate over a wide range of conditions from indoor to outdoor
High safety concerning with the personnel protection

23. Thank You