This document provides an overview of gas insulated substations (GIS) compared to conventional air insulated substations (AIS). It discusses the limitations of AIS related to space, infrastructure, environment, and cost. GIS were developed to address these limitations by using compact gas-insulated equipment using sulfur hexafluoride gas. The key components and features of GIS are described, including aluminum enclosures, standardized components, and flat voltage-time characteristics of SF6. Advantages of GIS over AIS include reduced space and construction costs, improved safety and reliability, and fulfilling aesthetic requirements for indoor applications. Potential disadvantages discussed include transient overvoltages during switching and long-term effects of arcing byproducts.

1. GAS INSULATED
SUBSTATION
RONAL PARMAR
140080707003
BIRLA
VISHVAKARMA
MAHAVIDHYALAYA

2. CONTENTS
 Introduction
 Conventional substation ( AIS )
 Limitation of AIS
 Need for GIS
 Introduction to GIS
 GIS unique features
 Components of GIS substation
 Advantages of GIS over conventional open air
substation
 Disadvantage of GIS
 Next presentation work

3. INTRODUCTION
 For maintaining proper voltage levels at transmission and
distribution level and for providing greater stability a number
of electrical transformation and switching setups have to be
created in between generating station and consumer ends.
These transformation and switching setups are generally
known as electrical substations.
 Based on nature of dielectric medium a substation is of two
types as following :
1. AIS (Air insulation sub-station )
2. GIS ( Gas insulation sub-station )

4. CONVENTIONAL SUBSTATION

5. LIMITATION OF AIS
 Physical factor
 Infrastructure factor
 Social & Environmental factor
 Commercial factor

6. NEED OF GIS
 Non availability of sufficient space. It is very much required to
establish a substation at load center. Establishing a
substation at load center is quite economical and profitable in
following ways :
A. Reduction in length of feeders
B. Improvement of the quality of voltage regulation due to
short length feeders
 Difficult climatic and seismic conditions at site, like high
altitude and atmospheric pollution
 Aesthetically “superior” to air insulated substations
 The higher the voltage, the more favorable gas insulated
technology becomes
 Overcomes or decreases the magnitude of limitations of AIS
site selection

7. INTRODUCTION OF GIS
 Gas insulated substations (GIS) have been used in power
systems over the last three decades because of their high
reliability, easy maintenance, small ground space requirement
etc. In India also, a few GIS units are under various stages of
installation.
 Gas insulated bus has a surge impedance (70Ω) more than
that of the conventional oil filled cables, but much less than
that of an over head line (300Ω - 400Ω). Further, the average
bus run for a compact GIS is much less than that for the
conventional station.
 life of GIS is affected by several factors such as:
A. conductive particles
B. particle discharges
C. contamination
 The GIS require less number of lightning arresters than a
conventional one. This is mainly because of its compactness.

8. CONTI….
 The basic consideration for insulation coordination is V-T
characteristic. The V-T characteristic of SF6 is considerably
flat compared to that of air.
 Air can withstand to very high voltages for very short time.
However, as the duration of voltage increases, the withstand
voltage falls off considerably.
 On the other hand, SF6 exhibits a flat characteristic, thus the
ratio of basic lightning impulse level is close to unity for GIS,
whereas for the conventional substations this ratio varies
between 0.6 and 0.86.
 Gas insulated substations are in service up to the highest
voltage of 800 kV, meeting almost all the requirements in
urban, industrial as well as rural areas.

9. GIS UNIQUE FEATURE
1. Wide spread application of aluminium enclosure materials for
standardized component models for all voltage ranges
2. The light weight enclosures have good conductivity, low eddy-
current losses and a high resistance to corrosion
3. Easy handling, as well as reduced stresses on foundation and
support structure are additional features
4. Standard arrangements can be easily modified and extended
with good co-ordination between the manufacturer and the
user.
5. A gas- tight barrier insulator in switchgear serve for the
separation of gas compartments and prevents neighbouring
switchgear parts from being affected during maintenance.

10. Components of GIS
substation
1. Circuit breaker
2. Disconnector switch
3. Earthing switch
4. Current transformer
5. Voltage transformer
6. Bus bar & connectors
7. Power transformer
8. Surge arrester
9. Cable termination
10. SF6 / air or SF6 / oil
bushing

11. ADVANTAGES OF GIS OVER CONVENTIONAL
OPEN AIR SUBSTATION
 Area and volume saving in construction for over or underground
applications.
 Greatly improved safety and reliability due to earthed metal
housing of all high voltage parts and much higher intrinsic
strength of SF6 gas as insulation.
 Short on site erection times
 Fulfilment of aesthetic requirements with indoor applications
 High service reliability
 Reduction in radio interference with the use of earthed metal
enclosures
 Use as mobile substations for transportation to load centres on
standard tracks.
 More optimal life cycle costs
 Not necessary that high voltage switchgear has to be installed out
doors.

13. DISADVANTAGE OF GIS
 Switching operation generate Very Fast Transients
Over Voltages (VFTOS).
 VFTOS may cause secondary breakdown inside a
GIS and Transient Enclosure Voltages (TEV)
outside the GIS.
 Field non-uniformities reduce withstanding levels of
a GIS.
 Prolonged arcing may produce corrosive/toxic by-
products.
 Support spacers can be weak points when arc by-
products and metallic particles are present.

14. NEXT PRESENTATION
WORK
 Type of GIS sub-station
 Construction of low & medium voltage GIS sub-
station
 Construction of high voltage GIS sub-station
 Maintenance of GIS sub-station
 GIS approach in the GRID
 Visit of 400/220KV GIS substation located at
DASTAN , bardoli ,

15. REFERENCE
 M.Bilal Latif “ Comparison of GIS substation over
conventional substation “ , IEEE
 http://www.pserc.wisc.edu/documents/publications/papers/20
01_general_publications/indicator.pdf