GAS INSULATED SUBSTATION

RONAL PARMAR140080707003

BIRLA VISHVAKARMA

MAHAVIDHYALAYA

CONTENTS IntroductionConventional substation ( AIS )Limitation of AISNeed for GIS Introduction to GISGIS unique featuresComponents of GIS substationAdvantages of GIS over conventional open

air substationDisadvantage of GISNext presentation work

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 )

CONVENTIONAL SUBSTATION

LIMITATION OF AISPhysical factorInfrastructure factorSocial & Environmental factorCommercial factor

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

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.

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.

GIS UNIQUE FEATURE1. Wide spread application of aluminium enclosure materials

for standardized component models for all voltage ranges2. The light weight enclosures have good conductivity, low

eddy-current losses and a high resistance to corrosion3. Easy handling, as well as reduced stresses on foundation

and support structure are additional features4. 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.

Components of GIS substation

1. Circuit breaker2. Disconnector switch3. Earthing switch4. Current transformer5. Voltage transformer6. Bus bar & connectors7. Power transformer8. Surge arrester9. Cable termination10. SF6 / air or SF6 / oil

bushing

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.

DISADVANTAGE OF GISSwitching 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.

NEXT PRESENTATION WORK Type of GIS sub-stationConstruction of low & medium voltage GIS sub-

stationConstruction of high voltage GIS sub-stationMaintenance of GIS sub-stationGIS approach in the GRID Visit of 400/220KV GIS substation located at DASTAN

, bardoli ,

REFERENCE M.Bilal Latif “ Comparison of GIS substation over

conventional substation “ , IEEE http://

www.pserc.wisc.edu/documents/publications/papers/2001_general_publications/indicator.pdf

Thank you