Important Notes on Gas Insulated Substation ( 12Marks)
Q.) What is Gas insulated substation (GIS)
Ans: A gas insulated substation (GIS) is a high voltage substation in which the major conducting structures are contained within a sealed environment with a dielectric gas known as SF6, or sulfur hexafluoride gas as the insulating medium. OR
A gas insulated substation (GIS) is a high voltage substation in which various equipment like Circuit Breakers, Bus bars, Isolators, Load break switches, Current transformers, Voltage transformers, Earthing switches, etc. are housed in separate metal-enclosed modules filled with SF6 gas.
Q.) State need of GIS OR State disadvantages of Air insulated substation (AIS)
Ans: In conventional substation i.e. AIS has following disadvanteges:-
1. large space is required for clearance.
2. More wastage of space in AIS.
3. Difficult to find sufficient large space/ Land nearer to load center.
4. As AIS is at open space, Fault occurrence due to atmospheric condition, so maintenance is needed at regular interval
5. Large planning & execution time required
6. Insulation deterioration (failure) with ambient conditions in case of AIS.
To overcome the disadvantages of AIS system GIS system is needed.
Q.) State advantages & disadvantages of Gas insulated substation (GIS)
Ans: Advantages:-
1. Safe
2. Reliable
3. Space saving
4. Maintenance Free
5. Low weight
6. Easy Assembled
Disadvantages:-
1. High initial cost
2. Transportation of SF6 gas at site may be difficult
3. Need to maintain cleanliness
4. Outage period is more if fault occurs.
Q.) State any 4 properties of SF6 gas as an electrical insulating medium.
Ans:
1. Dielectric strength of SF6 at atmospheric pressure is 2.35 times that of air.
2. Dielectric strength of SF6 gas is more than dielectric oil.
3. Breakdown voltage of SF6 is increases with pressure.
4. Non-Inflammable
5. Electronegative gas
6. Does not react with structural material upto 500 degree celcius.
7. Colourless
8. Odorless
9. Nontoxic
Q.) List the application of GIS
Ans:
1. Industrial complex 2. Large towns
3. Underground application 4.Sea shores, Lakes
5. Desserts 6. HVDC terminal station
7. Compensating substation
Q.) List the Essential Equipment’s/ components of GIS
Ans: 1. Busbar 2. Connectors/DIsconnectors 3. Circuit Breaker
4. Current transformer 5.Voltage transformer 6. Earth switch
8. Control panel
Q.) What is Partial Discharge? State causes of Partial Discharge(PD)
Ans: Partial Discharge - A flashover of part of the insulation system due to a localized electric field greater than the dielectric withstand capability of that part where the overall insulation system remains capable of withstanding the applied electrical field. OR
Gas insulated switchgear (GIS) is filled with SF6 gas as insulation, partial discharge can be caused by floating particles, loose or broken components such as a piece of metal shaving that gets too close to a conductor.
Partial discharge can occur in different type of medium whether it be in a solid, gas or liquid. In addition, partial discharge voltage varies depending on the insulation material.
Generally, partial discharge can occur at voltages higher than 5kV.
Causes of Partial discharge Factors include:
- Defects introduced during installation (poor installation)
- Design defects
- Voids in solid insulation maybe caused during manufacture (manufacturing defects)
- Particle contamination (lack of cleaning)
- Poor substation environments
- Over stressed in service
- Damages due improper services (Mechanical damage)
- Age (electrical stress wears out insulation)
Q.) Draw Single Line diagram of 132 kV GIS substation
Ans:(Home Work)
Q.) Prepare Trouble shooting chart for GIS
Ans: (Home Work)