MV GIS

[sky72]

I received a statement from supplier as below:

"GIS MV switchgear shall be used instead of AIS MV switchgear for substation located altitude >1500m above sea level. The voltage correction factor is about 0.7..at this altitude"

Could you please advise this statement is based on what standard or guideline?

Is it necessary to use GIS for this particular case?

Thanks

 

[cuky2000]

Q1: Is it necessary to use GIS for this particular case?
No, Gas insulated Switchgear (GIS) not necessarily need to be used. Air Insulated Switchgear (AIS) may be used at high altitude satisfactorily.

Only the components exposed to the air will be affected by high altitude such as bushings, busses, cooling systems, etc. The altitude may not affect equipment such as oil transformers winding, circuit breakers vacuum or SF6 bottles, etc.
_{Some components such as surge arrester are rated to operate up to 1800 m without derating. Instrument transformers and particularly VT, should be checked with the manufacturer for high altitude operation.}

Q2: "GIS MV switchgear shall be used instead of AIS MV switchgear for substation located altitude >1500m above sea level. The voltage correction factor is about 0.7..at this altitude"
70% derating factor (30% loss) appear to be to be too pessimistic

Q3: Could you please advise this statement is based on what standard or guideline?

For example, ANSI/IEEE C37-30 at 1500 meters above sea level provide the following derating factors:

a- Dielectric Strength (BIL): 95%. The 5% losses may be acceptable if appropriate surge arrester is selected.
b- Current rating: 99%. The loss of 1% may not be significant in most cases. This may be compensated if the ambient temperature is less than 40 oC. The current derating does not apply to interrupting current
c- Temperature rating: 98%. The 2% loss indicates that most equipment may operate at full capacity current rating if the operating temperature is around 39oC. Do to the fat that most sites at 1500 m altitude are cooler than 40oC this may not be an issue.

_{Other Reference Standards: ANSI/IEEE C37-20.2, C37-30, C37-40, C57-13,IEEE Std 1312,IEC 60076-2,DIN EN 60071-1 (VDE 0111Part 1)}