Transformers and elevation

[raider1]

I was asked a very interesting question at a class I was teaching on transformers.

"Does elevation above sea level need to be taken into account when sizing transformers?"

The only thing I could think of was that the air was thinner at higher elevations and ventilation might be affected by this.

I check some installation instructions for a couple of transformers and have not seen anything in regards to this.

Does anyone have any information regarding this?

Thanks,

Chris

 

[jghrist]

Standard service conditions for transformers include altitude not exceeding 3300 ft. The altitude affects the insulation, not the kVA rating, however. There are dielectric strength corretion factors for higher altitudes. See ANSI/IEEE C57.12

 

[barclayd]

For Dry-Type Transformers, most manufacturers recommend derating the KVA by 0.3% for every 330 feet above 3300 feet.
I think this is an IEEE, ANSI/NEMA standard.
The air is less dense at higher altitudes, and can not remove heat as efficiently as it can at lower altitudes.
It's not really a big issue unless you're in Katmandu.
db

 

[raider1]

Thank you both for the information.

The person that asked the question works in a town thats elevation is approximatly 9000 feet. Using the information that you gave me they would only need to derate the loading by approximatly 5%.

Thanks again,

Chris

 

[broadgage]

The thinner air at altitude has two adverse effects on transformers.

Firstly, as posted above, the thinner air is less effective at removing heat, and this generally requires a slightly reduced loading.
In the absence of detailed instruction from the manufacturer, the guide above seems reasonable.
Most high altitude locations are colder than most places at sea level, and this might counteract the reduced cooling capacity of the thinner air.

The other problem is that the thinner air is a less effective insulator, increasing the risk of flashover/insulation failure.
Dry type transformers, and the bushings of any transformer, would in theory appear to be at risk, and might require a different design with greater clearances. In practice though I have not heard that it is a problem.

(O/T, but in the days of vaccuum tube radio equipment, such equipment had increased clearences around HV components if intended for use in aircraft)

 

[Rockyd]

Raider,


How did Snowbird and Alta decide how to size their electrical equipment in the town? Someone has to know, or be building on empirical.

 

[raider1]

Raider,


How did Snowbird and Alta decide how to size their electrical equipment in the town? Someone has to know, or be building on empirical.

This question came from a person in Park City. They are building an 11 story hotel and asked about derating the transformers.

Chris