Has anyone heard of

[Inspectorcliff]

the derating of h.p. of an electric motor due to its location above sea level? I have seen the derating of efficiency on gas (combustible) engines. The efficiency change on pumps at 7000 ft versus, sea level. But this is my first, unless I have forgotten, on the change of efficiency of electric motors with a rise in altitude. We follow the equipment manufacturer's requirements for derating for elevation, such as on a 200 HP electric motor that has an auxiliary nameplate that derates the motor to 180 HP at 6500 feet elevation. The adjustable speed drive is likewise derated. So my question is, when sizing conductors, whether for the services entrance or the individual motor feeder, can I use the derated values for load calculations? I am asking this on behalf of a client. Thanks to all who participate.

 

[Sonny Boy]

Learn something every day.

Learn something every day.

Altitude. Standard motor ratings are based on operation at any altitude up to 3300 feet (1000 meters). High altitude derating is required above 3300 feet because of lower air density.

U.S. ELECTRICAL MOTORS
DIVISION OF EMERSON ELECTRIC CO.


ALTITUDE: The atmospheric altitude (height above sea level) at which the
motor will be operating; NEMA standards call for an altitude not
exceeding 1,000 meters (3,300 feet). As the altitude increases
above 1,000 meters (3,300 feet) and the air density decreases, the
air’s ability to cool the motor decreases. For higher altitudes, higher
grades of insulation or motor derating are required. DC motors
require special brushes for operation at high altitudes.

Rockwell Automation

 

[Lcdrwalker]

I have never heard of this either. Learned something new myself. IMHO I would say that as long as the motor has a plate with the derated HP, I would say that can be used to size the rest of the installation.

 

[Inspectorcliff]

It is odd, TMWOT, that it would have two ratings, A) 200 HP and B) 180 HP. I guess it shouldn't be, but now, would you size it at 125% of 200 HP or since we are at (whatever) 7,882 ft, shall we size it at 125% of 180 HP? Costs or just getrdun??150 HP at a 180 amps at 460v or 200 hp at a 240 amps.How much is wire again?? Thanks to all.

 

[petersonra]

the less dense air carries heat away less efficiently.

you still have to use the nameplate for your calcs.

 

[LarryFine]

As the altitude increases above 1,000 meters (3,300 feet) and the air density decreases, the air?s ability to cool the motor decreases.

As Johnny Carson used to say, "I did not know that!"

 

[cowboyjwc]

I just heard the same thing not to long ago, but I have no idea where it was. It may have been at a IAEI training on swimming pool.

I will say that I had never heard that either, but then again we're only 500' above sea level.