How does an undervoltage affect 1Ph equipment

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rob1kva

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This past Friday nite my facility {retirement community} experienced a brown-out,needless to say we lost several peices of 3Ph eqiupment.The apartment buildings use 208v 1Ph to feed each apartments heat pump & air handler.We were required to shut down power to each apartments HVAC equipment to prevent damage to it.The lead HVAC mechanic does not belive in this theory {as I & the facilities director do}.He adamantly belives a low voltage condition will have no bearing on the life of a 1PH motor. Thanks in advance for your viewpionts
 

George Stolz

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Off the hip, I would think undervoltage would cause excessive heat build-up in the windings, wouldn't it?

How much undervoltage constitutes a "brownout"?
 
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oliver100

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During the summer NYC Con Edison regularly lowers the voltage with 3-5% to shed down the demand. Brown-out IMO should be in excess of 10-15%.

Any voltage reduction affects equally both single phase and three phase motors. The current rises and the RI^2 in the widings produces untolerable heat.
The currecnt rise depends of the voltage reduction and the mechanical load.

In ideal world some kind of Overcurrent/Overload Protection should have saved the equipment under the browun-out conditions.
 

charlie b

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Re: How does an undervoltage affect 1Ph equipment

rob1kva said:
He adamantly belives a low voltage condition will have no bearing on the life of a 1PH motor.
Motors tend to be "constant power" devices," and I think that single phase motors are no exceptions. I hope that someone else will either confirm or refute this statement.

Power is voltage times current. If voltage goes down, and if power stays constant, it means that current must increase. If voltage is too low, the current will get high enough to damage the motor.
 

charlie b

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Minuteman said:
Brownout has the same effect as voltage drop.
True. I treat the two as being two ways of saying almost the same thing. "Brown out" means that the voltage is lower than normal, to a degree that the lights dim noticeably. You can get there by having too much voltage drop along the wires. Or you can get there if the utility equipment fails in such a way as to provide lower voltage.
 
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