Large Motor on Low load ?
Large Motor on Low load ?
(OP)
I have a 11000 volt 2540kW motor driving a compressor, the load on the compressor is decreasing over time and as a result it is being suggested that the compressor be "re-wheeled". Following this work the compressor load will be in the region of 700kW.
Are there any significant issues with running an exisitng 2540kW motor at or around 700kW?
regards
Crispin
Are there any significant issues with running an exisitng 2540kW motor at or around 700kW?
regards
Crispin





RE: Large Motor on Low load ?
InWatts1=700/.91 = 769.2 kW (a new 700 kW motor)
InWatts2=700/.8 =875 kW (your actual motor)
You will have a difference of 875-769.2 =105.8 kW
Depending on daily hours of work you will compare the investment of a new motor or the extra cost due to low efficiency.
If this is a Synchronous motor you could match the excitation close to unit power factor and the difference in power consumption will be reduced.
As a benefit, the life of the 2540 kW motor under 700 kW load will be extended due to very low operating temperature.
RE: Large Motor on Low load ?
"Venditori de oleum-vipera non vigere excordis populi"
RE: Large Motor on Low load ?
But there is another issue - the circuit breaker switching the motor off is likely to undergo greater stress (switching over voltage) with low load / low power factor motor compared to the one loaded to near-full rating. This is significant especially if the motor duty involves frequent start / stops and there is a possibility of switching over voltages causing failure of motor / circuit breaker.
RE: Large Motor on Low load ?
A modest second air compressor could also be used to keep the system pressurized when not doing production so as to avoid the heavy load that occurs when repressurizing the system. In 1 plant where I worked they had 6 or 7 air compressors so that they had backups and so that they could match the number or running air compressors to actual production needs.
Mike Cole, mc5w@earthlink.net
RE: Large Motor on Low load ?