Frequency change on an induction motor
Frequency change on an induction motor
(OP)
Can you please settle a professional dispute! A subcontractor is supplying a hydraulic powerpack driven by 3 x 3 phase 50Hz induction motors. We tested them at 50Hz and recorded current readings, my arguement is that this will reduce at a higher frequency. I base this on the inductive reactance increasing as the frequency increases. Rotor impedance will also increase, net result motor taking less current. Please advise if I am right or am I taking the client stand!





RE: Frequency change on an induction motor
RE: Frequency change on an induction motor
What is the motor nameplate voltage and frequency? What voltage did you apply for test? What voltage do you intend to apply at 60 Hz?
RE: Frequency change on an induction motor
If you kept the mechanical load constant, there are still two effects to consider: power factor and efficiency. I suspect power factor will be the bigger of the two. Looking at the equivalent circuit, it’s not clear which direction it would go. Increasing the series leakage reactance tends to reduce power factor while increase the parallel magnetizing reactance tends to increase power factor.
I seem to recall a figure showing possible effects of change in voltage and frequency for typical motor but I can’t find it.
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RE: Frequency change on an induction motor
Look at:
http://www.reliance.com/mtr/pwrspymn.htm
http://www.easa.com/mo/TN-pdfs/TN08-397.pdf
RE: Frequency change on an induction motor
If the hydraulic power pack motors drive direct coupled pumps, the mechanical power demand will increase due to the increased speed with the frequency increase.That will increase the current.
If the voltage is icreased to keep the motor strength ( V/HZ=400/50 = 480/60) and the load is regulated not to exceed the nominal motor HP load, the current will be reduced almost at inverse ratio to the voltage increase.
RE: Frequency change on an induction motor
RE: Frequency change on an induction motor