Too low power factor for a 3 phase induction motor

[AkaShri]

Hello,

I have recorded 3 phase current and 3 phase voltage waveforms for a small induction motor (3 hp) with Delta connection. Voltages (phase) were measured with respect to a common ground. Load on the motor is about 60-70%. However, calculated power factor (real power/apparent power) is quite low - 0.1, 0.2. This is because calculated real power (obtained by multiplication of voltage and current data followed by summation) is too low. Apparent power is obtained from rms values, hence, value is ok.

Can there be an issue like phase sequence (voltage and current channels) mismatch ?

 

[che12345]

Dear Mr. AkaShri (Mechanical)(OP)11 Apr 22 03:54
[highlight #1."...I have recorded 3 phase current and 3 phase voltage waveforms .... Voltages (phase) were measured with respect to a common ground. Load on the motor is about 60-70%. However, calculated power factor (real power/apparent power) is quite low - 0.1, 0.2. #1. This is because calculated real power (obtained by multiplication of voltage and current data followed by summation) is too low. ....#2. Can there be an issue like phase sequence (voltage and current channels) mismatch ?[/highlight]
#1. What do you mean by calculated real power (obtained by multiplication of voltage and current data followed by summation) ? The real power (kW) should be (voltage x current x power- factor x efficiency). For a small motor, the efficiency would be around say 0.9. The power-factor varies with the loading. May be as low as 0.4 at no load and increase to say 0.8 at full-load.
#2. I presumed you are taking the readings with say a basic simple voltmeter, amperemeter; NOT a kWmeter, power-factor meter. In this case, there is NO issue with (voltage and current channels) mismatch.
Che Kuan Yau (Singapore)

 

[AkaShri]

I have recorded current and voltage through data logger (sampling rate 18000 Hz).

 

[che12345]

Dear Mr. AkaShri (Mechanical)(OP)11 Apr 22 05:56
"....I have recorded current and voltage through data logger (sampling rate 18000 Hz)....".
In this case, there is NO issue with (voltage and current channels) mismatch.
Che Kuan Yau (Singapore)

 

[LittleInch]

Care to provide some actual data and calculations so we can see what is going on?

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[AkaShri]

Thank you Che and LittleInch for your comments.

 

[jraef]

If the motor is unloaded, a .2PF is not unheard of...


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