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P.F measurement for V.S.D


Karthik

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Hello,

we have a 11kV feeder connected to a Phase shift trafo, which is connected to a frequency converter, which is again connected to a 3 phase Induction motor.

If there were a p.f meter at the 11 kV feeder, would it measure the correct p.f.

I want to argue the case that there would be no necessity of p.f meter, since the measuremnt would be inaccurate(?).

How would u go about measuring the p.f in this case.

Please Help;p;

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Hello Karthik

 

Power factor meters generally measure displacement power factor only. They achieve this by measuring the angle between the current and the voltage.

The power factor of the input to an inverter or VSD is harmonic related, not displacement. To measure this, you need to measure the KVA and the KW and divide ther KW by the KVA.

I would agree with you that fitting a pf meter on the feeder to the VSD would be a waste of time and money. Even if you show that the pf is less than 1, there is nothing that can be easily done about this. You can not correct it with capacitors.

 

Best regards,

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