Dear All,

This is my first post in the forum.

I have a motor for a blower fan, at running conditon the load current will be constant. Our system has a bulk power factor capacitor controlled by a power factor controller with 6 steps set to maintain an overall power factor of 95%. The location of the motor under consideration is quite far from the bulk power factor correction. I want to add a static power factor capacitor to my motor taking consideration the standard installation of capacitor correction. I want to correct my PF on the motor to 0.95PF. I will set the static Power Factor capacitor to engage faster than the bulk capacitor, is my idea acceptable.. please advice...

Thanks

Hello dennis3834

Yes, you can apply static correction to the motor. This will reduce current in the cable supplying the motor and may save a few watts for you.
If you are using static correction, you should limit the correction to 80% of the magnetizing current of the motor. This may or may not take the motor to 0.95pf. You must be careful not to correct too much as you can cause resonance problems. You are best to use a separate contactor to control the capacitors and use the starter controls to control this contactor.
If you are using a soft starter, use the bypass control to control the capacitor contactor so that the capacitors are connected once the voltage reaches full voltage.DO NOT connect the capacitors to the output of the soft starter!

Best regards,

Marke,

Thanks for the early response. Just to clarify, what will happen if i set the correction to 80% of the magnetising current of the motor and my bulk capacitor is set to cater a 95% power factor of the system, when both the static capacitor and the bulk correction capacitor is connected, do the power factor of the motor get affected by the bulk capacitor??

Hello Dennis

The power factor of the motor does not actually change at all, it is the power factor as seen from the supply which is the combination of motor and capacitors.

If you apply static correction to the motor, you will reduce the amount of bulk correction required.
If the bulk correction is automatic, it will adjust to keep the power factor within limits.

Best regards,

Mark,

thanks for the enlightment

Can you provide me the equation how to compute the capacitor required when the magnetizing current is 100amp and motor voltage is 400volts, 3 phase. Lets assume that the capacitive current would be 80% of the magnetizing current..

Have a look at Power Factor Calculations

Best regards,