Capacitor

[boby]

why should we connect capacitors at load end and not at source side. calculation of kvar to be connected to 1000hp squirrel cage motor to improve the pf from 0.7 to 0.9 and more.

[marke]

Hello boby

 

As power factor correction is usually added to reduce the power factor or maximum demand penalty, it does not usually matter whether it is connected at the motor or at the supply, provided that it is connected on the load side of the metering. If you connect it on the supply side of the metering, you will still reduce the supply current but you will not get a reduction in penalty.

 

Bulk correction is usually connected at the supply and is controlled by an automatic controller.

Static crrection is usually controlled by the starter, and so is connected either near the motor or the starter.

Static correction near the motor will reduce the current in the cables between the supply and the motor and the starter and this could reduce the voltage drop if it is significant.

 

Best regards,

[jraef]

Technically, it doesn't matter. Practically, it is better to connect the caps as close as possible to the load to maximize the benefit of reducing line losses in the motor leads, but this is just icing on the cake, not entirely necessary. In fact if you have a solid state soft starter, you CANNOT connect the capacitors on the load side at all.

 

When connecting on the supply side however, be careful to make sure the capacitors are only on-line at the same time as the motor, otherwise you will over correct your supply and that can lead to other problems.

 

If in the second part of your post you were asking for assistance in selecting capacitors for your motor example, read this page and download the Electrical Calculations software, it will do that for you.

 

http://www.lmphotonics.com/pwrfact.htm