When should a capacitor be sized to overcompensate a motor?

The recommended practice is to size the capacitor to around 80% of the reactive power demand at no load condition. Overcompensation of motors is often is not intentional and usually happens when motors are relocated to a new starter location or when swapping motors with different magnetizing characteristics.

What happens if a power factor correction capacitor is too high?

If the power factor correction capacitor is sized higher than the recommended value, then there a possibility that the motor magnetizing inductance and the power factor capacitors form a resonant circuit as the motor is switched off and is slowing down.

What is a power factor correction capacitor?

Power factor correction (PFC) capacitors produce the necessary leading reactive power to compen-sate the lagging reactive power. They should be capable of withstanding high inrush currents caused by switching operations (> 100 x IR).

What happens if a capacitor bank size is higher than a motor?

The capacitor-B current is greater than the motor magnetizing current. It can also be observed that a stable operating point (at 130% voltage in this example) is possible with the higher capacitor bank size. This operating point can occur when the motor is switched off and the motor speed is slowing down.

What is a fixed capacitor?

Fixed capacitors means that you may have to pick certain discrete values so you can decide to leave the load as somewhat inductive (undercompensated) or capacitive (overcompensated). If the load inductance varies during operation then again you may have to pick some intermediate value and the cancellation may be fairly imperfect.

What is the difference between over compensating and under compensating?

C loads decreases Zc (f) with rising f. Thus over compensating is over.oading the voltage source with a reactive load that raises the VAR power above real power with more current and more conduction losses than under-compensating at the same <1 p.f. ZL (50Hz) is not always same as load R , but is for this simple example.