power factor, inductive or capacitive??
power factor, inductive or capacitive??
(OP)
Hello
Why is a capacitive power factor undesirable?
I am currently working on a project and have managed to build a controller that corrects the power factor by generating a greater or lesser inductance on the system.
The system load is inductive but a fixed capacitor is used to make the load capacive and hence a variable inductor can be used to correct the power factor and it bring it to unity.
However I have been adviced to not bring it to unity but rather make it a little inductive. Becuase I should not risk a capacitive power factor.
Why is this the case?
Surely the same amount of current would be drawn from a load with the same power factor no matter if it is inductive or capacitive.. the only thing I can assume is that it has something to do with the fact that the current is leading the voltage when the PF is capacitive..
Can anyone enlighten me please...
Michael
Why is a capacitive power factor undesirable?
I am currently working on a project and have managed to build a controller that corrects the power factor by generating a greater or lesser inductance on the system.
The system load is inductive but a fixed capacitor is used to make the load capacive and hence a variable inductor can be used to correct the power factor and it bring it to unity.
However I have been adviced to not bring it to unity but rather make it a little inductive. Becuase I should not risk a capacitive power factor.
Why is this the case?
Surely the same amount of current would be drawn from a load with the same power factor no matter if it is inductive or capacitive.. the only thing I can assume is that it has something to do with the fact that the current is leading the voltage when the PF is capacitive..
Can anyone enlighten me please...
Michael






RE: power factor, inductive or capacitive??
i feel capacitive (leading) p.f will increase the output voltage at no load conditions which can be undesirable. u can recall Ferraty Effect in long transmission lines!!! because of their high capacitive values, output voltage shoots up at no loads which is undesirable.
when u talk of unity p.f there is no capacitive or inducive current flowing but in case your power factor correction system fails u may get high voltages because of leading p.f
RE: power factor, inductive or capacitive??
RE: power factor, inductive or capacitive??
By the way, why wouldn't you use a PF corrector with several low rated capacitors?
RE: power factor, inductive or capacitive??
So in most cases, we correct motor power factor such that the power factor at no load is just slightly lagging (0.98 or 0.97).
There is nothing inherently wrong with a leading power factor. You do have to watch out for high voltage conditions.
For the average utility customer, there is no benefit for operating at a leading power factor. In fact, under the new Bonneville Power Administration power factor penalty, you would be charged for leading power factor greater than 0.97, same as for lagging power factor.
RE: power factor, inductive or capacitive??
so it would seem that the biggest problem with a leading power factor is with electric motors. Or no load scenarios where a higher than expected voltage may occur considering that the voltage leads the current when the load is capacitive.
RE: power factor, inductive or capacitive??
RE: power factor, inductive or capacitive??
the approximate voltage rise at little or no load on the transformer with the capacitor connected would be as follows:
V rise = (KVAR * transformer %Z)/KVA of Transformer
Generally the voltage rise will be very small. Typically, if the calculation results in a 2-3% voltage rise, this is acceptable.
In regards to connection to the motor terminals, if the capacitor is oversized for the motor and it is connected at the motor terminals, I suggest to simply place a contactor in series with the capacitor so that the contactor will de-energize when the motor is stopped and will isolate the capacitor from the motor when in the off position.
RE: power factor, inductive or capacitive??
On the other hand, operating at PF=100% or near 100% there are a risk of resonant circuit creating overvoltages level that could damage the equipment insulation.
RE: power factor, inductive or capacitive??