On no load Power Factor

Let we have one distribution board

Having two motors each one is 10 kw so total load on is =20KW
Let say having KVR=10KVAR

incoming breaker is 40A


Out going let say i have three beakers
20A for one motor
20A for second motor
20A for capacitor bank

Now let suppose
i switch on main breaker and capacitor bank breaker and switch off load breakers i mean motors breaker then what will be the power factor on power factor meter??????

I would assume that without the motors in the circuit the power factor would leading - what number it would be depends on the capacitors and other factors. In an ideal world the power factor would be zero and leading. Real power should be Zero or close to it - provided no other load is present and the power meter is after the main breaker. Remember capacitive reactance will draw current and the power drawn is measured in VARS. Power factor is the ratio of real power (watts) to apparent power (VA).

Dear sir i am dam sure about it... power factor meter is after the main breaker and there is no load except the two motors... and capacitors are not directly connected with the systems they are through magnetic contactors and will only be operate when there is any KVAR in the system in order to compensate it...

kindly help to to know what will be the power factor

with no loads on the system except the control power - which should be minimal then power factor should be very close to 1. Exception if you have a large control transformer, then I would expect something lower - like .07(70%) -0.8 (80)

dear sir can you please tell me how it would be close to 1???


while i studied power factor=kw/kva so if kw=0 then how p.f will be close to one????

It can be close to one because in a small control transformer the resistance to reactance ratio is much higher than in a power transformer. Remember that in a real transformer there is resistance. Large wire has small resistance and small wire has large resistance and compared to the reactance of the transformer winding. Therefore with the equivalent circuit looking more resistive the power factor climbs closer to one than if the reactance to resistance ratio was higher.

Yes Power factor = KW / KVA but remember if there is current draw KW and KVA are not zero. If there is no current the PF meter can read anything because the needle just stays where it is when it was turned off because it is off

sir what do you mean by ''small control transformer'' i am talking about a distribution transformer which is 11kv/415 100Kva and 50 HZ...

second thing you mean large wire has small resistance large in term of area????

Your motor starters have small transformers - those are what I was thinking about.
Is your power meter before or after the POWER transformer???

If the power meter is before the transformer then you are also monitoring the power losses in the transformer along with the motors. If so then the unloaded power factor is based on the characteristics of the transformer.

The name plate of the transformer would have the characteristic impedance needed to calculate the unloaded power factor. But an easy method would be to measure the unloaded power (watts) and determine the apparent power KVA = 1.732 * Vline * I line then PF=Watts/ KVA

Dear sir i have one distribution board rating 415 v after distribution transformer which is directly supply power to the two number of motors there is only three beakers in the Distribution board two for motors and one for capacitor bank and my control power to the power factor regulator which is in capacitor bank panel is getting supply after main breaker to the power factor regulator. now please help me if i shut down two load beakers i mean motors then what will be the power factor on power factor regulator???

Now you are saying that the capacitors are still energized. So again the power factor will be leading and at this point it ought to be close to zero as all the power being generated capacitve vars. If the Power meter is is the only thing connected to the distribtuon board and the capacitors are not on then the meter should probably read one but I suspect it will be randomas there is no current for the meter to monitor so it just hangs around the last reading before the power was removed from the board.

Dear sir i am confused now i have two things in my mind
1- if there is no current then angle between voltage and current is zero mean pi is zero and cos(0)=1 so my power factor will be one...
but on the other hand
power factor= KW/KVA so it Kw=0 then power factor will be zero please guide me which one is ok on no load condition when capacitors are not energized