# Powerfactor problem in power transformer at no load in night

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• #10863
surinder
Participant

dear sir,

I am facing problem in a 400 kva 11000/440v transformer. Its powerfactor drops to 0.2 in night at noload.

I have connected 150 KVAR capacitor bank in night by a timer. But it improved to 0.6 only. In day time powerfactor is ok around 0.95. So pl. suggest what i do now.

Thanks

Surinder

#13117
Spir Georges GHALI
Participant

@surinder said:
dear sir,

I am facing problem in a 400 kva 11000/440v transformer. Its powerfactor drops to 0.2 in night at noload.

I have connected 150 KVAR capacitor bank in night by a timer. But it improved to 0.6 only. In day time powerfactor is ok around 0.95. So pl. suggest what i do now.

Thanks

Surinder

Dear ;

As we know all, the Power Factor of any transformer without loads is a small or too small value depending on Transformer’s No-load current named ” iο ” as it’s almost Inductive Current, therefore, to improve the Power Factor for any transformer we use the following equation to calculate the Capacitors’ power should be installed :

Qο = Sn x iο

where :

• Qο : the Capacitors’ Power ” kVAR “
• Sn : the Transformer’s Power ” kVA “
• iο = the Transformer’s No-load Current ” % “

Refer to your information, I think that the value of No-load Current of this transformer is big enough, and may be you need more than ” 150 kVAR “, but if not, it will better to check if the installed Capacitors work correctly and the supply voltage is connected to all steps.

#13307
Anonymous
Guest

but no load current is so small.. as we know pf is inversely proportional to current then it should have been high when no load current is small right??

#13350
Spir Georges GHALI
Participant

@guest said:
but no load current is so small.. as we know pf is inversely proportional to current then it should have been high when no load current is small right??

Dear ;

As we know all, the ” no-load current ” of a transformer is the ” magnetizing current “, that means the current of the transformer’s impedance ” Reactance + Resistance “, and as the biggest one of those is the reactance, so the PF of no-load current is small or too small.

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