Powerfactor problem in power transformer at no load in night

@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.

@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.