Answer / pritish

in case of no load test, the supply voltage is rated but the current drawn by the induction motor is very less; no load current, which produces only the core loss of the stator and some mechanical loss.  in no load condition, the angle between V and I are high as a factor the pf will be less. hence to calculate the pf accurately LPF wattmeter is used. during loaded condition current increases and angle decreases hence pf increases.

any more clarification regarding this should be sent to pritish.nath@gmail.com

Answer / saurabh wani

We use LPF only for no load test because at no load only reactive component of current flows in any machine. In 3 phase induction motor magnitude of reactive component current is more because of air gap. So power factor under no load operation is low and we use LPF wattmeter . If we use here UPF then it will give reading at time of starting only and after 3to 4 sec pointer will stable at zero no deflection.

Answer / k.prakashchandra

In both the cases the pf is very low

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