Power factor in different voltages

[asmani]

Hi all.

In the following circuit, z is an inductive load (I mean inductance + resistance).

Here is the table of cosφ measured by power factor meter in different voltages:

Why it's increasing? Isn't cosφ independent of the voltage of the autotransformer?

 

[Windadct]

The inductance of the AutoTrans is changing as you adjust the voltage - try the same test with purely resistive load.

 

[asmani]

Thanks Windadct.
Isn't power factor meter just measuring load voltage? If yes, how can inductance of the AutoTrans effect?
(For purely resistive load, the increase was lesser.)

 

[Windadct]

The PF meter is really measuring the Phase angle between the V and I - this relationship is affected by everything in the circuit - including the AutoTrans.

So if your load was a pure resistor - the phase shift would be due to the Inductance of the Autotrans - at the different adjustment points. Techincally the total impedance of the source feeding the AutoTrans will have an effect as well - but not as pronounced as the data you are showing, unless you have a "weak" source like a isolation transformer - etc.

 

[asmani]

What do you mean by V?
How the inductance of AutoTrans changes, increase or decrease?
Thanks again

 

[Windadct]

V voltage and I current - the basic PF meter really measures the phase angle between the two - not a real power factor - but close enough for a lab exercise.

As for will the Inductance increase or decrease - I do not know - but looking at your data - what is your guess?