Power factor change with frequency -What Relation?

[gauthamtechie]

240V,50 Hz electrical appliance is rated at 2KW and has a lagging power factor of0.7.

What is the appliance's power factor when it is used on a 60Hz supply?

what is the supply voltage required to maintain the appliance at its rated power when operated off a 60Hz supply?

 

[alec_t]

Are these homework questions?

 

[gauthamtechie]

Are these homework questions?

These are not my homework questions but this one came up in search results when I looked for Power factor and frequency relation. The answer to this will clarify a lot of concepts about the same.,

 

[alec_t]

Hint: You can get the answers by drawing a vector diagram of the real and imaginary components of the power. That should clarify the concepts (just giving you the answers wouldn't ).

 

[gauthamtechie]

ok, I am getting the impedance to be 28.8+j28.2. So with the new frequency, I go about calculating the new X value. That is 60/50 times j28.2 = j 33.8. With this I calculate using vectors the power factor to be 0.63. That's working out. And With the new power factor, the new VA and new VAR is also found...
But here's my confusion: There's the formula R=V^2/P, so i apply X=V^2/Q (reactive power); I already know my new Q, through the new power factor..Now I try to check my answer : Q=V^2/X, but that's counter-productive! because With my higher Q, I need a higher X but this is formula Q= V^2/X gets me wrong.. R/Z and P/S are the same ratio right??

 

[alec_t]

Have you allowed for S being greater at 60Hz because you then have X=j33.8?

 

[gauthamtechie]

Have you allowed for S being greater at 60Hz because you then have X=j33.8?

Yes, I calculated S to by simply dividing the P value of 2000w by the new power factor I calculated earlier (0.63) and arrived at a greater S.