Power factor confusion

[gazdkw82]

I'm really struggling to get my head around power factor. I understand there is true power (kW)/apparent power (kva) and reactive power (kvar) however I'm struggling with knowing how to work out say KW if I have KVA/KVAr and vice versa etc

I'm currently doing a lot of mock exams (202) preparing for upcoming test which is at the end of October. A lot of the questions are based around the following for example

Transformer takes a load of 1500kva with an input power of 1430kw, what is the power factor. Is it true power over apparent power?

1430/1500??

 

[Leesparkykent]

KW=KVAxPF

1430/1500=0.953 PF

1500x0.953= 1429.5

KVA=KW/PF

 

[gazdkw82]

Abit confused. Would that mean



Pf= KW/KVA

So

1430(kW) devide by 1500 (kva) = pf 0.953

1430/1500=0.953??

How do you know if it's leading or lagging?

 

[telectrix]

DEPENDS ON THE LOAD. IF INDUCTIVE, IT'S LAGGING. IF IT'S CAPACITATIVE (RARE ), IT'S LEADING

 

[Bobster]

 

[gazdkw82]

That's brilliant!

 

[telectrix]

View attachment 33575

should have tilted the glass and poured more slowly. it's only yanks that like a pint of shaving foam.

 

[hightower]

Only southern pansies see the froth as waste. Anywhere past the Watford Gap and that froth is "usable"

 

[Karin]

It's only yanks that like a pint of shaving foam.

..and northerner's..

in fact, gaz, if you know how much creamed beer you have, and the extent of the 'northern tax' on it, you can calculate total disappointment with a pythagorean power triangle..

 

[ElectroChem]

1430/1500=0.953??

How do you know if it's leading or lagging?

You can't tell if a load is leading or lagging just from the KVA/KW/pf numbers. As the other poster has said it will depend on the nature of the load, with lagging loads being much more common. A specific power factor meter will tell you if your pf is leading or lagging too.

 

[D00DY_T00DY]

DEPENDS ON THE LOAD. IF INDUCTIVE, IT'S LAGGING. IF IT'S CAPACITATIVE (RARE ), IT'S LEADING

i now remember it is the capacitor charges and the fires it back into the circuit making it leading.
of course making inductive loads lagging
Not sure if that's any help for OP

 

[gazdkw82]

The questions Iv come across don't mention capacitive or inductive, it's very much like the OP type question

 

[Lucien Nunes]

Apparent power is a scalar value - it has only magnitude, not sign - so it doesn't indicate whether the pf is leading or lagging, that has to be stated separately. And of course if there's no indication of the phase angle in the question, you can't give one in the answer. In the real world we could probably assume it to be lagging, as most mixed loads are, but in the world of the exam question you shouldn't need to make such an assumption. For many purposes there's no point in knowing anyway - you can calculate circuit ratings and cable sizes and whatever by knowing the magnitudes of currents, without needing to know their phase angle from the voltage. If instead the question had given you a complex impedance or the voltage and current in mod-arg form, then you would have the information to calculate whether the load was leading or lagging.

The beer glass analogy is fun but it's not an accurate representation - you can't add kW to kVAR arithmetically to get kVA as the arrows suggest. They are in quadrature so the froth should be measured sideways and the vector sum calculated to give the complex power, of which apparent power is the modulus.

 

[telectrix]

Apparent power is a scalar value - it has only magnitude, not sign - so it doesn't indicate whether the pf is leading or lagging, that has to be stated separately. And of course if there's no indication of the phase angle in the question, you can't give one in the answer. In the real world we could probably assume it to be lagging, as most mixed loads are, but in the world of the exam question you shouldn't need to make such an assumption. For many purposes there's no point in knowing anyway - you can calculate circuit ratings and cable sizes and whatever by knowing the magnitudes of currents, without needing to know their phase angle from the voltage. If instead the question had given you a complex impedance or the voltage and current in mod-arg form, then you would have the information to calculate whether the load was leading or lagging.

The beer glass analogy is fun but it's not an accurate representation - you can't add kW to kVAR arithmetically to get kVA as the arrows suggest. They are in quadrature so the froth should be measured sideways and the vector sum calculated to give the complex power, of which apparent power is the modulus.

but what if we put a cadbury'sflake in that froth. would that count as power factor correction?