Hi everyone .

To answer a question u need to understand it 100%...and that's what I'm going for .
I have a question about transformers...and it says:

The transformer secondary is connected to an electrical load , and it delivers its rated current at rated voltage and 0.85 pf lagging , find primary voltage ?

Can any one explain please : what does rated means , and is the power of the load is only due to secondary voltage and as nothing to do with the primary voltage ...and also the underlined part please ??

 

Can you please post the complete question and not just part of the question?

 

transformers 'transform' the voltage, current from one side to the other.

The power input = the power output theoretically.
Real world we know there are losses.
The 'power factor' is one of the corrections we apply to determine real world conditions
In the real world power in is ALWAYS more than power out.

Rated levels are given in a piece of equipments specs.

12 V 25 VA transformer(watts)
operates from 110 VAC

So you plug the numerical values found there into your calculations.

 

the question says that a 50 KVA , 2400/240 V, 60 Hz before mentioning any load .....Where does the 50 KVA come from ?

 

And did you miss the lecture that explained VA ?

Also known as VARs or Volt-amps reactive.

 

VA is volt-amps which is just the product of the volts and amps that the transformer is rated for. It is the phasor (phase vector) sum of the real and reactive power.

 

And did you miss the lecture that explained VA ?

Also known as VARs or Volt-amps reactive.

Volt-amps (VA) are not the same as volt-amps reactive (VAR).

 

Volt-amps (VA) are not the same as volt-amps reactive (VAR). {

You are quite right I misspoke in haste.

The proper story is explained here very well.

http://en.wikipedia.org/wiki/AC_power

 

Hello,

Perhaps the following page will help you a bit:
http://mysite.du.edu/~jcalvert/tech/transfor.htm

This is one of the links from the EDUCYPEDIA page on transformers:
http://educypedia.karadimov.info/electronics/electricitytransformers.htm

Bertus

 

Thanks guts......some of u miss understood me ...my question that there is no load.....where does the 50 KVA come from?
also..does the KVA = Vp,rated*Ip,rated=Vs,rated*Is,rated

 

Thanks guts......some of u miss understood me ...my question that there is no load.....where does the 50 KVA come from?
also..does the KVA = Vp,rated*Ip,rated=Vs,rated*Is,rated

The 50 KVA is the transformer maximum rating. That actual KVA depends upon the load. If there is no load the KVA is essentially zero.

 

OK ...But is it true that KVA = (Vp*Ip)both rated=(Vs*Is)both rated

 

OK ...But is it true that KVA = (Vp*Ip)both rated=(Vs*Is)both rated

Neglecting the small transformer losses, yes.