What's the system total power factor? 1

[skyline1977]

Hi,
I am trying to solve a power factor question but I ended up with a different answer.
The question is as shown below:

My Answer is:

However, the correct answer is C. That is the p.f. =0.857.

My question is where is my mistake?

Thanks.

 

[waross]

S_t(KVA)=10(KW) + 40/.8(KVA) = 60 KVA WRONG
KW and KVA are directed quantities and may not be added arithmetically.
Two other issues:
1. This should be in the Student Engineer General Discussion Forum.
This thread will soon disappear.
2. We don't do homework. I have shown you where your mistake is. From there it is up to you to work out the correct answer.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[LionelHutz]

VA of the resistor and VA of the other load would appear to be able to add since both are VA. But they can't because each VA is a vector going in a different direction.

I hate angle calculations when doing PF calculations. I always use PF = W/VA and pythagorean theorem.

 

[waross]

I hate angle calculations when doing PF calculations. I always use PF = W/VA and pythagorean theorem.

I feel the same way, Lionel.
At the Watts, add the VARs and use Pythagoras' theorem for the VA and then do PF.

Bill
--------------------
"Why not the best?"
Jimmy Carter