Power factor question

[DT1878]

ahhhh brilliant pushrod thats much clearer thanks a lot.

 

[JUD]

This is what you need to know.( It is very similar to the impedance triangle)

VA² = W² + VAr²
so in your example W² = VA² - VAr²
W = sq rt ( VA² - VAr² )
W = sq rt (50² - 30²)
W = 40 k watts

Power factor = real power ÷ apparent power
= 40 ÷ 50
= 0.8

hope that is a bit clearer - if it isn't at least try and remember that since the hypotenuse part of the triangle is the longest that means that the VA figure will be bigger than the W.
So if the question says the apparent power is 15 VA what is the true power in watts you at least know you are looking for a smaller answer

Glad to see you're making use of the ² & ÷ symbols, but what about poor old √

Really good stuff by the way

 

[pushrod]

Glad to see you're making use of the ² & ÷ symbols, but what about poor old √

Really good stuff by the way

Cheers, tried it but couldn't get the 251 code to work on my ' pooter

 

[JUD]

You get it using HTML code &# 8730; (without space)

 

[pushrod]

You get it using HTML code &# 8730; (without space)

i couldn't find it in the full list of html codes , but now i see you actually included that one in your actual post - DOH!

 

[JUD]

i couldn't find it in the full list of html codes , but now i see you actually included that one in your actual post - DOH!

Yer just had a look at list. Not as big as I thought it was. I must have got them from a different website. If I find it again I'll post it up.

 

[JUD]

This is what you need to know.( It is very similar to the impedance triangle)

VA² = W² + VAr²
so in your example W² = VA² - VAr²
W = sq rt ( VA² - VAr² )
W = sq rt (50² - 30²)
W = 40 k watts

Power factor = real power ÷ apparent power
= 40 ÷ 50
= 0.8

hope that is a bit clearer - if it isn't at least try and remember that since the hypotenuse part of the triangle is the longest that means that the VA figure will be bigger than the W.
So if the question says the apparent power is 15 VA what is the true power in watts you at least know you are looking for a smaller answer

Would I be right in saying that

VA = √(W² + VAr²)
W = √(VA² - VAr²)
VAr = √(VA² - W²)

Seems to work with the 30, 40, 50 from this thread.

 

[pushrod]

Would I be right in saying that

VA = √(W² + VAr²)
W = √(VA² - VAr²)
VAr = √(VA² - W²)

Seems to work with the 30, 40, 50 from this thread.

Certainly would

 

[JUD]

Here's another good way of remembering it (for me anyway )

S = Apparent Power (VA), P = True Power (W), Q = Reactive Power (VAr)

S = √(P² + Q²)
P = √(S² - Q²)
Q = √(S² - P²)

PF (Power Factor) = P ÷ S

 

[DT1878]

thanks for the explanations