# Power factor correction..

Discussion in 'Math' started by bill4807, Nov 26, 2014.

1. ### bill4807 Thread Starter New Member

Nov 15, 2014
4
0
Hopefully someone with PFC knowledge can help me out here.
A formula of mine is not coinciding with A sizing Capacitor chart from a local distributer. And I am curious why?

This Formula:
C = KVAR / (2 * pie * F * V^2) Translation: 2 times 3.14 times frequency times voltage squared.

Assume KVAR= 10.188, F= 60, and V= 480.

The data sheet from a local distributor is saying a 10KVAR cap rating shoulds read/measure Min: 57uF--MAX: 66uF.

Can anyone clear this up for me?

2. ### bill4807 Thread Starter New Member

Nov 15, 2014
4
0
Rereading this I thought...Should I post this in the Electronics Forum? I know it is a simple math problem but getting to the answer may be more in the electronics field than math? I know I did not include many details about how I came up with the 10.188 but that should be irrelevant.

3. ### Ramussons Active Member

May 3, 2013
562
92
A fast mental workout says the manufacturer 1s correct.
Where did you get the formula from?

4. ### #12 Expert

Nov 30, 2010
16,685
7,323
I get 56.3 uf.

Look carefully: Is the sizing chart from the distributor or the manufacturer?
Motor quality has changed a lot in the last 20 years. A distributors chart might be way out of date.

5. ### t_n_k AAC Fanatic!

Mar 6, 2009
5,448
783
If the the 10 kvar is delivered by a single capacitor @ 480V working then the equivalent capacitance would be ~115uF.

6. ### #12 Expert

Nov 30, 2010
16,685
7,323
@t_n_k The title of the thread is about power factor correction for an inductive load, not total power delivered by a single capacitor...or am I missing something important?

Then I look at my math and see that I did not square the 480 volts.

Therefore, some doubt remains.
I hope we have been helpful in some way.

7. ### t_n_k AAC Fanatic!

Mar 6, 2009
5,448
783
The OP hasn't presented the question with great clarity.
Irrespective of that, a capacitor with a specific kvar "value" will have a capacitance value commensurate with the nominal kvar, operating voltage & frequency. What else could one conclude?

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8. ### #12 Expert

Nov 30, 2010
16,685
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Thanks. I was trying to draw a conclusion from the small scale work I do, and it doesn't stretch that far.

9. ### WBahn Moderator

Mar 31, 2012
18,087
4,917
I get that a single cap needs to be 117 uF to have that reactive power under those conditions (i.e., same as t_n_k). What conditions does the data sheet apply to? I could envision it being intended to size a set of caps in a three phase system, for instance.

10. ### bill4807 Thread Starter New Member

Nov 15, 2014
4
0
Thanks for the replies everybody!
I kept coming up with around 115 Micofarad also.
This is the manufacture datasheet.
It does specify 480V 60Hz 3 phase on the datasheet, so this is why then the formula I posted is for a single cap?
So how are they then coming up with the round abouts 56 Microfarads?
They must not be wired in parallel because i come up with 18 Microfarads?
They are wired in series parallel?

Or do you have to multiply the 480 x 1.73 before hand?

11. ### bill4807 Thread Starter New Member

Nov 15, 2014
4
0
Sorry did the parallel calculation wrong. I calculated it for series capacitance.

12. ### t_n_k AAC Fanatic!

Mar 6, 2009
5,448
783
Did you post a link to the data sheet?
Hard to comment unless one can view the manufacturer's information.
Even if the 10kvar is distributed across three phases the value of 56 uF remains a mystery.