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. This formula should come out with an answer in Micro Farads. 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?
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.
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 A distributors chart might be way out of date.
If the the 10 kvar is delivered by a single capacitor @ 480V working then the equivalent capacitance would be ~115uF.
@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.
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?
Thanks. I was trying to draw a conclusion from the small scale work I do, and it doesn't stretch that far.
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.
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?
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.