calculating the capacity of "KVAR" rated pole-capacitors

[Opcom]

Here's a little spreadsheet will find out the capacitance of those large oil filled capacitors that are used in industry for power factor correction.

These caps turn up from time to time, but the nameplate generally shows only the AC voltage and the KVAR rating. The capacitance is a definite and accurate value but stamping it on the nameplate has little value for an electrical engineer who is concerned only with power factor.

This is a problem for potential surplus and ham radio buyers and sellers because the real worth of it is not known.

They are usually physically larger than the typical 'electronic' filters, but there is nothing wrong with a robustly made part designed to last 200,000 hours.

[AB2EZ]

The spreadsheet appears to be correct ... if you plug in KVAC and KVAR, it will correctly calculate Xc (ohms), and C (uF)... but the accompanying equation is wrong

The equation is kvar = 2pfc (kv)^2 x 1000, where c is in farads. The same error can also be seen in the 2nd set of equations on the other attachment, along with numerous other errors involving factors of 1000 or 1,000,000

Stu

[N4LTA]

Just found some 10 KVAR 500 volt AC caps in an older textile facility  and recommended that they be removed.

They are 10 KVAR at 500 volts  so the line current at 500 volts is  10KVAR/.5KV = 20 amperes

That would make the reactance at 60 Hz  = E/I  or  500/20 or    25 ohms reactive

That would be about 106 uF at 500 volts AC using the formula  Xc = 1/(2 x pi x F x C)

That is not something that is worth messing with as they are heavy and are wired as a three phase wye bank.


Pat
N4LTA

[Opcom]

I got rid of the document and changed the formula in the spreadsheet. I had a lot of trouble with the math for some reason, not so much making the spreadsheet do it but writing it so it made sense. Thanks for pointing it out so others are not confused.

As for 500V caps, OK well wait until some rated for a high voltage such as 4160V or more show up.

PFC capacitors are large and heavy, but if it is free or cheap and will fit in the bottom of a rack next to the power transformer, I can overlook that.

Those things are very heavy duty, so I accept the larger size. I turned down a single 200KVAR capacitor rated 4160VAC  once because I didn't know how to determine the capacity and neither did the person offering it. That was 30uF. I should have accepted it at the time. 30uF following a choke is very nice! It was about 18" tall, 14" long, and 4" thick.

[N4LTA]

That 30uF would have been a good one.  I usually don't see them above 500V and lots at 250 volts. I believe that you can use them at DC at 2.8 x the AC rating but a 1400 volt DC rating is still a little low. I am sure there are some rated at  630 volts as lots of textile mills in the South used a 600 volt three phase distribution system.
Those would be  getting in the useful range.  They were used in the spinning rooms where they had multiple  3 phase motors that were lightly loaded and had low power factors. They used a three phase bank of caps right off the distribution panel bus.

Good finds would be ones rated at 2.5 KV or 5 KV removed from the older 2400 volt and 4160 volt lines as they were upgraded.


Pat
N4LTA

[The Slab Bacon]

Capacitors of that size kinda fall into the "horseshoes and hand grenades" catagory anyway. If they are just sitting there unhooked to anything, why not just hit em with a digital LCR meter? ? ? ?   

They (the meters) have gotten so cheap it would be very foolish for anyone who is a builder not to have one. They nay not be the most accurate animal around but they will give you a real good idea what you are dealing with. When you get to stuff that big, any more accuracy is really not needed.