[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

*To*: tesla-at-pupman-dot-com*Subject*: RE: What size PFC ...*From*: "John H. Couture" <couturejh-at-worldnet.att-dot-net> (by way of Terry Fritz <twftesla-at-uswest-dot-net>)*Date*: Wed, 06 Sep 2000 07:48:36 -0600*Delivered-To*: fixup-tesla-at-pupman-dot-com-at-fixme

Terry - Note that the equation you are using is correct for PFC only when the reactive volt amps (VAR) is used. It is a coincidence that with your problem the reactive volt amps (991) and the watts (900) are very close. It is obvious if the power factor was 80% instead of 67.2% you would need less than the 182.7 uf capacitance to correct the power factor to 100%. Your test amps would then be 9.38 amps instead of 11.16 amps. You can find the lower capacitance by using the K factor (multiplier) I showed in 1996. K = sin(arc cos(Power factor)) K = sin(arc cos(.8)) = 0.6 Without the capacitor the volt amps would be VA = 900/.8 = 1125 The reactive volt amps would be VAR = 1125 * .6 =675 The necessary PFC capacitor would then be C = 675/(2 x pi x F x Vi^2) C = 675/(6.283 x 60 x 120^2) = 124.3 uf This is less than the 182.7 uf because the power factor correction was only for 80%. As you can see if the 900 was used instead of the 675 the cap would be too large and would cause the power factor to be leading. Think of a right angle triangle. The base is 900 watts. The hypotenuse is 1125 and the vertical is 675 VAR. The power factor angle is Angle = arc cos(900/1125) = 36.87 degrees The power factor is Power factor = cos(36.87) = 80% Are there any other coilers who can verify the above? What would be the PFC capacitor if Terry found the "no cap" test was 13 amps instead of 11.16 amps? John Couture ------------------------- -----Original Message----- From: Tesla list [mailto:tesla-at-pupman-dot-com] Sent: Monday, September 04, 2000 12:30 PM To: tesla-at-pupman-dot-com Subject: RE: What size PFC ... Original poster: Terry Fritz <twftesla-at-uswest-dot-net> Hi John, Ok, we seem to be saying the same thing some how ;-)) You last equation seems oddly familiar ;-)) ">The PFC capacitance = 991.8/(6.283 * 60 * 120^2) = 182.7 uf" Much like Cpfc = Vo x Io / (2 x pi x F x Vi^2) ;-)) The difference is that I assume "Vo x Io" Is the "VARS" to be corrected. Since MicroSim found the more accurate data to get the real number 991.8 the true capacitance of 182.7 can be determined. However, suppose we do not have MicroSim or $2000 worth of test equipment... How can we determine the VARs? I think the point is, if you don't know the VARs, estimate it as "Vo x Io" and you will be close enough... An estimate, of course, but the basic idea is to find a capcitance value easily with the data at hand. Cheers, Terry At 11:15 PM 9/3/00 -0700, you wrote: > >The problem you show is different from the one I showed. The problem I >solved was for a 50% to 90% PF correction. Your problem is for a 100% >correction and a different no cap power factor. I will use your amperes. > >The 11.16 amps at 120 volts = 1339.2 VA >The 7.5 amps at 120 volts = 900 VA >The power factor is 900/1339.2 = .672 = 67.2% power factor >The power factor angle is arc cos(.672) = 47.78 degrees >The VARs to correct to 100% = 900 * tan(47.78) = 991.8 >The PFC capacitance = 991.8/(6.283 * 60 * 120^2) = 182.7 uf > >You would need 182.7 uf to correct your NST to 100% power factor. >Actually your NST is operating at 1339.2 Var without a cap. However, the 900 >VA is only a guess for the 100% power factor operation because of other >unknowns. You can confirm this only by test with a 182.7 uf cap. Even this >cap might give a leading power factor. > >As you can see this problem is complicated and can be done in several ways. >Try this on MicroSim. You should get the same answer. > >John Couture > >------------------------------ > > >-----Original Message----- >From: Terry Fritz [mailto:twftesla-at-uswest-dot-net] >Sent: Sunday, September 03, 2000 2:57 PM >To: John H. Couture >Subject: RE: What size PFC ... > > >Hi John, > >At 12:42 PM 9/2/00 -0700, you wrote: >> >>Terry - >> >>The rearranged equation is still incorrect when used with active volt amps. >>The equation is correct only when used with reactive volt amps. To convert >>active to reactive amps you need to use complex numbers or trig functions. >I >>prefer to use trig functions as I show in my post to the Tesla List 7-14-96 >>"PFC for Neons". Can it be that long ago? >> >>Note that using your "close enough" equation will always give you a leading >>power factor which is worst that a lagging power factor. It would be >>interesting to see what a model by microSim would show. >> >>To properly meter the TC load you need at least 4 meters, volts, amps, >>watts, power factor. The power factor meter is required to tell you if the >>load is leading or lagging. A VAR meter would help and save you having to >do >>the necessary calculations. >> >>Bart I am glad to hear that you are researching the problem. As Terry >>pointed out there may be other issues and your work may shed more light on >>the subject. >> >>John Couture >> >>------------------------------ >> > >I pulled up your old post: >============================================== >PFC for Neons > >· To: Tesla List >· Subject: PFC for Neons >· From: "John H. Couture" >· Date: Sun, 14 Jul 1996 17:55:23 GMT > >Uncorrected neon transformers are usually 50% power factor. To correct them >for 90% power factor add a capacitor calculated as follows: > > For 120 volts c uf = .079 V A > For 240 volts c uf = .020 V A > V = neon secondary volts A = neon secondary amps > >The factors K1 = sin(arccos(LPF)-sin(arccos(HPF)) > K1 = .43 for 50% to 90% power factor > >For 120 volts K2 = (.43 x 10^6)/(6.283 F V) F = 60 Hz > K2 = (.43 x 10^6)/(377 x 120^2) = .079 >For 240 volts K2 = .0198 or .02 > >Example: Neon 15000 volts 60 ma 120 volts 60 Hz > > C = .079 x 15000 x .06 = 71.1 uf > >sniped efficiency text... >====================================== > > > > So your saying I should have a 71.1 uF cap instead of my present 200uF on >my 15/60 coil... > >Let's look at the RMS current draw of my 15/60 coil with various PFC caps >using MicroSim: > >Cap size AC line current Notes >0uF 11.16 ARMS No PFC cap >71.1uF 9.19 ARMS John's equation >165.8uF 7.75 Arms "Terry's" equation >200uF 7.72 ARMS The "real" best PFC cap size > >Cheers, > > Terry >

- Prev by Date:
**Re: FIRST LIGHT** - Next by Date:
**potential sync. motor** - Prev by thread:
**RE: What size PFC ...** - Next by thread:
**Unused primary turns, Was Re: Re:Big Primaries, Small Caps** - Index(es):