Power Factor Correction

Hello, all. I'm an EE by trade but have never worked with, nor
designed, AC power distribution systems. On overhead medium-voltage
(say up to 69 kV) lines one often sees banks of subject capacitors on
the utility pole. While I certainly understand why they are used, I've
never understood how engineers decide exactly where to place them along
the distribution line. Is this done by first making a power factor
measurement at the candidate utility pole location or by just
guestimating based upon expected downstream inductively reactive loads?
Thanks for your reply and comment. Sincerely,
Reply to
J.B. Wood
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"J.B. Wood" wrote in news:r459rt$nba$ snipped-for-privacy@gioia.aioe.org:
It is done by knowing how many busuness and industrial zoned areas are nearby and what their consumption is comprised of.
A place with a lot of boiling water heaters is a resistive load (as I am sure you know), but a place full of high HP electric motors and other inductive loads 'raises eybrows'. So I am guessing here when I say that I feel reasonbly sure that they map it out by usage, constantly updated, and mount banks on poles as needed and sized as needed too. So small banks in some places on the fringes of an industrial area and huge banks within.
But I could be wrong, of course. They could simply mount huge banks at certain points and rest assured they have a lead on the current waveform. Guess number two.
Don't worry though, we'll al probably die before we find out.
Reply to
DecadentLinuxUserNumeroUno
Hello, and thanks for replying. Those are certainly reasonable guesses. Textbooks are great on theory but often come up short on application. My take on this would be since the electric utility would know the distribution main and branch MV line interconnections from a substation and the reactive volt-amperes at the load (industrial plant), they could just go back up from the aggregated loads to some convenient point on the distribution line, and knowing the transmission line characteristics (resistive loss per mile, etc) the amount of parallel capacitance required can be determined. Sincerely,
Reply to
J.B. Wood
???? 11/3/2020 1:46 ?.?., ? J.B. Wood ??????:
as I am sure you know, measuring the PF on MV lines would need to interrupt the circuit and mount potential and current transformers to feed the measuring equipment. On my visit here in a HV/MV substation (150/20 kV now) they had mounted LOTS of capacitors on the low side to compensate for the excess usage of air conditioning in the summer. I think that, unfortunately, the large usage of AC during the summer contributes A LOT to climate change, because of very high reactive power demand and the thermal load of the external units that emit heat to the environment. I personally use normal fans for cooling.
Reply to
Dimitris Tzortzakakis
Hello, and that would certainly be the way via direct measurement, but hardly practical if you're dealing with something like a 34.5/19.9 kV 4-wire distribution system, as is common in my residential environs. I'm unsure if MV PF measurement equipment even exists. Sincerely,
Reply to
J.B. Wood
Certainly as big consumers are billed with real energy, also kWh, and reactive energy (kVArh). There is a formula to calculate the PF. So if the utility knows that downstream there are two factories, with, say a PF of .60, will know what capacitors to use. There is also a penalty if their PF is too boad (too much reactive). economical penalty-so sometimes it is worth to do PF compensation on site. with capacitors goes without saying.the compensation is being done on the low side (230/400 Volt in Europe).
Reply to
Dimitris Tzortzakakis
"J.B. Wood" wrote in news:r4apb8$1st5$ snipped-for-privacy@gioia.aioe.org:
Somehow, they can tell at the generation point.
Not practical to examine in the field as you say.
I have seen sub stations with three sets of three phase feeds and three sets of three huge banks of caps and 9 circuit interruptor swing arms too.
Reply to
DecadentLinuxUserNumeroUno
They have clamp on current measuring devices these days. When clamped onto a wire, the wire itself acts as the primary of a current transformer.
Reply to
Michael Moroney
That actually makes sense. The wire the clamp goes around is effectively a single turn on the transformer and the clamp itself is multiple turns.
Reply to
Grant Taylor
Yes, but who would climb on the pole to clamp a live 20 kV circuit?(unless he's got suicidal tendencies!)
Reply to
Dimitris Tzortzakakis
???? 12/3/2020 1:48 ?.?., ? snipped-for-privacy@decadence.org ??????:
of course you mean disconnect switches (usually combined with earthing switches and oil circuit breakers)
Reply to
Dimitris Tzortzakakis
The linemen who are paid to do that, with a "hotstick", or it's part of a modified hotstick.
Nearly always they access the lines with a "cherry picker" bucket truck, probably with an insulated bucket.
Another thing I've seen are these small devices that clamp onto distribution lines that can apparently be read remotely. I first saw an ad for the things and since then I've seen them clamped onto distribution lines, one on each phase.
Reply to
Michael Moroney
Dimitris Tzortzakakis wrote in news:r4nr6r$o3e$ snipped-for-privacy@dont-email.me:
Detach the ground link to the ground rod at the base of the pole. Give it a couple 6 inch loops. Re-attach to gnd rod.
Then place your 'secondary' nearby and collect stray ground currents coming through. Charge up your... toothbrush... cell phone... Yeah... that's the ticket. Like waiting to detect neutrinos...
Works good though... Especially when lightning strikes.
Reply to
DecadentLinuxUserNumeroUno
Dimitris Tzortzakakis wrote in news:r4nr8h$o3e$ snipped-for-privacy@dont-email.me:
Little 8 inch long arms I would call disconnects. These are a few feet long each, IIRC. All inside the substation's containment plot. It is over by the grocery so if I go before I die, I'll takes a few snaps. It is a lot of converged feeds. Three sets of three from what I can recall seeing.
Reply to
DecadentLinuxUserNumeroUno
???? 19/3/2020 1:58 ?.?., ? snipped-for-privacy@decadence.org ??????:
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150 kV circuit breaker, upstream a disconnect switch. 4 150 kV lines, one directly from the new Atherinolakkos power station. when I took this photo we were all under the circuit breaker, which was live, goes without saying. we were told that if this circuit breaker trips, the result will be probably a blackout, long before a reclose. it supplies half of Iraklion with electricity.
Reply to
Dimitris Tzortzakakis
Dimitris Tzortzakakis wrote in news:r6afpe$v92$ snipped-for-privacy@dont-email.me:
Theses were not that big, and I have had the vid clip for years and another as well. :-)
Reply to
DecadentLinuxUserNumeroUno
Hello, everyone and if I may be permitted to revisit my question from a
while back for which there was only speculation in the responses: On
medium-voltage (say up to 69 kV) distribution lines, what tools do AC
power systems engineers use to establish/estimate the optimum location
for banks of shunt-connected capacitors? I'm thinking of software
programs but also how this might also have been accomplished perhaps via
handbook tables, nomographs or other means without the benefit of
computers. Sincerely,
Reply to
J.B. Wood
Still speculative, but I would assume the electrical company knows what equipment they have and how much reactive power it consumes, and would base it on that. Large customers likely have meters which measure reactive power and they would account for that. Otherwise they could measure how much the current lags the voltage at a point and compensate if needed.
(amusingly, I noticed a very old rural distribution circuit, delta connected single phase (so two conductors on pole) probably 4800 volts, which had what looked like a tiny capacitor. One small rectangular box with two leads. I didn't think they even bothered when the downstream load was a couple dozen houses/farms. It appeared the fuses/cutouts were disconnected so it was no longer in use)
Reply to
Michael Moroney
Thanks for taking the time to reply. I've got one of the "bible" EE handbooks, McGraw-Hill's "Standard Handbook for Electrical Engineers" that has extensive info on AC power distribution components (distribution transformers, oil/air circuit breakers, reclosers, cutouts, PF correction capacitors) but doesn't discuss methods for determining capacitor bank optimum location along a distribution line.
Also, my online searches revealed no equipment that can directly measure power factor or current lag at an arbitrary location along an MV distribution line. Would be kind of dangerous I would think. Sincerely,
Reply to
J.B. Wood
Doing a google for "waveform analyzer power factor" shows "power quality" test equipment on offer.
Dunno LV/MV though, but perhaps there is stuff that can be gleamed from reading their operations manuals?
Reply to
Adrian Caspersz

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