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,
--
J. B. Wood e-mail: arl snipped-for-privacy@hotmail.com

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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.
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On 3/10/20 10:42 AM, snipped-for-privacy@decadence.org wrote:

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,
--
J. B. Wood e-mail: arl snipped-for-privacy@hotmail.com

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???? 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.
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On 3/11/20 9:02 AM, Dimitris Tzortzakakis wrote:

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,
--
J. B. Wood e-mail: arl snipped-for-privacy@hotmail.com

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???? 11/3/2020 3:33 ?.?., ? 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).
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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.
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???? 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)
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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.
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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.
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On 3/12/20 9:59 AM, Michael Moroney wrote:

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.
--
Grant. . . .
unix || die
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???? 12/3/2020 8:30 ?.?., ? Grant Taylor ??????:


Yes, but who would climb on the pole to clamp a live 20 kV circuit?(unless he's got suicidal tendencies!)
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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.
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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.
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