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Phase angle distortion

Phase angle distortion

Phase angle distortion

(OP)
DO I have to worry about midline voltage regulators causing voltage or angle distortion on 3 phase loads when connected wye grounded on distribution circuits?

RE: Phase angle distortion

Yes.
When three single phase regulators are used they will also cause line to line voltage unbalance. If the loads from line to neutral are unbalanced, causing a neutral current and a neutral voltage drop, the regulators will correct the line to neutral voltages at the expense of phase angles and line to line voltages.

Bill
--------------------
"Why not the best?"
Jimmy Carter

RE: Phase angle distortion

(OP)
Is it less noticeable if all 3 regulators are set not to go beyond the tap of another?

RE: Phase angle distortion

Hello MBrooke,

Most of the single-phase regulators I've seen are configured to operate independently; I've been told it's done this way because the feeder loadings can be quite unbalanced, and slaving such regulators together would be counterproductive...which means any three-phase load connected downstream of these devices may sometimes end up operating on an ugly voltage profile.

A three-phase mid-feeder regulator on the other hand can be configured to either regulate from one phase alone or to a median voltage level derived from a composite / blended value from all three phases. This approach does not typically cause the same issues for three-phase loads, although the single-phase connected customers might squawk more.

CR

RE: Phase angle distortion

I see these single phase regulator banks on long rural circuits. The loads are predominantly single phase distribution transformers feeding a mix of residential and farm loads. It is almost impossible to achieve balanced loading and unbalanced loading causes neutral currents. These currents cause an IR voltage drop in the neutral. This shifts the neutral point of the vector diagram. The vector of the heavily loaded phase will also be disproportionately shortened. The shift of the neutral causes phase angle errors. Now the voltage of the most heavily loaded phase is increased more than the other phases. You end up with the correct voltage from line to neutral on all three phases, but phase angle errors and unequal phase to phase voltages. This is of no concern to the single phase customers who are in the majority. Three phase motors will act as induction generators as well as motors and will attempt to correct the phase angles and the phase to phase voltages.
The voltages and phase angles may be greatly corrected by the installation of a wye:delta transformer bank with the primary neutral connected but I don't advise such an installation. It has its own issues.
In the event of a phase loss, the bank will back feed into the lost phase and pick up and supply the load on that phase. The bank will probably be overloaded badly.
In the event of a ground fault on one phase the bank will back feed the fault and its fuses will shortly clear.
I suggest recommending that three phase customers be advised to install over sized motors and the smallest transformer bank possible be used to feed three phase loads, even if it is subject to moderate overloads.

Bill
--------------------
"Why not the best?"
Jimmy Carter

RE: Phase angle distortion

(OP)
@Waross Thanks for the info! smile Its what I was looking for.

If 3 phase customers are fed via a delta wye rather than a wye wye transformer, would this help or have any advantages? Should delta connected connected regulators be considered or would they be of greater disadvantage? Voltage issues are of a concern for the 3 phase customers much more than single phase customers. Its commercial and industrial who are the most likely to be inconvenienced by under voltage or phase angle shifts. Currently a large customer is about to be put online, and I am debating between a wye grounded wye grounded bank or a delta wye bank to feed them.

RE: Phase angle distortion

(OP)
Also forgot to thank crshears as well! Thanks smile

RE: Phase angle distortion

Single phase transformers banks tend to be line to neutral voltage. It takes less hardware to connect them than a line to line transformer. Three phase banks generally use what's in stock and so you get wye:wye. Three phase transformers are often delta:wye.
If the majority of your load is industrial then you may not have much unbalance and will be able to gang the regulators.
I'll have to think about the delta primary vs the wye primary for awhile. I can't give you a quick answer.

Bill
--------------------
"Why not the best?"
Jimmy Carter

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