Help me understand 3Phase high-leg open delta voltages

[synchro]

...
Lineman that was just out here says it is bad programming in the smart capacitors they installed a month ago, so at least I guess we have something to go on.

Perhaps the capacitor values are causing a resonance at a harmonic frequency such as the 3rd, and that is accentuating this harmonic strongly.

 

[Tulsa Electrician]

Ok, two transformers, most likely same size. Is there only 2 lines on the primary. Open wye primary?

A good pic of pole helps. Hopefully the cap is you issue.

Thank you for your reply

 

[tortuga]

And it definitely is an open delta service according to the power company.

What kinds of load are you running? How much single phase L-N, single phase L-L and 3 phase? As others have asked are you the only customer on the transformer? I have 'fixed' voltage issues by having the POCO convert open delta to just a regular delta by adding another bank. In another recent thread we were discussing the effects of B-C connected L-L single phase loads on open delta system capacity.

 

[Tulsa Electrician]

See if this is what you have.
Pull pic from the Internet
Then we're all in the same page.

 

[GoldDigger]

The output of a rotary or other phase converter for generating 3-phase from single phase can produce a derived phase which is, in addition to having poor regulation, can have phase angle problems.
But I would not expect that from a true POCO 3-phase system, unless there is a tap setting inconsistency beween phases along the way. In a closed delta system that could potentially cause large enough circulating currents to force abnormal phase angles at the transformer secondary.

 

[jvanick]

What kinds of load are you running? How much single phase L-N, single phase L-L and 3 phase? As others have asked are you the only customer on the transformer? I have 'fixed' voltage issues by having the POCO convert open delta to just a regular delta by adding another bank. In another recent thread we were discussing the effects of B-C connected L-L single phase loads on open delta system capacity.

we are the only customer on the transformers.. they are right outside the building on a pad.

I can't confirm wiring as they're pad mount and obviously we're not gonna mess with the power company's gear.



Service: 400amp from power company
Voltage inbalance exists on the rails BEFORE the panels, and even exists when the entire building is disconnected.
the more that I learn about open delta, this seems correct tho?

as far as major loads:
qty 3 - 3 phase motor loads (5hp)
qty 2 printing presses which use 3phase frequency drives and servo amplifiers (servo amplifiers are what are faulting out from high voltage). Manufacturer says open delta is no problem with these as long as the voltages after the buck boost transformers are less than 232v. Breakered at 40a each
qty 2 intermittent 'flash cure dryers' - 3phase 11kw heater load when first warming up, then cycling for a few seconds at a time.
very little L-L single phase... nearly all the other equipment is L-N 120v connections
I've confirmed there's no High-Leg to Neutral single breakers installed.
I'd have to clamp the feeds to get exact amperages, I haven't done that in a long time, but power company said that they saw nothing for concern when they were looking at the amount of current coming into the building.

Again, the head scratcher thing here is that everything has been fine since 2019 when we moved in... this just started a month ago... so almost nearly has to be the power company.

Yesterday after the lineman tagged out the caps things seemed better...

Time will tell

 

[kwired]

we are the only customer on the transformers.. they are right outside the building on a pad.

I can't confirm wiring as they're pad mount and obviously we're not gonna mess with the power company's gear.



Service: 400amp from power company
Voltage inbalance exists on the rails BEFORE the panels, and even exists when the entire building is disconnected.
the more that I learn about open delta, this seems correct tho?

as far as major loads:
qty 3 - 3 phase motor loads (5hp)
qty 2 printing presses which use 3phase frequency drives and servo amplifiers (servo amplifiers are what are faulting out from high voltage). Manufacturer says open delta is no problem with these as long as the voltages after the buck boost transformers are less than 232v. Breakered at 40a each
qty 2 intermittent 'flash cure dryers' - 3phase 11kw heater load when first warming up, then cycling for a few seconds at a time.
very little L-L single phase... nearly all the other equipment is L-N 120v connections
I've confirmed there's no High-Leg to Neutral single breakers installed.
I'd have to clamp the feeds to get exact amperages, I haven't done that in a long time, but power company said that they saw nothing for concern when they were looking at the amount of current coming into the building.

Again, the head scratcher thing here is that everything has been fine since 2019 when we moved in... this just started a month ago... so almost nearly has to be the power company.

Yesterday after the lineman tagged out the caps things seemed better...

Time will tell

Voltages should be proportionally correct to one another when you have a no load condition. If not POCO has imbalanced primary voltage or even a primary neutral issue.

Was this transformer setup selected for your application or was it just what was existing for a former occupant that maybe had different load demands? Undersized transformer(s) can contribute to your problems, though as I said everything should measure correctly when there is no load.

Trying to fix this with buck -boost may not be very successful unless load and voltage measured stays pretty constant at all times.

If incoming voltage changes, output from the buck boost will change proportionally. So bringing it down only works at a certain load level and incoming voltage, change either of those factors and your voltage may still be undesirable.