Overvoltage on the power supply to compressor motors

[Mirek2010]

Hope you may help me to understand how detrimental to compressor motor would be if it operated at voltages exceeding the manufacturer's specified 400V by 12%? so 448V.
I have vendor engineers saying since it exceeds 10% they cannot safely run the plant and of course the voltage monitoring relay trips when such occurrence happens (relay pod setting is 10% with range till 22%). The voltage is normally 425V as observed on the bus bar tap off unit, with transformer giving out max of 433V.

I am being challeneged to adjust transformer tappings and reduce the voltage at source.

Please advise how do you think I should deal with such issues,
Thank you very much

 

[Asymptotic]

I'm not quite following.

400V - compressor manufacturer specification
425V - nominal voltage observed at bus
433V - maximum voltage observed at bus
448V - ?

Do any other loads on that transformer require operation at the higher voltage?
If not, then changing the tap setting is a reasonable option.

Another option is to size and install a buck-boost transformer at the compressor wired for "buck" operation.
5% tap would reduce 425V to about 404V, and 448V to about 426V.

 

[Mirek2010]

Hello Asymptotic,
433V was what the transformer name plate stated as max output, I am new to the building, as part of the FM team; however the Schneider's load monitoring system indicates that the transformer gives out 446V on all three phases. Then the bus bar tap off unit on 9th floor is showing 446-8V and then on Level 16 are the chillers fed from L9.
Chiller commissioning eng reported (without measuring anything) that the voltage monitoring relay on the chiller package tripped and he left stating the overvoltage is exceeding manufacturer's limits and compressor cannot be run safely.
There is as well as I understand the issue that the transformers' output is excessive and non complying with current regs re supplied voltage ranges.
Not sure if we should instruct the maintenance team to step down the transformer output on tappings or not. No other plant in the building is suffering from the overvoltage issues.

Should we adjust the output from TX? or is there any other way to limit the voltage to the chillers on L16 (addition to existing building systems).

Thank you,

 

[anorlunda]

Before installing new equipment, ask your power company to check the voltage where your company connects. It may be too high there. If so, it is the power company's responsibility to adjust it.

 

[Asymptotic]

Hello Asymptotic,
433V was what the transformer name plate stated as max output, I am new to the building, as part of the FM team; however the Schneider's load monitoring system indicates that the transformer gives out 446V on all three phases. Then the bus bar tap off unit on 9th floor is showing 446-8V and then on Level 16 are the chillers fed from L9.
Chiller commissioning eng reported (without measuring anything) that the voltage monitoring relay on the chiller package tripped and he left stating the overvoltage is exceeding manufacturer's limits and compressor cannot be run safely.
There is as well as I understand the issue that the transformers' output is excessive and non complying with current regs re supplied voltage ranges.
Not sure if we should instruct the maintenance team to step down the transformer output on tappings or not. No other plant in the building is suffering from the overvoltage issues.

Should we adjust the output from TX? or is there any other way to limit the voltage to the chillers on L16 (addition to existing building systems).

Thank you,

Can you photograph and post a picture of the transformer nameplate? Different manufacturers do it different ways, but this 433 volt 'max voltage' specification sounds like it may be secondary voltage when the transformer tap changer is maxed out (and primary voltage is at nameplate specification).

No other plant in the building is suffering from the overvoltage issues.

What voltages are measured at those chillers? Most of my experience is with Trane, and their chillers have brought out and displayed internally-sensed line voltage data for maybe the last 20 years. I'd expect modern units regardless of manufacturer all do the same.

What controls the compressor motor? Is it a wye-delta circuit using electomechanical contactors, or is it based on some sort of electronic soft-starter or variable speed inverter drive?

Should we adjust the output from TX?

Only if you are in Texas :)
I've never seen 'TX' used as an abbreviation for it, but from context I'm guessing you mean 'transformer'.

You'll have to make that decision.

@anorlunda makes an excellent point in post #4, and one that didn't occur to me as it was never an issue with our local power company. Start there.

I can say that applying 446V to a 400V machine is inadvisable, and (so long as primary voltage is within spec) changing transformer tap selection is the usual way of dealing with this type of overvoltage situation. Just be sure the transformer primary is de-energized before switching the tap changer. Most aren't built to accommodate 'hot' operation, and would suffer catastrophic failure.

 

[Mirek2010]

Thank you all very much, I will confirm primary side voltage to start with.
By the way, the compressor motors have soft start modules only, no frequency inverters, I guess it was value engineering at first sight. And yest TX was to mean a transformer.
Thanks again, will update you if indeed we went down the road of changing tappings.