3 phase motor question.

Kalyke

Is there a spec for a voltage difference between phases in a 3 phase motor while running? Thanks.

2011

Kalyke wrote: »

Is there a spec for a voltage difference between phases in a 3 phase motor while running? Thanks.

Can you rephrase your question, I don't understand what you are asking?

Kalyke

2011 wrote: »

Can you rephrase your question, I don't understand what you are asking?

Sorry, I kinda rushed that one all right. We have a 3 phase water pump for a small scheme. For the last year or so it is "tripping" out , up to a dozen times a day. The people who maintain the equipment insist 1 of the phases is going out of balance by 12vac, causing the pump to go. The ESB are monitoring it at the moment , but off the record have confided in me their opinion that the quality of supply is within spec. I was just wondering is there a tolerance of the voltage between phases or does it have to be in perfect balance? Thanks again.

Bruthal

The same voltage would be expected as the supply voltage, 400v between phases here, minus some slight voltage drop caused by the motor load.

Kalyke

Bruthal wrote: »

The same voltage would be expected as the supply voltage, 400v between phases here, minus some slight voltage drop caused by the motor load.

Would a 12 volt drop on 1 of the phases be enough? When the ESB put on a monitor what do they measure?

Bruthal

Kalyke wrote: »

Sorry, I kinda rushed that one all right. We have a 3 phase water pump for a small scheme. For the last year or so it is "tripping" out , up to a dozen times a day. The people who maintain the equipment insist 1 of the phases is going out of balance by 12vac, causing the pump to go. The ESB are monitoring it at the moment , but off the record have confided in me their opinion that the quality of supply is within spec. I was just wondering is there a tolerance of the voltage between phases or does it have to be in perfect balance? Thanks again.

It wouldnt have to be a perfectly balanced voltage between phases, but it would usually be within a couple of volts.

12v seems a little high, I wonder where they measured that difference, phase to phase or phase to neutral. But even at that, I wouldnt have thought the 12v would be enough to cause problems for a motor.

What is actually tripping? Overload?

Kalyke

Bruthal wrote: »

It wouldnt have to be a perfectly balanced voltage between phases, but it would usually be within a couple of volts.

12v seems a little high, I wonder where they measured that difference, phase to phase or phase to neutral. But even at that, I wouldnt have thought the 12v would be enough to cause problems for a motor.

What is actually tripping? Overload?

At a guess I would say phase to neutral but cant be sure. He told me he noticed a drop of 12 volts just as the motor tripped. I say tripped , a control panel shuts the motor down, it is reset by turning a rotary switch, wait until all power drains from the display, rotary switch back on again and a reset button needs to be pressed. I think I did see message on the display of U-Volts.... Under voltage?

Bruthal

Kalyke wrote: »

At a guess I would say phase to neutral but cant be sure. He told me he noticed a drop of 12 volts just as the motor tripped. I say tripped , a control panel shuts the motor down, it is reset by turning a rotary switch, wait until all power drains from the display, rotary switch back on again and a reset button needs to be pressed. I think I did see message on the display of U-Volts.... Under voltage?

The esb monitor will record real time voltages over a duration, that may tell what is happening, there could be a problem with a phase or something like that.

2011

One phase could simply be loaded more than the others resulting in a larger volt drop than the other phases.

This may be due to a separate installation.

ESB Networks delivers electricity in a voltage range of 207 Volts to 253 Volts. This is in accordance with European Standard EN50160

See link:

http://www.eurelectric.org/Download/Download.aspx?DocumentID=11743

2011

I do not believe that this is causing the motor to trip.
Can you find out exactly what is tripping ?
I am guessing that it is an overload.

grousedogtom

Kalyke wrote: »

At a guess I would say phase to neutral but cant be sure. He told me he noticed a drop of 12 volts just as the motor tripped. I say tripped , a control panel shuts the motor down, it is reset by turning a rotary switch, wait until all power drains from the display, rotary switch back on again and a reset button needs to be pressed. I think I did see message on the display of U-Volts.... Under voltage?

U volts under voltage,
This trip error message in my experience is a displayed message on a variable
speeddrive which is controlling the pump the drive make is invertek and the rotary switch is actually the isolator built into the drive. Does this make sense or look familiar to your setup?

http://www.invertekdrives.com/

grousedogtom

I'm not sure for certain but can find out if the vsd is detecting an imbalance of 12 volts between phases I'd imagine it would trip itself out to protect the pumps motor.

Kalyke

The ESB say the monitoring concludes that the quality of the supply is within spec. The maintenance company are adamant it is not. Can I PM anyone with the results to comment?

2011

Kalyke wrote: »

The ESB say the monitoring concludes that the quality of the supply is within spec. The maintenance company are adamant it is not. Can I PM anyone with the results to comment?

Go for it.

2011

Kalyke wrote: »

The ESB say the monitoring concludes that the quality of the supply is within spec. The maintenance company are adamant it is not. Can I PM anyone with the results to comment?

Remember if a supply from the ESB fully meets the requirements of EN50160 it does not necessarily follow that there will be no issue somewhere else in an installation (such as at a control panel or on motor terminals). A number of issues within a customer's installation could cause this.

If ESB Networks are saying that there is no issue thier end I would be suprised if they are wrong.

Bruthal

2011 wrote: »

If ESB Networks are saying that there is no issue thier end I would be suprised if they are wrong.

Yes id say so, more because the recording test is such a simple one than anything else.

adrian92

As far as I know there is a sandard of 2% on voltage unbalance.

. It may be of use to find out what protective device is involved that switches off the motor.. Is it a voltage unbalance relay?perhaps the relay setting is oversensitive?

Perhaps it is a thermal overload device?

Apart from voltage unbalance causing motor problems there is also (what is called zero sequence shift) a voltage rise in neutral with respect to earth.

So, in summary I suggest you check out the protective relay- what function and what settings on it.

Furthermore may of use to measure
The 3 line voltages (ie phase to phase)
The 3 phase voltages (ie each phase-neutral)
The neutral to earth voltage.

Do this with motor in off and on situation.


This seems a lot but may be useful too if this tripping out is a recent occurreance and age of installation.

2011

adrian92 wrote: »

As far as I know there is a sandard of 2% on voltage unbalance.

The supply tollerances that ESB Networks have to meet are EN50160 (see link in post #9).

It may be of use to find out what protective device is involved that switches off the motor.. Is it a voltage unbalance relay?perhaps the relay setting is oversensitive?

I have never seen a device such as that installed on a motor supply.
If a phase voltage is significantly lower than the other two the motor will "single phase", stall and/or trip without any such device installed.

Apart from voltage unbalance causing motor problems there is also (what is called zero sequence shift) a voltage rise in neutral with respect to earth.

Generally 3 phase motors do not have a neutral wired to them as it serves no purpose.

3 phase motors are very simple devices (even more simple than a single phase motor). This should not be hard to diagnose with a good multimeter.

Bruthal

2011 wrote: »

I can't see the advantage of installing a device such as that.
If a phase voltage is too low the motor will "single phase", stall and/ortrip without any such device installed.

Its not about advantage of installing that device. It might be in the setup the OP has, or setup in a VSD.

adrian92

Perhaps there is a protective device.

Over insurance from the supplier.

Basically I am just saying do not blame the supply, rather look to see if there is a real problem - or the protective device the culprit.

Actual measurements , as I suggest, may help in identify

2011

Bruthal wrote: »

Its not about advantage of installing that device. It might be in the setup the OP has, or setup in a VSD.

There could be all sorts of perameters programmed into a VSD.
An "voltage unbalance relay" sounds a bit different to me, as I say I have never seen one fitted to a motor circuit.

adrian92

Kalyke wrote: »

Is there a spec for a voltage difference between phases in a 3 phase motor while running? Thanks.

Kalkye,

To answer your specific question, the answer is yes.

My understanding is the spec. Is 2% on the fundamental frequently of 50 Hz.
(Higher for other harmonic frequencies, such as would occur with use of vsd)

Others may be able to quote the exact EN. Or IEC. Standard Number.

adrian92

Late here. Perhaps I am confusing Total Harmonic Distortion. with unbalance. Apologies if I have given erroneous suggestions. Good night.

2011

Kalyke wrote: »

The people who maintain the equipment insist 1 of the phases is going out of balance by 12vac, causing the pump to go.

This suggests that one phase is 12V lower than the other two (with respect to earth I guess). I do not see anything in the O'Ps posts to suggest that there is an issue with harmonics.

Harmonic distortion is a very different kettle of fish. It means that instead of the wave form being a nice and smooth sine wave it is distorted. In a modern plant this is generally caused by nonlinear loads such as UPS systems and VSDs. This can cause all sorts of issues such as high neutral currents and over heating of some components.

Kalyke

I have got my hands on the ESB report. Anyone interested in having a look via PM?

Kalyke

Kalyke wrote: »

I have got my hands on the ESB report. Anyone interested in having a look via PM?

Anyone???

Mississippi.

Kalyke wrote: »

I have got my hands on the ESB report. Anyone interested in having a look via PM?

PM sent

emtulsk

Kalyke wrote: »

I have got my hands on the ESB report. Anyone interested in having a look via PM?

+1

Mississippi.

Theres nothing extra I can tell from the report but I know the fault a VSD shows may not actually be the fault it tripped out on, they are however very sensitive to insulation resistance problems so if the motor is reading anything less than around 50M ohms get it dried out