Can a difference in phase voltages cause a motor to fail?

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Can a difference in phase voltages cause a motor to fail?

Discuss Can a difference in phase voltages cause a motor to fail? in the UK Electrical Forum area at ElectriciansForums.net

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RogerMorris

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Here is the background:
A new Grundfos 3 phase sump pump was installed in a bore hole to pump groundwater to a holding tank.
After 6 weeks the motor failed, the installer measured the voltage of the 3 phases which at the time were
P1-237v
P2-250v
P3-233v
and suggested this was the likely cause of the motor failure and I should install a 3 phase voltage stabilizer.

Do you think he is correct?
 
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Yes voltage imbalance can be a very bad thing for a motor, even just a few percent but you have about about 5% difference there and I suspect that has led to the demise of the motor without question, a 2% different can lead to a 10% increase in winding temp' and a 5% can be a 50% increase... you have a voltage difference way beyond these figures.

I would have concerns myself if we see 2-3% variation and I believe NEMA limits require to be less than 5%, it get complicated because one has to factor, load, duty and so much more when seeing what a small variation will actually do to any given motor but given you voltage values I can only agree with the installer although I question if this variation was present when installed which opens a whole different direction to this thread although it is hard to prove unless documented, voltage variations can also appear at certain times of the day or night depending on network loading and balance.

PS - I can only go on the information you give, have you had the motor looked at by a motor service company, more often than not the characteristics of the damage in the motor can determine the likely cause of its demise, although it might be a small investigative charge to look it may save you money in the long run but I wouldn't be at all surprised if they confirm the story.
 
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Here is a very informative link which is written in simple to understand format and should help you understand the issue.
The graphs are in particularly helpful especially the temp' rise and the motor derating tables for voltage variation.
If you were in doubt beforehand I suspect you won't be after reading the link.

https://library.e.abb.com/public/0c4186f3e7354f6982124decf92742d8/AVC-20 white paper (low res).pdf

You seem to be located to Spain, I do not know the supply standards of the network providers but over here in the UK we could raise this as a issue with the DNO with hope of a solution on their part.
 
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Actually @pc1966 you have probably pulled me up on an error I made, I calculated the difference between the highest and lowest voltages and not the mean average of the 3ph ... either way it doesn't change the facts of the matter - Ill edit that 8% value to 5% ;)
 
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Does the pump have a starter with an overload relay, a thermostat or any specific protection other than fuses / MCBs? Because, while voltage imbalance can cause overheating that is often reflected in the line currents and ideally would be picked up by the protection rather than leading straight to motor failure.

If the imbalance is caused by large single-phase loads being haphazardly assigned to phases within the installation, it might be sufficient to rearrange them to bring the voltages at the pump within tolerance.
 
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You raise a point I missed @Lucien Nunes, why no protective devices tripped here to prevent the failure.

As this is Spain going from the profile I cannot comment of network reliability and whether this is rural or urban which may factor in to the voltage irregularities but a good point raise about balance within the property.
 
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Thanks very much for your comments and knowledge, it is rural Spain and I have since discovered that phase imbalance is not unusual.
The motor is a Grundfos 3VC 2.2kw and it is connected via a PROBD21P Digital Pro Pump Relay which as I understand it will cut the motor if the current is either too high of too low but not react to phase imbalance
 
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Can you (safely) measure the phase-phase voltages? They ought to be around 415V here.

Most likely the motor is connected only to the 3 phases, and not neutral, so an offset/imbalance in the neutral is much less of an issue.

Worth having as much information as possible in case of any dispute over the motor problem, though it still seems likely the supply is a problem.
 
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I would be looking at setting up a system that give extra monitoring, protection from voltage irregularities and redundancy.
I did a 2 pump system that usually runs each pump alternatively for drains and sewage but under exceptional circumstances (heavy rain) the level sensor will trigger both pumps for fast evac' and is monitored for overtemp, overcurrent, short circuit and earth leakage on each motor, a PLC program will recognise any condition raised, swap the program to 1 pump operation and raise the alarm, it has been running 3 yrs now no issues thus far, the previous system cost them 5k in call outs and tank emptyings one yr so already the investment has paid.
The above would probably push you for 2k to 3k (£) or if you really want to pull out all the stops then fitting VSD's and giving extra protection from clogging and stalling with anti-rag software adding another 1k to the pot...
Depends on your pocket, the size of the holding tank and the cost of failure to inconvenience and business if applicable.

As you have voltage issues I didn't have then your scenario would need extra to ensure you can reduce or eliminate the effects of voltage imbalance.
 
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So that particular measurement is not really looking a very likely reason for failure, but your L-N voltages look more balanced now as well so there might be some significant fluctuations in the supply balance.
 
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Like above, fitting a VSD 1ph - 3ph would eliminate voltage balance issues, 3ph it is more efficient and reliable and the VSD would be a better option for monitoring the motor however you have not mentioned what KW the motor is, using single to 3ph drives means you effectively load 1 ph up to create 3ph which won't be a issue with a small motor but as the size increases then we have to see if it suitable.
 
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I'll look it up, ignore the message if you just saw me post, I forgot you are going to need to run it at 230v 3ph not 400v.

A quick check for a ballpark figure would be 1ph - 3ph VSD and a 3ph 230v motor and the VSD will be about 20amps input needing a 32amp MCB front end device.

Given most submersible pumps are presealed and wired the spec's of the pump would need to match your VSD option and as we are not using 400v 3ph you will need to get a 230v 3ph pump.
 
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Woah slow down I am only DIY status ;-)
I have a motor (Grundfos 3VC 2.2kw MS402) which hopefully will be repaired.
My 3 phase supply is unbalanced and changes on a daily basis.
The VSD sounds an interesting solution.
Will it be possible to use that motor with a suitable VSD?
If so can you recommend a respected manufacturer and guide me as to the specs of a suitable device
 
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Given your status you will really need to get a pro in as this has to be spec'd correctly and VSD would need setting up, this is not DIY to be fair.
It will be expensive to try do this off this forum as any info you fail to give us could change how it should be done.
It nudges you in the right direction though.
 
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