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

[RogerMorris]

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?

 

[Darkwood]

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.

 

[Darkwood]

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.

 

[pc1966]

This on-line calculator gives 34.72% motor temperature increase. No idea how accurate that is!

3 Phase Imbalance Calculator

Calculate voltage imbalance.

www.hvacrschool.com

 

[pc1966]

Just realised the above are L-N but the calculator assumes L-L, however it helpfully tells you in red:

Shut down the equipment and rectify imbalance immediately​

 

[Darkwood]

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%

 

[pc1966]

I was wondering how easy it would be to correct the voltage imbalance, as going down the route of a 3-phase UPS seems like an expensive path?

 

[Lucien Nunes]

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.

 

[Darkwood]

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.

 

[pc1966]

Another thing not mentioned is what power this motor is.

 

[RogerMorris]

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

 

[RogerMorris]

MS 402

Submersible motors

product-selection.grundfos.com

Avel - electronica,lda

Electric control boxes and electronic relays for water pumping systems

www.avel.eu

 

[pc1966]

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.

 

[RogerMorris]

Yes the motor is only connected to the 3 phases not neutral and the voltages are now

L1 247v
L2 241v
L3 236v

L1-L2 421v
L2-L3 415v
L1-L3 422v

 

[Darkwood]

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.

 

[RogerMorris]

Thanks for the advice darkwood.

It has been suggested that I cut my losses with the 3 phase approach and install a single phase motor.
What are the downsides of that idea?

 

[stevethesparks]

Would a single phase to 3 phase vsd not be feasible?

 

[pc1966]

Yes the motor is only connected to the 3 phases not neutral and the voltages are now

L1 247v
L2 241v
L3 236v

L1-L2 421v
L2-L3 415v
L1-L3 422v

That on-line calculator is now saying:

• Average Voltage: 419.33
• Voltage Imbalance: 1.03%
• Motor Temp Increase: 2.14%

It is advisable to decrease imbalance to below 1% if possible​

 

[RogerMorris]

Do you mean something like this

Single phase input, Three phase output VFD | ATO.com

www.ato.com

 

[pc1966]

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.

 

[RogerMorris]

Yes. The reading will change day to day

 

[stevethesparks]

Do you mean something like this

Single phase input, Three phase output VFD | ATO.com

www.ato.com

I'm not the best to advise on choice of vsd, but yes. May be a much cheaper solution than changing the motor and may offer other advantages.

 

[Darkwood]

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.

 

[pc1966]

He said earlier it is 2.2kW so well within the sane range for a single phase supply.

 

[stevethesparks]

He said earlier it is 2.2kW so well within the sane range for a single phase supply.

Post #11 The motor is a Grundfos 3VC 2.2kw
Edit Beat me to it

 

[Darkwood]

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.

 

[RogerMorris]

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

 

[Darkwood]

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.

 

[RogerMorris]

So do you think a VSO is the best way to go?

 

[RogerMorris]

sorry VSD

 

[stevethesparks]

sorry VSD

I’d be inclined to contact both grunfos and the vsd company you listed with as much detail as you can and get their input. But as already said a vsd will need setting up I’m not sure that could be done pre delivery probably best on site

 

[ElectroChem]

Have we considered the possibility that the OP just had a bad pump?
I would think absolutely nothing of slapping a 3-phase motor on a supply that tested as 415-416-422 line voltages.
OP, any chance you were running the motor backwards? Submersible pumps can often still push water running the wrong way, but the flow will be reduced, as will the cooling effect on the motor, these pumps are over-powered for their size and rely on the water flow to properly cool them.
The installer jumping straight to the voltage imbalance smacks of "Yeah, definitely not my motor that failed, must be your supply"

 

[Mike Johnson]

Would not a 3Ph to 3Ph VFD stabilise the voltage and allow the existing pump to be used, Invertek where very helpful when I was looking to slow my swimming pool pump down, may be worth contacting them: Variable Frequency Drive Manufacturer | Variable Speed Drives | AC Drives | Invertek Drives - https://www.invertekdrives.com/

 

[LastManOnline]

You raise a point I missed @Lucien Nunes, why no protective devices tripped here to prevent the failure.

I also wondered about that. Normally speaking the mcb, s will only trip if they can't handle the staring current. The overload will trip if the motor is being overworked. But what about thermistor protection?. They are generally more sensitive to overheating than overloads. Its many years since I worked with motors but I would have thought that overload protection has moved on to the point where issues like the OP, s have being minimised

 

[Darkwood]

Would not a 3Ph to 3Ph VFD stabilise the voltage and allow the existing pump to be used, Invertek where very helpful when I was looking to slow my swimming pool pump down, may be worth contacting them: Variable Frequency Drive Manufacturer | Variable Speed Drives | AC Drives | Invertek Drives - https://www.invertekdrives.com/

The voltage imbalance that we speculate may have caused the demise of the motor would also play havoc with the VSD giving unwanted voltage DC bus ripple, this could cause unwanted tripping and/or reduce the life of the DC Bus cap's - we can however combat this by fitting DC chokes in combination with AC line reactors but we are ending up over egging the pudding here when we simply can eliminate the whole problem with a 1PH - 3PH VSD.

 

[Darkwood]

So do you think a VSO is the best way to go?

I think it is one solution of a few out there, a three phase voltage stabiliser is another and automatic one at that as it appears your voltage balance is somewhat unpredictable.

Now let's be clear here, this is all beyond what we would consider DIY and one should really consider getting a professional out to site and explain what you have to us, even consider having your supply monitored and data logged could give a better idea of the size of the issue if one even exists, we are going on the word of the installer here and it could be he simply made an error in testing, poor contact, cheap measuring instrument or simply fobbing you off to avoid replacing it at his own cost.

I don't think you have a cheap solution unless you want to simply swap the 3ph water pump for a Single phase version but I am not a big fan of going down that road if 3ph is available, single phase pump have more complexity to design so more things can fail, lower available starting torque, shorter life span and less efficient than its 3ph counterpart but it may do the job at the end of the day so like I said, get someone out on site to advice you based on the installation itself and like we are trying to do here - basing it on a mix of electrical theory experience and a few assumptions which may miss something crucial to design and/or advice.

A VSD option is unlikely to be suitable for your pump if it is simply rewound as I suspect it will be sealed and thus selecting the winding arrangements won't be an option unless you request the company to configure it for your VSD 3ph 230v option, this however leaves you with a pump that you simply cannot swap like for like in the future to match the pipework etc as you have customised the pump for yourself, suitable alternatives may exist that are off the shelf though.

If you want to maintain the 3ph pump option it looks like an expensive solution whichever direction you take, you could invest in a single phase pump and even buy a spare for less cost, as you may have found out by now submersible pumps are not cheap to say the least so you going to have to think about what route to take here.

 

[RogerMorris]

I will certainly use a professional to do the installation but what I wanted and you guys have given me is a discussion about some options, some I had considered and some I had never heard of!

Now when I talk to an installer I can at least ask pertinent questions and sound as if I know a little about the issues.

Thanks again for everyone's input

 

[Lucien Nunes]

Like some of the others I am still sceptical about the original cause of failure. A 2.2kW motor should be protected against catastrophic burnout by its overload protection, regardless of whether the underlying cause is mechanical overload or faulty supply. Before investing in expensive or complex solutions to the voltage imbalance, I would like to see more evidence that it was a key factor in the rapid failure.

Once the pump is returned in working order, I would connect it back up and measure the line currents under working conditions with the typical supply voltages that have been experienced. If the currents are excessive, then one of the solutions discussed will be needed. If not, there is a possibility that the failure was unrelated to the imbalance, however undesirable it might look on paper.

 

[James]

Also, remember it is not easy to overheat a submersible pump, the water normally keeps it cool enough even with a small overload