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?

 

[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