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?

 

[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