First Turn Failure on submersible pumps

[Marke]

Hi

We are currently hearing stories of a number of first turn failure on submersible pump motors. I know that some of these stories are totally incorrect and the first turn failure is a description given by the pump suppliers for other modes of failure, with no evidence of such, it seems to be a good excuse in some cases.

There are a number of quoted remedies for reducing first turn failure, and most involve the use of dv/dt filters on the output of the VFD to reduce the VFD to a quoted figure when the reality is that it is the peak insulation voltage of the insulation that is the problem.
Reducing the dv/dt will reduce the peak voltage for a given cable length, but from my understanding, quoting a required maximum dv/dt needs to be at a particular cable length and cable velocity factor to have any real meaning. - It is looking like a trend towards proving that the maximum dv/dt is 500V/uS or there will be no warranty on the motor.

Questions are being asked of suppliers about the guaranteed maximum dv/dt of the drive with no information on the installation, cable length etc.

One solution commonly used is a three phase reactor in series with the output of the VFD, sometimes with resistors and or capacitors, often without.
I have not seen any reference to the use of common mode chokes on the output of the VFD being used as a means of reducing first turn failure, but to my warped understanding, we use common mode filters (often referred to as Ferrite Rings) to reduce common mode leakage currents in EMC sensitive environments and also to reduce bearing currents and EDM, both of these are related to the high frequency energy in the output waveform as is the peak voltage impressed on the motor windings.
I expect that the common mode filter as used to reduce EDM would also be effective in reducing the peak voltage at the beginning of the motor windings and therefore reduce the probability first turn failure.

Any comments??

Mark Empson
Advanced Motor Control Ltd

 

[Marke]

I recently visited an installation where there were three single phase reactors in series with the output of the VFD. These reactors, one on each phase of the VFD were installed solely to reduce first turn failure.
I have seen many three phase reactors used on the output of the VFD for this purpose, but not single phase reactors.
Any comments?

Mark Empson
Advanced Motor Control Ltd

 

[davidbeach]

For series reactors, the only difference between single phase and three phase would be the enclosure. The three phase reactor would be three singles in one box rather than in three boxes.

 

[Marke]

Hi David
The three phase reactors are wound on a three phase core and the single phase reactors are wound on a single phase core. There will be coupling between the windings of the three phase reactors but none with the single phase reactors.

Mark Empson
Advanced Motor Control Ltd

 

[jraef]

Things like that tend to be the result of component availability in my experience...

Re: relationship of common mode noise filter to less winding damage:
Could simply be that VFD mfrs who are conscientious enough to think about putting in common mode noise filters are going to tend to be those who will also address standing wave propagation in their designs. Those who are out to make a quick buck by spewing out cheap drives and don't bother with common mode noise issues are highly unlikely to pay any attention to any other issues either.

"Will work for (the memory of) salami"