single phase service to 3-phase motor startup procedure

[yaxy]

We destroyed* the 3-phase pump motor for our neighborhood swimming pool and wonder if the startup procedure we've been using for at least a decade needs improvement.

Property has only single phase 240V service so we have a mechanical phase converter to provide 3-phase power to pump motor. Current procedure is to start the phase converter then a few seconds later close a separate service disconnect switch to start the motor. Phase voltages from converter are 175V, 175V and 5V before closing 2nd switch. Then 240V-260V as expected across each pair.

Does the lower, unbalanced voltages cause stress on the non-rotating motor for those few seconds? If so, would it be prudent to add a device such as a 3-pole contactor that energizes the motor only after all 3 legs are within spec? Does such a device even exist?

If it matters, motor is US Motors/Nidec Motor Corp EEQK1500 (aka Emerson BW37, aka Pentair EQ), 15 HP, 3515 RPM. Phase converter is 21-year-old Gerhard Werner Motor Werke (GWM Corp) WB0304FXA, 30 HP, 1760 RPM.

*Postmortem evidence may make for an interesting investigation into cause of failure.

Thank you for any help/advice!

 

[waross]

Hi Keith;
I was thinking not of the entire RPC but just the idler motor portion.
With that used as a sort of buffer with VFD, could the pump motor then be disconnected from the VFD/idler motor combination without upsetting the VFD too much?
Probably not a good idea and not economically feasible unless there was a surplus idler motor to hand.
Also and mostly to add to my knowledge of the quirks of VFDs.

Bill
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"Why not the best?"
Jimmy Carter