3 phase motor partial winding start

I have a customer with an old pump panel which uses autotransformer style reduced voltage starter. I have worked with wye/delta starters, but this is my first experience with this variation of reduced voltage starter. The old panel is a rusty mess so the plan is to replace it with a VFD to allow ramping up to speed and limiting the upper end. This is driving a 125 HP water pump supplying a distribution system (including water towers).

The word is that when they last ran the pump (more than a year ago) it blew up water lines so now they will not run it. There are two other pumps teed into their system that are 75HP and one of them has a soft starter. Right now, they only run the smaller pump on the soft starter.

I would expect that this is probably as simple as connecting the motor as shown in the "RUN CONN" diagram, carefully setting up the VFD parameters and starting it up with caution like any other pump. I do want to proceed with caution and would like to hear any input from the motor/drive experts.

Thanks!
Paul

Yes, you would connect it in the Run pattern permanently. just make sure to buy a VFD rated for 142A minimum, which shouldn't be an issue for anything calling itself 125HP. If the pump is centrifugal, you can use a "Normal Duty" / "Variable Torque" rated drive, but if you aren't sure, just get a Heavy Duty / Constant Torque version, it's the safe bet.

My one cautionary statement is that this is an old motor, designed before VFDs existed and without protection, it will not likely last long. To get the most life out of it, add at least a DV/DT filter to the output side of the VFD, a Sine Wave filter is better (but more $$). Or, you can do what a lot of people do; run it to destruction as is and then replace it with an Inverter Duty motor. But consider your down time costs with that route.

jraef said:

Yes, you would connect it in the Run pattern permanently. just make sure to buy a VFD rated for 142A minimum, which shouldn't be an issue for anything calling itself 125HP. If the pump is centrifugal, you can use a "Normal Duty" / "Variable Torque" rated drive, but if you aren't sure, just get a Heavy Duty / Constant Torque version, it's the safe bet.

My one cautionary statement is that this is an old motor, designed before VFDs existed and without protection, it will not likely last long. To get the most life out of it, add at least a DV/DT filter to the output side of the VFD, a Sine Wave filter is better (but more $$). Or, you can do what a lot of people do; run it to destruction as is and then replace it with an Inverter Duty motor. But consider your down time costs with that route.

Click to expand...

Thanks!

I had planned on advising the customer and providing options for a filter and disclaiming our company from insulation breakdown if they choose to run without a filter. We will do megger tests at the outset in any case.