1

I'm replacing a pump: 400 V, 4 kW, 2 pole. It is a wye-delta startup.

The control circuit is working correctly, as I've double checked it and extended the lead to feed another 4 kW motor. When it starts up in wye, I'm reading 9 A but then 57 A when it switches to delta. I've tested the windings insulation (1000 MOmh). Each winding read 0.95 ohms.

The pump is a Grundfos Model: PN-SN A-96501772-10001084 Type: CRN15-4 A-FGJ-A-E-HQQE Motor is tagged: MG112MC2-28FT130-H3.

I've tried increasing the run time in Wye from 2 up to 15 secondes to make sure the pump gets up to speed.

Any thoughts?

Benjamin Seguin
  • 11
  • 2

2 Answers2

0

If you can disconnect the motor shaft from the load, suggest starting it DOL (delta connected) and measuring currents in each phase. All phase currents should be the same, if not, then as others have suggested there may have a fault in one of the windings, which won't always show up when running the motor in star (Y). You can also connect it in Y, run it, and measure the voltage at the centre node (the star-point) and see if this is close to 0V (should be less than, say, 10% of line voltage). If not, then at least one winding is not right. Of course, you should never connect the star point to neutral. Cheers.

Fabio Barone
  • 556
  • 14
  • I have between 6.2 and 6.5 amps on each phase. Is this significant enough to show an issue on the winding? As for the centre node to ground, i am reading 5 volts. Thanks for your help – Benjamin Seguin Jul 13 '23 at 10:20
  • Follow-up questions: Re: currents you measured: Was that with the motor in Y or delta? Was the motor shaft disconnected from the load and the shaft turning normally? If yes, then it is unlikely that the differences in currents you measured (6.2 to 6.5A) indicate a problem. Re: voltage of star-point: what is to neutral to earth voltage? This has to be measured while the motor is drawing current at conductors located as close to the motor as possible. When you first had the problem, what was tripping out, the motor thermal overload, or the circuit breaker? – Fabio Barone Jul 15 '23 at 04:08
  • Question 2: How long was the motor running in delta before the trip occurred? Does the motor run indefinitely (say, about 30 seconds) and get up to full speed while in star without tripping out? – Fabio Barone Jul 15 '23 at 04:09
  • Open-transition star-delta starters are notorious for causing circuit breakers (not thermal overloads) to trip - this has been known for decades, this article from the 70s is useful reference: http://www.mastercontrols.com/Articles/Wooddall/TA_RWood.htm That paper suggests that a solution may be to swap **two** pairs of cables to keep motor direction the same, but which changes the magnetization of the windings. I recall seeing an app note on this, but cannot seem to locate it now. – Fabio Barone Jul 15 '23 at 04:19
0

Is the time delay for change-over, from wye to delta, adequate?

The change-over is to be effected only after the motor has attained its rated speed in the wye configuration.

Please check, for correctness, the power wiring also.

enter image description here

Image credit: Siemens

vu2nan
  • 15,929
  • 1
  • 14
  • 42