Anyone have any experience with a 3 phase Dahlander pole changing starter? The motor has 6 windings with 9 leads out. It's a delta/parallel wye squirrel cage motor used to rotate a board cooler. Starts in delta (slow speed) for 1 second, switches to paralled wye for 2 seconds (fast speed) and back to delta for 1 second. It's been running for 20 years with no problems until now. This is not a reversing starter but in the past week its started in the oposite direction for one cycle and then goes forward again. Its done this about 6 times in the past week. We're going to put a drive in place of the 4 contactors but I was curious if anyone has heard of this before.
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You don't need 4 contactors for a Dahlander motor, it is just the IEC terminology for exactly the same as a 2 speed 1 winding motor in NEMA terminology. It only takes 3 contactors to make it work. The 4th is then likely a reversing contactor, even though you may have never used it that way on purpose. Sounds to me like something has gone wrong with your control circuit and now it is reversing on you.