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750KW DC motor tripping main power breaker
4

750KW DC motor tripping main power breaker

750KW DC motor tripping main power breaker

(OP)
Hi you all. Thank you for letting me be a part of your group. I work as an electrician for a ski resort in Oregon. We recently installed a newly refurbished 750KW DC motor on one of our lifts. We use an older ABB DCS 800 drive on it. Since installing we have led lights flickering throughout the resort when it's running and are also experiencing nuisance tripping of our main breaker. We have a Merlin Gerin VIP 200 trip unit installed. We are uncertain about what could be causing the breaker to trip. It shuts down power to our whole East Side when it happens. I am an industrial electrician but feel a bit overwhelmed by this one. Looking for any advice on how to proceed with troubleshooting.

Thank you all very much.
David

RE: 750KW DC motor tripping main power breaker

"...Since installing we have led lights flickering throughout the resort when it's running and are also experiencing nuisance tripping of our main breaker....We are uncertain about what could be causing the breaker to trip...".
I have the following opinion for your consideration.
1. Based on the observations, it is likely a repetitive over-load i.e. over current, but not a short-circuit; that causes the breaker (nuisance) tripping.
2. Focus the trouble-shooting on the (refurbished) motor and the load, then the DCS. The breaker tripping is expected, not a nuisance when subjected to prolong/repetitive over-current. It is probably in order.
Che Kuan Yau (Singapore)

RE: 750KW DC motor tripping main power breaker

The drive settings are not appropriate for the new motor.
The drive may be failing or the parameters may be set wrong.
The armature circuit of a DC motor has very little resistance.
It only takes a few percentage of rated voltage to drive rated current through the armature.
But the effected voltage driving the armature current is the difference between the applied voltage and the back EMF.
The back EMF increases with spreed.
If the motor is accelerated too rapidly, the applied voltage becomes too much greater than the back EMF and the armature current may rise to an unsafe level.
Why was the motor replaced and is it possible that the drive may have been damaged in the event that led to the 750 kW motor being refurbished (replaced?).

--------------------
Ohm's law
Not just a good idea;
It's the LAW!

RE: 750KW DC motor tripping main power breaker

What motor refurbishment works were done? Did the repair shop do any testing?

What are the trip indications? Overcurrent? Overspeed?

What was the previous motor rating? Why was it replaced?

750 KW is a large motor for a lift.

Muthu
www.edison.co.in

RE: 750KW DC motor tripping main power breaker

Check the current on all three supply phases.
If a diode is open, the other phases may be drawing more current.

--------------------
Ohm's law
Not just a good idea;
It's the LAW!

RE: 750KW DC motor tripping main power breaker

If motor is ok, seem to be oscillations in armature current control loop.
Check DCS parameters.

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