Faults on three-phase motors
Faults on three-phase motors
(OP)
I'm trying to find some information on the effects of phase loss and line loss on three-phase motors.
Any information greatly appreciated.
Thanks
Any information greatly appreciated.
Thanks





RE: Faults on three-phase motors
RE: Faults on three-phase motors
RE: Faults on three-phase motors
Are you looking for something specific?
Keith Cress
kcress - http://www.flaminsystems.com
RE: Faults on three-phase motors
RE: Faults on three-phase motors
Loss of one phase while the motor is running causes severe heating in the motor due to negative sequence currents. The motor will generally keep running, but as itsmoked says, either the overloads are going to operate (if you are lucky) or the motor is going to fail dramatically.
RE: Faults on three-phase motors
RE: Faults on three-phase motors
The motor will run with one phase missing but the back EMF will still be generated on all three phases. This is how rotary phase convertors work. If one phase has low voltage, the induction generator action will try to bring the voltage up on that phase and overheat while trying. If the phase is missing there is no load and no current to over heat the motor.
Now consider a plant where one main fuse has failed. The motor will continue to run on single phase and the induction generator effect will try to supply the load with the missing phase back to the failed fuse. A lot of large motors with no load may simply keep the voltage up on the bad phase without overheating. Think sawmill with the large motors left running during a coffee break.
This situation will not arise often, but illustrates the importance of looking at the whole system rather than just the motor. If the phase is lost in the motor controller the action of the motor may not be the same as if a main fuse or a distribution panel fuse has failed. If the phase is lost in the controller and the motor is under a light load there may not be any problems until the next time that the motor tries to start. Even if the controls are on the failed phase, induction generator action may keep the controls energized.
Bill
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"Why not the best?"
Jimmy Carter
RE: Faults on three-phase motors
- a three-phase motor is running with two phases only (one of the phases was opened somehow after it was successfully started) and its speed is approx rated (no starting issues),
- its stator current is: Line1 = 100% of FLA, Line2 = 100% of FLA, Line3 = 0% of FLA,
- no thermal and/or overload protection installed for this motor.
How do You think: will this motor be overheated in this mode? Does it depends on stator internal connection circuit: star or delta? Why?
RE: Faults on three-phase motors
Keith Cress
kcress - http://www.flaminsystems.com
RE: Faults on three-phase motors
Keith Cress
kcress - http://www.flaminsystems.com
RE: Faults on three-phase motors
As the load is increased, the heating is also increased and the potential for failure increases.
In the case of 100% + 100% + 0%, there will be a difference in the heating of the windings as in a star connected motor, the current through winding 1 and winding 2 will be 100% and the current through winding 3 will be 0%.
In the case of a delta winding, the current through winding 1,2 will be higher than rated and so more heating will occur.
Best regards,
Mark Empson
L M Photonics Ltd
RE: Faults on three-phase motors
Marke: agree to all.
Anyway, I tried to find the answer in several books and found nothing. I wonder whether there is a common answer for all motors or maybe some motors tend to burn in this case while others don't?
RE: Faults on three-phase motors
Keith Cress
kcress - http://www.flaminsystems.com