electrical fault causes torque which damages load?
electrical fault causes torque which damages load?
(OP)
Does anyone have any experience with electrical fault in a motor or motor terminals causing damage to the load (presumablyl due to transient torques)?
I previously described an event that I believe fell in this category here thread237-67490
Also the theory of transient torques during an electrical fault was discussed a little in that thread.
We have just had another experience that I beleive may be attributable to a similar cause . When I get a chance I will post the details in here. In the mean time, any response to the question posted in bold above?
I previously described an event that I believe fell in this category here thread237-67490
Also the theory of transient torques during an electrical fault was discussed a little in that thread.
We have just had another experience that I beleive may be attributable to a similar cause . When I get a chance I will post the details in here. In the mean time, any response to the question posted in bold above?
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RE: electrical fault causes torque which damages load?
RE: electrical fault causes torque which damages load?
Best regards
Mark Empson
http://www.lmphotonics.com
RE: electrical fault causes torque which damages load?
RE: electrical fault causes torque which damages load?
Perhaps a synchronous motor with a would experience a similar effect given a dynamic load? To be honest I've never really considered it before now.
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RE: electrical fault causes torque which damages load?
The biggest torques occur in generators when synchronising out of phase, although we have come across broken gear teeth in a few cases.
RE: electrical fault causes torque which damages load?
RE: electrical fault causes torque which damages load?
Not sure if I agree about an out-of-step synch being worse than pole slip. The pole slip typically occurs under heavily loaded conditions with a weak field, so the prime mover is applying an accelerating torque near rated torque. As the pole slip occurs the machine accelerates then decellerates almost instantaneously as it recovers synchronous conditions. I was lead to believe that the torsional stress on the shaft is worse in this situation than an out-of-step synch where the machine is pulled into synch because the grid alone pushing or pulling the machine into synch, without the massive contribution of the prime mover adding to the problem. I'm open to discussion on this - I had it explained to me and the analysis seemed reasonable at the time. It's such an uncommon fault that I haven't studied it in great detail.
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One day my ship will come in.
But with my luck, I'll be at the airport!
RE: electrical fault causes torque which damages load?
RE: electrical fault causes torque which damages load?
RE: electrical fault causes torque which damages load?
I agree with your logic - I've only really discussed this at any length with one or two people who both have a lot of experience in generator behaviour (ex-CEGB research staff). Their opinion was that it was possible to recover given a sufficiently fast and powerful AVR. They have each forgotten more than I know about generators, so I don't often challenge them. Perhaps I should!
Most texts I've read seem to be very light on the pole slip condition, saying little more than 'it can happen under XYZ conditions and it is not a good state to be in'. If you know of any good published studies or research on it I'd appreciate the details. I'm sure GEC, Parsons, the CEGB, etc must have studied this in depth at some point in time and published the results.
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One day my ship will come in.
But with my luck, I'll be at the airport!
RE: electrical fault causes torque which damages load?
I guess the situations for motors would be similar, but rather than accelerating during the fault the motor would be decelerating due to the load and the trick would be enough area left under the curve for it to re accelerate without slipping a pole. The higher up the power transfer curve the motor operates, the more likely it would be to pull out of step during a transient loss of voltage.
What does in the shaft is that during pole slipping, the electric machine alternates between motor and generator every 180 electrical degrees, passing through maximum power transfer in both directions. The shaft becomes a torsion spring connecting two energy sources, both fighting each other. Run away, run very fast.
RE: electrical fault causes torque which damages load?
This happened in a rubber mixing unit driven by a DC motor. The slow speed rubber mixer (heavy ss cylinder), running a very low speed (after multiple stages of gearing), broke and simultaneously (as heard by the operator), the DC motor armature flashed over. The on-line event recorder for the motor saw a huge rise in the armature current just prior to trip. The question was (and still is), which came first, the chicken or the egg ?
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RE: electrical fault causes torque which damages load?
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One day my ship will come in.
But with my luck, I'll be at the airport!
RE: electrical fault causes torque which damages load?
What I do know is that I have experience with pumps out there where the impellers are threaded onto the pump shaft where any reverse rotation, be it a 'bump check' for rotation in the wrong direction, or any electrical anomaly that would act as such (torsional shaft reactions) the impeller would want to unthread due to either direction or inertia, jacking it into casing parts of the pump where the clearances are already close, and where there is no tolerance for backing off of the threads to any extent.
That would definitely qualify as the load being damaged by just the right kind of an electrical fault.
rmw