Motor backspin detector
Motor backspin detector
(OP)
Hello;
Can you give me some leads for a device to connect to the leads of a 4.16kV motor which would tell me if it is rotating?
Can you give me some leads for a device to connect to the leads of a 4.16kV motor which would tell me if it is rotating?





RE: Motor backspin detector
Can you use any of the more conventional methods like a proximitor detecting a flat or keyway on the shaft?
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RE: Motor backspin detector
The motor leads are the only thing available to measure.
RE: Motor backspin detector
As in, rotating in the wrong direction when powered?
OR
Being backdriven, e.g. by a pump, when unpowered?
Mike Halloran
Pembroke Pines, FL, USA
RE: Motor backspin detector
If you use PT's, guess this type of protection could work.
RE: Motor backspin detector
http://ww
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If we learn from our mistakes I'm getting a great education!
RE: Motor backspin detector
Scotty - variations of that meter are all I could find.
There doesn't seem to be anything like that meter which can be hardwired to the motor. But then, I don't think there is enough residual magnetism in an induction motor to provide a usable signal once it has been off for some time. This is likely especially true once the measuring device is connected via a VT.
RE: Motor backspin detector
Why connect something to MV leads for that?
RE: Motor backspin detector
I have been told that a Mutlin SR469 can do this, something proprietary. I have no direct knowledge of it or how it works, it came up in a competitive situation where what I was proposing did not have it and Mutlin won the order because they got the CE to specify it as a necessity.
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RE: Motor backspin detector
It's the 369 that has a backspin connection.
The description says it measures the frequency after the motor shuts down and at the same time it calculates a predicted time to stop. The unit will then use the time calculated when the back emf drops so low there is no signal available anymore.
This doesn't sound very promising for detecting the motor is rotating after the motor has been shut down for hours.
RE: Motor backspin detector
In the mean time, a company in Canada called MSE of Canada Ltd. makes a MV motor winding insulation monitor and they have a version with an analog output. With a little experimentation, I'd be willing to bet you could detect movement in the rotor with changes in that output. I did Zero Speed detection for DC Injection Brakes that way, but it involves putting a voltage on the motor. That's what this system does, so I'd think it would not be too difficult to adapt it.
http://www.msegroup.net/
http://www.msegroup.net/
"If I had eight hours to chop down a tree, I'd spend six sharpening my axe." -- Abraham Lincoln
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RE: Motor backspin detector
Roy
RE: Motor backspin detector
RE: Motor backspin detector
The complexity of the proposed detectors is nothing as compared to the complexity and cost of stopping the machine electrically.
Think 'sprag brake'.
Mike Halloran
Pembroke Pines, FL, USA
RE: Motor backspin detector
RE: Motor backspin detector
Mike - The pump would be disabled so it could not be started. Stopping the pump would be up to the customer. The pump rotating would mean there is a valve problem they have to address.
I now think a shaft sensor is the only practical solution after searching for a motor terminal way to do this. I believe to do it via the motor terminals would require injecting DC on 2 leads and measuring frequency on the third.
RE: Motor backspin detector
It was brought to my attention because it was making funny noises, and the bearings were real hot... in the middle of winter.
I don't think I'd want to be near a big one being backdriven.
Mike Halloran
Pembroke Pines, FL, USA
RE: Motor backspin detector
Dave G.
www.ReliabilityDirectStore.com
RE: Motor backspin detector
"An 'expert' is someone who has made every possible mistake in a very narrow field of study." -- Edward Teller
RE: Motor backspin detector
Had same problems with backspinning pumps before too -passing check valves on some pumps in parallel with other pumps! We didn't try monitoring the backspin, we monitored the backflow instead(out-of the-box thinking). I don't know if this works the same way in your case but it's just a thought!
RE: Motor backspin detector
It's common in mining also for uphill conveyors but there they use something on the gearbox.
RE: Motor backspin detector
We've already suggested a flow sensor as a possible solution. The motor isn't accessible so they won't be installing a proximity sensor.
RE: Motor backspin detector
We do have another unit employing DC braking system, but we used feedback from a tacho-gen mounted on the shaft of the motor to prevent starting of motor when backspinning. The gadget kicks-on when the motor is backspinning, bring the rotor to a stop before the softstarter engages to speed-up the motor.
But, as you said, they won't be installing a sensor due inaccessability!
If your pump is a vertical well pump, roydm's suggestion could be a solution. The equipment is just attached to the non-driving end of the shaft; uses steel balls that locks-in on backspin, but stays out on the correct rotation!