Coil withstand voltage fluctuation? 1

[powerjunx]

Hello, guys.

To answer my desperation of getting rid of magnetic contactor coil voltage "drop out" that leads to trip our plant, i been searching to address the cause of tripping as to stop the recurrence of such incident.

Here's the link that somewhat attracts my unanswered query;

http://www.cutler-hammer.ca/pmp/advantage_starter.html

I do hope that somebody had tried this starter and post their compelling satisfaction and suggestions.

thanks,








"Whenever you are asked if you can do a job, tell them, certainly I can! Then get busy and find out how to do it." Theodore Roosevelt.

 

[waross]

The correct approach is to correct the cause of the voltage dips that are causing your drop out.
Your motor starters are doing your job properly and protecting your motors.
Any time that the voltage is so low that the contactor drops out, it should, because the voltage is also too low to operate the motor safely without danger of burn-out.
I can suggest a scheme that would prevent your contactors from dropping out but I will do you a favor and not do it, bacause:
I don't want you to replace the inconvenience of motors stopping with the incnvenience of motors burning out.
It would put you in violation of the undervoltage release requirements of the NEC.
It would probably put you in violation of OSHA.

Tell us about your voltage problems and maybe we can help you there.
respectfully

 

[Marke]

I agree with waross.
You need to be very careful that you do not just shift the problem into a more expensive component!
Please give more information on the cause, magnitude and duration of the voltage dips.

Best regards,

Mark Empson

http://www.lmphotonics.com

 

[itsmoked]

Rather Marke, it is exchanging "inconvenience" for damage.

Keith Cress
Flamin Systems, Inc.-

http://www.flaminsystems.com

 

[aolalde]

Check the starting current of your motors and the line capacity. May be soft starting the motors will solve your problem.

 

[powerjunx]

That's a great comments, Waross and Marke as well.

I've chasing to compensate the voltage dop out slightly beyond the coil OEM specification of about 82%+/-2 of the nominal, let's say about 75% while taking care the load current of motor not to go beyond maximum permitted value, for a period of not more than 2 seconds.
Although, i am never quantitatively certain about the voltage sag magnitude and its duration but our system distinctly depicts the scenario of having such voltage dip upon evidently reacted on low voltage releases.
Long before as i observe, just a quick flicker of the flourescent lamps the coil releases to the extent it trips our plant.
For a brief info, our generating plant is configured having a export/import power capability to a power grid. Everytime, a fault or abnormilities occur outside our system a voltage fluctuation or the like affects our operation that includes this motor contactor coil drop out.
Again, anybody in this forum had used this product;

http://www.cutler-hammer.ca/pmp/advantage_starter.html

Thanks for valuable comments.









"Whenever you are asked if you can do a job, tell them, certainly I can! Then get busy and find out how to do it." Theodore Roosevelt.

 

[waross]

My first recomendation;
Check your system voltage. for 460 volt motors, your incoming voltage should be a solid 480 volts. If you are running 460 volt motors on 440 volts, for example, you are asking for trouble.
Your answer may be as simple as adjusting your plant voltage.

Next, check your generator settings.
Consider (carefully) reactors in the feeders from the supply to soften-up the system a little and allow the generator to keep the plant voltage up.
Does the generator have a quadrature circuit and is it turned on? (Parallel position)

You may try a constant voltage transformer to power the contactor coil only. Be careful that any voltage monitoring relays are still monitoring the line voltage.
If the plant voltage at the motor is low, you may use a small transformer connected as an autotransformer to boost the coil voltage a little.
respectfully

 

[ScottyUK]

What function does the affected contactor serve? And where does it derive its control power from? It is possible you have wider issues than merely a contactor dropping out.


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Sometimes I only open my mouth to swap feet...

 

[powerjunx]

Waross:
Our power center is rated 13.8KV/480V, the tap is on 480V which supplied to our MCC, and the motor subject itself. This motor located per feeder uses direct online scheme with a 120V/60Hz contactor coil connected thru control transformer 480V/120V.
Reactor and quadrature circuit were not present. Generator has ground neutral resistor 16 ohms. At present, we deliberately consider constant voltage transformer.. i don't know if it succeed. I also planned a buck-boost transformer to be connected after the existing control transformer but i never had the confidence and assurance to address the problem.
Would you elaborate tthe effects upon considering constant voltage transformer and buck-boost transformer configuration in conjuction with my application?

ScottyUk:
Contactor serves as the main control for our lube oil pumps where our prime mover solely defends on it. It's power is provided by a control transformer, as i stated above, 480V/120V. Lube oil pumping failure is the great issue, say we've 4 feeders loaded with single lube pump.
But i'm glad with you guys to point out and suggest any issue pertaining to my query.

Thanks.












"Whenever you are asked if you can do a job, tell them, certainly I can! Then get busy and find out how to do it." Theodore Roosevelt.

 

[Marke]

Hello powerjunx

OK I understand your issues, but without knowing how low the voltage drops or for how long, it is difficult to asses the risks.

If you are concerned only about the lube pumps, you could use a 24VDC coil for the contactor supplying the lube pumps, but be careful as if the voltage drops significantly for any period of time, you stand to damage the pumps due to the increased slip. If there is a voltage sag for only part of a second, then that should be OK. I would suggest some form of under voltage protection with a delay so that if the voltage is low for a significant period, the pumps are shut down.
If the pumps are operating near rated load, then you do not need much of a voltage sag to cause the pumps to begin to stall. This will cause the current to rise rapidly and could cause the over current protection to trip.

If the supply drops to zero and then returns, it is best to shut down the motors and restart due to the massive current and torque transients that are caused by the "auto reclose effect".

Best regards,

Mark Empson

http://www.lmphotonics.com

 

[powerjunx]

Marke, thanks for your valuable views.
We'd consider such option as you'd suggested. However, due to coil drop out problem as we've taking all possible solutions, our technical department wants to upgrade our MCC. Thus, we're looking some pretty good and not so expensive solution as to address the coil drop out.
Above, posted product link, attracted our attention which cost less than "NEMA 5 open type motor starter" and compact rather than considering VFD or softstarter.
Since none of us haven't use it before, i seeking some suggestion and perhaps a testimony regarding using this product.
Thanks, guys.







"Whenever you are asked if you can do a job, tell them, certainly I can! Then get busy and find out how to do it." Theodore Roosevelt.