not PLC but MCC related

I supplied a 25HP @ 460 VAC FWD / REV Fuji starter in combination with a MMS (manaul motor starter)for a mixer that is using "plugging" to stop the motor on a small rubber mixer. This is applying reverse voltage at command of stop until the motor reaches zero speed. A zero speed switch detects the motor is at zero speed and removes the reverse voltage to keep the motor from starting to turn backwards.

I used the MMS sized a little large to allow for this but small enough to hopefully protect the motor. I sized the contactors at 40HP at just a guess. It worked fine here at the shop but problems are in the field. Can anyone provide proper engineering information to allow for proper oversizing of components selected to do this job as opposed to my "guess"?

FYI, changing stopping logic is NOT an option.

more info

It would help immensely if you could outline the problems you are seeing. It's difficult to overrate something correctly when specifics aren't available. For instance, what is the duty cycle of the motor. Is it start/stopped often, or could it be classified as a continuous duty motor. This info, along with the problems you are seeing are needed before we can effectively help you.

Russ

OkiePC said:

My mills were contactor driven and would slam the contactor and motor in reverse momentarily to stop the mill when the e-stop was activated. The mill must stop within a certain distance or someone will eventually be seriously injured or killed.

What ever you do, the drive cannot fault. The mill must stop hard and fast no matter what.

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Robert,

Does this quote describe your application? If it does then this thread may be of some benefit.
http://www.plctalk.net/qanda/showthread.php?t=28013&highlight=rubber+mill

I'm not sure yet. It was my understanding that it might stop once a hour but I will check. The problem I am told is that the MMS and both contactors have fried. Black soot surrounds the components.

It worked fine here over and over. I don't knoe if they did something to be honest but I really am hoping to have mathmatics to insure I replace with proper size parts if change is required.

It does sound fishy to me that "they powered it up and the first time they turned it on it smoked". I am going seek more information.

Close but we are NOT using a drive but a plugging feature. I have also heard of the resistance breaking but that does not aplly to this application either. The panel was existing as was the logic. We replaced what was there with similar components and tested it thoroughly here.

I am going to dig a little deeper into this and try to get more info. In the mean time if anyone can provide typicel sizing on a plugging application for a 25HP motor @ 480 VAC that would help.

Are the forward and reverse contactors mechanically and electrically interlocked? Maybe they overlapped, shorting both of them momentarily...just a WAG...

Hi Robert

You have selected correct contactor size as per type II cordination of standard Also you must have 25-40A overload relay rating and 63A line fuses

g.robert said:

the MMS and both contactors have fried. Black soot surrounds the components.

It does sound fishy to me that "they powered it up and the first time they turned it on it smoked".

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When I first read this I thought that the control voltage (or all voltages) might be low and the contactors were not sealing in correctly. But then I reread that the manual motor starter was also fried. I find it impossible to determine with the information you have shared.

The contactors are both mechanically and electrically interlocked.

I am begining to believe the problem may lie in the MMS. I selected the MMS to provide the NEC required OCP and OL protection. This gives me a complete and in-expensive combo starter when paired with the contactor allowing remote starting. This also allow for a main disconnect switch to be mounted on the panel cover. Because of this disconnect switch, I need to go back with another MMS. Again, I have NOT seen the damaged components yet or even have a clear understanding of which components are bad. I feel confident the contactors are OK. I willing to bet it is the MMS that went. This could have put black soot on the surrounding components making the customer think they all went.

I would like to be sure what I put back will work and has been sizes with standard engineering practice. Maybe the million dollar question is; How would you size a MMS differently for this "plugging" application and still get the required OCP/OL protection for the 25HP motor?

g.robert said:

The panel was existing as was the logic. We replaced what was there with similar components and tested it thoroughly here.

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A couple of questions. What were the conditions of the components you replaced? Perhaps more importantly, why did the original components fail? Did you have the whole machine in your shop when you were testing? Was the testing done with material in the machine?

Vaughn, There were no replaced components. We simply matched the original panel BOM/ DWG but used IEC MMS to save $ and space. I do not know exactly what failed at this time or the exact circumstances in which they failed. I am in the process of getting that info.

The best I can do now is learn how you size a MMS differently for this "plugging" application and still get the required OCP/OL protection for the 25HP motor? This must not be an easy question to answer. Hopefully someone with previous experience in a similar application will provide that info. Thanks for everyone's attempts to help so far.

One thing you need to remember, the surge current will be quite high. The starting aka inrush current of the motor determined by the KVA code will also probably happen and then some during the initial PLUG.

Your current protection needs to be able to handle this.

You also might be right about the MMS letting its smoke out and covering everything else with soot.

If you want my opinion....

This project should have been done with an encoder-less vector AC Drive.

The drive can do all your looking to do without encountering all the kinds of problems your going to have with setting it up, and likely extend the service life considerably as compaired to using mechanical contactors & starters etc..

g.robert said:

Vaughn, There were no replaced components. We simply matched the original panel BOM/ DWG but used IEC MMS to save $ and space.

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I do know this from my panel shop days... IEC components are not equal in all ratings to NEMA, even though you would think any starter capable of controlling a 25HP motor would do the trick. Remember, the old NEMA starters were built like tanks.

I suggest you get a spec sheet for both old AND new components and compare EVERYTHING. You may be surprised what you find.

elevmike said:

If you want my opinion....

This project should have been done with an encoder-less vector AC Drive.

The drive can do all your looking to do without encountering all the kinds of problems your going to have with setting it up, and likely extend the service life considerably as compaired to using mechanical contactors & starters etc..

Click to expand...

That would be way too easy.