DC Contactor magnets destroyed. 3

[Thedroid]

We have several 1250hp synchronous motors using JC dc contactors to apply the field. Field amps are usually around 66. The contactors are three pole with two NO, and one NC. The NC contact connects the field windings to a discharge resistor, and the NO's apply the field when the motor is up to speed. The contactors are rated at 100A. These contactors use permanent magnets glued to the inside of the contactor cover to quench the arcs. Upon inspection, all of the magnets are shattered and clumped up inside of the contactor. The contacts themselves are in good condition, although they were covered with tracking marks. Now that there is hardly any magnet left, the material seperating the poles is getting dangerously thin, and looks overheated. I've been looking for a suitable replacement, but it looks like the JC is the only game in town. Is there anything we can do to minimize this if we use the same contactor again? Would going to a bigger contactor help? I really don't think it would, because the contacts themselves show no sign of damage or overheating, and the bigger contactor would still be the same design. Thanks

 

[Skogsgurra]

This sounds like something that Ametek should answer. If the magnets are Neodym types, there was a problem with brittleness and also corrosion in the early years. If Ametek cannot help, then Siemens has a range of DC contactors that may fit. But their "Bauweise" is very different and you may need to make mechanical arrangements to be able to use them.

Gunnar Englund

http://www.gke.org

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[ScottyUK]

ABB's R-Line contactors are an alternative, as is Telemecanique's equivalent bar & shaft design. Field experience says that the the Telemechanique DC contactor is extremely robust, having dealt with a number of them in very severe service. The ABB R-Line is about half the cost and is also good.


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If we learn from our mistakes I'm getting a great education!

 

[sreid]

Gigavac is making big inroads in the DC power contactor business.

http://www.gigavac.com/products/contactors/gigavac/index.htm

 

[Lakey]

Alternatively, you could assess some of the Albright range of contactors – maybe one the SW80B series.

http://www.albrightinternational.com/lang/en/index.html

Regards,

 

[jraef]

I think you meant JC as in Joslyn Clark, not the JC6 Series of Ametek contactors.

I had to do a lot of research on DC contactors last year for a project. Nothing I know of will fit that same footprint as the JC 5DP6 Series contactors. The problem is that was never a real high quality contactor, they are cramming a lot of switching capacity into a very tight space. JC was bought by Danaher a number of years ago and in my opinion their QC, which was never stellar, has gone down as Danaher dismembers them. But that contactor was popular with OEMs because of the small footprint.

ABB's will be close if you have a little wiggle room, but it is only a 2NO 1NC contact arrangement. Anything else with that contact arrangement and enough rating to handle the current will be physically a LOT bigger. My advice would be to replace the JC contactors for now and think about a redesign for the future.


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[jraef]

Oh, as to the magnets being destroyed? Probably damaged in shipping vibration. I've seen that. When you get the replacements, inspect them VERY thoroughly. Their packing method leaves a lot to be desired.


"If I had eight hours to chop down a tree, I'd spend six sharpening my axe." -- Abraham Lincoln
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[ScottyUK]

If space is a problem then forget all my suggestions - they are all big mill duty contactors. The coil assemblies are roughly the same size as the type jraef referenced.



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If we learn from our mistakes I'm getting a great education!

 

[Thedroid]

The contactors are Joslyn Clark, and they are the 2no 1nc variety. The original contactors were heavy duty GE field application relays, and lasted for 40yrs or so with minimal problems. They were replaced about 8yrs ago when we installed Motortronics soft starters and solid state excitation systems. The JC contactors came as part of the package. We do have some wiggle room, but not much. Another problem is that the heavy duty relays have dc coils, which would require more mods to use.

 

[jraef]

Oh yeah, Motortronics people "do loves themselves some JC contactors". It's a kind of incestuous relationship because JC uses Motortronics soft starters for their Fire Pump controllers. I don't think there was a lot of engineering thought put into it.


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[Thedroid]

We have a spotting cabinet built by them also, it has 6 contactors in it that look the same, in addition to the 5 field discharge contactors. These contactors just don't seem to cut it.

I'm checking into the ABB R-series bar contactors. Looks like they make a one just for this type of application. JOR model I believe. I wonder what they cost though? I haven't been in touch with them yet.

After looking at an old GE we had laying around, I noticed that the NC contact overlapped the NO's. I don't believe the Joslyn Clark's had any overlap. I wonder if this could be part of the problem?

 

[Skogsgurra]

You need overlap. If you don't have it, an arc starts and is maintained also when the NC closes. Reason is that the plasma has already formed. You need a quite low resistor value to avoid a continued arc. Best is to have overlap, the NC shall close before the NO open when the contactor drops out.

Gunnar Englund

http://www.gke.org

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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

 

[Thedroid]

Thats what I thought also. I wonder why these relays would be installed if it goes against good practice. I'm trying to find some info on the Telemecanique line, but have been unsuccessful so far.

 

[Skogsgurra]

You could also use a MOV (varistor). There are units that can handle your energy levels. Makes life easier.

Gunnar Englund

http://www.gke.org

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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

 

[Thedroid]

I'm still waiting for a quote from ABB, it will probably take awhile. I couldn't seem to find any info on the Telemecanique line of bar contactors, but I have somebody looking for some info. How important is the time constant spec?