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 Post subject: 4160 V, 2530 HP Slip-Ring Motor Arc Flash Event
PostPosted: Tue May 12, 2020 8:34 am 
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Joined: Tue Mar 08, 2011 11:23 am
Posts: 34
Location: Utah
We have a 4160 V, 2530 HP Slip-Ring motor that had an arc flash event during start up. Apparently this they had a similar event with this same motor about 7 yrs. ago. I am assuming that we had a gap between the ring and brush that led to the arching a had also acquired some carbon dust build up.

A couple of questions here:
• Any other thoughts on what may have caused this and what is the likelihood of having another event while running vs. start-up?
• Has anyone else experienced similar events and how often does this happen?
• How often does this happen as I have never heard of an arc flash event in a motor/slip-ring compartment?
• What proactive measures practices is industry taking to prevent this, PMs, designs, etc.?
• Are there any measures that could be takes to reduce or redirect the energy? We have a vent fan drawing air into the slip-ring compartment through a filter and exhausting through the fan along with an inspection door. Has anyone ever heard of using designs similar to that of arc hesitant gear to vent the blast to a safe area?

Any and all feedback is greatly accepted and appreciated!
Thanks!!
James


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 Post subject: Re: 4160 V, 2530 HP Slip-Ring Motor Arc Flash Event
PostPosted: Wed May 13, 2020 7:00 am 
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Joined: Tue Mar 08, 2011 11:23 am
Posts: 34
Location: Utah
Attached are a few photos for reference.


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 Post subject: Re: 4160 V, 2530 HP Slip-Ring Motor Arc Flash Event
PostPosted: Mon May 18, 2020 8:03 am 

Joined: Sun Sep 21, 2008 8:24 pm
Posts: 7
Hi Kimo

There would have been a difference in electrical noise as this was building to flash over. A transistor radio set off station would have picked up the normal noise and alert you to the changing noise and impeding failure. A TR should be a standard maintenance tool.

These are great pictures. Would you mind if we use them in our maintenance training courses?

Cheers and health
Dave Smith
President
Canada Training Group


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 Post subject: Re: 4160 V, 2530 HP Slip-Ring Motor Arc Flash Event
PostPosted: Mon May 18, 2020 12:55 pm 

Joined: Fri Jan 29, 2010 7:27 am
Posts: 2
Location: Dearborn MI
Check to make sure the brush-holder springs are maintaining correct pressure on the brush and that the brushes are not binding in the holder. Also, there is an optimum amperes per square inch current density for particular carbon formulations. Check with your brush supplier/manufacturer to see if your operating conditions are within spec for the brushes you have.

Ray


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 Post subject: Re: 4160 V, 2530 HP Slip-Ring Motor Arc Flash Event
PostPosted: Mon May 18, 2020 5:33 pm 

Joined: Sun Feb 14, 2010 9:28 pm
Posts: 21
Location: Queensland
At start, the would rotor open circuit voltage on such a motor might be ~2kV and as such insulation is key. Cleanliness of the slipring box requires routine atention in brush dust removal. Brush lifting & slip ring shorting devices can extend the time between such servicing where warranted.
If your motor starting device (resistance steps / LRS / other) did present an open circuit then the situation is exacerbated.
Certainly brushgear maintenance or issues with brushes hanging up due to dimensional tolerance issues are not uncommon.


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 Post subject: Re: 4160 V, 2530 HP Slip-Ring Motor Arc Flash Event
PostPosted: Thu May 21, 2020 1:15 pm 
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Joined: Tue Mar 08, 2011 11:23 am
Posts: 34
Location: Utah
tfordsk wrote:
Hi Kimo

There would have been a difference in electrical noise as this was building to flash over. A transistor radio set off station would have picked up the normal noise and alert you to the changing noise and impeding failure. A TR should be a standard maintenance tool.

These are great pictures. Would you mind if we use them in our maintenance training courses?

Cheers and health
Dave Smith
President
Canada Training Group

Dave are you referring to just a standard/normal of the off the shelf transistor radio? Do you just use this during start up of the motor?
Yes you are free to use the photo's for training.


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 Post subject: Re: 4160 V, 2530 HP Slip-Ring Motor Arc Flash Event
PostPosted: Thu May 21, 2020 1:27 pm 
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Joined: Tue Mar 08, 2011 11:23 am
Posts: 34
Location: Utah
rayk wrote:
Check to make sure the brush-holder springs are maintaining correct pressure on the brush and that the brushes are not binding in the holder. Also, there is an optimum amperes per square inch current density for particular carbon formulations. Check with your brush supplier/manufacturer to see if your operating conditions are within spec for the brushes you have.

Ray

Thanks Ray,
We are learning more that the brushes where the fault took place do not move easily, not sure if this is a result of extreme heat from two known flashes. We have the found the specifications for the spring tension and looking to test ours. We have also learned that the motor manufacturer recommends electro graphite brushes, where we using metal graphite brushes. Not sure if these were causing excess carbon dust or if they have a higher current density than the recommended brushes?


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 Post subject: Re: 4160 V, 2530 HP Slip-Ring Motor Arc Flash Event
PostPosted: Thu May 21, 2020 1:34 pm 
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Joined: Tue Mar 08, 2011 11:23 am
Posts: 34
Location: Utah
GBISON wrote:
At start, the would rotor open circuit voltage on such a motor might be ~2kV and as such insulation is key. Cleanliness of the slipring box requires routine atention in brush dust removal. Brush lifting & slip ring shorting devices can extend the time between such servicing where warranted.
If your motor starting device (resistance steps / LRS / other) did present an open circuit then the situation is exacerbated.
Certainly brushgear maintenance or issues with brushes hanging up due to dimensional tolerance issues are not uncommon.

Thanks GBISON, We are making sure we are doing better inspection of the slip ring box while the motor in down as well as looking into slip ring maintance/repair.
Anyone have recomendations and/or suggestions here?


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 Post subject: Re: 4160 V, 2530 HP Slip-Ring Motor Arc Flash Event
PostPosted: Mon Jun 01, 2020 12:38 pm 

Joined: Sun Sep 21, 2008 8:24 pm
Posts: 7
Hi Kimo

Thanks for supporting our training with the use of your pictures, I appreciate that.

Yes nothing more fancy than a plain radio. One of our instructors, before cell phones, tracked down a Bonneville Power substation in dense fog following high line noise on his truck radio set off station.

If you have an intermittent arc or corona you will find the problem with a radio very quickly. In our mobile testing and maintenance training labs we teach this.

We regularly have experienced electrical techs amazed at how well it works.

Cheers and health
Dave


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 Post subject: Re: 4160 V, 2530 HP Slip-Ring Motor Arc Flash Event
PostPosted: Mon Jun 15, 2020 1:22 pm 
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Joined: Tue Jul 01, 2014 8:40 am
Posts: 98
Hi Kimo

As it looks like your inquiry has been answered by some very knowledgeable folks here. I too would like your permisison to use the photos in some of my sessions up here in Ontario Canada. Thank you Kimo, All the Best


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