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 Post subject: PPE within Substations
PostPosted: Mon Jun 30, 2008 12:33 pm 

Joined: Mon Jun 30, 2008 12:07 pm
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Location: Charlotte, NC
I am performing arc flash calculations on substation equipment for 4kV, 12kV, and 25kV systems. Does anyone have an answer/opinion on wearing appropriate arc flash for opening circuit breaker doors to verify equipment name plates or to view relay settings on either electromechanical or electronic relays? Further, what about viewing AC panel circuit breakers for station service, or checking/changing Voltage Regulator settings?

It doesn't make since to me that personnel should have to wear moon suits or de-energize equipment to inspect ratings and settings. Do those situations count as "exposed live parts?" Should the PPE requirements apply here? What do you think?


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PostPosted: Mon Jun 30, 2008 2:01 pm 
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Location: New England
Everything you described would still retain the energized parts behind metal doors, ie, deadfront. If you have no exposed parts, then you don't need Arc Flash.

The NFPA TABLE 130.7 says for Switcgear over 1KV,
Reading a panel meter wile operating a meter switch is Level 0.

One thing you might consider is some minimum for all electric work, ie, Level 0 or Level 1.


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PostPosted: Mon Jun 30, 2008 6:24 pm 
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If you're talking about outdoor substations, you will be exposed to live parts everywhere. The only question is what to use as a working distance. If you are in front of a medium voltage breaker, you will probably be about 5-6 feet from the exposed bushings.

I expect that most utilities will end up requiring at least Level 1 just to be in a substation. There will be resistance to wearing long sleeves of any material in the warmer climates, but I think that this is where things are headed.


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PostPosted: Tue Jul 01, 2008 6:59 am 

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Location: Charlotte, NC
The substation is outdoors. Also, how does NFPA Table 130.7 (C) (9) (a) calculate risk categories for specific operations? Can different categories be calculated using the NFPA 70E Equation or IEEE 1584 for specific operations?


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PostPosted: Tue Jul 01, 2008 5:40 pm 
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You have to read the NOTES in the table to see the parameters upon which they were based, ie, 65KA and 2 cycle clearing time. This is not hard and fast, but in general, using the IEEE formulas will routinely result in lower IE numbers. It depends where you are on the grid, but most utilities generally have relatively low short circuit current values. 3000A Isc is not unusual for 13.8KV overhead feeders. Most utility equipment is only rated to 8KAIC. So with the lower arcing currents and a reasonable clearing time the IE numbers can be low. I just finished a 13.8KV Switchgear fed directly from the utility, Isc utility was 2340A and 52MVA. There were pole mounted fuses that cleared in .4 secs at arcing current of 2000A. IE numbers were 3.4 cal, Level 1. The beauty with IEEE formulas is that they are not task related, you can perform any task in Level 1. The table would have you in anything from Level 1 to Level 4 depending on what you were doing.

Not all switchyards have exposed energized parts. Utility switchyards are almost always exposed, but Industrial ones are often all deadfront. You have to use the NFPA formula(s) to calculate flash boundary D=(5.3*MVA*t)1/2. The 4 foot rule only applies to under 600V gear.


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PostPosted: Mon Aug 04, 2008 11:58 am 
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If you are dealing with a utility substation, the requirements for FR clothing would fall under the National Electric Safety Code (NESC). Specifically it is addressed in Section 41, Table 410-1.

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PostPosted: Tue Aug 05, 2008 5:08 am 

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If you are a utility engineer, I would not just blindly follow the NESC tables. I suggest going through the calculations and utilizing your utilities MAD for the equipment you would normally work on/near deenergized and determine an appropriate distance for situations like racking a breaker in/out, switching etc…


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PostPosted: Thu Sep 18, 2008 7:57 am 
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Sorry, I did not mean to suggest "blindly" following the tables but was merely pointing out to the OP that the proper document for utility substations is the NESC not NFPA.

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PostPosted: Wed Oct 01, 2008 7:29 pm 

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What are grounds keepers i.e. mowers, painters etc. wearing?


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PostPosted: Thu Oct 02, 2008 7:54 am 
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Location: Charlotte, NC
PPE in Substations

I am seeing PPE levels all across the board! Talked with one municipal utility that is requiring 8 cal PPE just to enter an outdoor substation. When I questioned the logic, given that in this situation the lowest live parts were 9 feet or more above the ground and anything lower than that was enclosed and 5 to 6 feet above ground level, the response I got was "just because we are concerned about liability".

I have seen the results when substation breakers fail violently but have yet to see one that ruptures the enclosure. Seen some pretty badly deformed cabinets and buckled steel support legs as well! Most likely it might blow the bushings, and if it did my biggest concern would be the shrapnel from the porcelain which is as sharp as a razor, but I don't have a PPE chart for porcelain.

So far with the work we have done we are not encountering major problems on the high voltage portion of the systems. But also before we started with the calcs, we already knew that arc flash had not been a problem with our clients in the past and we think the calcs show why that is the case.

With respect to PPE for the people mowing and if it comes down strictly to liability, then we must ask if they are qualified to be there to start with. We gravel it and keep the grass and weeds killed so we do not have to mow.

I would be concerned about personnel and the equipment if they are mowing that close to it. I do recall a case years back when a guy mowing caught a voltage regulator ground and broke it. He then touched the floating 7200 volt ground and did not make it out alive! Gravel is a better choice and roundup is probably cheaper than mower gas these days!

As far as painters go, I would not allow it to happen on energized equipment anyway, and then you are dealing with approach distances for qualified personnel, unless it is only touch up at ground level.

Hope it helps,
Alan


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PostPosted: Thu Oct 02, 2008 9:53 am 
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What happens if your calculated arc flash boundary extends past the fence? I see that becoming a big problem for utilities.


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PostPosted: Thu Oct 02, 2008 9:55 am 
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acobb wrote:
Most likely it might blow the bushings, and if it did my biggest concern would be the shrapnel from the porcelain which is as sharp as a razor, but I don't have a PPE chart for porcelain.



Easy, just wear this :)


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PostPosted: Thu Oct 02, 2008 1:03 pm 
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Move the fence

If the fence is that close to the equipment it probably should have already been moved! I was about to add that my porcelain PPE would probably include a layer of Kevlar.

Thanks,
Alan


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PostPosted: Thu Oct 02, 2008 4:00 pm 
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You make jest, but wait. I'll the next 70E release has just that - Kevlar FR.


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PostPosted: Thu Oct 02, 2008 6:40 pm 
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Gotta be real!

So do we need full battle gear?


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PostPosted: Thu Mar 19, 2009 1:01 pm 

Joined: Thu Mar 19, 2009 11:01 am
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zrjohnso wrote:
I am performing arc flash calculations on substation equipment for 4kV, 12kV, and 25kV systems. Does anyone have an answer/opinion on wearing appropriate arc flash for opening circuit breaker doors to verify equipment name plates or to view relay settings on either electromechanical or electronic relays? Further, what about viewing AC panel circuit breakers for station service, or checking/changing Voltage Regulator settings?

It doesn't make since to me that personnel should have to wear moon suits or de-energize equipment to inspect ratings and settings. Do those situations count as "exposed live parts?" Should the PPE requirements apply here? What do you think?


What about operating the breaker or recloser in an outdoor substation with the door open? What are utilities requiring.


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PostPosted: Thu Mar 19, 2009 7:12 pm 
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The door open should not be a problem if it is just the control portion as all we deal with is the case. The high voltage cabinet is still closed and elevated. I still am convinced that you cannot make an issue for arc flash hazard in that case! Have not seen the numbers to prove it either. I have seen many substation breakers fail and in many cases it has been violent and destructive to the equipment. Would I have wanted to be there....not at all, but do I think I would have been injured....NO!


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PostPosted: Fri Mar 20, 2009 3:38 pm 
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"the employer shall ensure that an assessment is performed to
determine potential exposure to an electric arc for employees who work on or near energized parts or equipment."

Our interpretation is that some one must be interacting with the equipment in a way that would increase the potential (probability) of an arc. Reading nameplates, unless done in the vicinity of someone doing other work that does meet increase the potential, does not meet this test.

We are all aware of equipment failing when no one is around. The chances of these failures occurring when someone is reading the nameplate is very low.


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