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 Post subject: Does it require the application arc flash calculation in Gas insulated switchgear
PostPosted: Mon Mar 31, 2014 6:16 am 
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Normally, arc flash study was conducted for metal clad switchgear and other.
by the way, front part is totally blocked in gas insulated switchgear(34.5kV) such as ZX1, GHA and 8DA10.
Does this kind of GIS switchgear also require arc flash study?
The most of vendors mention only reduction of arc flash occurence possiblity.
But specific proof is not provided.


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PostPosted: Wed Apr 02, 2014 5:07 am 
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Location: Rutland, VT
I am not familiar with that type of switchgear, so I was hoping someone who has would respond. I did look at ABBs website of the GIS and there is no racking out of breakers and the breakers can be remotely operated.

Since there is a chance of something happening, I would think it would not hurt to have a arc flash study done and it appears it was done.

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PostPosted: Wed Apr 02, 2014 5:24 am 
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Correct me if I am wrong I am not an expert but GIS switchgear is basically just minimizing the risk of an arc flash by decreasing the minimum distance needed for an arc flash to occur. When switches loads the flash will extinguish much faster than when the insulator is air. Here in the Netherlands in the past they used oil filled breakers, now mostly SF6 gas breakers and vacuum breakers.

If we look at this in an arc flash point of view, what if the vacuum breaker is defected and air fills in? Then you still need to do an arc flash study and wear appropriate PPE when interacting with the equipment locally, at least that is what I would assume.


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PostPosted: Thu Apr 03, 2014 2:47 pm 
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GIS is known to be pretty reliable, at least the more modern versions. The old (1980's and older) stuff is not very reliable at all.

What we have here is the classic problem though that the 2015 edition of 70E will be addressing. The arc flash RISK is a mixture of both the likelihood of an arc flash and the magnitude of the hazard should it occur. SF6 equipment certainly changes the picture. There is also epoxy insulated equipment on the market that is similar except no SF6. Much of it is totally sealed except for the elbow connectors between modules. So you will have to do your own homework in deciding :

1. What is your company's policy on acceptable risk. Typically this requires less than 1 in a million odds for a multiple fatality scenario, 1 in 100,000 for a single fatality or multiple injuries requiring hospitalization, or 1 in 10,000 for a single injury requiring hospitalization. These are risks stated per year.
2. What is the chance of failure? I think that some material studying the issue was published from research at KEMA. GIS was pretty good, an order of magnitude better than most other equipment, but still there. So somehow you've got to get to an estimate of likelihood of failure at least to an order of magnitude, such as 1 in 10,000 unit-years.
3. What is the magnitude of the risk? If you can assume the hazard is over 1.2 cal/cm^2 then you can at least claim hospitalization. We don't have a way of quantifying the difference between a fatality and hospitalization except that it seems to be about 10% as likely for a fatality. Exceeding the arc flash hazard boundary for instance virtually gaurantees at least an injury requiring hospitalization. With arc flash PPE on, the risk is reduced by a factor of 20 (95% chance of minimal injury as per IEEE 1584). Since risk ranking (item #1) is usually powers of 10, this is the same result, and arc flash PPE achieves a factor of 10 reduction...so we can pretty much treat it as a single injury requiring hospitalization, unless your policies require 2 or more workers for the task, in which case it increases the risk by 1. This exercise requires NO actual calculations on our part by assuming that an injury requiring hospitalization will occur in the event of an arc flash.

So, no, arc flash calcualtions don't have to be done, but risk assessment still should be done. Frequently though for scenarios such as this, the net result is an acceptable risk.


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 Post subject: Re: Does it require the application arc flash calculation in
PostPosted: Tue Dec 19, 2017 9:11 am 
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GIS metal clad switchgear still have an air insulated section, which is the incomer section. This section contains line PTs, grounding switch and cable connections.

Vacuum circuit breaker mechanism can fail just like any other vacuum breaker (burned trip coil, charging motor failure, stuck limit switch, etc). This is when the fixed mounted circuit breaker become a disadvantage. The breaker can’t be racked out and someone has to open the front and remove the breaker’s cover to troubleshoot the mechanism. At this point, the switchgear is no longer arc resistance since IEC 62271-200 tests are done with all doors closed and covers on.

So, yes arc flash calculations still needs to be conducted.


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