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 Post subject: SKM PTW - Out of IEEE 1584 Range
PostPosted: Thu Apr 20, 2017 1:39 am 

Joined: Wed Dec 07, 2016 2:09 am
Posts: 1
When calculate arc flash for 33kV Vacuum Circuit Breaker, SKM will calculate the incident energy based on Lee Equation. A note will appear " Out of IEEE 1584 Range, Lee Equation Used, Applicable for Open Air Only. Existing Equipment type is not Open Air! "

The calculated incident energy for the 33kV VCB is level 4, below 40cal/cm2. A label can be produced via the SKM.

My question is can the label with the calculated result put on the switchgear? Can the operator wear the PPE and work on live?

Anyone had come across this, please advise and discuss. Thanks.

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 Post subject: Re: SKM PTW - Out of IEEE 1584 Range
PostPosted: Thu Apr 20, 2017 6:46 pm 
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Can you put a label on it? You can label anything any way you want. Whether it is right or not is an engineering judgement.

As to whether or not someone can wear a 40 cal suit and work on the equipment, that's a little harder to tell based on your limited information. You stated "switchgear" but there are many types such as overhead or pad mounted gear, metal clad, metal enclosed, switchboards, and even GIS with VCB''s. Switchgear is a generic term referring to equipment that does power switching. Each design has it's particular requirements as to work methods required to perform various tasks on the equipment. Whether or not a 40 cal suit makes this difficult or impossible depends on the work. For instance it might be prohibitively difficult to land a small control wire close to an energized bus bar in energized metal enclosed gear that uses bolt-in VCB's, although the issue has more to do with the dexterity limitations of the rubber glove work method (if you can find them with that voltage class) than to do with the arc flash suit and hood. On the other hand drawout breakers can easily be worked on when they are drawn out of the enclosure and placed on the floor or a bench for access or sometimes in the lockout position. And it is relatively easy to work on many types of bolted-in circuit breakers that have either separate low voltage control compartments or that have all the low voltage controls integral to the circuit breaker such as shunt trip, UV trip, and auxiliary contacts mounted on the front physically isolated from the power conductors such as it typical of an "Ensign" style circuit breaker commonly used by mining companies. In all of the low voltage cases where energized work can proceed easily, the medium voltage conductors are not generally exposed in most cases so the arc flash suit really isn't necessary except for racking equipment in and out of a cell.

As to the rest of your questions, the Lee equation has two parts. The first part calculates the amount of power/energy available from the arc based on a maximum power transfer assumption. This is the maximum amount of arc energy that would be theoretically available with any hypothetical scenario, irrespective of whether such a large arc is even possible. The second aspect is that the Lee equation assumes that incident energy decreases with the square of the distance. Test data and IEEE 1584 have shown that especially with larger enclosures used for switchgear, this assumption is not true for typical short working distances and thus we have an exponent less than 2. Thus depending on the distance, the Lee calculation may be wrong. OSHA has already indicated that the Lee equation should not be used for medium voltage as it has a significant error that can increase incident energy significanty over the value predicted

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