Arc flash protection benefits in medium voltage

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The first post in this series covered a new arc flash related standard, the 2018 edition of NFPA 70E. It has some changes, such as allowing the use of a permanently mounted test equipment, that will make life easier.

What is not changing are the benefits of arc flash protection. In an arc flash, current goes where it is not intended. It may jump from one conductor to another. Alternatively, current may jump from a conductor to ground. For either of these to happen in switchgear, typically the dielectric breakdown strength of air must be exceeded, or about 3 kV/mm of air gap.

This means that an arc across a centimeter might take tens of kilovolts. The actual value might be a tenth that because the shape of the arcing electrode influences the breakdown voltage. A rounded arc launch point will have a higher breakdown than a pointy one. Another factor that may lower the breakdown value is the insertion of a foreign object, like a metal tool, into the gap.

If the arc path is through machine operator or maintenance personnel, serious injury or death can result. Thus, there can be medical and legal costs as well as insurance ramifications.

Machines, too, can be damaged. An arc flash in the 50, 100 kV or higher range can burn insulation, damage equipment, start fires and cause other problems.

Therefore, the expenses of an arc flash include the cost of machine repair and loss of service. That can be quite expensive if a machine must be replaced.

So, the benefits for preventing and controlling arc flash in switchgear can be tallied up in lives gained and money saved. To learn more about available arc flash solutions, please click here or explore our full line of medium voltage offerings. You can also read our free white paper, “Evaluating the Arc-Flash Protection Benefits of IEC 61850 Communication.” The next post will look at the importance of proper installation.

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