If you can’t eliminate an arc flash hazard, the next best arc flash mitigation technique is substitution. Unfortunately there are not a lot of ways to perform substitution to mitigate arc flash: electrical energy cannot simply be replaced by some other form of energy to provide power to equipment.
Substitution of Electrical Equipment
You can, however, replace equipment. After performing an arc flash study, you may discover that one of the reasons for high incident energy is that your equipment is old and out of date. If equipment is out of date, it must be replaced: replacement equipment could be selected for a number of reasons, including:
- Selecting breakers and fuses with faster tripping times than those currently installed. As technology improves, newer protective devices generally trip faster than older ones. A faster tripping time leads to reduced arc flash incident energy. ” Per the equations in IEEE Std. 1584-2002, arc flash incident energy varies linearly with time. If the duration of the arcing fault doubles, the available energy doubles; halve the duration and you cut the energy in half.”
- Arc resistant switchgear as a substitute for currently installed switchgear. Arc resistant switchgear contains the energy of an arc flash inside the equipment and directs it away from personnel.
Zone Selective Interlocking
Another way to reduce arc flash incident energy is by taking advantage of Zone Selective Interlocking (ZSI). ZSI allows your breakers to communicate with each other to provide the fastest tripping time possible. You can read more about ZSI here. An important thing to note is that in order to take full advantage of ZSI, you need to make sure your devices are coordinated.
You can also mitigate arc flash hazards by adding an arc flash reduction maintenance switch to your system. The maintenance switch reduces incident energy levels on equipment downstream from the maintenance switch. The maintenance switch has its own analog circuit which is designed to trip faster than digital circuit breakers. More information can be found here.
To summarize, there isn’t a whole lot of substitution that can be done when dealing with electrical power systems. However, you can still replace out of date equipment with arc resistant ones. You can also add equipment that can perform zone selective interlocking, and can add equipment with a maintenance switch to your system.
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