How can we reduce the incident energy levels?
There are actually a number of ways we can lower the arc flash results, but each of them are going to hit at least one of the three elements we just discussed. We can increase the distance the person is standing from the potential arc source. We can decrease the amount of time that the arc flash will exist for. We can reduce the available fault current available to feed the arc flash (but this one typically has some drawbacks). Increase the working distance This is usually the easiest one to implement as long as you can think of a way to do it. It won’t require changing the system design or installing any permanent equipment (possibly).
Quick tip: if you can get outside of the arc flash boundary then you know for sure that you are working from a distance where the incident energy is less than 1.2cal/cm2.
1st Arc Flash Service consultants provides special care while doing one of the most hazardous jobs in the industry. Remember that a remote racking device is a tool which replaces the traditional system with something that can be operated from a distance. Remote switching. Remote switching is very similar to remote racking, but this is used to operate circuit breakers from the open to closed position or closed to open instead of racking them out onto the floor. The most well-known type of remote switching device in the industry is by CBSArcSafe and interestingly named the “chicken switch”. This device can be installed to the front of the switchgear over the operating mechanism. The worker can stand back outside the arc flash boundary and safely operate the breaker.
Differential protection. This method uses current to detect a fault… but it’s a little different than measuring the current passing through a single point (which then you are waiting for the relay to realize it is a fault and not just a big motor starting). The way differential protection works is by using a simple calculation that current in equals current out. Let’s say you have a switchgear line-up with a main breaker feeding a bus that then has six feeder breakers feeding power to the plant. If you were to have an arc flash inside this piece of switchgear then that means you would have a certain amount of current that is coming through the main breaker that is not going out one of the six feeder breakers. Differential protection basically looks at the current flowing through the main breaker and compares it to the sum of the current flowing through the six feeders… any difference and the system trips.
1st Arc Flash Service can consult which is probably the favorite among engineers for solutions using differential protection (feeder, bus, and transformer).