Arc flash calculations
Arc flash calculations
(OP)
Hello All,
I am performing arc flash analysis on small MV system, 12.47kV is the service voltage with some 12.47 equipment and goes down to 208V. I have couple of questions on the calculations:
1. For arc flash, IEEE 1584 equations are used which are typically for 3-phase faults. Why is line-ground fault not considered for arc flash? Is the reason that line-ground fault quickly turns into a three phase fault in 15kV or small systems?
2. Now the code requires to install a arc flash mitigation system for systems rated for 1200A or more. These arc flash mitigation is typically designed for a 3-phase arcing fault. For example a maintenance setting is provided for a 3-pole 2000A breaker. The maintenance setting reduces the instantaneous to 5000A to lower the arc flash energy, but the ground fault is set for a instantaneous of 2000A, which is still lower than the maintenance setting. Why is still the L-G not considered for arc flash?
I am performing arc flash analysis on small MV system, 12.47kV is the service voltage with some 12.47 equipment and goes down to 208V. I have couple of questions on the calculations:
1. For arc flash, IEEE 1584 equations are used which are typically for 3-phase faults. Why is line-ground fault not considered for arc flash? Is the reason that line-ground fault quickly turns into a three phase fault in 15kV or small systems?
2. Now the code requires to install a arc flash mitigation system for systems rated for 1200A or more. These arc flash mitigation is typically designed for a 3-phase arcing fault. For example a maintenance setting is provided for a 3-pole 2000A breaker. The maintenance setting reduces the instantaneous to 5000A to lower the arc flash energy, but the ground fault is set for a instantaneous of 2000A, which is still lower than the maintenance setting. Why is still the L-G not considered for arc flash?






RE: Arc flash calculations
RE: Arc flash calculations
RE: Arc flash calculations
RE: Arc flash calculations
It is probably the best resource on the specifics in question.
RE: Arc flash calculations
RE: Arc flash calculations
RE: Arc flash calculations
RE: Arc flash calculations
Arc flash study is identifying the worst case energy, which is for three phase fault and the trip settings are corresponding to that current. Now instead of three phase fault if there is a ground fault, the arc energy for the same fault current would be reduced to 1/sqrt3. So when the protective device operates, the arc energy would be restricted to much lower level. Hence there should not be any concern.