Note: The IEEE 1584-2018 standard no longer includes grounding in its calculations.
As per IEEE 1584 Std-2002., the type of grounding used in any low voltage system can affect the arc flash incident energy. EasyPower automatically determines which grounding type to use based on a short circuit algorithm.
For the equipment being evaluated, single line to ground fault is performed on A-Phase. The voltage per unit (Vpu) is computed on B and C phases of the equipment. The average of the two Vpu’s is compared with a threshold value that is specified in Tools > Options > System. This value is called Arc Flash Ground Vpu. This has a default value of 1.45, but you can modify it, if necessary.
Figure 1: Arc Flash Ground Vpu
If the calculated Vpu is less than the specified threshold, the system is considered to be effectively “solidly grounded.” Otherwise, it is considered “ungrounded or resistance grounded.”
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