Calculating Incident Energy Released With Varying Ground Fault Magnitudes on Solidly Grounded Systems

The IEEE Standard 1584-2002 is the recognized standard regarding the calculation of incident energy output from an ac three-phase arcing fault. While that standard does not provide incident energy calculations for the much more common single-phase-to-ground fault, it explains that the expectation is that such a ground fault will either self-extinguish or escalate into a three-phase fault. If the fault escalates, the three-phase calculations can be used. The amount of time that the arc burns as a single-phase fault before escalation is not defined, but a reference document used by the 1584 standard defines this escalation time as one to two cycles. No attempt is made to calculate the incident energy released during this escalation period. While exact answers to the question of how much additional energy would be released are best answered through additional testing, this paper attempts to bracket likely high and low ranges of incident energy that could be released from an arcing single-phase-to-ground fault prior to escalation into a three-phase fault. As this paper only provides a theoretical basis for the calculation of additional energy released from arcing ground faults prior to escalation, it is the opinion of the author that future standards should include testing of incident energy released from faults that begin as low-level arcing ground faults.