Incident Energy Calc of Faulted MV Cable in Manhole
Incident Energy Calc of Faulted MV Cable in Manhole
(OP)
It has been suggested by some of my colleagues that IEEE 1584 equations can be used to calculate the incident energy resulting from a faulted MV cable in a manhole. Am I correct in my understanding that the equations in IEEE 1584 are only applicable to a fault between conductors having an air gap? If this is correct, I don't see how the equations are applicable to finding the incident energy of a faulted medium voltage cable that won't have any air gap between phases or to the grounded shield. The only way I can trick the software to making this calculation is to insert a bus with an air gap at the manhole location, but this does not realistically model a faulted cable or splice and I don't have any confidence in the results. Does anyone have any experience or guidance with this situation?






RE: Incident Energy Calc of Faulted MV Cable in Manhole
An arc implies an air gap, however small.
Bill
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"Why not the best?"
Jimmy Carter
RE: Incident Energy Calc of Faulted MV Cable in Manhole
RE: Incident Energy Calc of Faulted MV Cable in Manhole
Bill
--------------------
"Why not the best?"
Jimmy Carter
RE: Incident Energy Calc of Faulted MV Cable in Manhole
Using ARCPRO, which was used for the NESC arc hazard tables (>1000V) might be an alternative, at least these are based on single phase faults. These are based on faults in air, however, so they are not strictly applicable either.
Do you have to label the equipment in manholes for arc flashes resulting from cable faults? If you are interacting with the cable or equipment in a way that might cause an arc, you are doing something like switching or removing a separable loadbreak connector. In these situations, the arc would be in air, not through the insulation. What kind of interacting with the cable or equipment would you be doing that would cause an insulation failure in the cable? I guess that moving the cables could initiate a fault if it the insulation was damaged and sitting there ready to blow.
RE: Incident Energy Calc of Faulted MV Cable in Manhole
I agree with jghrist that the IEEE 1584 equations don't really apply. But there is clearly some risk.
Even a fault caused by direct contact between conductors is not necessarily a bolted fault because the conductor material will quickly vaporized and arcing can ensue as the distance between the conductors increase.
Although a fault is likely to start as a line-to-ground fault in a cable, it may be something else before the fault is clear.
David Castor
www.cvoes.com
RE: Incident Energy Calc of Faulted MV Cable in Manhole
RE: Incident Energy Calc of Faulted MV Cable in Manhole
Under "Examine insulated cable, in manhole or other confined space", the "Arc Energy Hazard and Risk Assessment" is "Wide range of energy and confined space, risk moderate".
The HRC is 4, with a note "A job safety analysis is required to justify that this task be done with the equipment energized."
The "Substantiation for Selection of Hazard/Risk Category" is "Risk moderate --> HC 4 or 5, Insulating gloves required due to the nature of the task."
RE: Incident Energy Calc of Faulted MV Cable in Manhole
Unless the facility is under the control of an electric utility, you are better off trying to use NFPA 70E.
David Castor
www.cvoes.com