thread238-292509 IEEE1584 does n 1

[EddyWirbelstrom]

thread238-292509
IEEE1584 does not specify a short-circuit current calculation method.
Pre version 8 of SKM PTW arc flash analysis software to IEEE 1584 used the PTW ‘comprehensive’ short-circuit current calculation method which is the classical impedance reduction method without the multiplying factors used by IEC 60909-0.
Version 8 of SKM PTW arc flash analysis software to IEEE 1584 introduced the IEC 60909 option.
IEC 60909-0 Table 1 recommends using a ‘Voltage factors c’ when calculating max and min short-circuit current. I”k = c Un / ( √3 * Z ). The ‘c factor’ for low voltage is 0.95.
For voltages below 1000V, Amendment 1 Section 5.2 of IEEE 1584 recommends calculating two arcing currents, one using 100% of rated volts and one at 85% of rated volts. The higher resulting incident energy to be used.
If the IEC 60909 option is used in the PTW arc flash program, the ‘c factor’ of 0.95 will be used instead of the 0.85 factor when calculating the second arcing current.
This is not in accordance with Amendment 1 Section 5.2 of IEEE 1584.

 

[dpc]

I don't understand your concern. Per 1584, you use 85% of the calculated arcing current for a second incident energy calculation and take the worst case (below 1000V). The arcing current is determined based on the bolted (zero impedance fault current, however you chose to calculate that. I'm not seeing any conflicts - you just have to decide what value to use for the bolted fault current. I haven't looked at the specifics of how SKM computes the bolted fault current for AF calcs when the IEC option is specified. But keep in mind that the accuracy of the incident energy calculation in general leaves a lot to be desired, due to all of the variables and the large number of assumptions necessary to calculate an energy. It's an approximation at best.

The major shortcoming of IEEE 1584 is that it does not address how to account for fault current that varies with time during the fault.