The calculation of maximum and minimum short circuit currents has been discussed in IEC 60909 - Calculation of Maximum and Minimum Short-circuit Currents. What are the significance of these values?
The maximum calculated short-circuit current values are used for
- Selecting interrupting devices of adequate short-circuit interrupting and peak rating,
- Checking the ability of components of the system to withstand mechanical and thermal stresses,
- Determining the time-current coordination of protective relays.
The minimum values are used for setting the required sensitivity of protective relays.
The minimum short-circuit values are sometimes estimated as fractions of the maximum values. It is only necessary to calculate the maximum values of short-circuit current.