Ik ----- three-phase short-circuit current cycle component valid value, which is used as a calibration calculation for relay protection and a rated open-off flow of the check circuit breaker. The fixed value of the protection device should be calculated by using the three-phase short-circuit current cycle component valid value (under the maximum operating mode of the power system) when a short circuit occurs at the relay protection installation. the ish ----- three-phase short-circuit impact current, which is used to verify the dynamic stability of electrical equipment and bus lines. Ish ----- three-phase short-circuit stable effective value, used to verify the thermal stability of electrical equipment and bus lines. S----- temporary three-phase short-circuit capacity, used to verify the circuit breaker's break-out capacity and determine whether the bus short-circuit capacity exceeds the specified value, as the basis for selecting a current-limiting reactor