Generally speaking, the short-circuit current of a three-phase short circuit is the most large and harmful, so the key to short-circuit current calculation is the calculation of three-phase short-circuit current. Based on the short-circuit current based on the three-phase short circuit, the maximum short-circuit current has three calculation points, i.e. 100kV bus short circuit (K1 point), 10kV bus short circuit (K2 point), 0.4kV bus short circuit (K3 point).