As the key equipment of AC-DC hybrid distribution network, the protection and fault isolation of solid-state transformers (SSTs) are of great significance. When the DC distribution line short circuit fault occurs, the fault current rises very fast. According to the structure of solid-state transformer, this paper analyzes the DC distribution line fault, which has two stages: RLC resonance and inductor current free-wheeling. Based on this, a protection method using transient current mutation is proposed, which can quickly identify faults and protect DC lines by using the concavity and convexity of the current waveform. The simulation of DC distribution line fault of solid-state transformer by PSCAD/EMTDC verifies the correctness of theoretical analysis and practicability of the proposed protection method.

AC-DC hybrid distribution network,current derivative,protective relaying,solid-state transformer,concavity and convexity,protective relaying