The primary and secondary fusion switch is the key equipment in the construction of intelligent distribution network.Its feeder terminal unit（FTU）is installed near the primary equipment and is in the environment of electromagnetic interference.However

it is pointed out by the present research that the EMC requirement in current standards is not in conformity with the actual electromagnetic environment

and the control circuit at the secondary side is seriously affected by electromagnetic interference in the operation of the equipment.In order to promote the improvement of test standardization of primary and secondary fusion equipment

a kind of simulated electromagnetic interference test method based on spherical gap discharge for the electromagnetic interference immunity performance of primary and secondary fusion equipment is proposed in this paper.The test platform is set up to perform conduction interference immunity test of primary and secondary fusion for intelligent distribution switch and analyze the transfer characteristic of instrument transformer.This method can be used to simulate the discharge interference signals produced in such conditions as switching operation

breakdown discharge etc in the system

can generate stable high frequency interference signal at frequency around 1 MHz and perform continuous adjustment to the pulse strength and action time of the discharge signal by way of adjusting the circuit parameters.The obvious high frequency signal has been detected at the output end of the secondary side of the instrument transformer and the frequency spectrum is similar to that of the discharge signal in the main circuit.It is concluded by analyzing the transmission characteristics of instrument transformer that the high frequency interference signal can enter into the secondary circuit through capacitive coupling.This test method can provide reference and data support for the revision of EMC standards for primary and secondary fusion equipment.