Abstract: In view of the problem that the R type transformer used in the explosion proof power box of coal mine with the magnetic circuit closed, the excitation current is very large at the time of power up, which is easy to burn the fuse and cause the power box to fail.An impulse current suppression circuit for power frequency transformer was designed, which can reduce the impulse current by changing the current circuit of the transformer at the moment of power up, so as to avoid excessive impulse current to burn the fuse. Experimental verification showed that the circuit can effectively reduce the impulse current of R type transformer at the moment of power up, effectively avoid the damage of the fuse by the instantaneous excitation current, and improve the reliability of the power box.