The transient electromagnetic field generated by isolation switch’s operation is one of the important sources of electromagnetic interference in substation.To evaluate the level of electromagnetic disturbance at the primary side of the transformer

we analyzed the electromagnetic transient process.Then

we established models of distributed parameter in bus and models of switching arc’s extinguishing and restriking.Based on these models

numerical calculations of power network model under the operation mode of single-phase transformer and single circuit line were conducted

and characteristics of over-voltage and over-current were evaluated synthetically.The simulation results demonstrate that the bus current is composed of a series of cone-shaped damped oscillatory waves

the maximum voltage to ground among jump waves between isolation switch and circuit breaker is 586.2 k V

and the disturbance voltage conducted to transformer decreases to 514.4 k V

which will not cause insulation breakdown of main transformer.Moreover

interference signal’s frequency is determined by the length of the bus and the short line

and is limited in the range of 32.87 MHz.