PURPOSE: To forecast the generation of a creeping flashover, by arranging a simple antenna for receiving noise radio waves and an electric field intensity measuring apparatus which detects and measures the intensity of an electric field of the received noise radio waves to detect the generation of an external partial discharge with the measurement of the noise radio waves accompanying the generation of an external partial discharge.

CONSTITUTION: A voltage from a high voltage power source 1 is imposed on a stator coil winding 2 to create a creeping flashover via a coil support plate 3 between the winding 2 and a coil support bracket 4. A noise radio wave generated by an external partial discharge can be received with an electric field intensity measuring device 6 via a handy antenna 5 utilizing a copper wire. The maximum of the electric field intensity thus obtained increases gradually with a rise in the applied voltage to cause a creeping flashover after being accompanied by maximum electric field intensity with a greater pulsing property. With such an arrangement, when the antenna and the electric field intensity measuring apparatus are used jointly at a withstand voltage test, the creeping flashover can be forecast. A processing corresponding to the results of measurement enables smooth execution of a test.