Radiation Disturbance from AC Motors in Underground Coal Mines

The radiated electromagnetic disturbances produced by operating electromotor equipments in coal mines have some effects on the electromagnetic environment in coal mines. Based on the analysis of the Chinese national EMC standard on rotating electrical machines and the operation characteristics of the electromotor equipments in coal mines, it can be concluded that frequency spectrum of the radiated disturbances resulting from AC motors ranges from 9kHz to 1GHz. The radiated electromagnetic disturbances in the pumping house underground mines have been measured. The results show that the radiated emissions above 30MHz produced by the normal running electromotor system are quite low, which are comparable to the radiated emission limits set in the Chinese national standard GB 755-2008;the maximum radiated field strength reaches about 0.56V/m under 30MHz. However, when motors start or stop, the radiated field strength can reach about 1.26V/m or higher. Therefore, some shielding measures for monitoring and communication equipments should be taken to reduce the radiation interference from AC motors.