This series motors with box type steel structure, can be ajusted its speed using high voltage inverter; Forced cooling structure for the cooler or protective cover, ensure the cooling effect of motor under low frequency operation; Insulation structure for bearing, reduce the damage from shaft current and improve the life of bearing. This series motors have characteristics of high reliability, wide speed range, high precision, beautiful apperance, low noise, little vibration, and can be applied to fan, pump, compressor, mining machinery, engineering machinery installed in power plant, steel mill, mine and so on.