Daba Power Generation Co., Ltd. 300MW unit, each unit equipped with 2 sets of mechanical vacuum pumps, of which 1 run, 1 spare. The vacuum pump is used for vacuuming when the unit is started, and used for extracting the non-condensable gas in the condenser in normal operation. The pump is equipped with motor 160kW, speed 590r / min, rated current 330A, voltage 380V, Class B insulation, normal operation current 220 ~ 230A. Every summer, the motor temperature will exceed the limit, was forced to install a temporary cooling fan, but with little effect. Long-term high temperature motor will cause insulation aging, shorten its service life. The reason for the high temperature of the vacuum pump motor is as follows. 1 reason analysis (1) motor power, operating current, heat. (2) The fan speed is low, wind pressure, air volume is small. (3) fewer fan blades, resulting in a small amount of wind. (4) motor with dust, oil, reducing the cooling capacity. (5) The voltage of the bus where the vacuum pump motor is located is 380V. Due to the voltage drop of the cable and the uneven distribution of the load, the actual voltage applied by the motor is only 365V, which causes the running current to be large due to the low voltage. 2 Countermeasures Motor power, speed and vacuum pump match, can not be changed. Fan mounted on the motor shaft, the motor speed determines the fan speed, it can not be replaced. Although increasing the number of fan blades can play a role, but the increase in the number of blades, the dynamic balance is not easy to find, such as finding is not good, will cause increased motor vibration. (1) Lengthen the original fan cover 40cm, install a fan with the same diameter inside the axial fan, axial fan motor power 850W, speed 1489r / min, voltage 380V. The original fan to keep. Axial flow fan set up all the way to power control, axial fan and the main motor without a chain. After the start of the vacuum pump to start the axial fan operation, the vacuum pump outage after 30min axial fan, so that the main motor is fully cooled; (2) Regularly remove the motor dust, keep the motor heat sink clean, increase its cooling capacity; ( 3) The bus where the vacuum pump voltage is adjusted to 400V. 3 Effect (1) As the axial fan speed is high, the wind pressure air volume, cooling effect is greatly enhanced in the same ambient temperature and load current, the main motor temperature dropped 12 ℃. Summer main motor temperature no longer exceeded. (2) Axial fan can be man-made control, the main motor is out of service, the axial fan is still running, the main motor can be fully cooled. (3) Try to balance the load distribution of the 2-phase busbar to prevent the voltage drop of some busbar due to overload. (4) After the voltage is adjusted, the operating current of the vacuum pump is reduced to 210A, and the calorific value is relatively reduced. (5) slow down the insulation aging of the main motor, extending its service life.