Prediction And Optimization Of Ventilation Flow Field And Cooling Performance Of Large Motor In Pumping Station

The operation of a large motor in pump station will produce a lot of heat.If the heat can’t be dissipated timely and effectively,it will lead to too hot of the motor whichwill affect safe operation and service life.Forced draft of fan is a common ventilation cooling method for large motor.However,in engineering,the winding insulation failure caused by the local high temperature of motor or excessive ventilation which increases operation cost of ventilation system often happen.In view of the above problems,In this paper,a large motor in a pumping station is taken as the research object,and the operation heat of the motor is calculated by combining theoretical analysis with numerical simulation;carries out theoretical calculation and numerical simulation on the resistance of large motor ventilation system to accurately determine the fan operating conditions;numerically simulates the motor ventilation flow field,analyze the ventilation flow field law and the influence of rotor eccentricity;and numerically simulates the rotor blade The reasonable selection of fan and the optimal operation scheme of ventilation system are put forward.The main work and achievements of this paper are as follows.(1)The calorific value of the motor is calculated,including total energy consumption,iron core loss,copper loss of stator winding,copper loss of excitation winding and mechanical loss.The flow field of the motor ventilation system with multiple ventilation rates was simulated when the motor was running and the rotor was stationary respectively.The resistance of the system was calculated and the ventilation pressure curve was fitted.The results show that the resistance of the motor ventilation system when the rotor is stationary is close to the theoretical value,and the ventilation resistance when the rotor is rotating is slightly greater than that when the rotor is stationary.The application of system ventilation needs pressure curve and fan total pressure characteristic curve to solve fan operation condition and system air volume.(2)The ventilation flow field of the motor with the rotor centered and eccentric is simulated,and the ventilation flow field law is analyzed.The results show that the wind speed distribution in the stator core ventilation slot is uneven:The wind speed of the middle ventilation slot in the same row of vertical ventilation slot is the highest,and gradually decreases upward and downward;The wind speed of the ventilation slot along the circumferential direction changes periodically.The wind speed of the ventilation slot at the rotor pole spacing is higher than that at the magnetic pole.Therefore,for the ventilation slot at the same height,the average wind speed of a certain direction is calculated according to a magnetic pole and its interval.When the rotor is in the middle,the minimum wind speed is 78%of the maximum wind speed.The wind speed of the ventilation slot on the side of the main air duct is the highest,the wind speed on both sides decrease,and the wind speed on the opposite side is the lowest;Due to the rotor rotation,the wind speed in the downstream side of the main air duct is slightly higher than that in the upstream side according to the rotation direction.When the rotor is eccentric,the minimum wind speed is 73%of the maximum wind speed according to the maximum allowable eccentricity.The wind speed at the main ventilation duct side is always the maximum,which is not affected by the rotor eccentricity;In addition to the main ventilation side,The minimum wind speed is always in the direction of rotor deflection.(3)The influence of the fan blade and its shape on the forced ventilation of the fan is numerically simulated and analyzed.The blade was originally used for the self circulation ventilation motor without forced ventilation,and the ventilation volume was small;After forced ventilation with fan,because of the rapid increase of wind speed,compared with no blade,the blade becomes resistance,so it should be removed.For the self ventilation air cooling mode of the rotor with fan,the ventilation rate is nearly proportional to the rotor speed.The ▽45° shaped blade has small resistance of ventilation system,high wind speed at the most unfavorable point of motor and small resistance moment of rotor.At the same time,it can also be used for bidirectional rotating motor.(4)According to the numerical simulation of the flow field,the temperature rise of the winding in each part of the motor stator is calculated.The maximum temperature rise of the motor stator occurs in the minimum wind speed ventilation slot.When the rotor is in the middle,the maximum temperature difference of the motor is 2.9℃;when the rotor is eccentric,the maximum temperature difference of the motor is 4.2℃,which is greater than the temperature difference when the rotor is not eccentric.(5)According to the operation temperature and temperature rise control requirements of the most unfavorable point of stator winding,the minimum ventilation required for the motor under different ambient temperature is determined.Based on this,the number of fan start-up units and the frequency conversion ratio of variable frequency speed regulation operation are determined.On the premise of satisfying the cooling requirements,the ventilation system is optimized to improve the safety and economy of the unit operation.