对于具有功率Pr的电机，建议使用功率因数校正，在额定电压Ur下，无功功率Qc低于空载电机Q0吸收的无功功率的90%，以避免超前功率因数。考虑到在空载条件下，吸收的电流I0[A]仅为无功，如果电压以伏特表示，则结果是：电流I0通常在电机制造商提供的文件中给出。电机的单个功率因数校正存在以下风险：断开电源后，电机将继续旋转（剩余动能），并利用电容器组提供的无功能量自励，作为异步发电机。在这种情况下，电压保持在开关和控制装置的负载侧，危险过电压的风险高达额定电压值的两倍。然而，在图3的情况下，为了避免上述风险，正常程序是仅在电机运行时将PFC组连接到电机，并在断开电机电源之前将其断开。一般来说，
表3显示了一些ABB电机根据功率和极数进行功率因数校正的无功功率值。功率因数校正前的Pr Qc功率因数校正后的功率因数校正[kW][kvar]cos NU r I r[A]cos NU 2 I 2[A]400V/50 Hz/2极/3000 r/min 7.5 2.5 0.89 13.9 0.98 12.7 11 2.5 0.88 20 0.95 18.6 15 0.9 26.5 0.98 24.2 18.5 5 0.91 32 0.98 29.7 22 5 0.89 38.5 0.96 35.8 30 10 0.88 53 0.97 47.9

In the case of direct connection (diagrams 1 and 2) there is a risk that after disconnection of the supply, the motor will continue to rotate (residual kinetic energy) and self-excite with the reactive energy supplied by the capacitor bank, acting as an asynchronous generator. In this case, the voltage is maintained on the load side of the switching and control device, with the risk of dangerous overvoltages of up to twice the rated voltage value. However, in the case of diagram 3, to avoid the risk detailed above, the normal procedure is to connect the PFC bank to the motor only when it is running, and to disconnect it before the disconnection of the motor supply. As a general rule, for a motor with power Pr , it is advisable to use a PFC with reactive power Qc below 90% of the reactive power absorbed by the no-load motor Q0 , at rated voltage Ur , to avoid a leading power factor. Considering that under no-load conditions, the current absorbed I0 [A] is solely reactive, if the voltage is expressed in volts, it results: The current I0 is generally given in the documentation supplied by the manufacturer of the motor. Individual PFC of motors The usual c
Table 3 shows the values of reactive power for power factor correction of some ABB motors, according to the power and the number of poles. Pr Qc Before PFC After PFC [kW] [kvar] cosϕr I r [A] cosϕ2 I 2 [A] 400V / 50 Hz / 2 poles / 3000 r/min 7.5 2.5 0.89 13.9 0.98 12.7 11 2.5 0.88 20 0.95 18.6 15 5 0.9 26.5 0.98 24.2 18.5 5 0.91 32 0.98 29.7 22 5 0.89 38.5 0.96 35.8 30 10 0.88 53 0.97 47.9