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1前言为了保护电机,减少对电网的污染,当电机容量与电网变压器容量不符合IQ/Ie≤3/4+S/4P关系时(IQ电机起动电流；Ie电机额定电流；S变压器容量；P电机容量),电动机应采用降压起动。即：在电机起动时降低加在电动机定子绕组上的电压,当电动机起动后,再将电压恢复到额定值,使之在正常电压下运转。由于电流与电压成正比,所以降压起动可以
1 Preface In order to protect the motor and reduce the pollution of the power grid, when the motor capacity and the grid transformer capacity do not meet the relationship of IQ / Ie≤3 / 4 + S / 4P (IQ motor starting current; Ie motor rated current; S transformer capacity; P Motor capacity), the motor should be used to start buck. Namely: When the motor starts to reduce the voltage applied to the stator winding of the motor, when the motor starts, then the voltage back to the rated value, so that the normal operation of the voltage. As the current is proportional to the voltage, so step-down start can be