Motor stator string resistance voltage reduction starting control circuit

The starting current for direct starting of a three-phase asynchronous motor is 5 to 7 times the rated current. Because the starting current is large, direct starting is only suitable for small-capacity
motors. When the motor capacity is above 10kW,
decompression starting should be used to reduce the starting current, but at the same time it also reduces the starting
torque, so decompression starting is suitable for occasions where starting torque requirements are not high
. There are generally several methods for decompression starting: For
motors whose stator windings use delta connection during normal operation, Y-△
decompression starting can be used; three-phase autotransformer decompression starting can also be used;
stator winding circuit series resistors or Reactor, etc.: The essence of these starting methods is to reduce the voltage applied to the stator winding of the motor
during starting when the power supply voltage remains unchanged to limit the starting current, and then restore the voltage to the rated value after starting. value, the motor enters normal operation.     Figure 4-10 shows the motor predetermined series resistance voltage reduction starting control circuit . In the figure, KM1 is the power contactor, KM2 is the short-circuit resistance contactor, and KT is the starting time relay. R is the voltage starting resistor .     Circuit working conditions: Turn on the power switch os, press the start button SB2, KM1 is energized and self-locked, and KT is energized and starts timing. The stator of the motor is connected to a resistor ruler for decompression starting. After the time relay KT is delayed, the The delayed closing contact is closed, KM2 is energized, and the starting resistor is short-circuited, and the motor runs normally at the rated voltage . The delay length of KT is set according to the length of the motor starting process.