QJ3 series of manually operated auto-voltage start-up circuit

The circuit illustrated in Figure 3-47 involves a three-phase AC motor that is initially connected through a step-down autotransformer. To initiate operation, the power switch is closed, and the operating handle is pushed to the start position. Once the motor has started, the operating handle is pulled to the Run position, which disengages the autotransformer voltage regulator, allowing the motor to connect directly to the three-phase power supply for full voltage operation. At this stage, the trip coil at the YR station is energized, maintaining the operating handle in the Run position through an interlocking mechanism. To stop the motor, the stop button (SB) can be pressed.

This circuit design utilizes a step-down autotransformer to facilitate a soft start for the three-phase AC motor, which is particularly beneficial for reducing inrush currents and mechanical stress on the motor during startup. The autotransformer allows for a lower voltage to be applied initially, ensuring a gradual ramp-up to full operational speed.

The interlocking mechanism is a critical safety feature that prevents accidental disconnection of the motor while it is running. This mechanism ensures that as long as the motor is energized, the operating handle remains locked in the Run position, thereby preventing any unintentional stop commands that could lead to operational hazards. The trip coil serves as an actuator that maintains this lock, ensuring operational safety.

When the motor needs to be stopped, the stop button (SB) can be pressed, which will deactivate the trip coil and release the interlocking mechanism, allowing the operating handle to return to a neutral position. This design ensures that the motor can be safely and effectively controlled, providing both operational efficiency and safety for users.

Overall, this circuit configuration is well-suited for applications requiring controlled motor startup and reliable operational management, making it a valuable addition to industrial motor control systems. Circuit shown in Figure 3-47. Close the power switch os, operating handle to push the start position, then three-phase AC motor is connected through a step-down autotransformer after. To be started is completed, the operating handle to pull the Run position, autotransformer voltage regulator out of operation, the motor directly connected to the three-phase power supply for full voltage operation. At this time the trip coil is energized YR station, keeping the operating handle in the operating position by the interlocking mechanism.

When stop, press the stop button SB can.