Oct 28, 2020
Application of Soft Starter in the Control System of Bucket Wheel Stacker and Reclaimer
Bucket-wheel stacker-reclaimer is a large-scale bulk material loading and unloading machine. The power supply method generally adopts cable reel or sliding aluminum collector, the voltage level is AC380V 50Hz, three-phase four-wire system; if possible, high-voltage cable reel is used, and the voltage level is AC6kV 50Hz, three-phase three-wire power supply to the machine. In a three-phase four-wire power supply system that uses cable reels or sliding aluminum current collectors with a voltage level of AC380V 50Hz, the bucket wheel and cantilever belt conveyor in the drive mechanism use three-phase squirrel-cage asynchronous motors with greater power , The starting method adopts direct starting or autotransformer decompression starting, which has many shortcomings. Using direct starting, the starting current is large, generally 4-8 times the rated current of the motor, which causes a significant drop in the power supply voltage and affects the normal operation of other electrical equipment of the same power supply; when the autotransformer is used for step-down starting, two times will occur during the starting Impact torque and current cannot be started with load, the control circuit is complicated, and maintenance is inconvenient. Start with a soft starter, no impulse current, constant current start, and stepless voltage regulation to the best starting current.
2 Soft starter characteristics
(1) Make the starting current of the motor rise steadily to the set value with a constant slope, without inrush current to the grid.
(2) The motor maintains a constant current during starting. Ensure that the motor starts smoothly and is not affected by the grid voltage. This is due to the introduction of motor current feedback in the thyristor phase shift trigger circuit. When the grid voltage fluctuates, the control circuit can automatically change the conduction angle of the thyristor to keep the starting current at the original set value.
(3) The starting current rise rate can be adjusted to reduce the impact of torque on the load when the motor starts.
(4) The starting time is adjustable.
3 Soft starter control
Take a certain type of bucket wheel stacker and reclaimer as an example, the bucket wheel, cantilever belt drive mechanism motor is soft-started control, bucket wheel mechanism drive motor P=90kW, IN=164A, cantilever belt conveyor drive motor P=90kW, IN= 164A. The power supply system is powered by a sliding aluminum current collector, and the machine voltage is AC380V 50Hz, three-phase four-wire system.
The cantilever belt conveyor control is shown in the figure: the main circuit of the motor is controlled by the circuit breaker 9QM2, the forward and reverse control contactors 9KM2, 9KM3, the bypass operation contactor 9KM4, the thermal relay 9EH1, the semiconductor protection fuse FU1-3, and the soft starter CMC-S composition (the control principle of the bucket wheel drive motor running in one direction is the same as that of the cantilever belt conveyor).
The control signal is directly output by the PLC relay output module PK1, PK2, and the soft starter reset signal PK4; the soft starter fault alarm is sent out a passive normally open point from terminals 5 and 6 and the control power circuit breaker 9QM2, thermal relay 9EH1, control power The auxiliary contacts of the protective circuit breaker 9QF1 are sent to the PLC input module. Control and system protection are completed by PLC program.
Soft starter settings:
(1) Ramp time 5s
(2) Starting voltage 60%UN
(3) Current limit 1.5～3IN
(4) Stop time 10s
(5) Set the control function as free stop and start acceleration detection
The electronic soft starter is used to control the motor of the bucket wheel and cantilever belt drive mechanism. The starting is stable, there is no impact on the power supply system, and the control system works stably.