Sep 18, 2020
Application of motor soft starter on powerful belt conveyor
In underground coal mine production, three-phase asynchronous motors are widely used. In order to reduce mechanical shock and ease the working pressure of the power grid, various start-up methods are adopted for the motor, mainly including stator series reactor, y/△ and series autotransformer, and a large number of hydraulic coupling is used for the belt conveyor. Startup mode of the device. These startup methods all have the disadvantages of excessive equipment volume, voltage can not change linearly during startup, electrical and mechanical shock cannot be avoided during switching, and high equipment failure rate. In order to solve the above-mentioned problems, the currently commonly used advanced microprocessor control technology and power electronic technology motor soft starters can be used to eliminate electrical and mechanical shocks to the maximum extent and extend the service life of the equipment.
1 The working principle of the motor soft starter
The motor torque that controls the AC asynchronous motor is proportional to the square of the voltage applied to the stator terminal, and the motor current is proportional to the stator voltage. Therefore, the acceleration torque and starting current of the motor can be restricted by controlling the voltage applied to the stator of the motor to reduce the excessively high starting current and starting torque generated when the motor starts. The voltage change can be achieved by controlling the conduction angle of the thyristor. Each phase of the soft starter's main circuit consists of two thyristors in anti-parallel connection, using all-digital vectorless control technology. At work, after the CPU receives the control signal, it automatically controls the thyristor trigger pulse phase shift according to the user's setting, so that the motor starts smoothly according to the set curve. After the start, the CPU sends a signal to make the bypass vacuum contactor enter a normal working state, and the thyristor suspends work. When it needs to stop, a stop signal is given, and the CPU controls the vacuum tube contactor to disconnect, and at the same time controls the thyristor to trigger pulse phase shift (the direction is opposite to the direction at start), and the thyristor completes the soft parking process. During inertial parking, the CPU directly controls the vacuum contactor to disconnect, and the motor is powered off to achieve inertial parking.
2 Application of motor soft starter on strong belt conveyor
A sub-mine powerful belt conveyor system of a certain mining group has a total of 4 belt conveyors, which are responsible for about 70% of the coal transportation task of the entire mine. It works for more than 20 hours a day and has a heavy workload. It is the throat of the entire mine. The belt parameters are as follows:
L1=1812m; L2=1041m; L3=1423m;
Bl=B2=B3=1m; B4=0.8m; Ue=66OV;
The original driving methods of the above 4 belts are all direct start. Due to the long transport distance and large starting current, the magnetic starter and the upper-level power distribution switch are often tripped, causing heavy load failure, burning of the magnetic starter, and reducing the quality of the power supply. At the same time, the reducer, motor, and hydraulic coupling of the 4 belt conveyors were damaged to varying degrees, and the maintenance of drums and joints was large, and the accident rate was high, which seriously affected the normal production of the mine.
In order to completely solve the above-mentioned problems, 5 sets of mine-use flameproof motor soft starters were selected and installed, and good results were achieved.
(1) The starting current of the motor has been reduced from the original 1150A to about 700A. There has been no tripping due to excessive starting current, which improves the power supply quality of the power supply and improves the working conditions of the transformer and the switch.
(2) The belt start time is extended from 6 s to 12 s, which reduces the mechanical impact and the force of the belt conveyor has been significantly improved. The service life of the reducer, motor, fluid coupling, roller, joint, tape, etc. is prolonged, the maintenance cycle is greatly extended, and the material input is greatly reduced, and the requirements for the strength of the belt conveyor are also reduced.
(3) The accident rate is greatly reduced. After more than a year of operation, the effect is good. The soft starter has never had a drum failure, which completely eliminates the safe operation of the belt due to the failure of the reducer, motor, and hydraulic coupling.
(4) The motor soft starter circuit has no phase sequence, the starting process is stable and reliable, and the approximate constant current start can be realized. The effective starting torque can be increased by 3 to 4 times, and the impact jump of the reducer can be eliminated. At the same time, the starting capacity is increased. Ability and safety performance can be greatly improved.
(5) The soft starter adopts a quick-opening form, which combines the functions of a magnetic starter into one. On the basis of the first generation, the motor isolation commutation switch, comprehensive protection unit and operation display function are added, which can meet various control requirements in the production process, and at the same time realize the whole process protection of the motor. Due to the reliable quality of GRBⅢ mine flameproof motor soft starter, maintenance-free is realized.