Oct 22, 2020
Inverter used in coal yard bridge crane
The bridge crane has 4 functions, namely, the trolley travels left and right, the trolley travels forward and backward, the lifting of the grab and the opening and closing of the grab, which are respectively driven by electric motors. Among them, the traveling of the large trolley is driven by two electric motors. The opening and closing of the grab bucket are respectively driven by a motor, and these 5 motors are all wound rotor asynchronous motors. There are three speeds for large and small cars walking, grabbing bucket lifting, and grabbing bucket opening and closing. The speed is adjusted by switching the rotor circuit resistance, which is a stepwise speed regulation, which has a greater impact on the motor and the power grid, and has a greater impact on other electrical equipment .
The electrical system of the bridge crane is composed of air switch, contactor, knife switch, overcurrent relay, time relay, cam controller, limit switch, door switch and other components. The main types of protection are: ①Overcurrent protection, realized by an overcurrent relay, when the motor is overcurrent, the overcurrent relay acts to disconnect the power supply. ②Zero position protection refers to the zero position contact of the cam controller of the trolley, cart and grab. Only when the three cam controllers are placed in the zero position of the controller, the power is allowed to be turned on. ③Safety door switches are the safety switches on the front and rear beam doors of the bridge crane and the control room door. When the door is opened, the power is automatically cut off to prevent electric shock. ④ Emergency switch, when an emergency occurs, it can cut off the power supply. ⑤Limit switches are the left and right limit switches for trolleys, carts, grab up limit switches, grab open limit switches. When any of these switches is activated, the bridge crane is powered off and the handle must be retracted to the zero position , Make the mechanism run in the reverse direction to exit the limit position. ⑥ Loss of voltage protection. When the bridge crane voltage drops a lot or the power is cut off, the main contactor is released to disconnect the main power supply. ⑦Short circuit protection, the air switch plays a role of short circuit protection. When a serious short circuit fault occurs inside the bridge crane, the main power supply is cut off to prevent the accident from expanding.
Before operating the bridge crane, check whether the front and rear beam end doors and the control room door are closed. After closing, close the main switch, press the start button, the main circuit is connected, and the bridge crane enters the operating state. Then in the control room, operate the cam controllers of the trolley, the cart and the grab, and connect the control circuits of the motors to realize the functions of the bridge crane.
Since a large number of electrical components such as contactors and relays are used in the system, frequent actions of these components will cause contact wear, poor contact, coil overheating and even burning, loose wiring terminals, etc., which will cause a large number of failures and cause bridges. The crane does not work very well.
The use of frequency converter to transform the motor drive system has many advantages: ① When the frequency converter drives the motor, the speed changes very smoothly, which is stepless speed regulation, and the impact current is small when the motor starts. ②By controlling the operation of the inverter, the running direction and speed of the motor can be changed. ③The inverter has complete protection functions, such as over-current, over-load, over-voltage, etc., which can alarm and stop in time, reducing faults and improving safety performance. ④The inverter has a current limiting function, which can reduce the impact on the power grid. ⑤ After the frequency converter is used to control the motor, the original relay control system with mechanical contacts such as contactors and relays becomes the frequency converter without contact output control, which reduces the failure rate and improves the stability of the system.
After the system is reformed, the original motor is retained, the rotor slip ring is short-circuited, and the speed regulating resistor is removed. The original electrical control system is removed, and the original safety door switch and limit switch are retained. Keep the original big and small car, grab cam controller, and according to the actual needs of the work, change the big car from the left and right three gears to the left and right two gears, and the small car from the front and rear three gears to the front and rear first gears. , The lifting and opening and closing of the grab bucket are changed to one gear, that is, the lifting and closing of the grab bucket.
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