Variable Frequency Speed Control Of Cement Apron Feeder

The No. 3 limestone crusher in a cement factory uses 2P℉-1212 type impact crusher for primary crushing. The feeding system uses 1500× 12000 cement apron feeder, and the driving motor uses Y225M-4 three-phase AC asynchronous motor. Because the feeder can not adjust the linear speed of the system, when the feed surplus, can only rely on the way to stop the motor feeding, feeding quantity control has brought a certain difficulty, especially rainy weather, material viscosity, motor heavy load start and stop frequently, the motor and transmission system impact. In addition, interval feeding is not easy to control the uniformity of feeding, has a great impact on the particle size of broken discharge, difficult to meet the production requirements. We use frequency control technology to control the speed of the feeder, that is, according to the principle of N=6011-s, to realize the speed control of AC motor. Considering the requirements of crushing system, the frequency converter can not only control the variable speed operation of the motor, but also provide enough torque output. To this end, we choose ACS600 series frequency converters produced by ABB among many inverter brands, whose main characteristics are as follows: 1) Direct torque (DT℃) control technology, changes the traditional vector inverter control mode, zero speed does not need speed feedback, can achieve full torque output characteristics, dynamic response is fast, stable and controllable, starting torque up to 200% of rated torque, can withstand 150% overload for 1min.

2) To provide a full range of protection for the motor, including over voltage, over current, lack of phase and motor blocking and temperature rise protection, at the same time can realize the soft start of the motor, make the equipment run smoothly, thus extending the service life of the equipment, and can reduce vibration, impact and noise, provide a good working environment. The test shows that when the motor driven by cement apron feeder runs normally, the three-phase average current is only 30A(rated current 84.6A), and the motor selection is obviously larger. In order to save project investment, frequency conversion governor is selected after project demonstration. Specific parameters are shown in Table 1.

The installation and wiring of the frequency converter are relatively simple. Generally, the frequency converter is only connected to the main circuit cable of the motor in series. For the convenience of operation, a 10k2 speed adjusting potentiometer and a digital display tachometer can be added on the operating table, while the original start-stop control loop does not need to be changed. Combined with the technology status of the crushing system, in order to prevent the occurrence of adverse factors such as heating of motor winding caused by high harmonics during the subsequent no-load operation and low-frequency operation, the lower limit of frequency is set as 10Hz(speed 300r/min) and the upper limit as 50Hz(speed 1470r/min). Through the pointer potentiometer, Adjust arbitrarily according to the actual needs of production.

1) Wide speed range of feeding control to achieve stepless speed regulation, according to the actual incoming material and subsequent crushing situation in time to adjust the feeding amount, to achieve the expected effect of continuous and uniform feeding.

3) When the three-phase AC asynchronous motor without impact damage is started by direct starting mode, the starting current is about 5~7 times of the rated current. After the technical modification, the starting current is less than 1.7 times of the rated current, and the frequent stop motor interval feeding mode is eliminated, which greatly improves the running condition of the equipment and reduces the equipment maintenance workload of the workers on the post. 3) Significant power saving effect After more than two months of operation, the motor running parameters are shown in Table 2.

When the cement apron feeder runs normally, the operating frequency of the motor is 20~40Hz, the average current of the power grid is 8~15A, and the power saving rate is more than 40%.