Several problems that should be considered in the

Several problems that should be considered in the selection of ball mill motor

ball mill is driven by motor. Therefore, we cannot only consider the machine itself without considering electricity. When selecting the motor, we should consider the following aspects:

1. The load characteristics of the ball mill

⑴ the working speed of the ball mill is constant. Unless there are special requirements for speed change in the process, generally, the main motor of the ball mill does not require speed regulation

⑵ the ball mill is the equipment with the largest power consumption in the cement plant. As mentioned above, the power consumption of the ball mill accounts for about two-thirds of the power consumption of cement production

⑶ when the ball mill is in normal operation, its load is basically stable

⑷ the starting torque of the ball mill is 1.1 ~ 1.5 times the rated torque of the motor

2. Requirements for electric drive:

⑴ power specification

the rated power of the selected motor should be 1.05 ~ 1.1 times the actual motor power required by the ball mill to ensure that the load rate is above 90%. In this way, the motor is often in full load state during the working process, making full use of the power of the equipment

⑵ motor starting requirements

due to the large capacity of the main motor of the ball mill, the starting current should be limited. Otherwise, the starting current is too large, which is bound to cause a sudden drop in electrical voltage, so that the motors of other equipment in the factory "lose voltage", and even cause shutdown accidents

⑶ improve the power factor of the motor

on the one hand, select the appropriate motor type, on the other hand, it also depends on the compensation measures for the power factor

⑷ power supply voltage

in the electric drive of the ball mill, low-voltage power is used: 220V, 380V; Yes, high voltage power: 3000V, 6000V. Generally speaking, the motor of small ball mills adopts low-voltage electricity, and the main motor of large and medium-sized ball mills exceeding 300kW should use high voltage

3. Introduction to motors suitable for ball mill drive

⑴ asynchronous motor

except that small ball mills are driven by squirrel cage motors, most medium and small ball mills are driven by three-phase wound asynchronous motors. The winding motor has Jr, JRQ, and the rotating speed of the rotary table is required to be lower than 500r/min; The polishing time should be better than the consumption of yr series

the main disadvantages of asynchronous motor in ball mill drive are:

① simple equipment and low price

② there is enough starting torque to directly start the compression shear testing machine, which is mainly used for ball mills under the composite conditions of compression and shear resistance of various bridge plate and basin rubber bearings; Its starting torque can be controlled by connecting the series resistance of the rotor winding.

the frequency sensitive rheostat will automatically make the voltage of the digital circuit in the electrical check of the rotor circuit be + 5V during the reduction of the motor starting process? If there is no resistance, it will change to meet the requirements of improving starting performance When starting, as long as the power switch is turned on, the frequency sensitive rheostat of the motor will automatically reduce the resistance in the rotor circuit as the rotor speed rises, so that the motor speed rises smoothly

③ the starting current is small. The starting current can be controlled below 1.5 times the rated current, so it will not affect the normal operation of other equipment when it is used in lines with small capacitance

its only disadvantage is that the asynchronous motor has a low lagging power factor. This limits its application in ball mill drive. There are two ways to improve the power factor: one is suitable for large capacity high voltage electrostatic capacitors; The other is to apply the progressive camera, connect it with the rotor winding of the main motor, and improve the factor by changing the phase of the motor. The power factor of the motor can be increased to 0.95 ~ 1.0 by using the progressive camera. In addition, the power factor of asynchronous motor is related to the rated speed of motor. The lower the speed is, the lower the power factor is. Therefore, from the point of view of river power consumption, high-speed asynchronous motor should be preferred

⑵ synchronous motor

there are two kinds of synchronous motors driving the ball mill: ordinary low starting torque synchronous motor, TD series three-phase synchronous motor; Special synchronous motor for large low-speed and high torque ball mill -- three-phase synchronous motor for TDQ and TZ series ball mill

⑶ induction synchronous motor

induction synchronous motor has the following advantages:

① when starting, compared with asynchronous motor, it has the advantages of large starting torque and small starting current

② compared with synchronous motor, it has the advantage of advanced power factor during operation, so as to solve the problem of electric motionless compensation in cement plant

③ constant speed

the disadvantage is complex manufacturing and high price However, the induction synchronous motor as the driving motor of large ball mill has a bright future

⑷ selection principle of main motor of ball mill

in addition to the above motor characteristics, the following problems should be comprehensively considered:

① the initial investment and operation cost must be taken into account

② consider the motor type of other equipment in the cement plant, that is, the power factor of the power circuit of the whole plant

③ when determining the rated voltage, the electric transformation voltage and capacitance in the area where the cement plant is located should be considered

④ determine that the motor should be evaluated in a unified manner with the mechanical transmission scheme of the ball mill, and the mechanical manufacturing conditions of the reduction mechanism should be considered in the evaluation