North Heavy Industry has been producing various plate type apron feeder in coal handling plant for more than 50 years. The speed of various apron feeder in coal handling plant produced before 80's is not adjustable. The speed of the chain plate is 0.05m/s, which causes the limitation of users. With the expansion of production capacity and the upgrading of downstream machinery, the upstream machinery that is apron feeder in coal handling plant should be speed adjustable. An adjustable speed means an increase in production capacity. In order to meet the user's use requirements, according to the specific situation of the market at that time, we have adopted several different speed regulation methods.
1. Several speed regulation methods of asynchronous motor:
According to the motor table, the speed formula of the AC asynchronous motor is F -- -- stator power supply frequency P -- -- polar log S -- -- slip. According to the above formula, it can be seen that the speed regulation method of the asynchronous motor can change the slip, variable weight log and variable frequency, and several speed regulation methods.
(speed regulating pole change motor (cage) voltage regulator, the stator voltage adjustable resistance (rotor resistance), a pair of wound rotor asynchronous motor variant slip speed electromagnetic clutch (slip) cascade speed regulation for wound rotor / - with frequency control of motor speed 【 pay - direct - alternating frequency conversion speed regulating pole change motor 1.1 (cage) speed regulating pole change motor is generally divided into 4/6/8 extremely, when the motor of the number of certain, The speed of the motor is also fixed, so it is the pole speed regulation instead of the whole process speed regulation. The range of use is small, and there are certain limitations.
1.2 Variable slip speed regulation This speed regulation method at low speed, the slip rate (1-S) is too large, the loss of the slip is also very large, low efficiency. When the plate type feeder chooses this speed regulation, in order to ensure the reliability of use, generally will calculate the motor power, should choose a first gear, such as the calculated motor power is 45KW, the first time should use 55KW motor. This ensures that the apron feeder in coal handling plant does not have enough power at low speed. In addition, when this motor is used in metal mines, iron powder is easy to suck on the carbon brush of the slip ring, which will cause short circuit of the motor for a long time, resulting in accidents.
1.3 Frequency conversion speed regulation The so-called frequency conversion speed regulation is to uniformly change the power supply frequency of the motor stator 1. By changing the power supply frequency of the stator, the speed of the motor can be smoothly changed, and in the speed regulation process, from high to low speed, can maintain a limited slip rate. Therefore, it has high efficiency, wide range and high precision speed regulation performance, and has the mechanical characteristics of enough hardness. This speed regulation method is widely used.
1.3.1 Variable Frequency Speed Regulation of Asynchronous motor On the basis of keeping the power factor of the excitation motor basically unchanged during variable frequency speed regulation, the track of the induction motor should also be kept unchanged. If the above 3 parameters have changed, there will be a decrease in power, torque, motor power can not be fully used, resulting in waste. Therefore, the track can be kept unchanged when the frequency is changed. In order to keep the track unchanged when the frequency is changed, the voltage/frequency diameter is required to be fixed.
That is, the voltage must vary in proportion to the frequency. Plate type feeder as a semi-continuous feeding machinery, its working nature for low speed, large torque, with material start characteristics, its speed regulation form is a typical constant torque speed regulation. This requires a frequency conversion device to ensure that V1 varies proportionally with FL. Then Vl/fl= constant, which can ensure that the motor has the same overload capacity in the process of frequency change. When the voltage reaches 100%, the output torque is the maximum and constant.
1.3.2 Shortcomings of asynchronous motor speed regulation due to the decrease of speed in frequency conversion speed regulation below rated 50HZ, the rotational speed of self-cooling fan connected by coaxial will also decrease, and its cooling effect will decrease. If the capacity is not reduced, the motor will burn out due to temperature rise. Inverter output of power supply and power frequency power supply, there is a difference between the standard organization and performance of asynchronous motor is designed according to the power frequency power supply, so the ordinary asynchronous motor driven by frequency converter will produce high time after grand wave, the interference of power supply, such as lower level factor, radio interference, motor temperature rise, noise and vibration, These problems affect the performance of the motor to different extent. The noise is increased by 10-15dB compared with the power frequency power supply, and the wiring distance between the motor and the frequency conversion cannot exceed 100m at most. If it is too long, a reactor can be added between the two to solve the above problems. There are also some problems with overload protection. The frequency converter drives a motor and takes advantage of the inherent electronic overheating protection of the frequency converter. This component is set according to the rated current of the motor, so it can protect the motor from overload. When a single frequency converter drives two electric motors, problems arise because each motor has to be protected separately. Generally, a thermal relay is added to the main circuit of each motor. In practical application, we have realized that the general thermal relay with this setting can not effectively protect the motor overload in the whole speed range. Traditional thermal relay is bimetallic sheet structure, according to the current flow size and time (I2.T) to form the reverse time action characteristics. Its characteristic curve is only selected for power frequency power supply, only one (corresponding to 50HZ). The output of frequency converter not only changes in frequency, but also contains high harmonics. Especially after the extension of the cable, the original is not accurate. It is difficult to determine the thermal relay, because with the change of frequency, the reverse time curve of the thermal relay also changes. When operating at low speed (about 10HZ), the thermal relay works in advance. The motor can not work at low speed. We've had this problem in the past. Users use less frequency converter, they think that theapron feeder in coal handling plant should be started at low frequency, so as to protect the machinery to avoid certain damage, so that the start of a certain difficulty. By communicating with us, they understand the performance of frequency converter, and the problem is solved. If the thermal relay is modified and adjusted for low speed work, and the motor cannot be protected at high speed, in view of the existence of the above problems, the single machine drive should be preferred, that is, a frequency converter drives a motor.
1.3.3 frequency conversion motor frequency control of motor (VF) in order to adapt to the requirement of constant torque load (speed of rated frequency 50 hz), design and production of the frequency conversion motor professional manufacturer (called VF motor), its characteristic is the envelope to the application of frequency control of motor speed torque range is suitable for plate type feeder speed range, and can interlock and the material equipment, Achieve short range DCS control. The constant torque speed range of apron feeder in coal handling plant is 220-50H2. The appearance of variable frequency special motor not only solves the shortage of asynchronous motor in variable frequency speed regulation, but also expands the use space for the mechanical equipment of low speed, large torque and constant torque speed regulation.
1.4 Hydraulic motor speed apron feeder in coal handling plant design and selection, we also use the hydraulic motor speed control mode. The working condition of apron feeder in coal handling plant is low speed and large torque, and it also meets the working condition requirements of apron feeder in coal handling plant when applying hydraulic motor. Therefore, we choose the piston type low speed high torque hydraulic motor produced by Sweden Hegron company.
Hydraulic speed regulation is characterized by stepless speed regulation, soft starting characteristics, good shock absorption, is a kind of electromechanical products, but because of the high cost, generally higher than the price of frequency conversion speed regulation is several times higher, so from the cost performance consideration, less choice.
