Application of the hottest brushless Rheostat Star

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Application of brushless Rheostat Starter in alumina plant

[Abstract] this paper briefly describes the application status of wound asynchronous motor, the product structure characteristics and working principle of brushless Rheostat Starter, as well as the promotion and application status in aluminum oxide plant

[key words] starter; Brushless starter; Electromagnetic components; Rheostat; Rotor circuit; Steady speed

[Chinese classification number] tf821 [document identification code] B [article number] (2004)

1. Overview

three phase wound asynchronous motor is one of the main driving equipment in aluminum oxide plant. Because its rotor can be externally connected with resistance or reactance, it has the advantages of high power factor, high starting torque and changing running speed at start-up, and is widely used in ball mills, clinker kilns, blowers Vacuum pump and other equipment are used as dragging equipment. However, when starting the wound asynchronous motor, the resistance or reactor must be connected in series in the motor rotor circuit to increase the starting torque of the motor and reduce the starting current. During the starting process, the value of this resistance or reactance will change step by step from large to small, and the starting process of the motor will not end until it is finally zero, and the motor will enter the running state. The starting process of the motor can be completed with the help of a complex auxiliary starting device. Its starting auxiliary equipment is relatively complex, mainly including slip rings for connecting resistors, brushes, segmented metal resistors (or frequency sensitive resistors with smooth characteristic curves), brush lifting short-circuit devices and AC contactors for short-circuit rotor circuits. The installation and commissioning of this device are complex, the operation is troublesome, the accident rate is high, the maintenance is difficult, the consumption of spare parts is large, and the maintenance cost is high. And because the resistance is cut off in sections, the starting characteristic curve of the motor is stepped, which cannot start smoothly and realize stepless speed change, with poor characteristics and high energy consumption

the frequency sensitive rheostat commonly used now overcomes the characteristic that the two ends of the test piece must ensure the ladder shaped characteristic curve generated by the parallel resistance during the segmented cutting experiment, and realizes the linear change of resistance, stepless speed change and smooth and reliable characteristic curve during the starting process of the motor. However, it only solves the starting characteristics of the motor, and does not solve the complex starting auxiliary device of the motor

the brushless Rheostat Starter not only solves the poor starting characteristics of metal resistors and reactors, but also solves the complex problem of starting auxiliary devices with frequency sensitive resistors, which is often the basis for promoting the innovation and development of enterprises. The complex starting auxiliary devices of the original secondary circuit system of wound motor form a contactless electromagnetic element, which is directly installed on the rotor shaft of the motor, solving a major problem of the wound motor starting device, It shows strong vitality

2. Working principle

brushless Rheostat Starter is a new type of linear Rheostat Starter developed by using the principle of frequency sensitive rheostat. It is a contactless electromagnetic element composed of multi contact elements of the original secondary circuit system, which is equivalent to an equivalent impedance in series into the return circuit of the wound rotor, as the starting equipment with variable resistance during startup, The biggest difference between it and the traditional frequency sensitive rheostat starter is that it still participates in the whole process of motor driving after helping the motor complete the rheostat starting task, while the traditional frequency sensitive rheostat cannot participate in the motor driving operation. If the frequency sensitive rheostat starter is not cut off in time, it will cause the rheostat to overheat or even burn out. The asynchronous motor cannot be carried out at normal speed, the current will rise, and even burn out the motor

the brushless Rheostat Starter adopts the best magnetic circuit principle. It consists of coil winding, inner and outer iron cores, shaft sleeves, yoke plates, terminals and other parts to form a contactless electromagnetic element. It is installed at the slip ring position on the rotor of the original motor. Its unique structural characteristics make the brushless starter have a large impedance value at the beginning of startup, while the impedance value is almost zero in the running state. Throughout the starting process, the impedance value changes linearly and the curve is smooth, realizing the stepless speed change of the motor, which is stable and reliable, with large starting torque and small starting current. When the stator circuit of the motor is just powered on, the frequency of the induced voltage in the rotor winding circuit is 50Hz, which acts on the starter coil and becomes a load with large impedance and is brought to the rotor circuit. Therefore, the current in the rotor circuit decreases, and the current value in the corresponding stator circuit also decreases. As the speed changes from slow to fast, the frequency of the induced voltage in the rotor circuit also changes from high to low. When the rotor reaches the rated speed, The induction frequency of the rotor circuit is also close to zero, and the impedance of the starter is also close to zero, completing the starting task of the wound motor. At this time, the starter is still involved in the operation of the motor. At this time, the impedance value of the starter is close to zero, which is equivalent to the running state of the carbon brush slip ring. Therefore, the brushless rheostat will not affect the normal operation of the motor and is an ideal starting device

3. Application example

3.1 application of brushless Rheostat Starter on vacuum pump

in April 1999, the 3# vacuum pump motor of the fourth workshop was first transformed. The vacuum pump motor is a Jr 185KW motor produced by Guangzhou electric machinery factory, which uses the secondary circuit series frequency sensitive resistor starting mode, and uses the brush lifting short-circuit mechanism and AC contactor to cooperate with the short-circuit rotor circuit. The operation is extremely inconvenient. The short-circuit contact and motor rotor coil are often burned due to short-circuit startup. Sometimes the short-circuit contact is burned due to inflexible short-circuit mechanism, and the motor slip ring and carbon brush often fail. The consumption of spare parts is large and the maintenance cost is high, which can not meet the production requirements. After the transformation, the starting auxiliary device, frequency sensitive rheostat and secondary circuit of the wound motor are removed. The operation is simple, and the operator no longer has to worry about short-circuit starting, and the maintenance is very convenient. In the past six months of operation, there has been no fault, and the operation is simple and stable, which is deeply loved by the operators. See Table 1 before and after the transformation

Table 1 Comparison of technical data of vacuum pump motor before and after transformation

power operation during startup, electric operation temperature, annual power saving

current (a) (s) factor current (a) degree (℃) effect (yuan)

5603 before transformation The oil tank is short of 120.86 220 55

after the transformation, 5 springs are produced 4080.87 210 4020148

note: the electricity price is 0.46 yuan/kwh

from the comparison table of technical data before and after the transformation, it can be seen that the starting current of the motor after the transformation is reduced, the starting performance is changed, the running current is reduced, and the power factor is increased. When the ambient temperature is 30 ℃, the operating temperature of the starter is less than 40 ℃, and the starting performance is good. It is an ideal starting element

3.2 application of brushless Rheostat Starter in ball mill

on the basis of the successful transformation of more than a dozen vacuum pumps in the whole plant, we have transformed the 2# wet mill in the fourth workshop. 2 # wet mill is a ball mill equipped with motor jr12

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