Research on Optimization and Upgrading Technology of Repairing Process of Mine Asynchronous Motor

  Due to the heavy production task of coal mine, most of the equipment is in continuous operation with high load, and the environment is humid and harsh, which seriously affects the service life of the motor. Taking Dadougou Coal Industry as an example, the mine has been developed for a long time, and its electrical equipment is outdated. Every year, about 240 sets of burning motors of various types need to be self maintained. Replacing the motor not only affects the normal production of the mine, but also forms a hidden danger of safe operation, and also causes waste of materials and accessories, which increases the cost of coal production and increases the labor intensity of 

maintenance personnel. It is necessary to improve the motor maintenance process to improve the performance and life of the motor.

1. Analysis of motor burning

  a) Direct cause

  Based on the analysis of the causes of motor failures caused by various types of burning losses on site, it is concluded that there are two direct causes for the burning losses of asynchronous motors: one is that the motor is overloaded or forced to run, which leads to overheating of the motor, resulting in insulation degradation and breakdown; Second, the underground environment of the coal mine is humid, and there are harmful chemical corrosive gases, which erode the insulation of the motor, resulting in insulation degradation and breakdown.

  b) Basic Reason

  The fundamental reason for motor burning is that the heat resistance grade and limit working temperature of motor insulation material are low, which cannot meet the needs of the on-site working environment. When the current flowing through the motor winding exceeds the long-term allowable current, the heat generated will exceed the allowable value, accelerating insulation aging, shortening the life of the motor or rapidly damaging the motor, thus causing motor burning. The weakest place of temperature resistance in the motor is the insulating material, which is directly related to the service life of the motor. The insulating material is particularly vulnerable to accelerated aging and damage due to the impact of high temperature. Therefore, the heat resistance of the motor insulation material plays an important role in improving the reliability and life of the motor. In the past, the motor repaired by Dadougou Coal Industry was repaired according to the original design standard of the motor. The insulation of the motor that was originally disassembled and wound was not fundamentally improved, resulting in the low insulation of the motor after repair. The insulation degree shall be improved to make the motor meet the requirements of underground working environment. The heat resistance grade and limiting working temperature of the flange material shall be upgraded to increase the moisture resistance and corrosion resistance of the winding, improve the insulation strength and mechanical strength, improve the thermal conductivity and heat dissipation effect, delay the aging and extend the service life of the motor.

  2. Optimization and upgrading of insulation process

  a) Optimization ideas

  The insulation grade of the motor refers to the heat resistance grade of the insulating materials used. In order to prevent the thermal energy generated by the current from burning the insulation layer, the motor insulation grade is set as Grade A, E, B, F and H, as shown in Table 1. Class B and F heat resistance are the most common insulation grades of mining motors. Improving the insulation grade of motors can improve the performance and prolong the service life of motors. Therefore, it is necessary to comprehensively improve the motor maintenance process by improving the heat resistance level of the insulating materials used for the motor. Specifically, the overall performance of the motor can be improved by improving the insulation between layers and phases of the motor, improving the heat resistance level of insulating materials such as slot wedges and enamelled wire bushings, and upgrading the heat-resistant paint.

b) Project Design

  Improve the insulation between layers of motor and change the model of enamelled wire. Previously, QZ-2/130L polyacrylate copper enamelled wire was used, with a heat resistance rating of B and a maximum allowable temperature of 130 ℃, which can only meet the existing factory standard level of the motor. Now it is improved to QZY-2/180 polyacrylate imide enamelled wire, with a heat resistance rating of H and a maximum allowable temperature of 180 ℃. The temperature stability and insulation are improved by two levels, and the heat resistance, heat dissipation and chemical resistance of the motor are also improved simultaneously.

  c) Improve the interphase insulation of the motor and change the insulation material. Before, the insulation material in the motor was made of green shell paper, which was of class E heat resistance grade and the maximum allowable temperature was 120 ℃. It was modified into poly (vinyl acetate) film poly (vinyl acetate) fiber paper composite foil (DMD for short), which was of class F heat resistance grade and the maximum allowable temperature was 155 ℃ to improve the insulation between layers and phases.

  d) The heat resistance grade of motor slot wedge shall be improved, and the slot wedge shall be made of heat resistant materials. In the past, the stator core slot wedge of the motor used the temperature resistant material bamboo board, which is easy to carbonize after the motor temperature rises, resulting in insulation degradation or breakdown. It is improved to use the advanced high-temperature resistant material epoxy board like FR4 sheet and 3240 epoxy sheet grade A, class F heat-resistant grade. The epoxy board is made of glass fiber cloth and epoxy resin, which is heated and pressurized. It has good mechanical properties and more stable electrical properties under high temperature. It is suitable for high insulation structural parts used in machinery, electrical appliances and electronics. It has high mechanical and dielectric properties, good heat resistance and moisture resistance.

  e) Improve the heat resistance grade of enamelled wire bushing material. In the past, the enamelled wire casing of motor was made of PVC glass paint pipe, which has a heat resistance grade of A, low insulation but not high temperature resistance. The high-voltage silicon pipe, which has a heat resistance grade of F, was improved. The non alkali glass fiber braided pipe was coated with PVC resin, and the insulated casing, which was molded by heating, has good mechanical strength, excellent flexibility, good dielectric property and chemical resistance.

  f) Improve the overall insulation strength of the motor. The heat dissipation condition of the winding can be improved by good impregnation insulation treatment, so that the temperature rise of the motor is close to the heat-resistant level. At the same time, the selection of high-level paint can also improve the reliability of the heat resistance of the motor and extend the service life. Before, after winding down, the backward 10? 2 Melamine alkyd insulating paint is dipped in paint for insulation treatment. It is of Class B heat-resistant grade. The paint smell is intolerable when dipped in paint. The volatile solvent pollutes the air environment greatly, and the amount of paint hanging is not enough, which causes the insulation gap not to be dipped, resulting in gaps, bubbles, and weak insulation, leaving hidden dangers for motor burning. Improved use of 1042 imine epoxy insulation paint, class F heat resistance, which has excellent electrical, mechanical and moisture resistance, its application process range is wide, and it can easily realize low-temperature drying.

3. Field Application Effect

  After the optimization and upgrading of motor repair process, the number of motors burned in the mine has been significantly reduced after a one-year inspection, and only 53 new motors were added throughout the year. Compared with the original, the failure rate of the motor is greatly reduced, the quality of maintenance is significantly improved, a lot of labor and material costs are saved, and the effective production time of the mine is increased by 4 days.

4. Conclusion

  a) The key to improve motor maintenance quality is to improve the insulation level of old motors. By improving the insulation between layers and phases of the motor, the heat resistance grade of slot wedge, enamelled wire bushing, insulating paint and other materials is improved, and the overall insulation strength of the motor is improved, so that the overall performance of the repaired motor can be improved.

  b) After the optimization and upgrading of motor repair process, the maintenance quantity of motors in Dadougou Coal Industry Co., Ltd. was reduced from 240 to 53, the maintenance cost was greatly reduced, and the work intensity of maintenance personnel was greatly reduced. After the new 1042 insulating paint soaking and drying process is adopted, the motor maintenance cycle is shortened, which is more environmentally friendly and energy-saving. At the same time, the effective production time of the mine is reduced by 4 days due to motor failure

  c) After the optimization and upgrading of the motor repair process, Dadougou Coal Industry Co., Ltd. has saved expenses and increased income by a total of 4032140 yuan through technical innovation, and has achieved good technical and economic benefits, which can be used for reference by mines of the same type.