Insulation Structure Design and Anti-corona Measures of High-voltage Motors

The winding insulation structure design of a high-voltage motor is divided into three parts: the ground insulation structure design of the high-voltage winding insulation coil, the inter-turn insulation design of the high-voltage winding insulation coil, and the auxiliary insulation structure design of the high-voltage winding coil. The main role of the winding insulation structure of a high-voltage motor is to isolate electricity, but some parts also play a role in mechanical support, fixation or protection. The design of the high-voltage winding insulation structure and anti-corona treatment of the safety-enhancing brushless excitation synchronous motor are one of the core parts of the design of the safety-enhancing brushless excitation synchronous motor.

Safety-enhancing brushless excitation synchronous motors are generally large-scale motors with large stand-alone power and voltage levels of 6kV, 10kV and 13.8kV.The wire gauge carrying area of the electromagnetic wire of the motor winding is large, the design adopts rectangular copper wire, and the high-voltage winding adopts the manufacturing process of double-layer coil and open groove embedding method.

The ground insulation of the high-voltage winding coil mainly refers to the insulation of the straight part of the groove and the end part of the coil. When designing the insulation structure, it is first necessary to determine the thickness of the insulation side and the manufacturing method of the process. Both electrical and mechanical factors must be considered, as well as the cumulative effect of the dielectric strength test in the production process, the insulation dispersion and the average annual aging rate under actual operating conditions (attenuation of insulation properties).

At present, even the more advanced countries in the world have uneven motor manufacturing technology levels. Moreover, for the design of the insulation structure of the high-voltage winding insulation coil, although VPI vacuum overall impregnation insulation treatment is used, the selection of insulation materials, insulation structure methods and specific process manufacturing methods are not exactly the same, and the traditional manufacturing process methods unique to each manufacturer are still retained. So far, there are still several different insulation structure designs and process design schemes in some motor manufacturers.

The high-voltage winding coil is insulated from the ground. According to whether the linear part of the groove and the end part adopt the same insulation structure, it can be divided into two types: continuous 1/2 laminated winding type and composite winding type. The continuous 1/2-fold winding type can be divided into vacuum pressure solvent-free impregnation type and hot-molded one-time forming type. The composite wrap-around type can be divided into full-belt wrap-around hot-molded one-time forming type, foil-wrapped package (linear part) and belt-wrapped package (end part) hot-molded one-time forming type, composite wrap-around groove linear part insulation structure design, you can use mica insulation tape 1/2 stacked wrap, called full-belt insulation structure; you can also use mica foil baking roll, called foil baking roll insulation structure.

At present, the ground insulation structure design of high-voltage winding coils in the motor industry at home and abroad can be basically divided into VPI vacuum overall solvent-free paint-impregnated epoxy glass wire powder mica less tape insulation structure and hot-molded one-time epoxy glass wire powder mica more tape or foil insulation structure. Moreover, in the same motor manufacturing plant, in addition to the above two basic insulation structures, there are still composite wrap-around insulation structures with foil, and modern motors are all insulated by VPI vacuum overall impregnation after embedding the wire.

It must be pointed out here: the insulating structure of epoxy glass ribbon powder mica-less tape impregnated with VPI vacuum overall solvent-free paint was first used in Siemens, Germany. In the early 1980s, China introduced the above-mentioned insulating structure design technology and popularized it throughout the country. It has been used for more than 20 years. Although it has the characteristics of simple production technology and saving working hours, its insulation performance is not ideal.

At present, the operating experience of high-voltage and high-power motors at home and abroad has extremely highlighted that the high failure rate of insulation between the turns of the motor seriously threatens the safe operation of the motor, especially the safety-enhancing motor. The main reason is that at present, industrial and mining enterprises generally adopt high-voltage vacuum switches with a series of advantages, and the high-frequency oscillation operation generated by the high-voltage vacuum switch is damaged by the impact of overvoltage, and effective preventive and protective measures have not been taken accordingly. At the same time, because the motor products of China's motor industry are still not based on the development of new technologies, design improvements have been adopted accordingly, that is, the design of the overall structure of high-voltage and high-power motors, and the modern new overall structure of motor-electronic control protection integration has not yet been realized.

In the usual accident analysis, the failure caused by the breakdown of the insulation between the turns of the motor is misjudged as a ground breakdown. This is because in people's concept, the operating voltage of the insulation between the turns of the high-voltage motor is generally tens of volts, and therefore the importance of inter-turn insulation and the possibility of failure are ignored. When the motor is in an accident state or the electronic control system is closed and disconnected due to the use of a high-voltage vacuum switch, it will produce an instantaneous overvoltage shock with a high amplitude and a steep wave head.

In particular, it is pointed out that the instantaneous impact of the closing and breaking of the above-mentioned high-voltage vacuum switch overvoltage has an uneven distribution between the turns of the motor winding coil, which will inevitably lead to the breakdown of the insulation between the turns. Even if the overvoltage has not exceeded the strength of the inter-turn insulation, it will cause damage and aging of the inter-turn insulation, seriously endangering the safe operation and life of the motor.

The damage to the inter-turn insulation caused by the high-voltage winding coil in the production process is the main problem in the motor manufacturing process, especially the different technical quality and technological level of the technical operator, such as coil winding, expansion, shaping, insulation winding, coil insulation molding, loose wire and other processes in the production process, it is inevitable that different degrees of insulation damage will occur. In addition, the insulation of the windings and coils of the motor during operation also causes insulation damage and aging due to electromagnetic mechanical force and thermal stress, especially the large cross-sectional area of the wire gauge of the electromagnetic wire of the high-voltage and high-power motor and improper softening treatment will significantly reduce the insulation performance between the turns. Therefore, the design requires that the inter-turn insulation, in addition to being able to withstand electromagnetic and mechanical stress, should have high mechanical strength and flexibility.

The structural design of inter-turn insulation generally uses the insulation of the electromagnetic wire itself as the inter-turn insulation of the winding. Modern electromagnetic wires for high-voltage and high-power motors are all made of self-adhesive double polyester glass wire mica tape wrapped flat copper wire. The voltage level is 6kV, and the self-adhesive single polyester glass wire enameled flat copper wire or self-adhesive double polyester glass wire film enameled flat copper wire is selected; the voltage level is above 6kV, and the self-adhesive single and double polyester glass wire mica tape is used to wrap the enameled flat copper wire.

Compared with traditional electromagnetic wires, the electromagnetic wires selected for modern motor design have the characteristics of high breakdown voltage resistance, high heat resistance level, thin insulation thickness, good insulation flexibility and good scratch resistance. At the same time, they also have the high-strength characteristics of glass wire-wound electromagnetic wires, especially when the coil is wound, there is no need to wrap the reinforced insulating mica tape separately, which changes the structure of the insulation between the turns of the traditional insulating coil, simplifies the production process and saves working hours. After the insulating coil of a modern motor is wound and cured by heat discharge, the integrity of the coil is good, which greatly reduces the dispersion of the insulating copper wire in the breakdown performance and reduces its dielectric loss.

The scratch resistance of the electromagnetic wire insulation layer is one of the important performance indicators to judge the quality of the electromagnetic wire insulation, but at present, there are no clear and uniform regulations on it at home and abroad.