A netizen's message inspired the author to discuss the issue of phase insulation of three-phase motors again. The netizen said that the end of the winding of the ordinary 2-pole three-phase asynchronous motor produced by them always has a breakdown problem, from 30 kilowatts to 90 kilowatts of the motor are used in single and double mixed windings, the breakdown place is not the intersection position, but the overlapping position of the phase, and most of the problems are the first coil, the entire one-groove coil or half-groove wire is broken, and the interphase insulation is melted. The first question raised by the netizen: Is this an inter-turn insulation failure? The second question: Is the first coil not handled properly? The third question: Is it a problem with the methods of the workers? The reality is that with the same material, two masters, one of the masters has a suspended coil at the end, and the coil is crossed, and the operation is rough to the naked eye; Another master's craftsmanship looks more exquisite, but there are often breakdown problems.
First of all, turn-to-turn and phase-to-phase problems often go hand in hand, and when turn-to-turn problems occur, the interphase insulation will be damaged due to local heating problems, that is, accompanied by phase-to-phase insulation failures, and vice versa. However, it can be analyzed from the tendency, if the inter-turn insulation fault is preferential, it will preferentially affect the inter-turn insulation of the turn coil due to the problem of large current, that is, there is a channeling phenomenon, and most of the inter-turn insulation faults also have different degrees of fault appearance at the other end, otherwise it is considered that the interphase insulation is preferred.
Secondly, regarding the interphase insulation of the 2-pole motor, compared with the motor with the number of other poles, the span of the 2-pole motor coil is larger, especially for the coil with more turns, no matter what type of winding is adopted, there is an end shaping problem, otherwise it will lead to interference between the stator and the rotor and the physical space, and in the shaping process, especially the strong shaping after the padding of the interphase insulation, it will inevitably lead to insulation damage, and it is not surprising that the interphase insulation fault occurs.
Third, about the first coil, from the analysis of the process route of winding processing, one straight edge of the first coil is the most advanced groove, and the other side is the most advanced groove, especially for the situation of relatively tight space, the most advanced groove part has been affected by various factors, and the probability of injury is very large, which is also the key factor that the first coil is prone to problems; From the selection of wiring, if the first coil is still directly connected to the power supply, the impact on the coil will be stronger from the analysis of the voltage decay trend, which will naturally further aggravate the condition of coil failure. Therefore, especially for high-voltage motors or inverter motors, the protection of the first coil is a very critical process.
Finally, for the operation of workers, this is a key factor of manual operation, the beauty of the process is based on the minimization of coil damage, which can ensure the quality and very beautiful technical workers' operation methods should be used as the key to the quality control of any motor factory, and should also be taught and passed on as necessary.