1 What is inter-turn fault? The same winding is made up of many turns of wire. If the insulation is not good, a short circuit will occur between the superimposed coils, which is equivalent to a part of the coil being directly short-circuited and not working. After the inter-turn short circuit, the winding magnetic field of the motor will become asymmetric, and the current of the remaining coils will increase compared to before. During the operation of the motor, there will be problems such as increased vibration, increased current, and relatively reduced output.

During the operation of the motor, whether it is a test run or an actual run, if there is a turn-to-turn fault, the most direct phenomenon is that the current is unbalanced, there is a burnt smell, the motor has a dull sound, and there will be obvious vibration problems. In severe cases, there will be smoke and explosions. During the disassembly of the faulty motor, we will find that it is sometimes difficult to distinguish between phase-to-phase, ground-to-ground and turn-to-turn faults. Today we will only talk about how to identify turn-to-turn problems. Below we show you a picture of a faulty rotor. From the signs of the fault, can you tell what the fault is? This is a real photo taken at a fault analysis site. At that time, some people thought it was between turns, and some thought it was between phases. The final result was determined to be between phases, or it can be considered that the phase-to-phase is the main cause.

2 Analysis of the cause of the fault For this type of problem, we first conduct a comprehensive analysis of the location of the fault point and the spread of the fault. The fault point is exactly at the position of the phase-to-phase insulation, which is a necessary condition for phase-to-phase fault; the second step is to look beyond the phenomenon and explore the essence, which is to look at the opposite side of the fault point, that is, the other end of the winding. If it is a turn-to-turn fault, there will be relatively light burn marks on the opposite side, otherwise it is not a turn-to-turn problem. The actual inspection found that the fault point of the winding was limited to this end, which is a typical phase-to-phase fault. We will share with you the analysis of the causes of phase-to-phase faults in the winding in combination with actual cases later.

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