HIGH-FREQUENCY PROCESSES IN THE WINDINGS OF GENERAL-PURPOSE ELECTRICAL MACHINES IN THE PRESENCE OF DEFECTS IN THE GROUND-WALL INSULATION

Insulation defects in general and ground-wall insulation problems in particular are one of the main causes of failure in general-purpose induction motors. Most of the articles on this topic focus on more complex, expensive and comprehensive diagnostic methods, but they are not always appropriate and justified for electric machines of small and medium power, which are widely used in the agricultural sector. This article deals with the relevant problem of ground-wall insulation diagnostics. Namely, the development of such a diagnostic technique, which would not be resource-intensive, would not require complex equipment and would be easy to use. It has been verified that the use of a single-link replacement scheme for high-frequency testing can indicate the presence of a ground-wall insulation defect in a particular winding phase, but cannot be used for more detailed analysis, for example, to locate the defect. It is shown that when using a multilink replacement scheme, it is possible to model the damage to the ground-wall winding insulation when defects of different level are located along the entire length of the winding at the level of one coil. High-frequency tests were performed in this mathematical model and data were collected, namely the resonant frequency and input impedance at resonance, for defects of different degrees at different locations in the winding in the short circuit and open circuit modes. In parallel with the mathematical modeling, the resonant frequency was calculated using engineering formulas to control the results of the mathematical model. A number of experimental studies were also conducted on a specially prepared sample of a real 4A90L2 engine to verify the convergence of the mathematical modeling results with real experimental data. The experimental data confirm the adequacy of the model, and the results differ by no more than 5-7%, which indicates that the mathematical model is sufficiently accurate. As a result, a specific algorithm for implementing the method of detecting defects in the ground-wall insulation of multi-turn low-voltage electrical machines for general-purpose use by means of high-frequency effects by analyzing the input resistance and resonant frequency when comparing defective and defect-free phases in symmetrical three-phase windings is proposed. The proposed method makes it possible to determine the presence of a local or integral defect in the ground-wall insulation. In the case of a local defect, it makes it possible to determine the location of the defect down to the level of the winding coil. This method can also partially indicate the presence of defects in the longitudinal insulation.