Determining an additional diagnostic parameter for improving the accuracy of assessment of the condition of stator windings in an induction motor

Abstract

This paper has proposed and substantiated the application of an additional diagnostic parameter for assessing the state of stator windings of induction motors during operation. The dependences of the values of phase shifts between phase currents and phase voltages have been obtained. These dependences showed that when an inter-turn short circuit occurs in the stator windings, the phase shifts are the same for all phases of the motor. That has made it possible to obtain the dependence of the change in phase shift on the change in the engine shaft rotation frequency. This study's result has established the dependence of the rates of change of the phase angle on the engine shaft rotation frequency for both one and two damaged phases with varying degrees of damage. When analyzing these dependences, it was found that with an increase in the number of damaged phases of the electric motor, the linear section of the dependences decreases. In addition, with an increase in the degree of phase damage, the angle of inclination of the linear sections of the characteristics decreases. That has made it possible to determine an additional parameter for diagnosing the place and degree of an inter-turn short circuit of the windings in an induction motor with a squirrel-cage rotor. The values of the additional parameter, termed by this paper's authors as a "phase criterion" can be used to assess the condition and degree of damage to the stator winding of induction motors. The values of the phase criteria for various types of damage were: when phase A is damaged by 90 %, ξ=0.634, (deg)2/(rpm)2; when phase A is damaged by 80 %, ξ=0.393, (deg)2/(rpm)2; when phase A is damaged by 80 % and phase B is damaged by 90 %, ξ=0.25, (deg)2/(rpm)2; when phase A is damaged by 80 % and phase B is damaged by 90 %, ξ=0.173, (deg)2/(rpm)2. The results of this research could be used to select an effective method for diagnosing an inter-turn short circuit in the stator winding when building a diagnostic system for induction motors as part of drives of transport equipment

Structural diagram of the built-in diagnostic system for electric drives of vehicles

“…The next in terms of the number (15%) of the causes of failures is the occurrence of an inter-turn short circuit in the stator winding [3]. In the presence of this defect with a small number of short-circuited turns in the stator winding, the motor is in working condition [7][8][9]. In this case, the performance characteristics and energy indicators of the induction electric motor deteriorate [8,9].…”

“…In the presence of this defect with a small number of short-circuited turns in the stator winding, the motor is in working condition [7][8][9]. In this case, the performance characteristics and energy indicators of the induction electric motor deteriorate [8,9]. This defect is characterized by the fact that it can develop over time.…”

“…However, a priori data on vibration signals characteristic of different degrees of damage to the stator winding are required to identify the winding defect, its development and predict the run-up time to failure. It was shown in [9] that the coefficient of torque pulsations, which arise as a result of asymmetric modes of the motor windings, is greater at idle than when the motor is operating under load. This factor complicates the application of vibration methods when building a diagnostic system as part of the drive, since the motor in the drive is constantly under load during operation.…”

“…The simultaneous appearance of an inter-turn short circuit on two phases is a rather rare case. It is considered in the study [9], where the authors performed a comparison of the coefficient of torque ripples for the case of inter-turn shorting on one and two phases. As a result of the comparison, it was established that with a small number of damaged turns on both phases, the torque ripple coefficient is slightly lower than with the same number of damaged turns on one phase.…”

Method for Determining the Degree of Damage to the Stator Windings of an Induction Electric Motor with an Asymmetric Power System

“…Current methods based on the measurement of phase currents [26] and the study of changes in stator currents in different phases [27] also do not allow researchers to accurately determine the reasons for the manifestation of the asymmetry of the stator current system.…”