Experimental Determination of Diagnostic Signs of Damage to the Rotor Windings of High-Voltage Power Plant Motors in Startup Mode

Abstract

Induction electric motors are widely used as drives of various mechanisms in power engineering and industry. Their failure can lead to costly repairs, to a reduction in power, or, for example, to a complete shutdown of a power plant unit. One of the reasons for the failure of high-voltage induction motors operating under severe starting conditions is damage to the squirrel-cage rotor winding. Existing methods for monitoring the breakage of the winding bars of such electric motors are ineffective due to the peculiarities of their operating modes. Therefore, monitoring the condition of the bars of high-voltage motors at startup and searching for diagnostic signs is an urgent task. Initially, the studies were carried out with a model of a high-voltage induction motor, developed in the ANSYS software package. To confirm the results obtained for a real motor, research has also been conducted on the developed experimental bench. The recorded signals were processed based on the method of short-time Fourier transform in the MatLab environment. In the course of the study, it was shown that, in the presence of bar breaks, the spectrum of an induction motor exhibits sharply increased amplitudes of harmonic components of the dummy rotor winding at the lower side frequencies of the first orders; this confirms the possibility of using external magnetic field signal at startup to detect the presence of bar breaks in the squirrel-cage rotor winding of high-voltage induction motors with heavy prolonged starts.