Известия Томского политехнического университета: Инжиниринг георесурсов (May 2022)
METHOD OF DIAGNOSING BROKEN ROTOR BARS OF INDUCTION MOTORS BASED ON REGRESSION ANALYSIS OF THE STATOR CURRENT RESULTANT VECTOR MODULE
Abstract
The relevance of the research is conditioned by great dependence of uninterrupted operation of critical mechanisms driven by high-voltage induction motor, providing operation of oil and gas and chemical industry, metallurgy, electric power industry and other strategically important branches of the country. The issue of reliability of continuous operation is particularly acute in the operation of thermal power plants. Almost all electric drives of critical auxiliary mechanisms of thermal power plants are based on powerful high-voltage induction motors with squirrel-cage rotor. As a rule, specifics of operation of these motors are severe conditions of starting under load at increased temperatures and environmental pollution. Emergency stops of induction motors together with the responsible mechanisms at thermal power plants eventually cause power unit shutdown or lead to under-release of electricity and revision of the operating mode of the power system. Despite such consequences, in particular from damage to the short-circuited rotor winding of a high-voltage induction motor, a protection with sensitivity capable of detecting this defect has not yet been developed or introduced. Damage of rotor circuit has latent character, can exist for a long enough time, not critically affecting the operation of the machine, nevertheless, the fact of presence of breakage can be considered as an emergency condition of the machine in complex with the mechanism. According to the data of repairs and revisions of high-voltage induction motors, there are cases when up to 30 % of bars of the whole rotor were damaged simultaneously. When the integrity of the connection between the bar and the short-circuiting ring is broken, its deformation can occur only in the direction of the air gap, irreversibly damaging the active part of the stator. Operation of inductions motor with a broken core is accompanied by a number of additional negative side effects, such as increased power consumption, general reduction of machine performance and efficiency, generation of additional heat, increased wear of bearings. In case of diagnosing a short-circuited winding defect at an early stage of its development, it is possible to repair the rotor by the company itself. Early diagnosis of rotor core breaks of high-voltage auxiliary motors of thermal power plants is a difficult and at the same time extremely relevant purpose. The main aim of the research is the development and experimental testing of a method for diagnosing broken rotor bar in a high-voltage induction motor based on mathematical processing of signals from stator current sensors. Methods: theory of electrical machines, methods of digital signal processing, statistical methods of data processing, methods of approximation of experimental data, method of regression analysis. Presented studies were carried out on the experimental workbench, specially created for the purpose of diagnostics of broken rotor bars. Results. The paper introduces the method of diagnostics of broken rotor bars based on approximation of stator current signals. The criterion of rotor circuit damageability was revealed and the dependence of this criterion on the degree of damage to the «squirrel cage» of an induction motor was obtained.
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