Investigation the conditions of existence and disturbances of brush-collector contact

Abstract

Brush holders of complex design, one of the elements of which is an elastic gasket between the brush and the compression spring, have recently become widespread. Due to the almost unavoidable presence of irregularities in the collector profile, radial vibrations of the brush always occur, which is reflected in the change in contact pressure. As will be shown later, the pressure between the brush and the collector affects the electrical properties of the contact and thus the switching process. Since the change of pressure largely determines the operation of the brush, a distinction is made between: relatively stable contact with preservation of the contact pressure between the brush and the collector, close to the nominal value for the static state; pulsating contact - with contact pressure fluctuations to zero; intermittent contact. In the present work we consider pulsating contact, when the brush is not completely detached from the collector, i.e. the existence of contact is ensured during the entire period of commutation. Of particular interest from the point of view of revealing the role of mechanical factors is the study of the relationship between the shape of the volt-ampere characteristic and the value of the contact pressure, the pulsation of which, as mentioned above, is the basis for assessing the state of mechanics of the collector-brush assembly. Improving the productivity and reliability of railway and mining infrastructure is an important task in achieving this goal. In this article, in order to determine the reliability indicators of the brush-collector unit and the residual life of brushes of electric motors, a mathematical model for processing statistical data has been developed that allows classifying the types of failures, and, unlike existing models, determining the refined life of brushes based on the limiting height of their wear. A method for predicting the residual life of the electric brush of a DC electric motor is presented, which contains a list of con-trolled reliability indicators that are part of the mathematical model. The described model im-proves the accuracy of predicting and detecting failures on a DC motor. The derivation of the general formula for calculating the residual life of electric brushes is given. Based on the proposed mathematical model, a study and calculation of the reliability of the brush-collector unit was carried out, the minimum height of the brush during operation, the average rate of its wear, the standard deviation and the mathematical expectation of brush wear were determined.