The purpose of this study is to determine the signs displaying the insulation ageing process and allow predicting the change in its technical condition under operation of traction motors in locomotives. In order to choose the indicators of the insulation condition, the methods of linear electrical circuits were used to analyze the equivalent scheme of frame insulation. In the equivalent scheme, the dielectric micro- and macro-heterogeneities were taken into account. The most informative parameters of the frame insulation ageing process are those related to absorption and resorption processes over time. The return voltage has been selected as the main characteristic to determine the indicators of insulation condition. The analytical dependences for determining the frame insulation condition indicators have been obtained different from those currently used in the diagnosis of electrical machines. The choice of indicators will allow predicting changes in the technical condition of frame insulation in operation. The studies will allow us to change the regular preventive maintenance technology to the maintenance based on the facility condition.

The objective of the article is to determine the quality conditions of a locomotive traction motor frame insulation based on observations over the recovery voltage and classification of a tested insulation wear degree as well as to determine estimates of operating time until the insulation restoration or replacement with a new one. To classify the insulation quality conditions and to forecast its residual life until the restoration, a cluster analysis and discriminant analysis are used based on indicators reflecting the properties of an insulation recovery voltage curve. The study defines an information content received from frame insulation recovery voltage readings as compared with its resistance from the perspective of testing the insulation condition and predicting its residual life. Statistical characteristics of clusters corresponding to the insulation condition stages allow determining the limit values of predicting parameters and estimating the residual insulation life prior the restoration. To classify the insulation condition, an integrated evaluation of the insulation condition quality is proposed. Integrated evaluation is performed according to the recovery voltage curve and is used as an indicator during clustering. An experimental study of the proposed method practically confirmed its effectiveness.