Известия Томского политехнического университета: Инжиниринг георесурсов (Sep 2017)
Circuit simulation of partial discharge aspects
Abstract
The DC motors are used in most production processes of oil, mining, coal and other industries. Reliability of their operation largely depends on the state of insulation such as enamel wire insulation and the main insulation of large electrical machines. Insulation defects lead to unexpected failure of electrical machines and, as a consequence, to emergencies, downtime and high economic losses due to undersupply of products and costs of machine failure liquidation. There are a lot of reasons for DC motors failure; most of them are associated with insulation damage due to exposure by partial discharges. It is necessary to identify partial discharges at the early stage to be repaired in time; it will reduce unplanned stops and expenses to replace a failed motor. Since the beginning of the twentieth century a lot of attention is payed to investigation of occurrence and impact of partial discharges on insulation. The bulk of the research refers to the equipment operating on alternating voltage. For the equipment operating at constant voltage the reliable methods for detecting partial discharges have not been developed yet. So, the theme of identifying partial discharges in DC machines is quite urgent. A promising method for detecting partial discharges is the use of the pulsed method. The method is based on the diagnosis of the transition process in the winding-insulation system of the electrical machine when applying a high-voltage pulse to the input of a diagnostic windingmachine. According to the response from the diagnostic pulse it is possible to judge on the partial discharges presence in insulation and the voltage level at which they occur. For the detailed understanding of the transition process a circuit electric model is required to be developed in the winding insulation system based on partial discharges, since not all the winding states can be reproduced in real insulation machines. The aim of the research is to develop the electrical model to demonstrate and to study the method of detecting partial discharges with the aid of the supplied pulse voltage on the test object. Methods: circuit simulation of partial discharges manifestation observed in the experiment using the developed model in Micro-Cap. Results. The authors have developed the electrical model of the experimental setup in which the conditions for the occurrence of partial discharges are artificially created and controlled. The model allows showing the appearance of partial discharges identical to the ones observed in the experiment. This helped to identify the relationship between the form of the oscillograms observed in the experiment with the presence or absence of partial discharges in the test object.
