Reliability modelling of capacitor voltage transformer using proposed Markov model

Abstract

Capacitor voltage transformer (CVT) is one of the most important instrument transformers widely used to prepare the voltage signal for control and protection equipment. The measuring accuracy of CVT plays an important role in the proper operation of the protection system. Therefore, maintaining the accuracy of CVT throughout its lifetime at the desired level is of great significance, and proper maintenance activities must be implemented regarding the equipment conditions. Evaluating the reliability of the CVT over its lifetime is necessary to determine the proper maintenance. Until now, no proper model has been suggested to evaluate the reliability of CVT. Therefore, this paper proposes a new Markov model to evaluate the reliability of CVT. To obtain the model, initially, a Markov model is presented for each subsystem of CVT including capacitor voltage divider (CVD), electromagnetic unit (EMU), and high voltage bushing. Then, by integrating these models, a 10-state extended Markov model is proposed for CVT. Finally, by combining similar states, a 3-state model including healthy, low-quality and failure states is obtained. The simulation results show that the second capacitive group in the CVD subsystem, and the compensating reactor in the EMU subsystem play a major role in the CVT performance.