In recent years, medium voltage power cable has been widely used in the transmission and distribution network. However, the fault rate of cable accessories has increased year by year. During the fabrication and operation of cable accessories, the moisture can easily enter into cable accessories and make it damp, which will influence the insulation condition and lead to the failure of cable. Protective devices are important because they ensure that under fault Conditions, a high fault current cannot flow – as well as protecting the installation this, more importantly, ensures that consumers are not injured or killed as a result of an electrical fault .