The Effect of secondary-DC-loss Protection on the Reliability of substation protection system

Abstract

To solve the failure operation of remote backup protection for adjacent stations caused by the substation secondary DC power supply loss, numerous secondary dc loss(SDL) protection schemes have been carried out. However, there are few researches to evaluate the influence of SDL protection on the reliability of the conventional relay protection system of the substation, which may cause certain risks to the engineering application. In order to solve the above problem, a reliability model for the conventional relay protection system, which contains links of sampling, protection device and tripping, is established based on the fault tree analysis method. On this basis, a reliability model of the novel relay protection system including SDL protection is also built. The sequential Monte Carlo algorithm is used in this paper to access the protection system reliability. It obtains the failure sampling time and repair sampling time of one state switch through simulated sampling. With numerous simulations, the normal working time and working times of the system can be counted, and the system's Mean Time Between Failures(MTBF) will be obtained. The simulation results indicate that SDL protection will not reduce the overall reliability of substation relay protection system. On the contrary, it can improve substation protection reliability in the case of secondary DC power loss. This paper provides powerful theoretical support for the engineering application of SDL protection.