On the estimation of time-varying failure rate to the protection devices based on failure pattern

Compared with the mean failure rate (MFR), time-varying failure rate (TFR) has advantages in accuracy and is more suitable for reliability assessment. This paper proposes the estimation approach for the TFR of the relay protection device with the field data. According to the feature of protection devices failure, it first divides the data into random failure and aging failure. And then, for the random failure data, constant random failure rate (RFR) is estimated by using exponential distribution function, for the aging failure data, aging failure rate (AFR) is estimated with the Weibull, normal, lognormal and Rayleigh distribution functions, and the best estimation is determined by the coefficient of determination. Simulation results show that the aging failure obeys the Weibull distribution law. Finally, the general TFR is, obtained with the addition of the RFR and AFR, estimated with the field data in a regional power system.