Reliability Assessment Of The High Voltage Protective Device

Given to the interconnected power grid, the UHV and HVDC are mainly used in long distance and high capacity transmission area. While strengthened grid may give rise to enormous benefits, a small failure may lead to a disastrous cascading failure in the meantime. Since relay protection system being the first line of the power grid, it is essential to its reliability research. The evaluation method on the reliability of protective device in this thesis is discussed, the main contributions are as follows:Firstly, multiple factors of the protective relay were analyzed. The hardware, software and the rarely mentioned hardware-related software failure are the protection itself factor in affecting the reliability, the failure rate model was also introduced simply. Then the human reliability was taken into consideration, and the HCR (Human Cognitive Reliability) method was introduced into the protection reliability. Furthermore, this thesis discussed the influence of the partial maintenance and the whole maintenance, offering the foundation to the following reliability model.Then, a new method base on the three-parameter Weibull distribution for the time-varying failure rate calculation of the protective relay was proposed, which can make up for the deficiency that the current evaluation method of protection time-varying failure rate could not simulate the non-aging failure condition. In the parameter estimation of the three-parameter Weibull distribution, the least square method was used for the shape parameter and the scale parameter, and the iterative method was used for the positional parameter. Moreover, combined with some real grid data, the failure rate function of the protective relay was calculated and the differences between the current method and the new method were analyzed.Furthermore, for the line protections, Markov model for both the single protection and the double protections considering the multiple factors were proposed. On the assumption of constant failure rate, the influences of different parameters to the unavailability were analyzed and the optimal maintenance cycle under different failure rate was computed. On the assumption of time-varying failure rate, the difference of partial maintenance and complete maintenance was taken into consideration firstly, and influences of different maintenance strategies for the protective relays on unavailability were compared and analyzed.Lastly, a novel risk evaluation method for HV line protection was proposed. Dividing the different status of the HV line and the protection and taking the self-test into consideration, four risk indexes (explicit unnecessary operation risk, explicit unready operation risk, implicit unnecessary operation risk and implicit unready operation risk) were derived. Based on the Markov model, the calculation method of the four risk indexes was provided. Moreover, combined with both AC and DC protection data, the four risk indexes were computed. Ultimately, both the difference between unavailability and risk indexes on evaluating protective relays and the effects of self-check rate on risk were discussed and analyzed.