Reserch On Reliability And Condition Based Maintenance Of Relay Protection

The relay protection system is an important barrier to ensure the power grid operate safely and stably, and when the faults occur in power system, the protective devices is able to act quickly to cut off the fault location timely to limit the losses to a minimum range, so it can be regarded as" the protective umbrella" of the power grid. However, the relay protection system itself will also break down, and when the tripping or malfunction fault occurs, not only it is difficult to play a protective role, but also it will expand the range of the accident and make it worse. Reasonable maintenance can find out protection system fault timely and avoid the consequences above. However, how to repair and when we repair is an important issue in front of us.The application of the condition based maintenance technology can greatly improve the reliability of protection system and save the maintenance cost, therefore, it is of great practical significance to study it deeply. In this paper, the condition based maintenance (condition assessment) has been regarded as a separate state to establish Markov model of relay protection, and the following research work has been done1.This paper has analyzed the composition of the relay protection system, method of the reliability assessment and the process of the condition based maintenance, and summarized the related literature at home and abroad.2.Based on the CPU life statistical data of a certain type of microcomputer protection, the life frequency distribution histogram and cumulative frequency distribution histograms have been drawn by the histogram method, and then the conclusion that the condition based maintenance needs lots of basic data and the reliability evaluation model combine together. 3.Considering the condition based maintenance instead of the regular maintenance, the protection system state space models of self checking-regular maintenance and self checking-condition based maintenance have been established respectively, and the corresponding reliability indexes have been solved by the state space method, and the relationship curves of the reliability-maintenance efficiency and the failure rate-the regular maintenance cycle have been got by MATLAB simulation. The following conclusions have been obtained after analyzing the curve:when the self checking and regular maintenance coexist, improving maintenance efficiency can extend the maintenance cycle and save the maintenance cost, meanwhile, improving the efficiency of condition based maintenance and repair personnel can also improve the reliability of relay protection significantly.4.The Markov state space model considering condition assessment has been established, and then according to this model, the effect of the protected primary device to the reliability of relay protection has been analyzed. Through the MATLAB simulation, the curves of relationship between primary device failure rate and protection system reliability, repair rate and protection system reliability, have been obtained respectively.5.The state space model considering hidden fault has been established and analyzed to obtain the expressions of the steady-state probability of each state, providing a thinking for calculating the steady-state probability of hidden failures of the protection system by the state space method.The method proposed in this paper can provide technical guidance for the application of condition based maintenance technology in relay protection.