Identification And Prevention Technology Of Hidden Failure Of Relay Protection

The correct operation of relay protection is an important factor of ensuring system safety and stable operation.The failure or the incorrect operation of protection will cause serious damage to power system.As potential faults,hidden failures in relay protection are lethal for power system.Even they will cause the cascading failure.At present,hidden failure has become the important factor threatening the safe and stable operation of power system.Therefore,the study of identification as well as early warning and prevention technology of hidden failures in relay protection system becomes an important and urgent issue and has great value to ensure the safe and stable operation of power system.Firstly,the research aims at the identification of hidden failure.This paper summarizes the identification and solution of common hidden failure in secondary circuit.It is found that there are not on-line identification and solution for multi-grounding fault in secondary circuit of potential transformer.So,the impact on zero sequence directional protection caused by multi-grounding fault is analysed firstly.Then this paper analyses the characteristic of the affected voltage and current.And it is found that the zero sequence voltage of special phase is in phase with its negative sequence voltage under normal circumstance,however this is not true at this hidden failure.As a consequence,the identification method of multi-grounding fault in potential transformer and a new zero sequence direction algorithm which can avoid the mis-operation of the zero sequence directional protection are proposed.Secondly,the research aims at the early warning and prevention technology of hidden failures.In order to investigate hidden failure and assess the risk of cascading failure caused by hidden failure,this paper presents protection Markov model that changes with environment and load flow firstly.The protection Markov model is based on belief rule base,and it contains environmental factor and load flow factor.Secondly,hidden failure probability model is introduced by dividing hidden failure into two categories(continuous and discrete type).Thirdly,a cascading model with three assessment indexes including probability,structure and energy loss was developed.Finally,based on IEEE 118 system,the result of simulation indicates the accuracy of the proposed hidden failure model and risk assessment algorithm.