The Reliability Analysis Of Protective Relaying System And Its Application In Power Networks

As the first defence of power system, protective relaying plays an important rolein preventing failure and disturbance, it is significant part of power system, andwhether it could work normally will bring important effect to power system. With theaugmentation of power network, capability and the grade of voltage, the failuresinfluence wide section and more customers. To ensure power network work normally,the requirement of high speed, accuracy, reliable action of protective relaying will bemore significant, so how to increase the reliability becomes an increasing attentionsubject.Markov State Space Method has gotten extensive application in the reliabilityresearch of repairable system, and protective relaying system is repairable system, sothe paper uses Markov State Space Method to resolve the reliability of protectiverelaying system. When the reliability of protective relaying system is evaluated,protective relaying hardware system is constituted by several modules, so the paperuse Fault Tree Analysis to find the weakness and optimize the system.Aiming at the not complete definition of correct action rate, the paper uses actionnumber and operating time to measure the index which may be more reasonable, andcorrect action rate is defined as the sum of area fault correct action number andexternal fault correct not action number per unit time, incorrect action rate is definedas the sum of false action number and refusing action number per unit time. Aiming atmicrocomputer protection, based on traditional relay protection device, consideringsoftware factor, the paper evaluates the failure rate and the availability of protectiondevice roundly.Taking all factors which influence the reliability of protective relaying systeminto account synthetically in the paper, they are classified by hardware and software,the paper builds software module which uses Logarithmic Exponential Module tocalculate its failure rate and hardware module which uses Fault Tree Analysis tocalculate its failure rate, By state chart, Markov Module is applied to resolve thefailure rate and the availability of protection system, and an example is used tovalidate the method.Protective relaying module which has been build rarely refers the effect of back-up protection, the paper applies Markov State Space Method to analyze the allfailure states of main and back-up protection, following the acted principle ofprotective relaying, builds the module which takes back-up protection into account,and calculates the availability of main and back-up protection, the module reflects realthe effect of protective relaying system on power network. Then the module isvalidated in the reliability evaluation of distribution system. In contrast to fourconnection modes and their calculated results, it reflects the effect of protectiverelaying system on the reliability index of power network, if disconnection andalternative supply are added, they will weaken the effect of protective relaying on thewhole system. Furthermore, the changes of network topology structure which areleaded by different connection modes also affect the reliability of the distributionsystem.