Research On The Reliability Of Relay Protection In Digital Substation

With the issues of IEC61850, development of Ethernet technology and non traditional transformers, the substation automation technology was coming into digitalized stage, and the relay protections inevitably become all-digitalized. All-digital protection system had many merits, but its reliability problem was cared by many researchers. The difference between traditional protection and all-digital protection was analyzed firstly. The main factors affecting the failure of software or hardware in all-digital protection system was given. The reliability index of all-digital protection system was proposed.And the reliability evaluation system was established. Then the Markov model of all-digital protection was set up, the protection availability was calculated, Using the availability formula the comparing of traditional protection and all-digital protection was given. Because all-digital protection system secondary circuit had self monitoring ability, the all-digital protection system availability was significantly improved. At last the reliability block diagram was set up. Using the FMEA methods the failure modes of every component of all-digital protection were identified and analyzed. With the help of FMEA, the fault tree was constructed, and then the minimal cut sets were calculated. By qualitative analysis, the critical factors affecting the all-digital protection system were found out, and the various technical measures of improving all-digital protection system reliability were summarized. All of this were instructional for the designation and maintenance of all-digital protection system.