The IEC 60255-121:2014 standard and its impact on performance specification, testing and evaluation of distance protection relays

Different test methodologies have been used in the past by various relay manufacturers to specify and assess the distance protection relay performance. This lead to difficulties in selecting relays for the correct application and also in comparing relays from different manufacturers. The IEC 60255-121 standard “Functional requirements for distance protection” published in March 2014, specifies the minimum requirements for functional and performance evaluation of distance protection relays, describes the tests to be performed and how to publish the test results. This paper clarifies the most important aspects of this new standard, detailing how it will positively impact the power system protection community.