UNE-EN IEC 60255-187-1:2021

The object of this standard is to specify the minimum requirements for functional andperformance evaluation of (longitudinal) differential protection designed for the detection of faultsin ac motors, generators and transformers. This standard also defines how to document andpublish performance test results.This standard covers the differential protection function whose operating characteristic can bedefined on a bias-differential plane and includes specification of the protection function,measurement characteristics, compensation of energizing quantities, additional restraint orblocking methods (for over-excitation and magnetising inrush), starting and time delaycharacteristics. The standard also covers unrestrained differential protection functionstraditionally combined with the restrained (biased) differential element to form a single differentialrelay.The standard defines the influencing factors that affect the accuracy under steady stateconditions and performance characteristics during dynamic conditions. The test methodologiesfor verifying performance characteristics and accuracy are also included in this standard.The differential protection functions covered by this standard are as follows:This standard does not specify the functional description of additional features often associatedwith biased differential relays such as CT supervision (CTS), switch onto fault (SOTF) anddetection of geo-magnetically induced currents (GIC).This standard does not cover differential relays designed for bus bar protection (including highimpedance differential protection) or line protection. Additionally, this standard does not explicitlycover generator incomplete longitudinal differential, generator split-phase transverse differential,self-balancing or magnetic balanced protection scheme, differential protection of phase-shiftingtransformers, directional restricted earth fault protection, railway transformers, convertortransformers and reactors but the principles covered by this standard may be extended to provideguidance for these applications.The general requirements for measuring relays and protection equipment are defined inIEC 60255-1.