BS EN 60255-121:2014

1 Scope
2 Normative references
3 Terms and definitions
4 Specification of the function
5 Performance specifications
6 Functional tests
7 Documentation requirements
Annex A (informative) - Impedance characteristics
Annex B (informative) - Informative guide for
        the behaviour of timers in distance protection
        zones for evolving faults
Annex C (normative) - Setting example
Annex D (normative) - Calculation of mean, median
        and mode
Annex E (informative) - CT saturation and influence
        on the performance of distance relays
Annex F (informative) - Informative guide for testing
        distance relays based on CT requirements specification
Annex G (informative) - Informative guide for
        dimensioning of CTs for distance protection
Annex H (normative) - Calculation of relay settings
        based on generic point P expressed in terms of
        voltage and current
Annex I (normative) - Ramping methods for testing the
        basic characteristic accuracy
Annex J (normative) - Definition of fault inception angle
Annex K (normative) - Capacitive voltage instrument
        transformer model
Annex ZA (normative) - Normative references to
         international publications with their
         corresponding European publications

Defines minimum requirements for functional and performance evaluation of distance protection function typically used in, but not limited to, line applications for effectively earthed, three-phase power systems.

IEC 60255-121:2014 specifies minimum requirements for functional and performance evaluation of distance protection function typically used in, but not limited to, line applications for effectively earthed, three-phase power systems. This standard also defines how to document and publish performance tests. This standard covers distance protection function whose operating characteristic can be defined on an impedance plane and includes specification of the protection function, measurement characteristics, phase selection, directionality, starting and time delay characteristics. The test methodologies for verifying performance characteristics and accuracy are included in this standard. The standard defines the influencing factors that affect the accuracy under steady state conditions and performance characteristics during dynamic conditions. It also includes the instrument transformer requirements for the protection function. The general requirements for measuring relays and protection equipment are defined in IEC 60255-1.