Standards Development

Scope

This part of IEC 60255 specifies the minimum requirements for functional and performance evaluation of a.c. directional overcurrent protection functions, which will operate at a desired value of a.c. overcurrent flowing in a predetermined direction with relevant phasor as direction reference. Such an a.c. directional overcurrent protection function is a combination of directional characteristic and overcurrent characteristic, and the latter is specified in IEC 60255- 151. This document also defines how to document and publish performance test results.

The document covers single-phase, three-phase, positive-sequence, negative-sequence, zero15 sequence, residual, or neutral directional overcurrent protection functions with more than one input energizing quantity including electric current(s) and voltage(s) either hardwired from instrument transformers or as data over communication ports using an appropriate data communication protocol. This document also covers the directional overcurrent protection function using the wattmetric part of residual current as characteristic quantity. Specification of the protection function, measurement characteristics, directionality, start, and operate time delay characteristics are addressed. Annex A provides some commonly used operating characteristics.

The test methodologies for verifying performance characteristics and accuracy are included in this document. The document identifies factors that influence the accuracy under steady state conditions and performance characteristics during dynamic conditions.

The directional overcurrent protection functions covered by this standard correspond to those listed in Table 1.

Please see draft for Table 1 – Directional overcurrent protection designations

This document does not specify the functional description of additional features often associated with directional overcurrent protection functions such as voltage transformer IEC CD 60255-167  IEC 2023 – 9 – 95/546/CD supervision (VTS), current transformer supervision (CTS). Only their influence on the directional overcurrent protection function is covered in this document.

This document does not cover directional overcurrent protection based on other characteristic quantities than an a.c. current phasor, such as incremental quantities, d.c. current etc.

The general requirements for measuring relays and protection equipment are defined in IEC 60255-1.