This post describes the CT requirements for Relion 670 Relays applications.
To see other supported relays, click here.
Rated equivalent secondary e.m.f. requirements
Busbar protection

Distance protection


Breaker failure protection

Transformer differential protection

Restricted earth fault protection (low impedance differential) protection



Non-directional instantaneous and definitive time, phase and residual overcurrent protection

Non-directional inverse time delayed phase and residual overcurrent protection

Generator differential protection

Example 1 – (3 parts)



Example 2 – (3 parts)



Line differential protection


Directional phase & residual overcurrent protection

Current transformer requirements for CTs according to other standards
Current transformers according to IEC 61869-2, class P, PR

Current transformers according to IEC 61869-2, class PX, PXR (and old IEC 60044-6, class TPS and old British Standard, class X)

Current transformers according to ANSI/IEEE
