Specifications

7SR242 Duobias Applications Guide

2.1.6 Example 2 – Relay Replacement Using Existing CTs

Figure 2-11 Relay Replacement

It is recommended to wire all line CTs in star when connecting to the 7SR24 relay. Where the 7SR24 is used to

replace an older biased differential relay the existing CTs will often be re-used, it is recommended that any line

CTs connected in ‘delta’ are reconnected as ‘star’.

Usually the interposing CTs associated older schemes can be removed as both the vector group and current

magnitude compensation functions are carried out within the 7SR24. This requires ICT settings to be

programmed into the relay to correct for differences before the currents are applied to the differential algorithm.

When the relay is in balance the phase angle of the currents applied to each phase of the differential algorithm

will be in anti-phase.

Figure 2-12: AC Connections - Example 2