Section 3: Protection Functions; Current Protection: Differential Protection; Ict - Siemens 7SR242 Manual

7SR242 Duobias Description Of Operation

Section 3: Protection Functions

3.1

Current Protection: Differential Protection

Comprises both biased differential and high-set differential elements.
The fundamental frequency current is measured with the line CT inputs. These line currents are both multiplied
and vector corrected before being applied to the current differential elements.

3.1.1 ICT

The Wn ICT Multiplier setting is applied to the line currents – the CT secondary currents. The multiplier is used
to correct any CT ratio mismatch so that ideally nominal current (ICT = 1A) is applied to the biased differential
OUT
algorithm.
The Wn ICT Connection setting applies the correct vector compensation to the current applied to the differential
algorithm.
The nominal current ratio of the virtual interposing CT is 1:1. Note that where Yd settings are applied some
current distributions will result in a √3 multiplying factor being applied. See 'Applications Guide'.
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