Siemens SIPROTEC 4 7UT6 Series Manual page 526

Current Transformer Requirements
D.1 General Requirements
Caution: If earth fault differential protection is used, the requirement for the phase current transformer of the
REF side is as follows:
[wandlerueberpruefung-7ut6x, 1, en_GB]
Figure D-1
The CB layout within the power station unit is not specified.
x" = sub-transient direct-axis reactance of the generator in p.u.
d
u = transformer short-circuit voltage HV - LV in %
k
R = assumed with 0.1 Ω, (the consumption of the above devices is below 0.1
relay
VA)
526
1 / ≤ F ≤ 4, (for the starpoint transformer remains
4 Adap
CT verification for Devices 7UT6x
1 / ≤ FAdap ≤ 8)
8
SIPROTEC 4, 7UT6x, Manual
C53000-G1176-C230-5, Edition 09.2016