Siemens SIPROTEC 7UT613 series Manual page 110

2 Functions
Figure 2-22 Increase of pickup value of the stage on startup
Tripping Character-
istic
Figure 2-23 Tripping characteristic of the differential protection
110
Figure 2-23 illustrates the complete tripping characteristic of the 7UT613/63x. The
characteristic branch a represents the sensitivity threshold of the differential protection
(setting I-DIFF>) and considers constant error currents such as magnetising cur-
rents.
Branch b considers current-proportional errors which may result from transformation
errors of the main CTs or the input CTs of the device, or which for example may be
caused by mismatching or by the influence of tap changers in transformers with
voltage control.
For high currents which may give rise to current transformer saturation, characteristic
branch c provides for additional restraint.
7UT613/63x Manual
C53000-G1176-C160-2