2.2 Differential Protection
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7UT613/63x Manual
C53000-G1176-C160-2
Figure 2-38 Definition of current direction on a shunt reactor
2.2.5 Differential Protection for Mini-Busbars and Short Lines
A mini-busbar or branch-point is defined here as a three-phase, coherent piece of con-
ductor which is limited by sets of current transformers. Examples are short stubs or
mini-busbars. The differential protection in this operation mode is not suited to trans-
formers; use the function „Differential Protection for Transformers“ for this application.
Even for other inductors, like series or shunt reactors, the busbar differential protection
should not be used because of its lower sensitivity.
This operation mode is also suitable for short lines or cables. „Short“ means in this
context that the current transformer connections from the CTs to the device do not
cause impermissible load to the current transformers. On the other hand, capacitive
charging currents do not harm this operation because the differential protection is nor-
mally less sensitive with this application.
Since the current direction is normally defined as positive in the direction of the pro-
tected object, this results in the definitions as illustrated in figures 2-39 and 2-40.
The models 7UT613 and 7UT633 allow mini-busbars with up to 3 feeder or lines with
up to 3 terminals (“Teed lines”) to be protected, 5 feeders can be protected using
7UT635. Figure 2-41 shows the example of a busbar with 4 feeders.
Figure 2-39 Definition of current direction at a branch-point (busbar with 2 feeders)
Figure 2-40 Definition of current direction at short lines
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