Siemens 7UT51 Instruction Manual page 36

3
Application Examples
Bus 1
52
3 3
Radial Bus Differential Protection Including Bus Tie Breaker for Two
Figure 3.9
A typical radial transformer and feeder breaker
combination is illustrated in Figure 3.10. A 7UT513 is
shown providing primary differential protection (87,
87HS) for the transformer and distribution buswork,
excluding the feeder breakers. Assuming identical CT
ratios on the feeder breaker CTs, they can all be tied
together and brought to one set of phase-current
inputs on the 7UT513. Backup protection in the form of
thermal overload for both windings and overcurrent for
the transformer high voltage winding is also provided.
If it is desired to include the feeder breakers in the
protected zone, connections can be made as shown in
Figure 3.8 on page 35.
36
7UT513
87
B1
52
52 52
3
7UT513
87
B2
52
Tie
52
3
- Bus Distribution System
Ground differential protection could also be
implemented using a 7UT513 with connections from a
grounded-neutral CT to the 87N element, as shown in
Figure 3.3 on page 32.
Note: There must not be any source(s) on the
feeders. The relay will not operate correctly for
a phase-to-ground-fault on a feeder if there is
an active source connected to a non-faulted
feeder.
7UT51 v3
52
Bus 2
52 52
3 3
PRIM-2330C