Schweitzer Engineering Laboratories SEL-421-4 - Figure 5.2 Main and Alternate Line-Current Source Assignments; Figure 5.3 Combined Currents for Line-Current Source Assignment; Figure 5.4 Breaker Current Source Assignments

5.3
Date Code 20171021 Instruction Manual SEL-421 Relay
Protection Functions
Current and Voltage Source Selection
Figure 5.4 shows the assignment of breaker currents for as many as two circuit
breakers. These assigned breaker currents are used in breaker monitoring and
breaker failure functions. These same breaker currents can also be assigned as
line currents (e.g., line-current assignment LINE1 := IW in Figure 5.2).
All the available current and voltage source selection settings combinations are
covered in Table 5.1, Table 5.2, and Table 5.3. Notice that global setting
NUMBK (Number of Breakers in Scheme; see Table 8.3 on page 8.2) influences
available settings combinations covered in Tabl e 5.1, Table 5 .2, and Table 5.3. In
general, if NUMBK := 1, then no settings directly involving a second circuit
breaker are made (i.e., Breaker 2 current source setting BK2I is automatically set
to NA and hidden, as indicated with the shaded cells in the BK2I columns in
Table 5.1 and Table 5.2). Also, for source-selection setting ESS := N, the settings
are forced to certain values and hidden, as indicated with the shaded cells in the
ESS := N rows in Table 5 .1.
Figure 5.2 Main and Alternate Line-Current Source Assignments
Figure 5.3 Combined Currents for Line-Current Source Assignment
Figure 5.4 Breaker Current Source Assignments
IW
IX
SEL-421
Main
Breaker
Alternate
Breaker
LINEI := IW
ALINEI := IX
IW
IX
SEL-421
LINEI := COMB
IW
SEL-421
BK1I := IW
IX
SEL-421
BK2I := IX