4-10
Loss-of-Potential, Load Encroachment, and Directional Element Logic
Date Code 20001006
SEL-351 Instruction Manual
Directional Element Routing
Refer to Figure 4.4 and Figure 4.11.
The directional element outputs are routed to the forward (Relay Word bit 32GF) and reverse
(Relay Word bit 32GR) logic points and then on to the direction forward/reverse logic in
Figure 4.12.
Loss-of-Potential
Note if all the following are true:
•
enable setting ELOP = Y,
•
a loss-of-potential condition occurs (Relay Word bit LOP asserts),
•
and internal enable 32IE (for channel IN current-polarized directional element) is not
asserted
then the forward logic point (Relay Word bit 32GF) asserts to logical 1, thus, enabling the neutral
ground and residual ground overcurrent elements that are set direction forward (with settings
DIR1 = F, DIR2 = F, etc.). These direction forward overcurrent elements effectively become
nondirectional and provide overcurrent protection during a loss-of-potential condition.
As detailed previously (in Figure 4.8 and Figure 4.9), voltage-based directional elements are
disabled during a loss-of-potential condition. Thus, the overcurrent elements controlled by these
voltage-based directional elements are disabled also. But this disable condition is overridden for
the overcurrent elements set direction forward if setting ELOP = Y.
Refer to Figure 4.1 and accompanying text for more information on loss-of-potential.
Direction Forward/Reverse Logic
Refer to Figure 4.4 and Figure 4.12.
The forward (Relay Word bit 32GF) and reverse (Relay Word bit 32GR) logic points are routed to
the different levels of overcurrent protection by the level direction settings DIR1 through DIR4.
Table 4.1 shows the overcurrent elements that are controlled by each level direction setting. Note
in Table 4.1 that all the time-overcurrent elements (51_T elements) are controlled by the DIR1
level direction setting.
In most communications-assisted trip schemes, the levels are set as follows (see Figure 5.4):
Level 1 overcurrent elements set direction forward (DIR1 = F)
Level 2 overcurrent elements set direction forward (DIR2 = F)
Level 3 overcurrent elements set direction reverse (DIR3 = R)
If a level direction setting (e.g., DIR1) is set:
DIR1 = N (nondirectional)
Summary of Contents for SEL-351
Page 14: ...Courtesy of NationalSwitchgear com ...
Page 16: ...Courtesy of NationalSwitchgear com ...
Page 40: ...Courtesy of NationalSwitchgear com ...
Page 74: ...Courtesy of NationalSwitchgear com ...
Page 146: ...Courtesy of NationalSwitchgear com ...
Page 186: ...Courtesy of NationalSwitchgear com ...
Page 220: ...Courtesy of NationalSwitchgear com ...
Page 304: ...Courtesy of NationalSwitchgear com ...
Page 340: ...Courtesy of NationalSwitchgear com ...
Page 380: ...Courtesy of NationalSwitchgear com ...
Page 450: ...Courtesy of NationalSwitchgear com ...
Page 506: ...Courtesy of NationalSwitchgear com ...
Page 528: ...Courtesy of NationalSwitchgear com ...
Page 534: ...Courtesy of NationalSwitchgear com ...
Page 536: ...Courtesy of NationalSwitchgear com ...
Page 550: ...Courtesy of NationalSwitchgear com ...
Page 562: ...Courtesy of NationalSwitchgear com ...
Page 570: ...Courtesy of NationalSwitchgear com ...
Page 584: ...Courtesy of NationalSwitchgear com ...
Page 602: ...Courtesy of NationalSwitchgear com ...