Schweitzer Engineering Laboratories SEL-251 - Selectable Setting Groups

2-20 Specifications Date Code 20000421
SEL-251, -2, -3 Instruction Manual
The SEL-251 Relay is reset (79RS = 1, shot = 0) and has four open intervals set (four shots to
lockout).
In the example, a permanent ground fault greater than 50NL in magnitude occurs beyond the line
recloser. Because 50NLT and the line recloser fast curve are properly coordinated, the line re-
closer operates twice on its fast curve and the SEL-251 Relay doesn't trip. After operating on
two fast curves, the line recloser disables its fast curve and operates on its slow curve.
During the two line recloser fast curve operations, the 50NL element picked up and dropped out
twice without the SEL-251 Relay tripping. Because SEQ(1) = 50NL, the shot counter incre-
mented twice, so shot = 2. Every time SEQ(1) increments the shot counter, the reset interval
timer is reinitialized.
Because 79SH = 1 for shots 0 and 1 only, 50NLT is now disabled at shot = 2. 50NLT will re-
main cut out until the newly reinitialized reset interval timer expires. The line recloser then
operates on its two slow curves, causing the relay shot counter to increment to shot = 4. The line
recloser then goes to lockout. When the SEL-251 Relay reset interval timer expires,
shot = 0 again.
Sequence coordination prevents the SEL-251 Relay from tripping for a fault beyond a line
recloser. However, proper coordination was present between the line recloser fast curve and
50NLT in this example.
No phase overcurrent elements were enabled for tripping in this example. This is usually not the
case in practice but was done to simplify the example.
SELECTABLE SETTING GROUPS
The relay accepts six groups of relay and logic settings.
Program relay elements and logic with the SET command. To program group 1 settings and
logic, use SET 1 and provide the requested information. The COPY command makes it easy to
copy settings and logic from one group to another (e.g., COPY 1 4 copies Group 1 to Group 4).
Afterward, you can edit Group 4 settings and logic with the SET command.
The relay determines which group of settings and logic to use by monitoring the setting group
selection inputs (SS1, SS2, and SS3). To use inputs, program one or more of the setting selec-
tion inputs SS1, SS2, and SS3 to the respective inputs IN1, IN2, and IN3. You can also use the
GROUP command to specify a setting group.