Schweitzer Engineering Laboratories SEL-321 - Directional Comparison Unblocking Scheme Logic; Zone 1 Extension Logic Setting; Remote-End-Just-Opened (REJO) Enable Setting (EREJO); Switch-Onto-Fault Logic Setting

5-18 Applications Date Code 20011026
SEL-321/321-1 Instruction Manual
Directional Comparison Unblocking Scheme Logic
For this application the Directional Comparison Unblocking logic is not required.
The Directional Comparison Unblocking logic is disabled by setting EDCUB = N.
EDCUB = N
NN
N
- Other Settings Affected
KEY, ECTT, ATB and EKEY elements.
Zone 1 Extension Logic Setting
For our example the Zone 1 extension logic is not required. Setting EZ1EXT = N, disables the
scheme logic.
EZ1EXT = N
NN
N
- Other Settings Affected
Z1X element.
Remote-End-Just-Opened (REJO) Enable Setting (EREJO)
In the example for the relay at Breaker 3, we select EREJO = N. This disables the REJO logic.
EREJO = N
NN
N
- Other Settings Affected
TA, TB, TC, and 3PT element.
Switch-Onto-Fault Logic Setting
The 50H element is intended for use as a high-set non-directional phase overcurrent detector in
the Switch-Onto-Fault logic. If a line breaker is closed into a close-in three-phase bolted fault
where line-side potential transformers are used, polarizing voltage for the three-phase distance
elements is never established. In this situation, the distance elements do not operate. In this
instance, the 50H element is provided to help prevent a failure to trip the line breaker.
The 50H element measures current magnitude in each phase with no dependence on polarizing
voltages. This element is non-directional and should be used only in the switch-onto-fault logic
mask (MTO) when the line breaker is closed to test the line on a radial basis. If fault duty in
front of the line terminal is much greater than behind it, the 50H element can also be used in the
unconditional trip logic mask (MTU) to provide rapid clearance of close-in faults.
Typical 50H settings are 50% - 70% of three-phase fault duty at the local bus.