2-16 Specifications Date Code 20011026
SEL-321/321-1 Instruction Manual
Pole Open Logic
This logic discriminates between a partially and fully-open line terminal. The Three-Pole Open
(3PO) condition asserts when all three phases of the line are disconnected. The Single-Pole
Open (SPO) condition asserts when one or two phases of the line remain energized.
A pole is open if the one (or two) 52A inputs associated with that phase are deasserted and if the
current in that phase is below pickup of the four overcurrent elements 50L1 - 50L4.
The output of this logic influences both phase and ground distance element operations. SPO and
3PO conditions have independent Time Delayed Dropout (TDDO) timers.
Timer Settings
Single-Pole Open Delay SPOD Stabilizing time delay after single-pole reclose.
Three-Pole Open Delay 3POD Security time delay for dissimilar breaker pole
closing.
Trip-Open Pole Delay TOPD Any trip which occurs while TOPD is timing results
in a three-pole trip.
Outputs
Phase A Open SPOA Blocks 21AG, 21AB, and 21CA elements.
Phase B Open SPOB Blocks 21BG, 21AB, and 21BC elements.
Phase C Open SPOC Blocks 21CG, 21BC, and 21CA elements.
Single-Pole Open SPO Blocks all quadrilateral ground distance, clears
LOP, and asserts 32QF. Includes SPOD delay.
Three-Pole Open 3PO Blocks all ground distance. Includes 3POD delay.
Trip-Open-Pole TOP TOPD timer is timing.
Supporting Drawing: Figure 2.39 and Figure 2.40.
Stub Protection Logic
The LOP condition can enable a definite-time overcurrent element to detect faults on bus
sections not having PTs or to provide backup protection if potentials are lost. The same 50M
overcurrent element used in the LOP logic serves as the fault detector for this logic. If ELOP =
N or N1, this logic is not enabled.
Timer Setting
Stub Protection Coord. Delay 50MFD Define-time delay for 50MF.
Output
Stub Protection O/C Element 50MF Asserts for faults during LOP conditions if 50M
asserted for 50MFD delay.
Supporting Drawing: Figure 2.41.
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