5-20 Applications Date Code 20011026
SEL-321/321-1 Instruction Manual
Advanced Loss-of-Potential Logic
Inputs into the LOP logic are:
3PO three-pole open condition (indicates circuit breaker open condition)
SPO single-pole open condition (indicates circuit breaker pole open condition)
OSB out-of-step block
V
1
positive-sequence voltage (V secondary)
I
1
positive-sequence current (A secondary)
V
0
zero-sequence voltage (V secondary)
I
0
zero-sequence current (A secondary)
The circuit breaker has to be closed (Relay Word bit 3PO =SPO = logical 0) for the LOP logic to
operate.
Loss-of-potential is declared (Relay Word bit LOP = logical 1) when a 10 percent drop in V
1
is
detected, with no corresponding change in I
1
or I
0
. If the LOP condition persists for 60 cycles, it
latches in. LOP resets (Relay Word bit LOP = logical 0) when V
1
returns above 50 V secondary
and V
0
is less than 5 V secondary. Note that ILOP disables all distance elements.
The loss-of-potential enable setting, ELOP, selects between original and advanced LOP logic. It
also routes the LOP Relay Word bit to directional logic. Setting ELOP operates as follows:
•
N1 Relay sets LOP element when LOP condition is detected using advanced LOP
logic.
Distance and directional elements are not blocked.
Set the LOP element in a SEL
OGIC
®
control equation to indicate condition, if
desired.
•
Y1 Relay sets LOP element when LOP condition is detected using advanced LOP
logic.
Distance elements and directional elements are blocked.
Set the LOP element in a SEL
OGIC control equation to indicate the LOP condition,
if desired.
•
Y2 Relay sets LOP element when LOP condition is detected using advanced LOP
logic.
Distance elements are blocked and directional elements default forward.
Set the LOP element in a SEL
OGIC control equation to indicate the LOP condition,
if desired.
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