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5.25
Date Code 20171021
Instruction Manual
SEL-421 Relay
Protection Functions
Pole-Open Logic
Pole-Open Logic
The SEL-421 pole-open logic detects single-, double-, and three-pole open con-
ditions. The relay uses the same processing for single- and double-pole open con-
ditions. Pole-open logic supervises various protection elements and functions that
use analog inputs from the power system (e.g., distance elements, directional ele-
ments, LOP logic).
Setting EPO (Enable Pole Open) offers two options for deciding the conditions
that signify an open pole. These options are listed in
NOTE:
The 3PO, SPOA, SPOB, SPOC,
and SPO Relay Word bits shown in
are used in some
protective elements of the SEL-421.
Separate Relay Word bits SPOBK
n
,
3POBK
n
, 2POBK
n
(
n
= 1 or 2), and
3POLINE are not affected by the EPO
setting and are used in the
autoreclose logic only (see
and
in the SEL-400 Series Relays Instruction
Manual
).
Set EPO to V only if you use line-side potential transformers for relaying pur-
poses. Do not select option V if shunt reactors are applied because the voltage
decays slowly after the circuit breaker(s) opens. If you select EPO := V, the relay
can incorrectly declare LOP during a pole-open condition if there is charging cur-
rent that exceeds the open-pole current threshold.
Table 5.23
Open-Phase Detection Relay Word Bits
Name
Description
B1OPHA
Breaker 1 A-Phase open
B1OPHB
Breaker 1 B-Phase open
B1OPHC
Breaker 1 C-Phase open
B2OPHA
Breaker 2 A-Phase open
B2OPHB
Breaker 2 B-Phase open
B2OPHC
Breaker 2 C-Phase open
LOPHA
Line A-Phase open
LOPHB
Line B-Phase open
LOPHC
Line C-Phase open
Table 5.24
Pole-Open Logic Settings
Setting
Prompt
Range
Default
EPO
Pole Open Detection
52, V
52
27PO
Undervoltage Pole Open Threshold (V)
a
a
1 V steps.
1–200
40
SPOD
Single-Pole Open Dropout Delay (cycles)
0.000–60
0.500
3POD
Three-Pole Open Dropout Delay (cycles)
0.000–60
0.500
Table 5.25
EPO Setting Selections
Selection
Description
52
Phase undercurrent and circuit breaker auxiliary contact input status
V
Phase undercurrent and phase undervoltage
Table 5.26
Pole-Open Logic Relay Word Bits (Sheet 1 of 2)
Name
Description
SPOA
A-Phase open
SPOB
B-Phase open
Summary of Contents for SEL-421-4
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