R.1.20
SEL-421 Relay Reference Manual Date Code 20111215
Protection Functions
Open Phase Detection Logic
Open Phase Detection Logic
Some line relaying applications (e.g., circuit breaker failure protection)
benefit from fast open phase detection. The resetting time of the instantaneous
overcurrent elements using filtered quantities can be extended after the
corresponding phase(s) is open if subsidence current is present. The SEL-421
open phase detector senses an open phase in less than one cycle. This
information is used for purposes such as quickly disabling instantaneous
overcurrent elements in the circuit breaker failure schemes and open pole
detection.
The open phase detection logic uses both the half-cycle and one-cycle cosine
digital filter data shown in Figure 3.1 on page A.3.3 to achieve the high-speed
response to an open phase condition. Table 1 .1 9 lists the output Relay Word
bits.
Pole Open Logic
The SEL-421 pole open logic detects single-, double-, and three-pole open
conditions. The relay uses the same processing for single- and double-pole
open conditions. Pole open logic supervises various protection elements and
functions that use analog inputs from the power system (e.g., distance
elements, directional elements, LOP logic).
Setting EPO (Enable Pole Open) offers two options for deciding the
conditions that signify an open pole. These options are listed in Tabl e 1.2 1.
Table 1.19 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 1.20 Pole Open Logic Settings
Name Description 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
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