Schweitzer Engineering Laboratories SEL-421-4, Instruction Manual

Page: 184 / 1518

5.24
SEL-421 Relay Instruction Manual Date Code 20171021
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 overcur-
rent elements using filtered quantities can be extended after the corresponding
phase(s) is open if subsidence current is present. The SEL-421 open-phase detec-
tor senses an open phase in less than one cycle. This information is used for pur-
poses 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 9.2 on page 9.5 in the SEL-400 Series Relays
Instruction Manual to achieve the high-speed response to an open-phase condi-
tion. Table 5.23 lists the output Relay Word bits.
Table 5.20 Fault Type
Label Fault Type
AG A-Phase-to-ground
BG B-Phase-to-ground
CG C-Phase-to-ground
AB A-Phase-to-B-Phase
BC B-Phase-to-C-Phase
CA C-Phase-to-A-Phase
ABG A-Phase-to-B-Phase-to-ground
BCG B-Phase-to-C-Phase-to-ground
CAG C-Phase-to-A-Phase-to-ground
ABC Three-phase
Table 5.21 Fault Location Settings
Setting Prompt Range
Default
(5 A)
Z1MAG Positive-Sequence Line Impedance Magnitude (

) (0.25–1275)/I
NOM
7.80
Z1ANG Positive-Sequence Line Impedance Angle (°) 5.00–90 84.00
Z0MAG Zero-Sequence Line Impedance Magnitude (

) (0.25–1275)/I
NOM
24.80
Z0ANG Zero-Sequence Line Impedance Angle (°) 5.00–90 81.50
EFLOC Fault Location Y, N Y
LL Line Length 0.10–999 100.00
Table 5.22 Fault Location Relay Word Bit
Name Description
RSTFLOC Fault locator analog quantity reset in progress.
a
a
Use Global setting RSTFLOC shown in
Table 8.20 on page 8.8
to reset the stored fault location
analog quantity FLOC. Relay Word bit RSTFLOC will assert momentarily while the clearing action
proceeds.
When reset, the value contained in FLOC is set to a very large number (greater than 1037).
Resetting this value has no effect on the event reports stored in the SEL-421, nor does it have an
effect on DNP3 event access.