Schweitzer Engineering Laboratories SEL-421-4, Instruction Manual

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5.163
Date Code 20171021 Instruction Manual SEL-421 Relay
Protection Functions
Synchronism Check
For a single-circuit breaker application, you can use either bus-side potentials or
line-side potentials for line relaying; connect the three-phase voltage source to
potential inputs VAY, VBY, and VCY. If a single-phase voltage source is avail-
able on the other side of the circuit breaker for synchronism check, connect the
source to potential input VAZ, VBZ, or VCZ.
Voltage Magnitude and Angle Compensation
The Figure 5.122 example continues in Figure 5.123 . The Figure 5.123 example
demonstrates possible voltage input connections (presuming ABC phase rota-
tion). The synchronism-check voltage reference (V
P
) is from the A-Phase voltage
(V
A
) of the line. You can connect phase-to-phase voltage V
BC
originating from
Bus 1, and connect phase-to-neutral voltage V
C
from Bus 2. Thus, Bus 1 voltage
V
BC
lags synchronism-check voltage reference V
P
by 90 degrees, and Bus 2 volt-
age V
C
lags the synchronism-check voltage reference V
P
by 240 degrees. To
compensate for these steady-state angle differences, set KS1A for Bus 1 and
KS2A for Bus 2.
KS1A := 90 .
Synchronism Source 1 Angle Shift (0, 30, …, 330 degrees)
KS2A := 240 .
Synchronism Source 2 Angle Shift (0, 30, …, 330 degrees)
Figure 5.122 Example Synchronism-Check Voltage Connections to the SEL-421
Bus 2 Bus 1
Relay rear panel
(partial)
Three-phase line
voltage connections
Separate, single-phase
bus/source
voltage connections
Line
BK2
BK1
VAY VBY VCY
VAZ VBZ VCZ
1
3
1