R.2.58
SEL-421 Relay Reference Manual Date Code 20111215
Auto-Reclosing and Synchronism Check
Synchronism Check
Voltages V
P,
V
S1
, and V
S2
are used in the logic in the balance of this section to
check for healthy voltage and determine voltage phase angle for synchronism-
check element operation.
Figure 2.26 Normalized Synchronism-Check Voltage Sources VS1 and VS2
Voltage Checks and
Blocking Logic
Two conditions can cause the synchronism-check function in the SEL-421 to
abort. These conditions are out-of-range synchronism-check input voltages
and block synchronism check configurations that you specify in SEL
OGIC
control equations.
Voltage Magnitude Checks
For synchronism check to proceed for a given circuit breaker (BK1 or BK2),
the voltage magnitudes of the synchronism-check voltage reference V
P
and
the corresponding normalized synchronism-check voltage source on the other
side of the circuit breaker (normalized voltage V
S1
for Circuit Breaker BK1
and normalized voltage V
S2
for Circuit Breaker BK2) must lie within a
healthy voltage window, bounded by voltage threshold settings 25VH and
25VL (see Figure 2.27).
The relay asserts Relay Word bits 59VP, 59VS1, and 59VS2 to indicate
healthy synchronism-check voltages V
P
, V
S1
, and V
S2
, respectively (see
Figure 2.27). If either of the voltage pairs (V
P
and V
S1
or V
P
and V
S2
) does
not meet this healthy voltage criterion, synchronism check cannot proceed for
the circuit breaker associated with the corresponding voltage pair.
(b)
(a)
V
BC
V
BC
∠90˚
∠90˚
∠240˚∠240˚
∠240˚
∠90˚
Synchronism-check
Voltage Source 1
Synchronism-check
Voltage Source 2
No effective
magnitude adjustment
Adjusted for angle
Adjusted for angle
Normalized synchronism-check
Voltage Source 1
Adjusted for magnitude
(=1 )
Apply
KS1A := 90
Apply
KS2A := 240
Apply
KS1M := 0.58
Apply
KS2M := 1.00
3
90˚
V
S1
V
BC
3
Normalized synchronism-check
Voltage Source 2
V
S2
3
V
C
V
C
V
C
240˚
V
C
V
BC
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