R.2.60
SEL-421 Relay Reference Manual Date Code 20111215
Auto-Reclosing and Synchronism Check
Synchronism Check
Angle Checks and
Synchronism-Check
Element Outputs
After the relay determines that voltage magnitudes are healthy and determines
that no block synchronism check conditions exist, the relay must check
voltage phase angles across the circuit breakers before a final synchronism-
check element output can be available for supervising circuit breaker closing.
The following discussion/examples use Circuit Breaker BK1. Synchronism-
check element output operation for Circuit Breaker BK2 is similar (replace
BK2 for BK1 in associated settings and Relay Word bits).
Angle Difference Settings ANG1BK1 and ANG2BK1
Each circuit breaker has two angle difference windows. For Circuit Breaker
BK1, the maximum angle difference settings are ANG1BK1 and ANG2BK1.
Often, a greater phase angle across the circuit breaker is tolerated for a manual
close. Typically, you set angle setting ANG1BK1 for synchronism check in
auto-reclosing Circuit Breaker BK1 (e.g., ANG1BK1 := 20 degrees), and you
set angle setting ANG2BK1 for synchronism check when manually closing
Circuit Breaker BK1 (e.g., ANG2BK1 := 35 degrees).
Synchronism-Check Element Outputs 25W1BK1 and 25A1BK1
Angle difference setting ANG1BK1 affects synchronism-check element
outputs 25W1BK1 and 25A1BK1. Figure 2.29, Figure 2.30, and Figure 2.31
illustrate the operation of synchronism-check element outputs 25W1BK1 and
25A1BK1.
These outputs operate for a voltage phase angle within and without the angle
difference setting ANG1BK1 for the following three conditions:
➤ no slip
➤ slip—no compensation
➤ slip—with compensation
The operational differences between synchronism-check element outputs
25W1BK1 and 25A1BK1 are apparent in the “slip—with compensation”
example (Figure 2.31).
The second angle difference setting (ANG2BK1) for Circuit Breaker BK1
operates similarly to affect synchronism-check element outputs 25W2BK1
and 25A2BK1.
“No Slip”
Synchronism Check
Refer to the paralleled system beyond the open circuit breaker in Figure 2.20.
For such a system, there is essentially no slip across the open circuit breaker
(the monitored voltage phasors on each side are not moving with respect to
one another). In a “no slip” system, any voltage angle difference across the
open circuit breaker remains relatively constant.
The four drawings shown in Figure 2.29 are separate, independent cases for a
“no slip” paralleled system. If the phase angle between the synchronism-check
voltage reference V
P
and the normalized synchronism-check voltage source
V
S1
is less than angle setting ANG1BK1, synchronism-check element outputs
25W1BK1 and 25A1BK1 both assert to logical 1. The relay declares that the
per-phase voltages across Circuit Breaker BK1 are in synchronism.
Otherwise, if the phase angle is greater than or equal to angle setting
ANG1BK1, element outputs 25W1BK1 and 25A1BK1 both deassert to
logical 0; the relay declares that the per-phase voltages across Circuit Breaker
BK1 are out-of-synchronism.
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