5.169
Date Code 20171021 Instruction Manual SEL-421 Relay
Protection Functions
Synchronism Check
Angle Difference Settings ANG1BK1 and ANG2BK1
NOTE: If the relay is using a remote
data acquisition system, such as TiDL,
the operating times will be delayed by
1.5 ms. Use caution when setting the
relay for synchronism check to
account for this added delay.
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 5.128, Figure 5.129, and Figure 5.130 illus-
trate the operation of synchronism-check element outputs 25W1BK1 and
25A1BK1.
These outputs operate for a voltage phase angle within and without the angle dif-
ference 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” exam-
ple (Figure 5.130).
The second angle difference setting (ANG2BK1) for Circuit Breaker BK1 oper-
ates 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 5.119.
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 cir-
cuit breaker remains relatively constant.
The four drawings shown in Figure 5.128 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.
The out-of-synchronism phase angles in Figure 5.128 appear dramatic for a “no
slip” paralleled system. This is for illustrative purposes; these angles are not usu-
ally this large in actual systems.
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