Sel SEL-421 - Synchronism Check; Generalized System

R.2.50
SEL-421 Relay Reference Manual Date Code 20111215
Auto-Reclosing and Synchronism Check
Synchronism Check
Synchronism Check
Synchronism-check elements prevent circuit breakers from closing if the
corresponding phases across the open circuit breaker are excessively out of
phase. The SEL-421 synchronism-check elements selectively close circuit
breaker poles under the following criteria:
➤ The systems on both sides of the open circuit breaker are in
phase (within a settable voltage angle difference).
➤ The voltages on both sides of the open circuit breaker are
healthy (within a settable voltage magnitude window).
You can use synchronism-check elements to program the relay to supervise
circuit breaker closing; include the synchronism-check element outputs in the
close SEL
OGIC control equations. These element outputs are Relay Word bits
25W1BK1, 25A1BK1, 25W2BK1, 25A2BK1, 25W1BK2, 25A1BK2,
25W2BK2, and 25A2BK2 (see Synchronism-Check Logic Outputs on
page R.2.53 and Angle Checks and Synchronism-Check Element Outputs on
page R.2.60).
An example best demonstrates the synchronism-check capability in the
SEL-421. This subsection presents a typical synchronism-check system.
Generalized System
The generalized system single-line drawing in Figure 2.19 shows a partial
circuit breaker-and-a-half or ring-bus substation arrangement. Presuming that
both Circuit Breakers BK1 and BK2 are open, the system is split into three
sections: Bus 1, Bus 2, and Line.
LEADBK2 Leader Breaker = Breaker 2
FOLBK0 No Follower Breaker
FOLBK1 Follower Breaker = Breaker 1
FOLBK2 Follower Breaker = Breaker 2
NBK0 No Breaker Active in Reclose Scheme
NBK1 One Breaker Active in Reclose Scheme
NBK2 Two Breakers Active in Reclose Scheme
LLDB1 Live Line
—Dead Bus 1 (59L AND 27BK1)
DLLB1 Dead Line
—Live Bus 1 (27L AND 59BK1)
DLDB1 Dead Line
—Dead Bus 1 (27L AND 27BK1)
LLDB2 Live Line
—Dead Bus 2 (59L AND 27BK2)
DLLB2 Dead Line
—Live Bus 2 (27L AND 59BK2)
DLDB2 Dead Line
—Dead Bus 2 (27L AND 27BK2)
Table 2.25 Auto-Reclose Logic Relay Word Bits (Sheet 3 of 3)
Name Description