Sel SEL-421 - Supervising Auto-Reclosing of Circuit Breaker BK1; PT Connections; Manual Closing of Circuit Breaker BK1

R.2.55
Date Code 20111215 Reference Manual SEL-421 Relay
Auto-Reclosing and Synchronism Check
Synchronism Check
Supervising Circuit
Breaker Closing via
Synchronism Check
Use the synchronism-check element outputs to control circuit breaker closing.
Some examples follow (the ellipsis indicates other elements that you can add
to these SEL
OGIC control equations):
Supervising Auto-Reclosing of Circuit Breaker BK1
3P1CLS := 25A1BK1 OR … Three-Pole BK1 Reclose Supervision (SELOGIC
Equation)
Manual Closing of Circuit Breaker BK1
BK1MCL := 25W2BK1 OR … Circuit Breaker BK1 Manual Close (SELOGIC
Equation)
PT Connections
Figure 2.24 is an example of connecting PTs to the SEL-421 for two circuit
breakers. The Bus 1 and Bus 2 single-phase voltages are connected to relay
voltage inputs VAZ and VBZ, respectively. They could just as easily have
been connected to any of the other voltage inputs. The voltage connected to
voltage input VAZ (setting SYNCS1 := VAZ; see Figure 2.24) is not
necessarily from A-phase on Bus 1. Likewise, the voltage connected to
voltage input VBZ (setting SYNCS2 := VBZ; see Figure 2.24) is not
necessarily from B-phase on Bus 2. The connection can be from any phase-to-
neutral or phase-to-phase voltage (as long as you do not exceed the relay
voltage input ratings). Settings in the SEL-421 compensate for any steady-
state magnitude or angle difference with respect to a synchronism-check
voltage reference, as discussed next in this example.
Three-phase line voltages are connected to relay voltage inputs VAY, VBY,
and VCY (these voltage inputs are also used for distance elements fault
location, loss-of-potential, load encroachment, and directionality). Only one
of these single-phase voltage inputs is designated for use in synchronism
check. In this example, this voltage input is also designated the synchronism-
check voltage reference (setting SYNCP := VAY; see Figure 2.24). As the
synchronism-check voltage reference, the relay makes all steady-state
magnitude and angle adjustments for the Bus 1 and Bus 2 synchronism check
voltages (connected to voltage inputs FAZ and FBZ, respectively, as discussed
in the preceding paragraph) with respect to this designated reference line
voltage, VAY, as discussed later in this example.
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
available on the other side of the circuit breaker for synchronism check,
connect the source to potential input VAZ, VBZ, or VCZ.
25A1BK2 Same operation as 25W1BK2, except for the restrictive operation
(0 closure attempt) when setting 25SFBK2  OFF and the system is
slipping (see Figure 2.31)
25A2BK2 Same operation as 25W2BK2, except for the restrictive operation
(0 closure attempt) when setting 25SFBK2  OFF and the system is
slipping (see Figure 2.31)
FAST2 Bus 2 frequency greater than line frequency (f
S2
> f
P
)
SLOW2 Bus 2 frequency less than line frequency (f
S2
< f
P
)
Table 2.26 Synchronism-Check Relay Word Bits (Sheet 2 of 2)
Relay Word Bit Description