P.4.62
SEL-411L Relay Protection Manual Date Code 20151029
Autoreclosing and Synchronism-Check
Synchronism Check
command to Circuit Breaker BK1. If case (b) in Figure 4.30 represents the
time at which the CLOSE command occurs, then V
S1
is the normalized
synchronism-check voltage source position at the instant the close is issued
and V
S1
is the position of V
S1
when Circuit Breaker BK1 actually closes.
Slip Frequency
If the slip frequency exceeds setting 25SFBK1, synchronism-check cannot
proceed via element output 25A1BK1. Synchronism check stops because
element output 25A1BK1 deasserts to logical 0 for an out-of-range slip
frequency condition, regardless of other synchronism-check conditions such
as healthy voltage magnitudes.
Synchronism check remains possible (although not necessarily advantageous)
if you use element output 25W1BK1 and the slip frequency exceeds setting
25SFBK1. Synchronism-check element 25W1BK1 does not measure slip. In
this instance, synchronism-check occurs (25W1BK1 is logical 1) when the
phase angle difference between reference V
P
and V
S1
is less than angle setting
ANG1BK1.
Synchronism-Check Element Output Effects
A contradiction seems to result from analysis of case (a) in Figure 4.30; it
appears that element output 25A1BK1 should assert to logical 1 because V
S1
is within angle setting ANG1BK1. Note in this case, however, that V
S1
is
approaching synchronism-check reference V
P
. This is where element output
25A1BK1 behaves differently than element output 25W1BK1, for setting
25SFBK1 set to some value other than OFF. As V
S1
approaches V
P
,
25A1BK1 remains deasserted (equals logical 0) until the phase angle
difference between reference V
P
and V
S1
equals zero degrees.
At this zero degrees difference between V
P
and V
S1
point, element output
25A1BK1 asserts to logical 1. We know the systems will truly be in
synchronism (0 degrees between reference V
P
and V
S1
) a period later (this
period is setting TCLSBK1, Circuit Breaker BK1 Close Time). Thus, if a
CLOSE command occurs right at the instant that element output 25A1BK1
asserts to logical 1, then there will be a zero degree phase angle difference
across Circuit Breaker BK1 when Circuit Breaker BK1 actually closes.
Closing Circuit Breaker BK1 at a phase angle difference of 0 degrees between
reference V
P
and V
S1
minimizes system shock when you bring two
asynchronous systems together.
Element output 25A1BK1 remains asserted to logical 1 as V
S1
moves away
from reference V
P
. When the phase angle difference between reference V
P
and
V
S1
is again greater than angle setting ANG1BK1, element output 25A1BK1
deasserts to logical 0.
Alternative
Synchronism-Check
Source 2 Settings
You can program alternative input sources for the synchronism-check function
in the relay. Alternative inputs give you additional flexibility to synchronize
other portions of your power system.
The SEL
OGIC control equation ALTS2 determines when the relay uses
alternate Synchronism-Check Voltage Source 2 in place of regular
Synchronism-Check Voltage Source 2. When ALTS2 is logical 1, the relay
substitutes alternative Synchronism-Check Voltage Source 2 (ASYNCS2) and
corresponding settings AKS2M and AKS2A for the regular Synchronism-
Check Voltage Source 2 values SYNCS2, KS2M, and KS2A. The result is a
normalized synchronism-check voltage source V
S2
derived from the
alternative source.
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