Schweitzer Engineering Laboratories SEL-351A - Synchronism Check Elements (Not in SEL-351 A-1); Table 3.13 Synchronism Check Elements Settings and Settings Ranges

3.36
SEL-351A Relay Instruction Manual Date Code 20080213
Overcurrent, Voltage, Synchronism Check, and Frequency Elements
Synchronism Check Elements (Not in SEL-351A-1)
Synchronism Check Elements (Not in SEL-351A-1)
NOTE: If global setting VSCONN =
3V0, the synchronism check elements
are unavailable, and E25 = N is the
only possible setting. See Broken-
Delta VS Connection (Global setting
VSCONN = 3V0) on page 2.15 for
details.
Enable the two single-phase synchronism check elements by making the
enable setting:
E25 = Y
Figure 2.12–Figure 2.15, Figure 2.24, and Figure 2.25 show examples where
synchronism check can be applied. Synchronism check voltage input VS is
connected to one side of the circuit breaker, on any desired phase. The other
synchronizing phase (VA, VB, or VC voltage inputs) on the other side of the
circuit breaker is setting-selected.
The two synchronism check elements use the same voltage window (to assure
healthy voltage) and slip frequency settings (see Figure 3.27). They have
separate angle settings (see Figure 3.28).
If the voltages are static (voltages not slipping with respect to one another) or
setting TCLOSD = 0.00, the two synchronism check elements operate as
shown in the top of Figure 3.28. The angle settings are checked for
synchronism check closing.
If the voltages are not static (voltages slipping with respect to one another),
the two synchronism check elements operate as shown in the bottom of
Figure 3.28. The angle difference is compensated by breaker close time, and
the breaker is ideally closed at a zero degree phase angle difference, to
minimize system shock.
These synchronism check elements are explained in detail in the following
text.
Voltage Input VS
Connected Phase-to-
Phase or Beyond
Delta-Wye
Transformer
Sometimes synchronism check voltage V
S
cannot be in phase with voltage
V
A
, V
B
, or V
C
(wye connected PTs); or V
AB
, V
BC
, or V
CA
(delta-connected
PTs). This happens in applications where voltage input VS is connected
➤ Phase-to-phase when using a wye-connected relay
➤ Phase-to-neutral when using a delta-connected relay
➤ Beyond a delta-wye transformer
For such applications requiring V
S
to be at a constant phase angle difference
from any of the possible synchronizing voltages (V
A
, V
B
, or V
C
; V
AB
, V
BC
, or
V
CA
), an angle setting is made with the SYNCP setting (see Table 3.13 and
the SYNCP setting discussion that follows).
Synchronism Check
Elements Settings
Table 3.13 Synchronism Check Elements Settings and Settings Ranges
(Sheet 1 of 2)
Setting Definition Range
25VLO Low voltage threshold
for “healthy voltage” window
0.0–300.0 V secondary
25VHI High voltage threshold
for “healthy voltage” window
0.0–300.0 V secondary
25SF Maximum slip frequency 0.005–0.500 Hz
25ANG1 Synchronism check
element 25A1 maximum angle
0°–80°
25ANG2 Synchronism check
element 25A2 maximum angle
0°–80°
Courtesy of NationalSwitchgear.com