3-38
Overcurrent, Voltage, Synchronism Check, Frequency, and Power Elements
Date Code 20001006
SEL-351 Instruction Manual
If the weak-infeed portion of the POTT logic is enabled (setting EWFC = Y) and these voltage
elements are used in the logic, they can still be used in other applications (if the settings are
applicable). If the weak-infeed portion of the POTT logic is not enabled, these voltage elements
can be used in any desired application.
S
YNCHRONISM
C
HECK
E
LEMENTS
Enable the two single-phase synchronism check elements by making the enable setting:
E25 = Y
Figure 2.7 through Figure 2.10 in
Section 2: Installation
show examples where synchronism
check can be applied. Note that Figure 2.8 shows a delta-connected (phase-to-phase) voltage
example. Synchronism check voltage input VS is connected to one side of the circuit breaker, on
any desired phase (or phase-to-phase for delta-connected voltage inputs). The other synchronizing
phase (VA, VB, or VC for wye-connected voltage inputs; VAB, VBC, or VCA for delta-connected
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 3.26). They have separate angle settings (see Figure 3.27).
If the voltages are static (voltages not slipping with respect to one another), the two synchronism
check elements operate as shown in the top of Figure 3.27. The angle settings are checked for
synchronism check closing.
If the voltages are not static (voltages slipping with respect to one another) or setting
TCLOSD = 0.00, the two synchronism check elements operate as shown in the bottom of
Figure 3.27. 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 with a Different CT Configuration than the Reference Phase
or Beyond a Delta-Wye Transformer
Sometimes synchronism check voltage V
S
cannot be in phase with voltage V
A
, V
B
, or V
C
(wye-connected voltage relays); or V
AB
, V
BC
, or V
CA
(delta-connected voltage relays). 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 3.10 and the SYNCP setting discussion that follows).
Summary of Contents for SEL-351
Page 14: ...Courtesy of NationalSwitchgear com ...
Page 16: ...Courtesy of NationalSwitchgear com ...
Page 40: ...Courtesy of NationalSwitchgear com ...
Page 74: ...Courtesy of NationalSwitchgear com ...
Page 146: ...Courtesy of NationalSwitchgear com ...
Page 186: ...Courtesy of NationalSwitchgear com ...
Page 220: ...Courtesy of NationalSwitchgear com ...
Page 304: ...Courtesy of NationalSwitchgear com ...
Page 340: ...Courtesy of NationalSwitchgear com ...
Page 380: ...Courtesy of NationalSwitchgear com ...
Page 450: ...Courtesy of NationalSwitchgear com ...
Page 506: ...Courtesy of NationalSwitchgear com ...
Page 528: ...Courtesy of NationalSwitchgear com ...
Page 534: ...Courtesy of NationalSwitchgear com ...
Page 536: ...Courtesy of NationalSwitchgear com ...
Page 550: ...Courtesy of NationalSwitchgear com ...
Page 562: ...Courtesy of NationalSwitchgear com ...
Page 570: ...Courtesy of NationalSwitchgear com ...
Page 584: ...Courtesy of NationalSwitchgear com ...
Page 602: ...Courtesy of NationalSwitchgear com ...