Sel SEL-421 - Voltage Checks for Auto-Reclosing and Manual Closing; Live Line;Live Bus

R.2.44
SEL-421 Relay Reference Manual Date Code 20111215
Auto-Reclosing and Synchronism Check
Voltage Checks for Auto-Reclosing and Manual Closing
Voltage Checks for Auto-Reclosing and Manual
Closing
Voltage elements are available for a final check of line and bus voltages before
an auto-reclose or manual close is issued. These voltage elements and
corresponding pickup settings are enabled with Reclosing Voltage Check
enable setting EVCK := Y. Figure 2.17 shows the application of these voltage
elements and Figure 2.18 shows their implementation. Check voltages for
arrangements of up to two circuit breakers (global setting NUMBK := 2), as
shown in Figure 2.17. If the SEL-421 is only connected to a single breaker
(global setting NUMBK := 1), then settings 27BK2P and 59BK2P and their
associated elements (LLDB2, DLDB2, and DLLB2) are not available.
Voltages V
P
, V
S1
, and V
S2
in Figure 2.17 and Figure 2.18 come from
corresponding voltage source selection settings SYNCP, SYNCS1, and
SYNCS2 in the Synchronism Check subsection (see Figure 2.22). Figure 2.24,
Figure 2.25, Figure 2.26, and accompanying text in Synchronism Check on
page R.2.50 explain an example where:
SYNCP = VAY (V
P
is the voltage from voltage input VAY, referred to as the
line voltage)
SYNCS1 = VAZ (V
S1
is the normalized voltage from voltage input VAZ,
referred to as the bus 1 voltage)
SYNCS2 = VBZ (V
S2
is the normalized voltage from voltage input VBZ,
referred to as the bus 1 voltage)
Figure 2.25, Figure 2.26, and accompanying text in Synchronism Check
explain the origin and normalization of voltages V
S1
and V
S2
to the V
P
voltage base. This normalization example concerns both voltage angle and
magnitude. The pickup settings in Figure 2.18 are made on the V
P
voltage
base. V
P
is the voltage reference for voltage angle and magnitude. Only
voltage magnitude is of concern for the settings in Figure 2.18, not voltage
angle.
Figure 2.17 implies that three-phase voltage is available from the line PTs.
But, resultant voltage V
P
corresponds to only one phase of this three-phase
voltage (e.g., setting SYNCP = VAY; V
P
is the normalized voltage from
voltage input VAY). All the voltage elements in Figure 2.18 are single-phase
voltage elements – detecting live or dead voltage on the bus side with a single-
phase voltage element and likewise on the line side.
Whether or not synchronism check logic is used, it still has to be enabled for
the respective breaker (E25BK1 := Y and E25BK2 := Y) in order that the
corresponding voltage source selection settings (SYNCP, SYNCS1, and
SYNCS2) can be made.
Live Line/Live Bus
Note in Figure 2.17 that live line/live bus is not available for either circuit
breaker. Voltage elements 59VP, 59VS1, and 59VS2 in Synchronism Check
(see Figure 2.23 and Figure 2.27) are available for such a function (e.g., 59VP
AND 59VS1 for live line/live bus 1).