5.7
Date Code 20171021 Instruction Manual SEL-421 Relay
Protection Functions
Current and Voltage Source Selection
SELOGIC setting ALTV controls the switching between voltages VY and VZ for
line voltage (assert setting ALTV to switch to designated alternate line voltage
ALINEV := VZ). Setting ALTV is automatically hidden and set to NA if
ALINEV := NA (no voltage switching can occur). Reasons for switching from
one three-phase voltage to another may be for loss-of-potential or bus switching/
rearrangement.
Default line voltage source VY and alternate line voltage source settings
(ALINEV and ALTV) identify the voltages used in the following elements/fea-
tures described later in this section and in other sections:
➤ Fault location
➤ Open-phase detection logic
➤ LOP (loss-of-potential) logic
➤ FIDS (fault-type identification selection) logic
➤ Directional elements
➤ CVT (capacitor voltage transformer) transient detection logic
➤ Series-compensation line logic
➤ Load-encroachment logic
➤ OOS (out-of-step) logic
➤ Distance elements
➤ SOTF (switch-onto-fault) logic
➤ POTT (permissive overreaching transfer tripping) scheme logic
➤ Metering on page 7.1, including synchrophasors
Default Applications
Use setting ESS (Current and Voltage Source Selection) to easily configure the
relay for your particular application. Five application settings (ESS := N, 1, 2, 3,
or 4) cover both single circuit breaker and two circuit breaker configurations. If
you select one of these five setting choices, the relay automatically determines
the following settings:
NOTE: Setting BK2I is hidden if
setting NUMBK, Number of Breakers
in the Scheme, is set to 1.
➤ LINEI—Line Current Source (IW, COMB)
➤ BK1I—Breaker 1 Current Source (IW, IX, NA)
➤ BK2I—Breaker 2 Current Source (IX, COMB, NA)
23VYVZ or NA
24VYVZ or NA
a
NA = not applicable.
Shaded cells indicate settings forced to given values and hidden.
Table 5.4 Available Voltage Source Selection Setting Combinations
a
(Sheet 2 of 2)
NUMBK (number of
breakers)
ESS
(source selection)
Line Voltage Source
ALINEV (alternate
line voltage source)
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