R.1.14
SEL-421 Relay Reference Manual Date Code 20111215
Protection Functions
Current and Voltage Source Selection
Figure 1.11 ESS := Y, Single Circuit Breaker With Current Polarizing Source
Tapp ed Power Tra nsf o rme r
Using ALTI and ALTV
SELOGIC control equations ALTI and ALTV give great flexibility in choosing
alternate CT and PT inputs to the SEL-421. The relay switches immediately to
the alternate source when these SEL
OGIC control equations become true. The
relay delays a subsequent ALTI or ALTV switch for 8 cycles after the initial
switch to give time for the system to settle.
Test the SEL
OGIC control equation programming that you use to switch ALTI
and ALTV alternate sources. It is possible to create a toggling condition where
the relay repeatedly switches between sources. Examine each line of SEL
OGIC
control equation programming to verify that this toggling condition does not
occur in your protection/control scheme.
One method for exercising caution when implementing alternate current
source and alternate voltage source switching is to use SEL
OGIC control
equation protection latches (PLT01–PLT32) to switch alternate sources. For
Table 1.11 ESS := Y, Current Polarizing Source
Setting Description Entry Comments
NUMBK Number of Circuit Breakers in Scheme (1, 2) 1
LINEI Line Current Source (IW, COMB) IW
ALINEI Alternate Current Source (IX, NA) NA
ALTI Alternate Current Source (SEL
OGIC Equation) NA Hidden
BK1I Breaker 1 Current Source (IW, IX, NA) IW
BK2I Breaker 2 Current Source (NA) NA Hidden
IPOL Polarizing Current (IAX, IBX, ICX, NA) IAX
ALINEV Alternate Line Voltage Source (VZ, NA) NA Default
ALTV Alternate Voltage Source (SEL
OGIC Equation) NA Hidden
SEL-421 Relay
BUS
CB
IW
VAZ IAX
(Delta-connected Tertiary)
VY
3
1
Analog Input
IW
IAX
VY
VAZ
Function
Line protection
Ground directional
element current polarization
Line protection
Synchronism check
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