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5.11
Date Code 20171021
Instruction Manual
SEL-421 Relay
Protection Functions
Current and Voltage Source Selection
ESS := Y, Other Applications
Set ESS to Y for applications that are not covered under the five default applica-
tions.
Tapped Line
illustrates a tapped EHV transmission overhead line. A power trans-
former is located at Substation T along the tapped line. An SEL-421 is located at
all three EHV terminals (Substations S, R, and T). The SEL-421 Relays operate
in a DCB (directional comparison blocking) trip scheme to provide high-speed
clearance for all faults internal to the tapped EHV transmission line. For a com-
plete explanation of this example, see
230 kV Tapped Transmission Line Applica-
.
Set NUMBK (Number of Breakers in Scheme) to 2 so you can program the auto-
reclosing function and synchronism-check elements to control both of the low-
side circuit breakers.
Figure 5.8
ESS := 4, Double Circuit Breaker Configuration
Table 5.9
ESS := 4, Current and Voltage Source Selection
Setting
Prompt
Entry
Comments
NUMBK
Number of Circuit Breakers in Scheme (1, 2)
2
LINEI
Line Current Source (IW)
IW
Automatic
ALINEI
Alternate Current Source (NA)
NA
Automatic
ALTI
Alternate Current Source (SEL
OGIC
Equation)
NA
Hidden
BK1I
Breaker 1 Current Source (IX)
IX
Automatic
BK2I
Breaker 2 Current Source (COMB)
COMB
Automatic
IPOL
Polarizing Current (NA)
NA
Automatic
ALINEV
Alternate Line Voltage Source (VZ, NA)
NA
ALTV
Alternate Voltage Source (SEL
OGIC
Equation)
NA
Hidden
SEL-421 Relay
BUS 1
BUS 2
CB1
CB2
3
3
3
3
IW
IX
VAZ
VY
VBZ
1
1
Analog Input
IW+IX
IW
IX
VY
VAZ
VBZ
Function
CB2 protection
Line protection
CB1 protection
Line protection
Synchronism check Circuit Breaker 1
Synchronism check Circuit Breaker 2
I
CB1
I
CB2
I
LINE
Summary of Contents for SEL-421-4
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