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5.10
SEL-421 Relay
Instruction Manual
Date Code 20171021
Protection Functions
Current and Voltage Source Selection
ESS := 4, Double Circuit Breaker Configuration—Common Current Inputs
Set ESS to 4 for circuit breaker-and-a-half applications using combined current
input IW.
illustrates this application along with the corresponding cur-
rent and voltage sources. Current input IX provides circuit breaker failure protec-
tion for Circuit Breaker 1; the corresponding CTs are located on the line-side of
Circuit Breaker 1. The relay calculates the current flowing through Circuit
Breaker 2 (I
CB2
= IW + IX= I
CB1
+ I
CB2
+ IX = I
CB1
+ I
CB2
- I
CB1
) to provide
independent circuit breaker failure for Circuit Breaker 2.
Figure 5.7
ESS := 3, Double Circuit Breaker Configuration
Table 5.8
ESS := 3, Current and Voltage Source Selection
Setting
Prompt
Entry
Comments
NUMBK
Number of Circuit Breakers in Scheme (1, 2)
2
LINEI
Line Current Source (COMB)
COMB
Automatic
ALINEI
Alternate Line Current Source (NA)
NA
Automatic
ALTI
Alternate Current Source (SEL
OGIC
Equation)
NA
Hidden
BK1I
Breaker 1 Current Source (IW)
IW
Automatic
BK2I
Breaker 2 Current Source (IX)
IX
Automatic
IPOL
Polarizing Current (NA)
NA
Automatic
ALINEV
Alternate Line Voltage Source (VZ, NA)
NA
ALTV
Alternate Voltage Source (SEL
OGIC
Equation)
NA
Hidden
Analog Input
IW+IX
IW
IX
VY
VAZ
VBZ
Function
Line protection
CB1 protection
CB2 protection
Line protection
Synchronism check Circuit Breaker 1
Synchronism check Circuit Breaker 2
3
3
1
1
Busbar 1
Busbar 2
1
SEL-421
Breaker 1
Breaker 2
IW
IX
VY
VAZ
VBZ
Line 1
Line 2
Summary of Contents for SEL-421-4
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