Schweitzer Engineering Laboratories SEL-421-4 - Table 5.8 ESS:= 3, Current and Voltage Source Selection; Figure 5.7 ESS:= 3, Double Circuit Breaker Configuration

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. Figure 5.8 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