Schweitzer Engineering Laboratories SEL-421-4 - Figure 5.9 Tapped EHV Overhead Transmission Line; Figure 5.10 ESS:= Y, Tapped Line

5.12
SEL-421 Relay Instruction Manual Date Code 20171021
Protection Functions
Current and Voltage Source Selection
Figure 5.10 illustrates the tapped overhead transmission line with a motor-
operated disconnect (MOD) on the high side of a power transformer and two cir-
cuit breakers on the low side.
Figure 5.9 Tapped EHV Overhead Transmission Line
Figure 5.10 ESS := Y, Tapped Line
SEL-421
SEL-421
BK1S
BK1R
BK2S
CB1 CB2
BK2R
SEL-421
S
R
MOD
(HV)
(LV)
T
(HV)
(LV)
MOD
SEL-421 Relay
IW
VY
1
1
3
3
VAZ
VBZ
CB2CB1
Analog Input
IW
VY
VAZ
VBZ
Function
Line protection
Line protection
Synchronism check Circuit Breaker 1
Synchronism check Circuit Breaker 2
Tripping
Direction