R.1.12
SEL-421 Relay Reference Manual Date Code 20111215
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
applications.
Tapped Line
Figure 1.9 illustrates a tapped EHV transmission overhead line. A power
transformer 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 complete explanation of this example, see Section 5:
Substation Automatic Restoration in the Applications Handbook.
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 1.9 Tapped EHV Overhead Transmission Line
Table 1.9 ESS := 4, Current and Voltage Source Selection
Setting Description 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
SEL-421
BK1S
BK1R
BK2S
CB1 CB2
BK2R
SEL-421
S
R
MOD
(HV)
(LV)
T
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