6.53
Date Code 20171021 Instruction Manual SEL-421 Relay
Protection Applications Examples
345 kV Tapped Overhead Transmission Line Example
345 kV Tapped Overhead Transmission Line Example
Figure 6.11 shows a three-ended 345 kV transmission line with SEL-421 protec-
tion at Stations S and R. A tap midway between Stations S and R feeds an auto-
transformer. This example explains how to calculate settings for the SEL-421 at
Station S that protects the 345 kV circuit between Substation S, Substation R,
and the autotransformer. The 345 kV and 138 kV windings of the autotrans-
former are wye-connected and solidly grounded. The tertiary voltage windings
are delta-connected and lag the other windings by 30 degrees.
This application example uses communications-assisted tripping with PLC
(power line carrier) communication to provide high-speed protection for faults
along the 345 kV circuit. The relay uses distance elements and residual ground
directional overcurrent elements in this protection scheme.
Another SEL-421 located on the 138 kV side of the autotransformer blocks high-
speed tripping at Stations S and R for faults on the 138 kV side of the autotrans-
former.
MIRRORED BITS Transmit Equations (Outputs)
TMB1A (SELOGIC Equation) KEY1 OR EKEY
AND RMB1A
TMB2A (SEL
OGIC Equation) KEY3 OR EKEY
AND RMB2A
TMB3A (SEL
OGIC Equation) TPA AND NOT 3PT
TMB4A (SEL
OGIC Equation) TPB AND NOT 3PT
TMB5A (SEL
OGIC Equation) TPC AND NOT 3PT
TMB6A (SEL
OGIC Equation) NA
TMB7A (SEL
OGIC Equation) NA
TMB8A (SEL
OGIC Equation) NA
TMB1B (SEL
OGIC Equation) NA
TMB2B (SEL
OGIC Equation) NA
TMB3B (SEL
OGIC Equation) NA
TMB4B (SEL
OGIC Equation) NA
TMB5B (SEL
OGIC Equation) NA
TMB6B (SEL
OGIC Equation) NA
TMB7B (SEL
OGIC Equation) NA
TMB8B (SEL
OGIC Equation) NA
a
Parameter
n
is 1 for BK1, 2 for BK2, and L for Line.
Table 6.13 Settings for 500 kV Parallel TX Example (Sheet 7 of 7)
Setting Prompt Entry
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