Schweitzer Engineering Laboratories SEL-421-4, Instruction Manual

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6.57
Date Code 20171021 Instruction Manual SEL-421 Relay
Protection Applications Examples
345 kV Tapped Overhead Transmission Line Example
Current and Voltage Source Selection
The voltage and current source selection is for one circuit breaker. The relay
derives the line current source from current input IW when you set ESS to N.
ESS := N .
Current and Voltage Source Selection (Y, N, 1, 2, 3, 4)
Figure 6.12 illustrates the current and voltage sources for this particular applica-
tion. The relay uses potential input VY and current input IW for line relaying;
potential input VAZ is for synchronism check.
Synchronism Check on page 5.158
describes how to apply the synchronism check function.
Breaker Monitor
Circuit Breaker Configuration
Set the relay to indicate that Circuit Breaker 1 is a three-pole trip circuit breaker.
BK1TYP := 3 .
Breaker 1 Trip Type (Single-Pole = 1, Three-Pole = 3)
Circuit Breaker 1 Inputs
The SEL-421 uses a normally open auxiliary contact from the circuit breaker to
determine whether the circuit breaker is open or closed.
52AA1 := IN101 .
A-Phase N/O Contact Input -BK1 (SEL
OGIC
Equation)
Group Settings
Line Configuration
The SEL-421 has four transformer turns ratio settings that convert the secondary
potentials and currents that the relay measures to the corresponding primary val-
ues. These settings are the potential transformer and current transformer ratios
PTRY, PTRZ, CTRW, and CTRX. Use the Y potential input for line relaying and
the Z potential input for synchronism checks. Use the W current input for line
relaying. The settings VNOMY and VNOMZ specify the nominal secondary
line-to-line voltage of the potential transformers (see
Figure 6.12 ).
CTRW := 200 .
Current Transformer Ratio—Input W (1–50000)
PTRY := 3000 .
Potential Transformer Ratio—Input Y (1–10000)
VNOMY := 115 .
PT Nominal Voltage (L–L)—Input Y (60–300 V secondary)
PTRZ := 3000 .
Potential Transformer Ratio—Input Z (1–10000)
VNOMZ := 115 .
PT Nominal Voltage (L–L)—Input Z (60–300 V secondary)
Figure 6.12 Circuit Breaker Arrangement at Station S
SEL-421
VAZ
IW
VY
BK1
3
1 3
34
5 kV Bus