6.69
Date Code 20171021 Instruction Manual SEL-421 Relay
Protection Applications Examples
345 kV Tapped Overhead Transmission Line Example
This application uses 50P1 as an instantaneous overcurrent element; you do not
need time delay.
67P1D := 0.000. Level 1 Time Delay (0.000–16000 cycles)
This application uses 50P1 as a nondirectional overcurrent element; you do not
need torque control.
67P1TC := 1. Level 1 Torque Control (SELOGIC Equation)
Residual Ground Instantaneous/Definite-Time Overcurrent Elements
This application example has three levels of residual ground overcurrent ele-
ments. You will use these overcurrent elements later in the DCB scheme. The
Level 2 residual ground overcurrent element is set forward-looking to serve as a
tripping element. The Level 3 residual ground overcurrent element is set as both a
nondirectional (50G3) and reverse-looking (67G3) starting element. Be sure to
set residual ground elements above any loading unbalance.
Disable Level 1 residual ground overcurrent element; this particular application
does not use this element.
50G1P := OFF. Level 1 Pickup (OFF, 0.25–100 A secondary)
Enable Level 2 residual ground overcurrent element for DCB tripping. Ground-
distance elements measure fault resistance consisting of arcing resistance and
ground return resistance. Ground return resistance can consist of tower footing
resistance and tree resistance. The total ground fault resistance can lie outside of
the ground-distance characteristics. Residual overcurrent protection is the best
method available for detecting high-resistance ground faults because this method
of protection provides the greatest sensitivity. Set the pickup to 20 percent of the
nominal current (5 A).
50G2P := 1.00. Level 2 Pickup (OFF, 0.25–100 A secondary)
Enable Level 3 residual ground overcurrent element to send the blocking signal
for out-of-section faults. Set the pickup of Level 3 residual ground overcurrent
element (50G3) at Station S to half the remote forward-looking residual ground
overcurrent element (50G2) at Station R.
Equation 6.35
This measure provides security during out-of-section faults, because the blocking
elements are twice as sensitive as the tripping elements.
50G3P := 0.50. Level 3 Pickup (OFF, 0.25–100 A secondary)
You do not need to add intentional time delays for Level 2 and Level 3 pickups.
67G2D := 0.000. Level 2 Time Delay (0.000–16000 cycles)
67G3D := 0.000. Level 3 Time Delay (0.000–16000 cycles)
Set Level 2 torque control equation to the forward decision from the ground
directional element, 32GF.
67G2TC := 32GF. Level 2 Torque Control (SELOGIC Equation)
50G3P
S
50G2P
R
2
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