6.6
SEL-421 Relay Instruction Manual Date Code 20171021
Protection Applications Examples
230 kV Overhead Distribution Line Example
Use Level 1 high-set instantaneous phase overcurrent element for SOTF protec-
tion.
E50P := 1. Phase Instantaneous/Definite-Time Overcurrent Elements (N, 1–4)
This application does not require residual ground overcurrent protection.
E50G := N. Residual Ground Instantaneous/Definite-Time Overcurrent Ele-
ments (N, 1–4)
This application does not require negative-sequence overcurrent protection.
E50Q := N. Negative-Sequence Instantaneous/Definite-Time Overcurrent Ele-
ments (N, 1–4)
Use inverse-time overcurrent protection to provide backup protection for high-
resistance ground faults. The 51S1 element provides backup protection for unbal-
anced faults if the step distance protection fails to operate.
E51S := 1. Selectable Inverse-Time Overcurrent Element (N, 1–3)
Set E32 to AUTO or AUTO2 and the relay automatically calculates the settings
corresponding to the ground directional element (32G).
E32 := AUTO2. Directional Control (Y, AUTO, AUTO2)
Communications-assisted tripping is not required.
ECOMM := N. Communications-Assisted Tripping (N, DCB, POTT, POTT2,
POTT3, DCUB1, DCUB2)
Fuses or molded case circuit breakers often protect potential transformers. Oper-
ation of one or more fuses, or molded case circuit breakers, results in a loss of
polarizing potential inputs to the relay. Loss of one or more phase voltages pre-
vents the relay from properly determining fault distance or direction.
Occasional loss-of-potential (LOP) to the distance relay, while unavoidable, is
detectable. When the relay detects the loss-of-potential, the relay can block dis-
tance element operation, block or enable forward directional overcurrent ele-
ments, and issue an alarm for any true LOP condition.
NOTE: If line-side PTs are used, the
circuit breaker(s) must be closed for
the LOP logic to detect an LOP
condition. Therefore, if three-phase
potential to the relay is lost while the
circuit breaker(s) is open (e.g., the PT
fuses are removed while the line is de-
energized), the relay cannot detect an
LOP when the circuit breaker(s) closes
again.
Set ELOP to Y1 for this application example. This choice reduces the chances of
false tripping because of a loss-of-potential condition.
ELOP := Y1. Loss-of-Potential (Y, Y1, N)
You do not need Advanced Settings for this application example.
EADVS := N. Advanced Settings (Y, N)
Ta b l e 6 . 3 LO P E n a b l e Op tion s
Option Description
N The LOP logic operates but does not disable voltage-polarized directional ele-
ments, distance elements, and forward directional overcurrent elements. Use
LOP in this case for alarm only.
Y The relay disables all voltage-polarized directional elements and distance ele-
ments, but enables forward directional overcurrent elements. These forward
directional overcurrent elements effectively become nondirectional and provide
overcurrent protection during an LOP condition.
Y1 The relay disables all voltage-polarized directional elements and distance ele-
ments. The relay also disables the overcurrent elements controlled by the volt-
age-polarized directional elements.
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