6.59
Date Code 20171021 Instruction Manual SEL-421 Relay
Protection Applications Examples
345 kV Tapped Overhead Transmission Line Example
You can select a common time delay or an independent time delay per zone for
phase and ground-distance protection. If you choose independent timing, evolv-
ing faults (such as those changing from single phase to multiphase) cause the
timer to reset and result in additional delay. Select common time delay for this
application.
ECDTD := Y. Distance Element Common Time Delay (Y, N)
The SOTF logic permits tripping by specified protection elements for a settable
time after the circuit breaker closes.
ESOTF := Y. Switch-Onto-Fault (Y, N)
Do not enable the Out-of-Step logic for this application example.
EOOS : = N. Out-of-Step (Y, N)
The relay has a load-encroachment feature that prevents operation of the phase-
distance elements during heavy load. This unique feature permits the load to
enter a predefined area of the phase-distance characteristics without causing
unwanted tripping.
ELOAD := Y. Load Encroachment (Y, N)
Use Level 1 high-set instantaneous phase overcurrent element for SOTF
protection.
E50P := 1. Phase Instantaneous/Definite-Time Overcurrent Elements (N, 1–4)
Use residual ground overcurrent elements for the DCB trip scheme. The Level 2
residual ground overcurrent element (67G2) is forward-looking and provides
communications-assisted tripping. The Level 3 residual overcurrent element
(67G3) is reverse-looking and blocks the tripping at Station R during out-of-sec-
tion faults behind Station S. Enable three levels of residual ground overcurrent
protection.
E50G := 3. Residual Ground Instantaneous/Definite-Time Overcurrent
Elements (N, 1–4)
This application does not require negative-sequence overcurrent protection.
E50Q := N. Negative-Sequence Instantaneous/Definite-Time Overcurrent
Elements (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 both the communications-assisted and step distance protection fail
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)
Use the DCB tripping scheme.
ECOMM := DCB. 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.
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