Schweitzer Engineering Laboratories SEL-421-4 - Table 6.4 Options for Enabling Pole-Open Logic

6.12
SEL-421 Relay Instruction Manual Date Code 20171021
Protection Applications Examples
230 kV Overhead Distribution Line Example
for the ground-distance elements and residual ground directional overcurrent ele-
ments. A polarizing quantity was not available for choice I, so I is not selected for
this particular application example.
ORDER := QV. Ground Directional Element Priority (combine Q, V, I)
SEL
OGIC control equation E32IV must assert to logical 1 to enable V or I for
directional control of the ground-distance elements and residual ground direc-
tional overcurrent elements. Set E32IV equal to logical 1.
E32IV := 1. Zero-Sequence Voltage and Current Enable (SELOGIC Equation)
Pole-Open Detection
The setting EPO offers two options for deciding what conditions signify an open
pole, as listed in Table 6.4.
Select the second option because a 52A contact is available. The relay uses both
open-phase detection and status information from the circuit breaker to make the
most secure decision.
EPO := 52. Pole-Open Detection (52, V)
Pole-Open Time Delay on Dropout
The setting 3POD establishes the time delay on dropout after the Relay Word bit
3PO deasserts. This delay is important when you use line-side potential trans-
formers for relaying. Use the 3POD setting to stabilize the ground-distance ele-
ments in case of pole scatter during closing of the circuit breaker.
3POD := 0.500. Three-Pole Open Time Dropout Delay (0.000–60 cycles)
Trip Logic
This logic configures the relay for tripping. These settings consist of four catego-
ries:
➤ Trip equations
➤ Trip unlatch options
➤ Trip timers
➤ Three-pole tripping enable
Table 6.4 Options for Enabling Pole-Open Logic
Option Description
EPO := V The logic declares a single-pole open if the corresponding phase undervoltage
element asserts and the open-phase detection logic declares the pole is open.
Select this option only if you use line-side potential transformers for relaying
purposes. A typical setting for the 27PO, pole-open undervoltage threshold, is
60 percent of the nominal line-to-neutral voltage.
Do not select this option when shunt reactors are applied because the voltage
slowly decays after the circuit breaker opens. With this option selected, the
relay can incorrectly declare LOP during a pole-open condition if there is
charging current that exceeds the pole-open current threshold.
EPO := 52 The logic declares a single-pole open if the corresponding 52A contact (e.g.,
52AA1) from the circuit breaker deasserts and the open-phase detection logic
declares that the pole is open.