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6.8
SEL-421 Relay
Instruction Manual
Date Code 20171021
Protection Applications Examples
230 kV Overhead Distribution Line Example
Zone 2 Mho Ground-Distance Element Reach
Zone 2 mho ground-distance reach must meet the same requirement as that for
Zone 2 mho phase-distance protection; i.e., set the reach equal to 120 percent of
the line.
Z2MG = 1.2Z1L = 2.34
Z2MG : =
2.34
.
Zone 2 (OFF, 0.05–64
secondary)
Zero-Sequence Current Compensation Factors
Zero-sequence current compensation helps to keep the phase and ground-dis-
tance elements at the same reach if you set the reach equal per zone (for example,
Z1MP = Z1MG). Ground-distance elements should measure fault impedance in
terms of positive-sequence impedance only. The relay automatically calculates
the setting for the Zone 1 zero-sequence current compensation factor when you
set k0M1 to AUTO.
k0M1 :=
AUTO
.
Zone 1 ZSC Factor Magnitude (AUTO, 0.000–10)
When you enter AUTO as the setting for k0M1, the relay calculates the zero-
sequence current compensation as follows:
Equation 6.4
Zone 2 uses the same zero-sequence current compensation factor as that for Zone
1 because the Advanced Settings are disabled.
The relay displays the following values for k0M1 and k0A1:
k0M1 :=
0.727
.
Zone 1 ZSC Factor Magnitude (AUTO, 0.000–10)
k0A1 :=
–3.65
.
Zone 1 ZCS Factor Angle
Distance Element Common Time Delay
Set the appropriate timers Z1D and Z2D for both phase and ground-distance ele-
ments.
NOTE:
If the relay is using a remote
data acquisition system, such as TiDL,
the operating times will be delayed by
1.5 ms. Use caution when setting the
relay coordination times to account
for this added delay.
You do not need to delay Zone 1 distance protection; it trips instantaneously.
Z1D :=
0.000
.
Zone 1 Time Delay (OFF, 0.000–16000 cycles)
Zone 2 distance protection must coordinate with downstream Zone 1 distance
protection, plus downstream circuit breaker operating time and a safety margin.
A typical Zone 2 phase and ground-distance time delay setting is 20 cycles.
Z2D :=
20.000
.
Zone 2 Time Delay (OFF, 0.000–16000 cycles)
SOTF Scheme
SOTF logic is enabled when the circuit breaker closes. This logic provides pro-
tection for a short duration (setting SOTFD) until other protection (such as trip-
ping from SEL
OGIC
control equations TR, TRCOMM, and TRCOMMD) is
available. The TRSOTF SEL
OGIC
control equation defines which protection ele-
ments cause the relay to trip when the SOTF scheme is active. Assertion of the
protection elements assigned to TRSOTF during the SOTFD time causes the
relay to trip instantaneously.
k01
Z0MAG Z0ANG
Z1MAG Z1ANG
–
3 Z1MAG Z1ANG
•
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=
Summary of Contents for SEL-421-4
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