Schweitzer Engineering Laboratories SEL-421-4, Instruction Manual

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6.33
Date Code 20171021 Instruction Manual SEL-421 Relay
Protection Applications Examples
500 kV Parallel Transmission Lines With Mutual Coupling Example
Zone 2 ground-distance elements tend to underreach for faults at the remote bus
because residual current flows in the same direction for both parallel lines. Apply
the following expression for the forward compensation factor so that Zone 2
ground-distance elements see ground faults at the remote bus when zero-
sequence mutual coupling is a concern.
Equation 6.17
k0M := 1.540 .
Forward Zones ZSC Factor Magnitude (0.000–10)
k0A := –9.0 .
Forward Zones ZSC Factor Angle (–180.0 to +180.0 degrees)
Set the reverse compensation factor equal to the forward compensation factor so
that Zone 3 ground-distance protection has the same reach for external faults as
the remote Zone 2 ground-distance protection.
K0MR := 1.540 .
Reverse Zones ZSC Factor Magnitude (0.000–10)
k0AR := –9.0 .
Reverse Zones ZSC Factor Angle (–180.0 to +180.0 degrees)
Parallel Line Out-of-Service
When the parallel line is out-of-service, Zone 2 and 3 ground-distance elements
overreach; these elements still coordinate properly during external faults because
the elements overreach by the same amount. Consider using an alternate settings
group if Zone 2 ground-distance protection provides time-delayed backup protec-
tion; Zone 2 ground-distance protection and downstream Zone 1 ground-distance
protection could coordinate poorly.
Distance Element Common Time Delay
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.
Set the appropriate timers Z1D, Z2, and Z3D for both phase and ground-distance
elements.
There is no need to delay Zone 1 distance protection since it trips instanta-
neously.
Z1D = 0.000 .
Zone 1 Time Delay (OFF, 0.000–16000 cycles)
Zone 2 distance protection must coordinate with downstream Zone 1 distance
protection, 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)
Set Zone 3 for zero time delay.
Z3D := 0.000 .
Zone 3 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-
k0
Z
0L1
Z
1L1
+ Z
0M
–
3 • Z
1L1
------------------------------------------------ =
14.48

82.1
 
3.98

87.6

+ 7.86

76.6
  
–
3 • 3.98

87.6
 
------------------------------------------------------------------------------------------------------------------------------- =
1.54 –9
 
=