4.49
Date Code 20080213 Instruction Manual SEL-351A Relay
Loss-of-Potential, Load Encroachment, and Directional Element Logic
Directional Control Settings (Not in SEL-351A-1)
From a primary system study or metering values, derive a0N as follows:
Equation 4.17
Adjust the final setting value of a0N from the above derived value of a0N,
depending on your security philosophy, etc.
The a0N factor increases the security of the zero-sequence voltage-polarized
directional elements: low-impedance grounded or ungrounded/high-
impedance grounded. It keeps the elements from operating for zero-sequence
current (system unbalance), which circulates due to line asymmetries, etc.
59RES—Wattmetric 3V0 Overvoltage Pickup (Petersen Coil Grounded
System)
Setting Range:
1.00–430.00 V secondary (300 V nominal voltage inputs, VA, VB, VC)
If preceding setting ORDER does not contain P (Petersen Coil directional
element is not enabled) or the model does not have a 0.2 A nominal neutral
channel (IN), then setting 59RES is not made or displayed.
Setting 59RES should be set greater than the value of 3V
0
zero-sequence
voltage present for normal system unbalance. It is part of the enabling logic
for the wattmetric element part of the Petersen Coil directional element (see
Figure 4.13).
The 3V
0
input to Figure 4.13 may come either from a calculation or from a
direct measurement, as described in Zero-Sequence Voltage Sources on
page 4.15. When using a broken-delta PT connection to terminals VS-NS as the
zero-sequence voltage source (global setting VSCONN = 3V0), there are
some special considerations in making the 59RES setting that are related to
the scaling of the VS-NS input signal. The 59RES setting must be entered on
the same secondary base as the voltage terminals VA, VB, and VC. See Settings
Considerations for Petersen Coil Grounded Systems on page 4.52 for an
example.
32WFP and 32WRP—Wattmetric Forward and Reverse Pickups (Petersen
Coil Grounded System)
Setting Range:
0.001–150.000 Ω secondary (300 V nominal voltage inputs, VA, VB, VC;
0.2 A nominal neutral channel input, IN)
If preceding setting ORDER does not contain P (Petersen Coil directional
element is not enabled) or the model does not have a 0.2 A nominal neutral
channel (IN), then settings 32WFP and 32WRP are not made or displayed.
where:
3I
0
pri = standing system unbalance current (zero-sequence; A
primary)
I
1
pri = Maximum load current (positive-sequence; A primary)
a0N
3I
0
pri
··
I
1
pri
·
---------------
·
⎝⎠
⎜⎟
⎛⎞
CTR
CTRN
-----------------
⎝⎠
⎛⎞
• =
Courtesy of NationalSwitchgear.com
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