4.41
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)
elements at all times (assuming it has sufficient operating quantity). If there is
not sufficient operating quantity during an event (i.e., internal enable 32VE is
not asserted; see Figure 4.7), then no directional control is available. The
neutral-ground and residual-ground overcurrent elements will not operate,
even though these elements are designated with the DIRn (n = 1–4) settings to
be directionally controlled (see Figure 4.17 and Figure 4.18).
If setting:
ORDER = OFF
then all of the ground directional elements are inoperable. Note in Figure 4.17
and Figure 4.18 that setting ORDER = OFF effectively makes the neutral-
ground and residual-ground overcurrent elements nondirectional (the
directional control outputs of Figure 4.17 and Figure 4.18 are continuously
asserted to logical 1).
Petersen Coil Considerations for Setting ORDER
Note in Figure 4.17 that if setting ORDER = P, the residual-ground
overcurrent elements are not controlled by the directional control logic (much
like when ORDER = OFF). In such a scenario, where only the wattmetric
directional element provides ground overcurrent element directional control
(setting ORDER = P), presumably there is no bypass around the Petersen Coil.
With the tuned Petersen Coil in place (and not shorted out by a bypass), very
little current flows for a ground fault. With such low current levels, the
neutral-ground overcurrent elements (referenced in Figure 4.18) are the
elements that detect the ground fault, not the residual-ground overcurrent
elements (referenced in Figure 4.17). The residual-ground overcurrent
elements (including forward and reverse fault detectors 50GF and 50GR,
respectively; see Figure 4.7) should be set above any ground fault current level
with the Petersen Coil in place.
If there is a bypass around the Petersen Coil and the bypass is used at times
(i.e., shorting out the Petersen Coil), much higher currents can flow for a
ground fault when the bypass is closed. In such a scenario, setting ORDER
should be set something like ORDER = QP or ORDER = QVP (see Table 4.2).
Then, the residual-ground elements (Figure 4.17) are controlled by the
directional control logic and provide directional protection for higher ground
fault currents.
50P32P—Phase Directional Element Three-Phase Current Pickup
Setting Range:
0.50–10.00 A secondary (5 A nominal phase current inputs, IA, IB, IC)
0.1–2.00 A secondary (1 A nominal phase current inputs, IA, IB, IC)
The 50P32P setting is set to pick up for all three-phase faults that need to be
covered by the phase overcurrent elements. It supervises the positive-sequence
voltage-polarized directional elements F32P and R32P (see Figure 4.21).
If the load-encroachment logic is enabled (enable setting ELOAD = Y), then
setting 50P32P is not made or displayed, but is fixed internally at:
0.5 A secondary (5 A nominal phase current inputs, IA, IB, IC)
0.1 A secondary (1 A nominal phase current inputs, IA, IB, IC)
Courtesy of NationalSwitchgear.com
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