Date Code 20001006 Overcurrent, Voltage, Synchronism Check, Frequency, and Power Elements 3-21
SEL-351 Instruction Manual
Note: All overcurrent element SELOGIC Control Equation torque control settings
are set directly to logical 1 (e.g., 51PTC = 1) for the factory default set-
tings. See SHO Command (Show/View Settings) in Section 10: Serial
Port Communications and Commands for a list of the factory default
settings.
51PTC = IN5 Input IN5 deasserted (51PTC = IN5 = logical 0):
Then logic point TCP = logical 0 and, thus, the Torque Control Switch
opens and phase time-overcurrent element 51PT is defeated and nonopera-
tional, regardless of any other setting.
Input IN5 asserted (51PTC = IN5 = logical 1):
Then only the corresponding directional control input from Figure 4.18 has
to be considered in the control of logic point TCP (and, thus, in the control
of the Torque Control Switch and phase time-overcurrent element 51PT).
If directional control enable setting E32 = N, then logic point
TCP = logical 1 and, thus, the Torque Control Switch closes and phase
time-overcurrent element 51PT is enabled and nondirectional.
Sometimes SELOGIC Control Equation torque control settings are set to provide directional control.
See Directional Control Provided by Torque Control Settings at the end of Section 4: Loss-of-
Potential, Load Encroachment, and Directional Element Logic.
Reset Timing Details (51PT Element Example)
Refer to Figure 3.14.
Any time current I
P
goes above pickup setting 51PP and the phase time-overcurrent element starts
timing, Relay Word bit 51PR (reset indication) = logical 0. If the phase time-overcurrent element
times out on its curve, Relay Word bit 51PT (curve time-out indication) = logical 1.
Setting 51PRS = Y
If electromechanical reset timing setting 51PRS = Y, the phase time-overcurrent element reset
timing emulates electromechanical reset timing. If maximum phase current, I
P
, goes above pickup
setting 51PP (element is timing or already timed out) and then current I
P
goes below 51PP, the
element starts to time to reset, emulating electromechanical reset timing. Relay Word bit 51PR
(resetting indication) = logical 1 when the element is fully reset.
Courtesy of NationalSwitchgear.com
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