Date Code 20001006 Loss-of-Potential, Load Encroachment, and Directional Element Logic 4-7
SEL-351 Instruction Manual
should be supervised by !LOP in a torque control setting. This also effectively happens in the
directional element in Figure 4.15, where ZLOAD and LOP are part of the logic.
In the above setting example, phase instantaneous overcurrent element 50P6 is set above any
maximum load current level - if 50P6 picks up, there is assuredly a fault. For faults below the
pickup level of 50P6, but above the pickup of phase time-overcurrent element 51PT, the
!ZLOAD*!LOP logic discriminates between high load and fault current. If an LOP condition
occurs (LOP = logical 1), the pickup level of 50P6 becomes the effective pickup of phase time-
overcurrent element 51PT (51PT loses its sensitivity when an LOP condition occurs):
51PTC = !ZLOAD*!LOP + 50P6 = !ZLOAD*NOT[LOP] + 50P6
= !ZLOAD*NOT[logical 1] + 50P6 = 50P6
Use SEL-321 Relay Application Guide for the SEL-351 Relay
The load-encroachment logic and settings in the SEL-351 Relay are the same as those in the SEL-
321 Relay. Refer to Application Guide 93-10 (SEL-321 Relay Load-Encroachment Function
Setting Guidelines) for applying the load-encroachment logic in the SEL-351 Relay. Note that
Application Guide AG93-10 discusses applying the load-encroachment feature to phase distance
elements in the SEL-321 Relay. The SEL-351 Relay doesn’t have phase distance elements, but the
principles and settings example are still applicable to the SEL-351 Relay.
DIRECTIONAL CONTROL FOR NEUTRAL GROUND AND RESIDUAL GROUND
OVERCURRENT ELEMENTS
The directional control for overcurrent elements is enabled by making directional control enable
setting E32. Setting E32 and other directional control settings are described in the following
subsection Directional Control Settings.
Three directional elements are available to control the neutral ground and residual ground
overcurrent elements. These three directional elements are:
• Negative-sequence voltage-polarized directional element
• Zero-sequence voltage-polarized directional element
• Channel IN current-polarized directional element
Courtesy of NationalSwitchgear.com
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