Schweitzer Engineering SEL-351P - Use Overcurrent Element Torque Control Logic to Enable;Disable or Desensitize Elements (Phase Elements Example); Desensitize Delay Curve - Maintain Coordination (Phase Elements Example)

Date Code 990215 Factory-Set Logic 1-11
SEL-351P Manual Técnico
Use Overcurrent Element Torque Control Logic to Enable/Disable or Desensitize
Elements (Phase Elements Example)
With Relay Word bit SV8 = logical 1 (cold load pickup scheme actively engaged for the phase
overcurrent elements), both the following occur:
• Fast curve-phase (51P1T) is disabled (see top of
Figure SECTION 1: .15)
• Delay curve-phase (51P2T) is desensitized (see top of
Figure SECTION 1: .16)
With Relay Word bit SV8 = logical 1, SEL
OGIC setting 51P1TC = logical 0 in top of Figure
SECTION 1: .15. This disables Fast curve-phase (51P1T).
With Relay Word bit SV8 = logical 1, SEL
OGIC setting 51P2TC in top of Figure SECTION 1:
.16 is controlled by phase instantaneous element 50P5. Element 50P5 asserts to logical 1 when
phase current exceeds its pickup setting, 50P5P (see Figure 3.2). Pickup setting 50P5P
corresponds to EZ setting Cold load pickup-phase. With Relay Word bit SV8 = logical 1,
SEL
OGIC setting 51P2TC enables Delay curve-phase (51P2T) when phase current exceeds
pickup setting 50P5P.
Desensitize Delay Curve – Maintain Coordination (Phase Elements Example)
In
Figure SECTION 1: .5, the normal Min. trip-phase for Delay curve-phase (51P2T) is 51P2P.
When the cold load pickup scheme is actively engaged for phase elements, the effective Min.
trip-phase for Delay curve-phase, is 50P5P. This effective Min. trip-phase is derived as follows:
50P5P = 51P2P * [Cold load pickup-phase (multiples of Min. trip-phase)]
When the cold load pickup scheme is actively engaged for the phase elements, the lower portion
of the 51P2T phase overcurrent element (below pickup 50P5P) is effectively disabled. Note that
the 51P2T phase overcurrent element is not shifted – coordination is maintained.