Schweitzer Engineering SEL-351P - Cold Load Pickup Scheme; Enable Cold Load Pickup Scheme

Date Code 990430 Factory-Set Logic 1-7
SEL-351P Manual Técnico
Phase current input channels IA, IB, and IC are rated 1A nominal. Current input channel IN is
rated 0.05 A nominal. The neutral ground overcurrent elements (derived from current input
channel IN) can be more sensitively set than the residual ground overcurrent elements (derived
from phase current input channels IA, IB, and IC).
For example
, for the Fast curve-ground element, a neutral ground overcurrent element (51N1T)
is used when a more sensitive setting is needed, as opposed to the complimentary residual ground
overcurrent element (51G1T). This is taken care of automatically when EZ settings are made.
See
Figure SECTION 1: .15 and Figure SECTION 1: .19 for more details on the operation of
the Fast curve-ground element.
C OLD L OAD P ICKUP S CHEME
The cold load pickup scheme activates to prevent tripping on cold load pickup current. Both the
following occur when the cold load pickup scheme activates:
• Fast curves are disabled
• Delay curves and SEF (Sensitive Earth Fault) element are desensitized
The delay curves and SEF element are not shifted in the desensitization process – coordination is
maintained.
Enable Cold Load Pickup Scheme
The cold load pickup scheme begins in
Figure SECTION 1: .1 (top). The logic at the top of this
figure is enabled when either
of the following EZ settings is made (enabling the loss of load
diversity timer, SV6PU):
• Cold load pickup-phase ≠ OFF (Relay Word bit CLP = logical 1)
• Cold load pickup-ground ≠ OFF (Relay Word bit CLG = logical 1)