Cold load pickup, occurring as the result of a permanent
fault and long outage, is often maligned as the cause of many protective device
misoperations. Figure shown below, illustrates several cold load pickup curves
developed by various sources. These curves are normally considered to be
composed of the following three components:
1) Inrush – lasting a few cycles
2) Motor starting – lasting a few seconds
3) Loss of diversity – lasting many minutes.
When a lateral fuse misoperates, it is probably not the result of this loss of diversity,
i.e., the fuse is overloaded. This condition is rare on most laterals. Relay
operation during cold load pickup is generally the result of a trip of the
instantaneous unit and probably results from high inrush.
Likewise, an FCI operation would not appear to be the result
of loss of diversity but rather the high inrush currents. Since inrush occurs
during all energization and not just as a result of cold load pickup, it can be
concluded that cold load pickup is not a major factor in the application of
Fcls.
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