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2.3
THERMAL IMAGE UNIT
A Thermal Image Unit is included among the relay functions. This unit provides protection against overheating due to
overloading conditions. The operating time curve is set from the time curve family available, as a function of the time
constant τ1 (settable between 3 and 600 minutes). The cooling time constant τ2 can be set between 1 and 6 times
the heating time constant τ1. Refer to Annex 1 for a detailed explanation on the operating principles of this unit.
2.4
COLD LOAD PICKUP (ONLY OPTION 2 MODELS)
This unit avoids undesired operation of the overcurrent units in case of high currents produced when energising a line
that has been open during a long period of time.
This unit detects when the current values of the three phases are lower than 4% of the rated current (In). In this
moment, a timer (T IN) is started.
If the currents return to values above 4% In before the timer countdown has finished, the unit returns to its original
status.
When the timer countdown has finished, the tap settings of the instantaneous phase units (50PH and 50PL) is
multiplied by a constant K50P, and the phase TOC (51P) tap settings are multiplied by a constant K51P. A status
signal turns on indicating that the Cold Load Pickup is enabled, and the corresponding event is generated.
For exiting the CLP status, when the current values of the three phases are above 8% In, a T OUT timer is started.
If the current values fall below 8% In before the timer countdown has finished, the unit remains in CLP status.
If the timeout finishes and current values are still above 8% of In, the CLP status is disabled and the relay returns to
its original settings. The CLP status signal is deactivated, and the corresponding event is generated.
The T IN and T OUT timer values, as well as the multiplying constants K50P and K51P, and the function permission
are settings associated to the COLD LOAD PICKUP. These settings are included in the ADVANCED SETTINGS
group. They will be described in detail in the SETTINGS section.
I<4%In
Normal
status
T OUT
In, rated current
I, phase currents: Ia, Ib, Ic
2-8
PRODUCT DESCRIPTION
T IN
I>4%In
I<8%In
T OUT
MIF Digital Feeder Protection
T IN
Cold Load
Pickup
I>8%In
GEK-106273L
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