ABB RELION REX640, Техническое руководство, Страница: 387 / 1960

4.1.5.6 Application
The lines and cables in the power system are constructed for a certain maximum
load current level. If the current exceeds this level, the losses will be higher than
expected. As a consequence, the temperature of the conductors will increase. If the
temperature of the lines and cables reaches too high values, it can cause a risk of
damages by, for example, the following ways:
• The sag of overhead lines can reach an unacceptable value.
• If the temperature of conductors, for example aluminium conductors, becomes
too high, the material will be destroyed.
• In cables the insulation can be damaged as a consequence of overtemperature,
and therefore phase-to-phase or phase-to-earth faults can occur.
In stressed situations in the power system, the lines and cables may be required
to be overloaded for a limited time. This should be done without any risk for the
above-mentioned risks.
The thermal overload protection provides information that makes temporary
overloading of cables and lines possible. The thermal overload protection estimates
the conductor temperature continuously. This estimation is made by using a
thermal model of the line/cable that is based on the current measurement.
If the temperature of the protected object reaches a set warning level, a signal is
given to the operator. This enables actions in the power system to be done before
dangerous temperatures are reached. If the temperature continues to increase to
the maximum allowed temperature value, the protection initiates a trip of the
protected line.
4.1.5.7 Signals
T1PTTR Input signals
Table 434: T1PTTR Input signals
Name Type Default Description
I3P SIGNAL - Three-phase currents
BLK_OPR BOOLEAN 0=False Block signal for oper-
ate outputs
ENA_MULT BOOLEAN 0=False Enable Current multi-
plier
AMB_TEMP FLOAT32 0 The ambient temper-
ature used in the cal-
culation
1MRS759142 F Protection functions
REX640
Technical Manual
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