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.
• Overheating can damage the insulation on cables which in turn increases the risk of
phase-to-phase or phase-to-ground faults.
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.
4.1.4.6 Signals
Table 267: 49F Input signals
Name
Type Default Description
I_A SIGNAL 0 Phase A current
I_B SIGNAL 0 Phase B current
I_C SIGNAL 0 Phase C current
ENA_MULT BOOLEAN 0=False Enable Current multiplier
BLK_OPR BOOLEAN 0=False Block signal for trip outputs
AMB_TEMP FLOAT32 0 The ambient temperature used in the calculation
Table 268: 49F Output signals
Name
Type Description
TRIP BOOLEAN Trip
PICKUP BOOLEAN Pickup
ALARM BOOLEAN Thermal Alarm
BLK_CLOSE BOOLEAN Thermal overload indicator. To inhibite reclose.
1MAC059074-MB A Section 4
Protection functions
615 series ANSI 273
Technical Manual
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