Application - ABB RELION Series Technical Manual

Section 4
Protection functions
4.1.3.5
4.1.3.6
256
The thermal time constant of the protected circuit is given in seconds with the Time
constant setting. Please see cable manufacturers manuals for further details.
T1PTTR thermal model complies with the IEC 60255-149 standard.

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.
• Overheating can damage the insulation on cables which in turn increases the risk
of phase-to-phase or phase-to-earth 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.
Signals
Table 268: T1PTTR Input signals
Name Type
I_A SIGNAL
I_B SIGNAL
I_C SIGNAL
BLK_OPR BOOLEAN
ENA_MULT BOOLEAN
AMB_TEMP FLOAT32
Default Description
0 Phase A current
0 Phase B current
0 Phase C current
0=False Block signal for operate outputs
0=False Enable Current multiplier
0 The ambient temperature used in the calculation
1MRS758755 A
REC615 and RER615
Technical Manual