ABB REL670 2.2 IEC, Applications Manual

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9.7 Thermal overload protection, one time constant,
Celsius/Fahrenheit LCPTTR/LFPTTR
IP14512-1 v7
9.7.1 Identification
M17106-1 v7
Function description IEC 61850
identification
IEC 60617
identification
ANSI/IEEE C37.2
device number
Thermal overload protection, one time
constant, Celsius
LCPTTR 26
Thermal overload protection, one time
constant, Fahrenheit
LFPTTR 26
9.7.2 Application
M15283-3 v9
Lines and cables in the power system are designed 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 the equipment might be
damaged:
• The sag of overhead lines can reach unacceptable value.
• If the temperature of conductors, for example aluminium conductors, gets too
high the material will be destroyed.
• In cables the insulation can be damaged as a consequence of the
overtemperature. As a consequence of this phase to phase or phase to earth
faults can occur.
In stressed situations in the power system it can be required to overload lines and
cables for a limited time. This should be done while managing the risks safely.
The thermal overload protection provides information that makes a temporary
overloading of cables and lines possible. The thermal overload protection estimates
the conductor temperature continuously, in Celsius or Fahrenheit depending on
whether LCPTTR or LFPTTR is chosen. This estimation is made by using a
thermal model of the line/cable based on the current measurement.
If the temperature of the protected object reaches a set warning level AlarmTemp , a
signal ALARM can be given to the operator. This enables actions in the power
system to be taken before dangerous temperatures are reached. If the temperature
1MRK 506 369-UEN B
Section 9
Current protection
Line distance protection REL670 2.2 IEC 505
Application manual