Thermal Overload Protection, One Time Constant Fahrenheit/Celsius Lfpttr/ Lcpttr (26); Identification; Application - ABB Relion 670 Series Applications Manual

Section 7
Current protection
tINNonDir is the definite time delay for the non directional ground fault current protection, given
in s.
OpVN is set Enabled to activate the trip function of the residual over voltage protection.
tVN is the definite time delay for the trip function of the residual voltage protection, given in s.
7.7 Thermal overload protection, one time constant
Fahrenheit/Celsius LFPTTR/LCPTTR (26)
7.7.1

Identification

Function description
Thermal overload protection, one
time constant, Fahrenheit
Thermal overload protection, one
time constant, Celsius
7.7.2

Application

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 ground 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 LFPTTR or LCPTTR (26) 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
can be given to the operator. This enables actions in the power system to be taken before
164
IEC 61850 IEC 60617
identification identification
LFPTTR
LCPTTR
1MRK 511 358-UUS A
ANSI/IEEE C37.2
device number
26
26
AlarmTemp , a signal ALARM
Application manual
IP14512-1 v7
M17106-1 v7
M15283-3 v8