Application - ABB REC650 Applications Manual

1MRK 511 286-UUS A
6.6.2
6.6.3
Application manual

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, get 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 without risks.
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 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 continues to increase to the
trip value TripTemp, the protection initiates trip of the protected line.
Setting guidelines
The parameters for the Thermal overload protection one time constant, Fahrenheit/
Celsius LFPTTR/LCPTTR (26) are set via the local HMI or PCM600.
The following settings can be done for the thermal overload protection.
GlobalBaseSel: Selects the global base value group used by the function to define (IBase),
(VBase) and (SBase).
Operation: Disabled/Enabled
IRef: Reference, steady state current, given in % of IBase that will give a steady state (end)
temperature rise TRef. It is suggested to set this current to the maximum steady state
current allowed for the line/cable under emergency operation (a few hours per year).
TRef: Reference temperature rise (end temperature) corresponding to the steady state
current IRef. From cable manuals current values with corresponding conductor
temperature are often given. These values are given for conditions such as ground
Section 6
Current protection
129