ABB RED650, Applications Manual

Page: 187 / 454

• 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
continues to increase to the trip value
TripTemp , the protection initiates trip of the
protected line.
8.5.3 Setting guideline
IP14994-1 v1
M15094-3 v8
The parameters for the Thermal overload protection, one time constant, Celsius/
Fahrenheit LCPTTR/LFPTTR are set via the local HMI or PCM600.
M15094-5 v10
The following settings can be done for the thermal overload protection.
Operation : Off / On
GlobalBaseSel is used to select a GBASVAL function for reference of base values,
primary current ( IBase ), primary voltage ( UBase ) and primary power ( SBase ).
Imult : Enter the number of lines in case the protection function is applied on
multiple parallel lines sharing one CT.
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 earth temperature, ambient air temperature, way of laying of cable and earth
thermal resistivity. From manuals for overhead conductor temperatures and
corresponding current is given.
1MRK 505 393-UEN B
Section 8
Current protection
Line differential protection RED650 2.2 IEC 181
Application manual