Setting Guidelines - ABB REQ650 Applications Manual

Section 6
Current protection
6.8.3
132
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, 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.

Setting guidelines

The parameters for the Thermal overload protection one time constant, Celsius/
Fahrenheit LCPTTR/LFPTTR 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), (UBase) and (SBase).
Operation: Off/On
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.
Tau: The thermal time constant of the protected circuit given in minutes. Please refer
to manufacturers manuals for details.
TripTemp: Temperature value for trip of the protected circuit. For cables, a maximum
allowed conductor temperature is often stated to be 90°C (194°F). For overhead lines,
the critical temperature for aluminium conductor is about 90 - 100°C (194-212°F). For
a copper conductor a normal figure is 70°C (158°F).
AlarmTemp: Temperature level for alarm of the protected circuit. ALARM signal can
be used as a warning before the circuit is tripped. Therefore the setting shall be lower
than the trip level. It shall at the same time be higher than the maximum conductor
temperature at normal operation. For cables this level is often given to 65°C (149°F).
1MRK 505 291-UEN A
Application manual