ABB Relion 670 Series Applications Manual page 156

Section 8
Current protection
8.5.3 Setting guideline
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.
Operation : Disabled / Enabled
GlobalBaseSel is used to select a GBASVAL function for reference of base values, primary current
( IBase ), primary voltage ( VBase ) 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
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 temperature, ambient air
temperature, way of laying of cable and ground 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 190°F (88°C). For overhead lines, the critical
temperature for aluminium conductor is about 190-210°F (88-99°C). For a copper conductor a
normal figure is 160°F (71°C).
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 150°F (66°C). Similar values are stated for overhead lines. A
suitable setting can be about 60°F (16°C) below the trip value.
ReclTemp : Temperature where lockout signal LOCKOUT from the protection is released. When the
thermal overload protection trips, a lock-out signal is activated. This signal is intended to block
switch in of the protected circuit as long as the conductor temperature is high. The signal is
released when the estimated temperature is below the set value. This temperature value should be
chosen below the alarm temperature.
8.6 Directional underpower protection GUPPDUP (37)
150
TRef . It is suggested to set this current to the maximum steady state current
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