ABB Relion 670 Series Applications Manual page 187

1MRK 505 370-UUS Rev. K
Tau1Low: Multiplication factor to adjust the time constant Tau1 if the current is lower than the set value
ILowTau1. ILowTau1 is set in % of IBase1.
Tau2High: Multiplication factor to adjust the time constant Tau2 if the current is higher than the set value
IHighTau2. IHighTau2 is set in % of IBase2.
Tau2Low: Multiplication factor to adjust the time constant Tau2 if the current is lower than the set value
ILowTau2. ILowTau2 is set in % of IBase2.
The possibility to change time constant with the current value as the base can be useful in different
applications. Below some examples are given:
• In case a total interruption (low current) of the protected transformer all cooling possibilities will be
inactive. This can result in a changed value of the time constant.
• If other components (motors) are included in the thermal protection, there is a risk of overheating of
that equipment in case of very high current. The thermal time constant is often smaller for a motor
than for the transformer.
ITrip: The steady state current that the transformer can withstand. The setting is given in % of IBase1 or
IBase2.
Alarm1: Heat content level for activation of the signal ALARM1. ALARM1 is set in % of the trip heat
content level.
Alarm2: Heat content level for activation of the output signal ALARM2. ALARM2 is set in % of the trip
heat content level.
LockoutReset: Lockout release level of heat content to release the lockout signal. When the thermal
overload protection trips a lock-out signal is activated. This signal is intended to block switching on of the
protected circuit transformer as long as the transformer temperature is high. The signal is released when
the estimated heat content is below the set value. This temperature value should be chosen below the
alarm temperature. LockoutReset is set in % of the trip heat content level.
ThetaInit: Heat content before activation of the function. This setting can be set a little below the alarm
level. If the transformer is loaded before the activation of the protection function, its temperature can be
higher than the ambient temperature. The start point given in the setting will prevent risk of no trip at
overtemperature during the first moments after activation. ThetaInit: is set in % of the trip heat content
level.
Warning: If the calculated time to trip factor is below the setting Warning a warning signal is activated.
The setting is given in minutes.
7.5.3.1 Setting example
Calculation of the operate time with the available current is performed only if the calculated final
temperature is greater than the operate level temperature.
where:
t
operate
t
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Busbar protection REB670
Application manual
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is the time to operate
is the time constant
Section 7
Current protection
181