The time constants can be changed if the current is higher than a set value or lower than a setvalue. If the current is high it is assumed that the forced cooling is activated while it isdeactivated at low current. The setting of the parameters below enables automaticadjustment of the time constant.Tau1High: Multiplication factor to adjust the time constantTau1 if the current is higher thanthe set valueIHighTau1.IHighTau1 is set in % ofIBase1.Tau1Low: Multiplication factor to adjust the time constantTau1 if the current is lower than theset valueILowTau1.ILowTau1 is set in % ofIBase1.Tau2High: Multiplication factor to adjust the time constantTau2 if the current is higher thanthe set valueIHighTau2.IHighTau2 is set in % ofIBase2.Tau2Low: Multiplication factor to adjust the time constantTau2 if the current is lower than theset valueILowTau2.ILowTau2 is set in % ofIBase2.The possibility to change time constant with the current value as the base can be useful indifferent applications. Below some examples are given:• In case a total interruption (low current) of the protected transformer all coolingpossibilities 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 ofoverheating of that equipment in case of very high current. The thermal time constant isoften smaller for a motor than for the transformer.ITrip: The steady state current that the transformer can withstand. The setting is given in % ofIBase1 orIBase2.Alarm1: Heat content level for activation of the signal ALARM1. ALARM1 is set in % of the tripheat content level.Alarm2: Heat content level for activation of the output signal ALARM2. ALARM2 is set in % ofthe trip heat content level.ResLo: Lockout release level of heat content to release the lockout signal. When the thermaloverload protection trips a lock-out signal is activated. This signal is intended to blockswitching on of the protected circuit transformer as long as the transformer temperature ishigh. The signal is released when the estimated heat content is below the set value. Thistemperature value should be chosen below the alarm temperature.ResLo is set in % of the tripheat content level.ThetaInit: Heat content before activation of the function. This setting can be set a little belowthe alarm level. If the transformer is loaded before the activation of the protection function, itstemperature can be higher than the ambient temperature. The start point given in the settingwill 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 settingWarning a warning signal isactivated. The setting is given in minutes.7.7 Breaker failure protection CCRBRF IP14514-1 v6Section 7 1MRK 504 158-UEN ACurrent protection122Application manual
