UseStartValue: Gives which current level should be used for the activation of theblocking signal. This is given as one of the settings of the steps: Step 1/2/3/4.Normally, the step having the lowest operation current level should be set.7.4.3.4 Switch onto fault logic M15282-106 v4In case of energizing a faulty object there is a risk of having a long fault clearancetime, if the fault current is too small to give fast operation of the protection. Theswitch on to fault function can be activated from auxiliary signals from the circuitbreaker, either the close command or the open/close position (change of position).This logic can be used to issue a fast trip if one breaker pole does not closeproperly at a manual or automatic closing.SOTF and under time are similar functions to achieve fast clearance atasymmetrical closing based on requirements from different utilities.The function is divided into two parts. The SOTF function will give operation fromstep 2 or 3 during a set time after change in the position of the circuit breaker. TheSOTF function has a set time delay. The under time function, which has 2ndharmonic restrain blocking, will give operation from step 4. The 2nd harmonicrestrain will prevent unwanted function in case of transformer inrush current. Theunder time function has a set time delay.Below the settings for switch on to fault logics are described.SOTF: This parameter can be set: Off/SOTF/Under Time/SOTF+Under Time.ActivationSOTF: This setting will select the signal to activate SOTF function; CBposition open/CB position closed/CB close command.StepForSOTF: If this parameter is set on step 3, the step 3 start signal will be usedas current set level. If set on step 2, the step 2 start signal will be used as current setlevel.HarmBlkSOTF: This is used to On/Off harmonic restrain during SOTF conditions.tSOTF: Time delay for operation of the SOTF function. The setting range is 0.000 -60.000 s in step of 0.001 s. The default setting is 0.100 st4U: Time interval when the SOTF function is active after breaker closing. Thesetting range is 0.000 - 60.000 s in step of 0.001 s. The default setting is 1.000 s.ActUnderTime: Describes the mode to activate the sensitive undertime function.The function can be activated by Circuit breaker position (change) or Circuitbreaker command.tUnderTime: Time delay for operation of the sensitive undertime function. Thesetting range is 0.000 - 60.000 s in step of 0.001 s. The default setting is 0.300 sSection 7 1MRK 504 169-UEN ACurrent protection126 Transformer protection RET650 2.2 IECApplication manual
