4.2.1.4 Operation principleThe function can be enabled and disabled with the Operation setting. Thecorresponding parameter values are "On" and "Off".The operation of non-directional earth-fault protection can be described by using amodule diagram. All the modules in the diagram are explained in the next sections.A070437 V3 ENFigure 132: Functional module diagram. Io represents the residual current.Level detectorThe operating quantity can be selected with the setting Io signal Sel. The selectableoptions are "Measured Io" and "Calculated Io". The operating quantity is comparedto the set Start value. If the measured value exceeds the set Start value, the leveldetector sends an enable-signal to the timer module. If the ENA_MULT input isactive, the Start value setting is multiplied by the Start value Mult setting.The IED does not accept the Start value or Start value Mult settingif the product of these settings exceeds the Start value setting range.The start value multiplication is normally done when the inrush detection function(INRPHAR) is connected to the ENA_MULT input.TimerOnce activated, the timer activates the START output. Depending on the value ofthe Operating curve type setting, the time characteristics are according to DT orIDMT. When the operation timer has reached the value of Operate delay time inthe DT mode or the maximum value defined by the inverse time curve, theOPERATE output is activated.When the user-programmable IDMT curve is selected, the operation timecharacteristics are defined by the parameters Curve parameter A, Curve parameterB, Curve parameter C, Curve parameter D and Curve parameter E.If a drop-off situation happens, that is, a fault suddenly disappears before theoperate delay is exceeded, the timer reset state is activated. The functionality of thetimer in the reset state depends on the combination of the Operating curve type,Type of reset curve and Reset delay time settings. When the DT characteristic isselected, the reset timer runs until the set Reset delay time value is exceeded. WhenSection 4 1YHT530004D05 DProtection functions264 615 seriesTechnical Manual
