t s k AB U UU CDE = ⋅× < −< − +GUID-4A433D56-D7FB-412E-B1AB-7FD43051EE79 V2 EN (Equation 108)t[s] operate time in secondsA the set value ofCurve parameter AB the set value ofCurve parameter BC the set value ofCurve parameter CD the set value ofCurve parameter DE the set value ofCurve parameter EU measured voltageU< the set value ofStart valuek the set value ofTime multiplier11.3.2.3 IDMT curve saturation of undervoltage protectionFor the undervoltage IDMT mode of operation, the integration of the operate timedoes not start until the voltage falls below the value of Start value. To cope withdiscontinuity characteristics of the curve, a specific parameter for saturating theequation to a fixed value is created. The Curve Sat Relative setting is the parameterand it is given in percents compared with Start value. For example, due to thecurve equation B, the characteristics equation output is saturated in such a way thatwhen input voltages are in the range from Start value to Curve Sat Relative inpercents under Start value, the equation uses Start value * (1.0 - Curve SatRelative / 100 ) for the measured voltage. Although, the curve A has nodiscontinuities when the ratio U/U> exceeds the unity, Curve Sat Relative is set forit as well. The Curve Sat Relative setting for curves A, B and C is 2.0 percent.However, it should be noted that the user must carefully calculate the curvecharacteristics concerning also discontinuities in the curve when the programmablecurve equation is used. Thus, the Curve Sat Relative parameter gives anotherdegree of freedom to move the inverse curve on the voltage ratio axis and iteffectively sets the maximum operate time for the IDMT curve because for thevoltage ratio values affecting by this setting, the operation time is fixed, that is, thedefinite time, depending on the parameters but no longer the voltage.11.4 Frequency measurement and protectionAll the function blocks that use frequency quantity as their input signal share thecommon features related to the frequency measurement algorithm. The frequencyestimation is done from one phase (phase-to-phase or phase voltage) or from thepositive phase sequence (PPS). The voltage groups with three-phase inputs use PPSas the source. The frequency measurement range is 0.6 xFn to 1.5 xFn. When thefrequency exceeds these limits, it is regarded as out of range and a minimum orSection 11 1YHT530004D05 DGeneral function block features838 615 seriesTechnical Manual
