t s k AB U UU CDE = ⋅× − >> − +GUID-6E9DC0FE-7457-4317-9480-8CCC6D63AB35 V2 EN (Equation 84)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 multiplier11.3.1.3 IDMT curve saturation of overvoltage protectionFor the overvoltage IDMT mode of operation, the integration of the operate time doesnot start until the voltage exceeds the value of Start value. To cope with discontinuitycharacteristics of the curve, a specific parameter for saturating the equation to a fixedvalue is created. The Curve Sat Relative setting is the parameter and it is given inpercents compared to Start value. For example, due to the curve equation B and C, thecharacteristics equation output is saturated in such a way that when the input voltagesare in the range of Start value to Curve Sat Relative in percent over Start value, theequation uses Start value * (1.0 + Curve Sat Relative / 100 ) for the measured voltage.Although, the curve A has no discontinuities when the ratio U/U> exceeds the unity,Curve Sat Relative is also set for it. The Curve Sat Relative setting for curves A, B andC is 2.0 percent. However, it should be noted that the user must carefully calculate thecurve characteristics concerning the discontinuities in the curve when theprogrammable curve equation is used. Thus, the Curve Sat Relative parameter givesanother degree 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 the voltageratio values affecting by this setting, the operation time is fixed, that is, the definitetime, depending on the parameters but no longer the voltage.11.3.2 IDMT curves for undervoltage protectionIn the inverse-time modes, the operate time depends on the momentary value of thevoltage, the lower the voltage, the faster the operate time. The operate time calculationor integration starts immediately when the voltage goes below the set value of the Startvalue setting and the START output is activated.The OPERATE output of the component is activated when the cumulative sum of theintegrator calculating the undervoltage situation exceeds the value set by the inverse-Section 11 1MRS758755 AGeneral function block features752 REC615 and RER615Technical Manual
