For the undervoltage IDMT mode of operation, the integration of the operate time does not start until the voltage falls below the value of Start value. To cope with discontinuity characteristics of the curve, a specific parameter for saturating the equation to a fixed value is created. The Curve Sat Relative setting is the parameter and it is given in percents compared with Start value. For example, due to the curve equation B, the characteristics equation output is saturated in such a way that when input voltages are in the range from Start value to Curve Sat Relative in percents under Start value, the equation 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 set for it 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 curve characteristics concerning also discontinuities in the curve when the programmable curve equation is used. Thus, the Curve Sat Relative parameter gives another degree of freedom to move the inverse curve on the voltage ratio axis and it effectively sets the maximum operate time for the IDMT curve because for the voltage ratio values affecting by this setting, the operation time is fixed, that is, the definite time, depending on the parameters but no longer the voltage.