In inverse-time modes, the operation time depends on the momentary value of the current: the higher the current, the faster the operation time. The operation time calculation or integration starts immediately when the current exceeds the set Start value and the START output is activated.
The OPERATE output of the component is activated when the cumulative sum of the integrator calculating the overcurrent situation exceeds the value set by the inverse-time mode. The set value depends on the selected curve type and the setting values used. The curve scaling is determined with the Time multiplier setting.
- The Minimum operate time setting defines the minimum operating time for the IDMT curve, that is, the operation time is always at least the Minimum operate time setting.
- Alternatively, the IDMT Sat point is used for giving the leveling-out point as a multiple of the Start value setting. (Global setting: ). The default parameter value is 50. This setting affects only the overcurrent and earth-fault IDMT timers.
The grey zone in Figure 3 shows the behavior of the curve in case the measured current is outside the guaranteed measuring range. Also, the maximum measured current of 50 x In gives the leveling-out point 50/2.5 = 20 x I/I>.