8.2.7.2 Time delayThe time delay for step 1 can be either definite time delay (DT) or inverse timedelay (IDMT). Step 2 is always definite time delay (DT). For the inverse timedelay three different modes are available:• inverse curve A• inverse curve B• inverse curve CThe type A curve is described as:kt U UU= - >æ öç ÷>è øIEC09000051 V1 EN (Equation 70)The type B curve is described as:2.0480 0.03532 0.5ktU UU×= -- >× ->æ öç ÷è øIECEQUATION2287 V1 EN (Equation 71)The type C curve is described as:3.0480 0.03532 0.5ktU UU×= +- >× ->æ öç ÷è øIECEQUATION2288 V1 EN (Equation 72)The highest phase (or phase-to-phase) voltage is always used for the inverse timedelay integration, see Figure 117. The details of the different inverse timecharacteristics are shown in section "Inverse time characteristics"1MRK 502 034-UEN - Section 8Voltage protection227Technical Manual
