7.2.7.2 Time delayThe time delay for step 1 can be either definite time delay (DT) or inverse time delay(IDMT). Step 2 is always definite time delay (DT). For the inverse time delay threedifferent 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 37)The type B curve is described as:2.0480 0.03532 0.5ktU UU×= -- >× ->æ öç ÷è øIECEQUATION2287 V1 EN (Equation 38)The type C curve is described as:3.0480 0.03532 0.5ktU UU×= +- >× ->æ öç ÷è øIECEQUATION2288 V1 EN (Equation 39)The highest phase (or phase-to-phase) voltage is always used for the inverse timedelay integration, see Figure 72. The details of the different inverse timecharacteristics are shown in section "Inverse time characteristics".1MRK 511 287-UEN A Section 7Voltage protection167Technical manual
