[ ] =- ×æ öç ÷ç ÷ç ÷ç ÷è ø0.339 0.235tdt s PickupniEQUATION1647 V1 EN (Equation 121)where:Pickupn is the set pickup current for step ntd is set time multiplier for step ni is the measured currentThe RD inverse curve gives a logarithmic delay, as used in the Combiflex protectionRXIDG. The curve enables a high degree of selectivity required for sensitive residualground-fault current protection, with ability to detect high-resistive ground faults. Thecurve is described by equation 122:[ ] = - × ×æ öç ÷è ø5.8 1.35 ln it td PickupnsEQUATION1648 V1 EN (Equation 122)where:Pickupn is the set pickup current for step n,td is set time multiplier for step n andi is the measured currentThe timer will be reset directly when the current drops below the set pickup current levelminus the hysteresis.21.3 Inverse time characteristicsWhen inverse time overcurrent characteristic is selected, the operate timeof the stage will be the sum of the inverse time delay and the set definitetime delay. Thus, if only the inverse time delay is required, it is of utmostimportance to set the definite time delay for that stage to zero.1MRK 502 048-UUS A Section 21Time inverse characteristics739Technical manual
