detected, the operate timer is reset and the saved values of start time andintegration are cleared.Inv. curve BThe inverse time equation for curve type B is:t s kIIIIrSr[ ] = − 22 2GUID-805DCB50-71D2-4721-830B-3343E1A5500B V1 EN (Equation 71)t[s] Operate time in secondskMachine time MultI2 Negative-sequence currentIS SetStart valueIr SetRated currentIf the fault disappears, the negative-sequence current drops below the Start valuesetting and the START output is deactivated. However, the function does not resetinstantaneously, but instead it depends on the equation or the Cooling time setting.The timer can be reset in two ways:• With a drop in the negative-sequence current below start value, the subtractionin the denominator becomes negative and the cumulative sum starts todecrease. The decrease in the sum indicates the cooling of the machine and thecooling speed depends on the value of the negative-sequence current. If thesum reaches zero without a fault being detected, the accumulation stops andthe timer is reset.• If the reset time set through the Cooling time setting elapses without a faultbeing detected, the timer is reset.The reset period thus continues for a time equal to the Cooling time setting or untilthe operate time decreases to zero, whichever is less.4.4.4.6 ApplicationIn a three-phase motor, the conditions that can lead to unbalance are singlephasing, voltage unbalance from the supply and single-phase fault. The negativesequence current damages the motor during the unbalanced voltage condition, andtherefore the negative sequence current is monitored to check the unbalancecondition.When the voltages supplied to an operating motor become unbalanced, the positive-sequence current remains substantially unchanged, but the negative-sequencecurrent flows due to the unbalance. For example, if the unbalance is caused by an1YHT530004D05 D Section 4Protection functions615 series 463Technical Manual
