8.9.6 Monitored dataTable 145:NS2PTOC Monitored dataName Type Values (Range) Unit DescriptionNSCURR REAL - A Negative sequencecurrent in primary amps8.9.7 Operation principleThe negative sequence time overcurrent protection for machines (NS2PTOC)function directly measures the amplitude of the negative phase sequence componentof the measured current. NS2PTOC sets the START, ST1 or ST2 outputs active andstarts to count trip time only when the measured negative sequence current value risesabove the set value of parameters I2-1> or I2-2> respectively.To avoid oscillation in the output signals, a certain hysteresis has been included. Forboth steps, the reset ratio is 0.97.Step 1 of NS2PTOC can operate in the Definite Time (DT) or Inverse Time (IDMT)mode depending on the selected value for the CurveType1 parameter. If CurveType1=Definite, NS2PTOC operates with a Definite Time Delay characteristic and ifCurveType1 = Inverse, NS2PTOC operates with an Inverse Time Delaycharacteristic. Step 2 can only operate in the Definite Time (DT) mode. Thecharacteristic defines the time period between the moment when measured negativesequence current exceeds the set start levels in parameter I2-1> or I2-2> until the tripsignal is initiated.Definite time delay is not dependent on the magnitude of measured negative sequencecurrent. Once the measured negative sequence current exceeds the set level, thesettable definite timer t1 or t2 respectively, starts to count and the corresponding tripsignal gets activated after the pre-set definite time delay has elapsed. Reset time indefinite time mode is determined by the setting parameters tResetDef1 or tResetDef2respectively. If NS2PTOC has already started but not tripped and measured negativesequence current drops below the start value, the start outputs remains active for thetime defined by the resetting parameters.A BLOCK input signal resets NS2PTOC momentarily.When the parameter CurveType1 is set to Inverse, an inverse curve is selectedaccording to selected value for parameter K1. The minimum trip time setting ofparameter t1Min and reset time parameter ResetMultip1 also influence step operation.However, to match the heating characteristics of the generator, the reset time isdepending on the setting of parameter K1, which must be set according to thegenerators negative sequence current capacity.22K I t=EQUATION2112 V1 ENSection 8 1MRK 502 048-UEN ACurrent protection246Technical manual
