Note:A minimum value of 8% negative phase sequence current is required for successful operation.Since sensitive settings have been employed, we can expect that the element will operate for any unbalancedcondition occurring on the system (for example, during a single pole autoreclose cycle). For this reason, a long timedelay is necessary to ensure co-ordination with other protection devices. A 60 second time delay setting may betypical.The following example was recorded by an IED during commissioning:Ifull load = 500AI2 = 50Atherefore the quiescent I2/I1 ratio = 0.1To allow for tolerances and load variations a setting of 20% of this value may be typical: Therefore set:I2/I1 = 0.2In a double circuit (parallel line) application, using a 40% setting will ensure that the broken conductor protectionwill operate only for the circuit that is affected. A setting of 0.4 results in no pick-up for the parallel healthy circuit.Set I2/I1 Time Delay = 60 s to allow adequate time for short circuit fault clearance by time delayed protections.P14D Chapter 6 - Current Protection FunctionsP14D-TM-EN-8 127
