P12x/EN T/Eb6 - Schneider - error

P12x/EN AP/Eb6Application GuidePage 78/78MiCOM P120/P121/P122/P123In addition, note that phase error of the applied core balance current transformer should beless than 90 minutes at 10% of rated current and less than 150 minutes at 1% of ratedcurrent.Abbreviations used in the previous formula are explained below:Where:VK = Required CT knee-point voltage (volts),Ifn = Maximum prospective secondary earth fault current (amps),Ifp = Maximum prospective secondary phase fault current (amps),Icn = Maximum prospective secondary earth fault current or 31 times I> setting(whichever is lower) (amps),Icp = Maximum prospective secondary phase fault current or 31 times I> setting(whichever is lower) (amps),Isn = Stage 2 & 3 Earth Fault setting (amps),Isp = Stage 2 and 3 setting (amps),RCT = Resistance of current transformer secondary winding (ohms)Rrp = Impedence of relay phase current input at 30InRL = Resistance of a single lead from relay to current transformer (ohms),Rrp = Impedance of relay phase current input at 30In (ohms),Rrn = Impedance of the relay neutral current input at 30In (ohms).34.4 High Impedance Restricted Earth Fault ProtectionThe High Impedance Restricted Earth Fault element shall remain stable for through faultsand shall operate in less than 40ms for internal faults provided that following equations aremet when determining CT requirements and the value of the associated stabilising resistor:Rs =V K ≥[K * (If) * (R CT + 2R L )] / I S4 * Is * RsK = 1 for Vk/Vs less or equal to 16K = 1.2 for Vk/Vs greater than 16Where:V K = Required CT knee-point voltage (volts),Rs = Value of Stabilising resistor (ohms),If = Maximum through fault current level (amps).V K = CT knee point voltage (volts),I S = Current setting of REF element (amps),R CT = Resistance of current transformer secondary winding (ohms),R L = Resistance of a single lead from relay to current transformer (ohms).