a This factor depends on the design of the protection function and can be afunction of the primary DC time constant of the close-in fault current.k This factor depends on the design of the protection function and can be afunction of the primary DC time constant of the fault current for a fault at the setreach of zone 1.The a- and k-factors have the following values for the different types of distancefunction:High speed distance: (ZMFPDIS and ZMFCPDIS)Quadrilateral characteristic:a = 1 for primary time constant Tp £ 400 msk = 3 for primary time constant Tp £ 200 msMho characteristic:a = 2 for primary time constant Tp £ 400 ms (For a = 1 the delay in operationdue to saturation is still under 1.5 cycles)k = 3 for primary time constant Tp £ 200 msQuadrilateral distance: (ZMQPDIS, ZMQAPDIS and ZMCPDIS, ZMCAPDIS andZMMPDIS, ZMMAPDIS)a = 1 for primary time constant Tp £ 100 msa = 3 for primary time constant Tp > 100 and £ 400 msk = 4 for primary time constant Tp £ 50 msk = 5 for primary time constant Tp > 50 and £ 150 msMho distance: (ZMHPDIS)a = 1 for primary time constant Tp £ 100 msa = 3 for primary time constant Tp > 100 and £ 400 msk = 4 for primary time constant Tp £ 40 msk = 5 for primary time constant Tp > 40 and £ 150 ms22.1.6.3 Breaker failure protection M11621-3 v5The CTs must have a rated equivalent limiting secondary e.m.f. Eal that is largerthan or equal to the required rated equivalent limiting secondary e.m.f. Ealreqbelow:sr Ral alreq op ct L 2pr rI SE E 5 I R RI Iæ ö³ = × × × + +ç ÷è øEQUATION1380 V2 EN-US (Equation 138)where:Iop The primary operate value (A)Ipr The rated primary CT current (A)Isr The rated secondary CT current (A)Ir The rated current of the protection IED (A)Rct The secondary resistance of the CT (W)RL The resistance of the secondary cable and additional load (W). The loop resistancecontaining the phase and neutral wires, must be used for faults in solidly earthed systems.The resistance of a single secondary wire should be used for faults in high impedanceearthed systems.SR The burden of an IED current input channel (VA). SR=0.020 VA/channel for Ir=1 A andSR=0.150 VA/channel for Ir=5 ASection 22 1MRK 505 393-UEN BRequirements430 Line differential protection RED650 2.2 IECApplication manual
