sr Ral alreq op ct L 2pr rI SE E 5 I R RI Iæ ö³ = × × × + +ç ÷è øEQUATION1380 V2 EN-US (Equation 128)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 A24.1.6.2 Non-directional instantaneous and definitive time, phase and residualovercurrent protection M11622-3 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 1,5 I R RI Iæ ö³ = × × × + +ç ÷è øEQUATION1381 V2 EN-US (Equation 129)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 24 1MRK 511 401-UEN ARequirements602 Bay control REC670 2.2 IECApplication manual
