21.1.6.1 Busbar protection SEMOD129059-4 v6The CT can be of high remanence or low remanence type and they can be usedtogether within the same zone of protection. Each of them must have a rated equivalentlimiting secondary e.m.f. Eal that is larger than or equal to the required rated equivalentlimiting secondary e.m.f. Ealreq below:The high remanence type CT must fulfills n Ra l a lre q f ma x CT L 2pn nI SE E 0.5 I R RI I³ = × × × + +æ öç ÷è øEQUATION1667 V1 EN-US (Equation 90)The low remanence type CT must fulfills n Ra l a lre q f ma x CT L 2pn nI SE E 0.2 I R RI I³ = × × × + +æ öç ÷è øEQUATION1668 V1 EN-US (Equation 91)whereIfmax Maximum primary fundamental frequency fault current on the busbar (A)Ipr The rated primary CT current (A)Isr The rated secondary CT current (A)In The nominal current of the protection IED (A)Rct The secondary resistance of the CT (W)RL The resistance of the secondary wire and additional load (W). The loopresistance containing the phase and neutral wires, must be used for faults insolidly grounded systems. The resistance of a single secondary wire should beused for faults in high impedance grounded systems.SR The burden of an IED current input channel (VA). SR=0.020 VA/channel for Ir=1A and SR=0.150 VA/channel for Ir=5 A.The non remanence type CTCTs of non remanence type (for example, TPZ) can be used but in this case the CTswithin the differential zone must be of non remanence type. They must fulfill the samerequirements as for the low remanence type CTs and have a rated equivalent secondarye.m.f. Eal that is larger than or equal to required secondary e.m.f. Ealreq below:Section 21 1MRK 505 370-UUS ARequirements528 Busbar protection REB670 2.2 ANSIApplication manual
