The maximum prolongation principle (see Section 5.2) achieves a very good approximationwith respect to the real and imaginary components (amplitude and phase-angle) of theoriginal current signal.8.3 Restrained amplitude comparison GUID-C63404B3-74ED-4F30-B8F4-102269DF75CB v1The restrained amplitude comparison function is basically a differential current measurementIdiff with the sum of all the current amplitudesIrstnt acting in a restraining sense.8.3.1 Amplitude comparison GUID-76851268-2E64-477C-BE35-6734072EE485 v1The differential currentIdiff is the geometric sum of all the currents flowing towards and awayfrom the busbar. It is calculated from the fundamental components of the currents conductedby the feeders and the bus-tie breakers: 1 1Re ImN Ndiff Ln Lnn nI I j I IECEQUATION18080 V1 EN-US (Equation 8)8.3.2 Restraint current GUID-C73AE084-EE73-4593-8320-DB35B2AD916E v1The stability factork is derived from the restraint currentIrstnt which is the sum of the currentsof the various feeders. The following is an example for the determination ofIrstnt for phase L∈{L1,L2,L3}: Nrstnt Ln Lnn 1I Re I j Im I IECEQUATION18081 V1 EN-US (Equation 9)The stability factork thus becomes: 1 11Re ImRe ImN NLn Lnn ndiffNrstnt Ln LnnI j IIk I I j I IECEQUATION18082 V1 EN-US (Equation 10)Where,k stability factor per protection zoneI_Ln fundamental component after the Fourier filter in phaseL of feedernN total number of feeders and bus-tie breakers per protection zone1MRK 505 399-UEN B Section 8Busbar protectionDistributed busbar protection REB500 41Application manual© Copyright 2019 ABB. All rights reserved
