Bus zone IProtection zone IIBus‐tie breakerCTsBus zone IIProtection zone II12000060-IEC18000274-1-en.vsdIEC18000274 V1 EN-USFigure 32: Bus-tie breaker (closed) and one set of CTsBus zone IProtection zone ICTs 1Bus zone IIProtection zone IICTs 2Bus‐tie breaker12000061-IEC18000275-1-en.vsdIEC18000275 V1 EN-USFigure 33: Bus-tie breaker (closed) and two sets of CTs9.2.1.3 Short-circuiting of a CT GUID-B263A94F-7291-41BF-AF2D-2C131A16B951 v2The bus-tie breaker is excluded from the measurement when bus zones are also connected byan isolator, for example:1. Coupled transversely by parallel isolators2. Coupled longitudinally by parallel longitudinal isolatorsConcerning 1. Coupled transversely by parallel isolatorsThe current flowing via the coupling between the busbars (Figure 34) is represented in thebusbar protection by two current vectors of opposite direct (V+, V-). The vectors are assignedaccording to measuring system S1 (vector V+) and S2 (vector V-).When switching a feeder from busbar S1 to S2 (load switching), both isolators Q1 and Q2 areclosed for a certain time, that is, busbars S1 and S2 are directly connected.• During this time, measuring systems S1 and S2 are connected to form one commonmeasuring system (S1/S2) to match the primary system.• For the same time the bus-tie breaker measurement is blocked, that is, the two vectors V+and V- are excluded.The reasons for blocking the bus-tie breaker measurement are the following:While the busbar sections are in parallel (Q1 and Q2 closed), the current (Ik1) of any fault thatoccurs will divide into a part flowing directly (Ik11) and a part flowing via the bus-tie breaker(Ik12). If included, the bus-tie breaker current (Ik12) would be represented by the two vectorswith opposing directions (V+, V-) and assigned to the common measuring system (S1/S2). Theconsequence would be that the:Section 9 1MRK 505 399-UEN BSpecial applications of BBP58 Distributed busbar protection REB500Application manual© Copyright 2019 ABB. All rights reserved
