ABBDistributed busbar protection REB500 including line and transformer protection Product Guide

REB500 system in a simple way.

Fig. 5 Bay unit

Central unit (500CU03)

The hardware structure is based on standard 

racks and only a few different module types 

for the central unit (see Fig. 4).

The modules actually installed in a particular 

protection scheme depend on the size, complexity and functionality of the busbar system.

A parallel bus on a front-plate motherboard 

establishes the interconnections between the 

modules in a rack. The modules are inserted 

from the rear.

The central unit is the system manager, i.e. it 

configures the system, contains the busbar 

replica, assigns bays within the system, manages the sets of operating parameters, acts as 

process bus controller, assures synchronization of the system and controls communication with the station control system.

The variables for the busbar protection function are derived dynamically from the process 

data provided by the bay units.

The process data are transferred to the central processor via a star coupler module. Up to 

10 bay units can be connected to the first central processor and 10 to the others. Central 

processors and star coupler modules are 

added for protection systems that include 

more than 10 bay units. In the case of more 

than 30 bay units, additional casings are 

required for accommodating the additional 

central processors and star coupler modules 

required.

All modules of the central unit have a plugand-play functionality in order to minimize 

module configuration.

One or two binary I/O modules can be connected to a central processing unit.

The central unit comprises a local HMI with 20 

programmable LEDs (Fig. 6), a TCP/IP port 

for very fast HMI500 connection within the 

local area network.

Distributed busbar protection REB500

including line and transformer protection

Page 9 

Functionality Busbar protection 

The protection algorithms are based on two 

well-proven measuring principles which have 

been applied successfully in earlier ABB lowimpedance busbar protection systems:

• a stabilized differential current measurement

• the determination of the phase relationship 

between the feeder currents (phase comparison)

The algorithms process complex current vectors which are obtained by Fourier analysis 

and only contain the fundamental frequency 

component. Any DC component and harmonics are suppressed.

The first measuring principle uses a stabilized 

differential current algorithm.

The currents are evaluated individually for 

each of the phases and each section of busbar (protection zone).

where N is the number of feeders. The following two conditions have to be accomplished 

for the detection of an internal fault:

where

kst stabilizing factor

kst max stabilization factor limit. 

A typical value is kst max = 0.80

IK min differential current pick-up value

The above calculations and evaluations are 

performed by the central unit.

The second measuring principle determines 

the direction of energy flow and involves comparing the phases of the currents of all the 

feeders connected to a busbar section.

The fundamental frequency current phasors 

1..n (5) are compared. In the case of an internal fault, all of the feeder currents have almost the same phase angle, while in normal 

operation or during an external fault at least 

one current is approximately 180° out of 

phase with the others

The algorithm detects an internal fault when 

the difference between the phase angles of all 

the feeder currents lies within the tripping 

angle of the phase comparator (see Fig. 8).

Distributed busbar protection REB500

including line and transformer protection

The task of processing the algorithms is 

shared between the bay units and the central 

processing unit. Each of the bay units continuously monitors the currents of its own fee-der, 

preprocesses them accordingly and then filters the resulting data according to a Fourier 

function. The analog data filtered in this way 

are then transferred at regular intervals to the 

central processing unit running the busbar 

protection algorithms.

Depending on the phase-angle of the fault, 

the tripping time varies at Idiff/Ikmin5 between 20 and 30 ms including the auxiliary 

tripping relay.

Optionally, the tripping signal can be interlocked by a current or voltage release criteria 

in the bay unit that enables tripping only when 

a current above a certain minimum is flowing, 

respectively the voltage is below a certain 

value.

Breaker failure protection

The breaker failure functions in the bay units 

monitor both phase currents and neutral current independently of the busbar protection. 

They have two timers with individual settings.

Operation of the breaker failure function is 

enabled either:

• internally by the busbar protection algorithm (and, if configured, also by the internal line protection, overcurrent or pole 

discrepancy protection features) of the bay 

level

• externally via a binary input, e.g. by the line