ABBDistributed busbar protection REB500 including line and transformer protection Product Guide

Centralized installation

19" mounting plates with up to three bay units 

each, and the central processing unit are 

mounted according to the size of the busbar 

system in one or more cubicles (see Fig. 23). 

A centralized installation is the ideal solution 

for upgrading existing stations, since very

little additional wiring is required and compared with older kinds of busbar protection, 

much more functionality can be packed into 

the same space.

Combined centralized and distributed 

installation

Basically, the only difference between a distributed and a centralized scheme is the 

mounting location of the bay units and therefore it is possible to mix the two philosophies

Distributed busbar protection REB500

including line and transformer protection

Page 7 

System design Bay unit (500BU03)

The bay unit (see Fig. 4) is the interface 

between the protection and the primary system process comprising the main CTs, isolators and circuit-breaker and performs the 

associated data acquisition, pre-processing, 

control functions and bay level protection 

functions. It also provides the electrical insulation between the primary system and the 

internal electronics of the protection.

The input transformer module contains four 

input CTs for measuring phase and neutral 

currents with terminals for 1 A and 5 A. Additional interposing CTs are not required, 

because any differences between the CT 

ratios are compensated by appropriately configuring the software of the respective bay 

units.

Optional input transformer module also contains five input voltage transformers for the 

measurement of the three-phase voltages and 

two busbar voltages and recording of voltage 

disturbances or 6 current transformers for 

transformer differential protection. (see 

Fig. 12).

In the analog input and processing module, 

the analog current and voltage signals are 

converted to numerical signals at a sampling 

rate of 48 samples per period and then 

numerically preprocessed and filtered accordingly. Zero-sequence voltage and zero-current 

signals are also calculated internally. The Process data are transferred at regular intervals 

from the bay units to the central processing 

unit via the process bus.

Every bay unit has 20 binary inputs and 16 

relay outputs. The binary I/O module detects 

and processes the positions of isolators and 

couplers, blocking signals, starting signals, 

external resetting signals, etc. The binary 

input channels operate according to a patented pulse modulation principle in a nominal 

range of 48 to 250 V DC. The PC-based HMI 

program provides settings for the threshold 

voltage of the binary inputs. All the binary output channels are equipped with fast operating 

relays and can be used for either signaling or 

tripping purposes (see contact data in Table 

8).

A software logic enables the input and output 

channels to be assigned to the various functions. A time stamp is attached to all the data 

such as currents, voltages, binary inputs, 

events and diagnostic information acquired by 

a bay unit.

Where more binary and analog inputs are 

needed, several bay units can be combined to 

form a feeder/bus coupler bay (e.g. a bus coupler bay with CTs on both sides of the bus-tie 

breaker requires two bay units).

The bay unit is provided with local intelligence 

and performs local protection (e.g. breaker 

failure, end fault, breaker pole discrepancy), 

bay protection (Main 2 or back-up bay protections) as well as the event and disturbance 

recording. 

Distributed busbar protection REB500

including line and transformer protection

In the event that the central unit is out of operation or the optical fiber communication is disrupted an alarm is generated, the bay unit will 

continue to operate, and all local and bay protection as well as the recorders (event and 

disturbance) will remain fully functional 

(stand-alone operation).

The hardware structure is based on a closed, 

monolithic casing and presented in two 

mounting solutions:

• Without local HMI: ideal solution if convenient access to all information via the central unit or by an existing substation 

automation system is sufficient.

• With local HMI and 20 programmable LEDs 

(Fig. 5): ideal solution for distributed and 

kiosk mounting (AIS), since all information 

is available in the bay.

For the latter option it is possible to have the 

HMI either built in or connected via a flexible 

cable to a fixed mounting position (see

Fig. 28).

In the event of a failure, a bay unit can be easily replaced. The replacement of a bay unit 

can be handled in a simple way. During system start-up the new bay unit requests its 

address, this can be entered directly via its 

local HMI. The necessary setting values and 

configuration data are then downloaded automatically.

Additional plug-and-play functionality

Bay units can be added to an existing