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Home / Download Center / Electrical Engineering Books and Technical Guides / Relay control and protection guides / How to design Bay Control Unit (BCU) in a substation automation system

Bay Control Unit (BCU)

The main function of BCU is to monitor the whole system remotely away. The status of primary equipment or auxiliary devices can be obtained from auxiliary contacts. Therefore it is possible to detect and indicate both the OPEN and CLOSED position or a fault or intermediate circuit-breaker or auxiliary contact position.

How to design Bay Control Unit (BCU) in a substation automation system
How to design Bay Control Unit (BCU) in a substation automation system (photo credit: Edvard Csanyi)

In addition to the monitoring functions, BCU also support all control functions that are required for operating medium-voltage or high-voltage substations. The main application is reliable control of switching and other processes.

With integrated logic, the user can set, via a graphic interface, specific functions for the automation of switchgear or substation. Functions are activated via function keys, binary input or via communication interface.

Switching authority is determined according to parameters, communication or by Local/Remote switch. If it is set to “LOCAL” , only local switching operations are possible. The following sequence of switching authority is laid down: “LOCAL”; DIGSI PC program, “REMOTE”.

Every switching operation and change of breaker position is kept in the status indication memory.

The switch command source, switching device, cause (i.e. spontaneous change or command) and result of a switching operation are retained.

Eidbabiker Single Line Diagram
Eidbabiker Single Line Diagram

Command processing

All the functionality of command processing is offered. This includes the processing of single and double commands with or without feedback, sophisticated monitoring of the control hardware and software, checking of the external process.

Control actions using functions such as runtime monitoring and automatic command termination after output are also included.

IEC 61850

The International Electrotechnical Committee (IEC) Technical Committee (TC) 57 was established in 1964 because of an urgent need to produce international standards in the field of communications between the equipment and systems for the electric power process, including telecontrol, teleprotection, and all other telecommunications that control the electric power system.

The new communication standard IEC 61850 is introduced in Substation Automation replacing almost all traditional wires by serial communication. Based on mainstream communication means like Ethernet it provides a high flexibility regarding communication architectures.

The scope of the standard IEC 61850 is to support the communication for all functions being performed in substation.

The goal of the standard is interoperability. Up to now, the communication for SA was based on proprietary serial communication mechanisms complemented with conventional parallel copper wiring.

The latter is used especially from the process to the switchgear. With the advent of IEC 61850 there is a comprehensive global standard for all communication needs in the substation being introduced now.

Title:Design of a Bay Control Unit (BCU) in a substation automation system – Thesis – Azza Siraj El-Dien M. El-Amien at Department of Electrical And Electronic Engineering; Faculty of Engineering; University of Khartoum
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Design of a Bay Control Unit (BCU) in a substation automation system - Thesis
Design of a Bay Control Unit (BCU) in a substation automation system – Thesis

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  1. mosayeb
    Dec 20, 2021

    Hi dear; can we use protection function of BCU relay in DCS substations?
    Do you have any related experience?
    Is it routine?
    I mean may it lead to a protection malfunction?

  2. arun dharmik
    Aug 17, 2021


  3. Murat Mamati
    Sep 27, 2019

    e.mail contact adres please ?

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