CHAPTER 11
EMNG 3025 Transmission & Distribution
Chapter Eleven: Substation Bus Scheme
Substation Bus Scheme Overview
Definition: A Substation Bus Scheme refers to a systematic arrangement of bus bars within an electrical substation where bus bars act as nodal points that connect various incoming and outgoing circuits.
Introduction: Substation bus schemes are essential to the reliability and efficiency of power delivery in electric systems. They employ different methods to connect electrical circuits in the power system to ensure efficient electrical power transfer.
Objectives of Study
To provide a concrete definition of Substation Bus Schemes.
To introduce the concept of Substation Bus Schemes.
To explore the various types of Substation Bus Schemes.
To discuss the location and significance of substations.
Importance of Bus Bars in Substations
Bus bars are crucial components in substations as they serve as the central points connecting different electrical feeders.
Their role is to facilitate the handling of electrical circuits reliably and efficiently, thereby maintaining the stability and integrity of power systems.
Types of Substation Bus Schemes
The main substation bus schemes include:
Single Bus Scheme
Double Bus–Double Breaker Scheme
Main-and-Transfer Bus Scheme
Double Bus–Single Breaker Scheme
Ring Bus Scheme
Breaker-and-a-Half Scheme
Single Bus-Bar Scheme
Definition: This is the simplest type of substation bus scheme.
Components:
It consists of a single set of bus bars connected to generators, transformers, and load feeders.
All feeders are interconnected through circuit breakers and a set of isolators.
Characteristics:
Simple and straightforward design, suitable for basic power loads.
Double Bus Bar Scheme
Overview: This scheme features two bus bars - a main bus bar and a spare bus bar.
Connection: Each incoming line and feeder can connect to either bus bar using circuit breakers and isolators.
Advantages:
Offers high flexibility and reliability due to the redundancy provided by the spare bus bar, allowing continuous operations even during maintenance or faults.
Main and Transfer Bus Bar Scheme
Description: This scheme is an extension of the single bus bar scheme, incorporating an additional transfer bus.
Functionality:
A tie circuit breaker connects the main bus to the transfer bus.
Normal operations involve all circuits being connected to the main bus.
If a circuit breaker needs maintenance, the tie circuit breaker can be closed to connect the main and transfer bus, allowing uninterrupted service.
Double Bus-Single Breaker Scheme
Connection Strategy:
Every circuit connects to both buses.
Some configurations may allow half of the circuits to operate on each bus independently.
Limitation:
Failure of a bus or circuit breaker can lead to service loss for half of the connected circuits, highlighting the need for careful system design.
Ring Bus Scheme
Configuration:
Circuit breakers are arranged in a ring, with circuits connected between these breakers.
Operational Protocol:
During normal operations, all breakers are closed.
In case of a circuit fault, two breakers associated with the faulty circuit will trip, providing a protective mechanism.
Maintenance can occur on the ring without service interruptions, as lines remain in service even when the ring is temporarily broken.
Breaker-and-Half Scheme
Description: This scheme structures connections such that two circuits interface with three circuit breakers, hence the name 'Breaker-and-Half'.
Normal Operation:
Under standard conditions, all breakers are closed, keeping both bus bars energized.
Fault Tolerance:
If a circuit fault occurs, two adjacent circuit breakers will trip, allowing for continued service to the unaffected circuits.
In the event of a bus bar fault, only the breakers adjacent to the bus bars will trip, ensuring that no circuit loses power due to a bus fault.