Modelling And Evaluating Effect Of Control And Protection Of The Reliability Of Power Distribution System

ABSTRACT

This study deals with modeling and evaluating effect of protection and control on reliability of power distribution systems.

Analysis of the customer failure statistics has shown that the distribution systems make the greatest contribution to the unavailability of power supply to customers. To improve their liability, consideration is being given to increasing the level of automation and control. It is desired that the reliability improvement related to the automation and control could be quantified. The objective of the work is thus to develop analytical models and techniques in order to include the effect of automation and control in the reliability assessment of distribution systems.

Automating a distribution system is an effective means to provide a more reliable and economical system in the fast growing technological world. This paper delivers into automating a system using two- stage restoration (partial automation) and put forward a feeder automation system based on substation automation platform that can be applied to electrical distribution systems for high economic-technical efficiency. Improved reliability is evaluated when feeder automation is applied to distribution. This paper studies three different feeders and decides on the most probable reliable feeder among them.

TABLE OF CONTENTS

TITLE PAGE

APPROVAL PAGE

DEDICATION

ACKNOWELDGEMENT

ABSTRACT

TABLE OF CONTENT

CHAPTER ONE

• INTRODUCTION
• BACKGROUND OF THE PROJECT
• PROBLEM STATEMENT
• AIM/OBJECTIVE OF THE PROJECT
• SIGNIFICANCE OF THE PROJECT
• SCOPE OF THE PROJECT

CHAPTER TWO

LITERATURE REVIEW
2.1      OVERVIEW OF THE STUDY
2.2     RELIABILITY PRINCIPLES
2.3      DIFFERENT TYPES OF INTERRUPTION

2.4      RELIABILITY EVALUATION

2.5      RELIABILITY INDICES
2.6     REVIEW OF RELATED STUDIES

2.7     MAJOR CAUSES OF INTERRUPTION IN DISTRIBUTION SUBSTATION

CHAPTER THREE

3.1      RELIABILITY ASSESSMENT, METRICS AND INDICES

3.2     RELIABILITY ANALYSIS

3.3     NETWORK MODELING

3.4    RELIABILITY INDICES

CHAPTER FOUR

4.1      INTRODUCTION

4.2    TWO STAGE RESTORATION

4.3     CASE STUDY ON DIFFERENT TYPES OF DISTRIBUTION SYSTEMS

4.3.1         Urban feeder modeling and evaluation

4.3.2         Urban feeder modeling and evaluation

4.3.3       Industrial feeder modeling and evaluation

CHAPTER FIVE

5.1       CONCLUSIONS

5.2       RECOMMENDATION

5.2       REFERENCES

CHAPTER ONE

1.0                                                                INTRODUCTION

1.1                                    BACKGROUND OF THE STUDY

Electric power system is basically set up to supply electricity with little or no interruptions to its customers. The number of interruptions that occur while the system performs its intended function is part of what determines the overall reliability of the system. The other factor that determines its reliability is the quality of electricity delivered. Furthermore, the capability of a power system to continuously deliver quality electricity means that the customers are satisfied and the electricity providers are having favorable returns on their investment as they continue their business of supplying electricity. As electricity consumption has become an important factor that affects the drive needed for technology to grow and to facilitate the development of modern society, it is very important therefore to take seriously the issue of reliability of an electric power system.

Generation, transmission and distribution are the three subsystems of an electric power system. At the generating station, electricity is generated and transmitted through the high voltage transmission lines to the distribution substations. The distribution substation system considered covers the electrical system between the substation fed by the subtransmission system and the supply line to the consumers’ meters i.e. 11kV to 0.415kV transformation (Theraja and Theraja, 2005). The distribution substations are usually sited relatively near the customers for effective delivery, monitoring and maintenance of the substation and the customer end and are usually referred to as secondary distribution substation system. Distribution systems basically serve as the link from the distribution substation to the customer. Reliable and safe transfer of electricity to the customers covered by the distribution area is ensured by this system and is the main subject studied in this dissertation.

In terms of reliability evaluation and modeling, generating stations have justifiably received more attention than the other systems because they are individually capital intensive. In addition, in the event of generation inadequacy and generation loss there is usually widespread catastrophic effects on the society and environment. It impacts directly on the whole system and even distribution system will not be able to perform its duty because there will be no electricity to supply to customers. However based on published research work and studies, distribution systems have begun to receive moderate attention compared to past decades. In most cases, when there is disturbance in form of failure which results in outages in the distribution system it affects only the localized territory. Only in few cases does the fault move up in to the system largely as a result of protection failure. Analysis of the customer failure statistics of most electricity companies shows that the distribution system makes the greatest individual contribution to the unavailability of supply to a customer (Gonen, 2014). In effect, the purpose of establishing generating stations and the hurdles overcome to transmit electricity is defeated when it does not get to the user end as a result of distribution system failure. This makes distribution system to be highly important. The distribution systems account for up to 90% of all customer reliability problems, improving distribution reliability is the key to improving customer reliability (Billinton and Jonnavithula, 1996).

Meanwhile, as the main aim of a power system is to meet the electricity needs of the customers and this can only be achieved when the components making up the system are performing their intended function properly for as long as the system is in operation, it is important that the demand for electricity and its supply be properly viewed and included in setting up the system. Therefore, due to its high impact on the cost of electricity and its corresponding effect on customer satisfaction, distribution reliability is very important. However, as in any other viable engineering system, there are challenges that face power distribution system which tends to make the system unreliable. One of these is the issue of serving its main purpose which is to supply quality electricity with little or no interruptions. This problem is inevitable in power systems across the world but the way they are managed is what makes it different from country to country.

Distribution Automation (DA) optimizes a utility’s operations and directly improves the reliability of power distribution system. Utilities using Distribution Automation can achieve significant reduction in outage time for customers with minimal circuit reconfiguration resulting improved reliability indices. The gauge of effectiveness of DA implementations depends on the failure rate of the implemented automation technology.

The Distribution Automation involves the automatic control and protection of electric power distribution feeders thereby improving system reliability which is the main aim of the study.

1.2                 PROBLEM STATEMENT

A distribution substation consists of supply line, power transformer, outgoing feeders, switching device, and protection device to ensure efficient operation. 11/0.415kV substations are common sight on streets and perform the function of distributing power supply to a number of customers in a given neighborhood. The substation is the final stage of electric power distribution system as the circuits leaves the substation at 415V and delivered by three-phase, 4-wire system. The voltage between any two phases is usually lower than the actual 415V and between a phase and neutral is 240Vand most times when measured is less than 230V as a result of voltage drop.

In Nigeria, daily electric power interruption is largely becoming a consistent phenomenon in wide area network of electricity distribution and this is basically due to insufficient power generation, transmission faults and distribution system faults and failures. Unavailability of power supply to customers can occur several times a day and sometimes for weeks and in worst cases for months. There are instances where several interruptions occur in a day especially at the residential loads, which causes untimely failure of home gadgets, darkening of light bulbs, and reduced efficiency and performance of high-power appliances. Damage of electronic devices and burning of light bulbs have also occurred due to over voltages. There are also few cases of deliberate outages due to weather especially rainfall. This is to protect most residential areas from voltage surge that may enter into the power system when lightning occurs owing to the fact that not all residential areas were inspected and certified by the electrical companies when the buildings were completed. Most electrical designs in residential houses are usually not done by professional engineers especially in the middle-class and low-income earner’s settlements.

Considering the fact that the presently installed capacity in Nigeria cannot serve all the customers, it is incumbent that the available power generated be judiciously served with little or no interruptions. That is, when power is generated and available in the system, the distribution subsystem must be up to its task of delivering quality power to the customers. Hence there is the need for the reliability evaluation of a typical distribution substation and its availability.

Integration of new technologies, automation and increased penetration of distributed generation is expected to make improving and even sustaining high reliability standards a complex task.

1.3                 AIM AND OBJECTIVES

The aim of this dissertation is to conduct a reliability evaluation of secondary distribution substation system in Nigeria. The objectives of the study are:

1. To determine the effect of automated control and protection of feeders on the reliability of power distribution system
2. To determine the reliability of electric distribution feeder using distribution automation.

• To reduce the rate of power failure

1. To model and evaluate the reliability of the system in terms of SAIDI, CAIDI, SAIFI and ENS on rural, urban and industrial network.

1.4       SIGNIFICACE OF THE STUDY

It is in management of the power systems that reliability evaluation becomes significant. Reliability evaluation does not in any way make a system more reliable but it helps in system planning and identification of weak components.

Distribution automation is a very effective means to minimize outage durations. Automated and remotely controlled service restoration can eliminate the need to perform switching operations manually and could have a significant effect on the system reliability. In order to enable such an effect to be quantitatively evaluated, this paper examines the inherent features of the control systems and describes the concepts and models which more truly reflect the behavior of the automation and control systems.

1.5       SCOPE OF THE STUDY

Scope of this study covers the modelling and evaluating effect of control and protection of the reliability of power distribution system which involves automating a distribution. In this work, automation of a system using two- stage restoration (partial automation) and put forward a feeder automation system based on substation automation platform was applied to electrical distribution systems for high economic-technical efficiency,