Lightning Strike On Medium Voltage Distribution And High Voltage Transmission Line In Sierra Leone Using Pscad/Emtdc

ABSTRACT

The continuity of supply in order to fulfil the demand of consumers is of great concern and has become need of an hour. Transient condition due to various possibilities leads to over voltage. This over voltage on various Electrical elements are of great concern and are meant to be studied in depth in order to reduce the chances of power failure and any other faulty conditions. The focus of this paper is to see the effect of lightning on the medium voltage distribution and high voltage transmission line.

Through the analysis of lightning to the harmfulness of the power transmission line, puts forward the specific measures to prevent lightning accidents, improving insulation, installing controllable discharge lightning rod, reducing the tower grounding resistance, adding coupling ground wire and the proper use of send arrester electrical circuit transmission line. And take on the unit measures nearly were compared, statistics and analysis.

In order to design the system PSCAD/EMTDC software was used for designing and further investigation was done with the help of the said software. The consequences of transient over voltages caused due to lightning condition and the effective method for eliminating such condition with the help of surge arrester is discussed under this paper.

TABLE OF CONTENTS

TITLE PAGE

APPROVAL PAGE

DEDICATION

ACKNOWELDGEMENT

ABSTRACT

ABBREVIATIONS

TABLE OF CONTENT

CHAPTER ONE

• INTRODUCTION
• BACKGROUND OF THE STUDY
• PROBLEM STATEMENT
• AIM AND OBJECTIVES OF THE STUDY
• SCOPE OF THE STUDY
• METHODOLOGY
• PROJECT ORGANISATION

CHAPTER TWO

LITERATURE REVIEW

2.0      LITERATURE REVIEW

2.1      REVIEW OF THE STUDY

2.2      REVIEW OF RELATED STUDIES

2.3      PROBLEMS IN THE DISTRIBUTION NETWORK

2.4      THE HARM OF LIGHTNING ON TRANSMISSION LINES

2.5      LIGHTNING TRIP OUT OF TRANSMISSION LINE

2.6      HIGH VOLTAGE TRANSMISSION LINE LIGHTNING PROTECTION MEASURES OF POWER

2.7     LIGHTNING OVERVOLTAGES

2.8      SURGE ARRESTERS

CHAPTER THREE

3.0      METHODOLOGY

3.1       IMPLEMENTATION OF SYSTEM IN PSCAD SOFTWARE

3.2      DESIGNING OF LIGHTNING STRIFE ON THE AC SIDE OF THE TRACTION SUBSTATION AND IN DC SIDE OF TRACTION SUBSTATION WITH THE IMPROVED DC SYSTEM DESIGNED IN PSCAD

CHAPTER FOUR

4.1      SIMULATION AND RESULT

CHAPTER FIVE

• CONCLUSIONS

5.3     REFERENCES

ABBREVIATIONS

CEB                                     Ceylon Electricity Board

DD3                                    Distribution Division 3

kVA                                     kilovolt Ampere

kW                                      kilo Watt

kWh                                   kilo Watt hour

LV                                       Low Voltage

MV                                     Medium Voltage

HV                                      High Voltage

HT                                       High Tension

LT                                        Low Tension

PDS                                    Power Distribution Substation

DT                                       Distribution Transformer

SPD                                    Surge Protection Device

In                                        Nominal Discharge Current

Iimp                                    Impulse current

Uc                                       Continuous Operating Voltage

Up                                       Protection Voltage

BIL                                      Basic Insulation Level

ac                                        Alternating Current

PPM                                   Programmable Polyphase Meter

TDT                                     Time of Day Tariff

CT                                       Current Transformer

MOV                                  Metal oxide varistor

CHAPTER ONE

1.0                                                                                                            INTRODUCTION

1.1                                                                                  BACKGROUND OF THE STUDY

Lightning surges are the major source that causes failure of power electronic equipment in low voltage (LV) power distribution systems, specially for the equipment with low immunity parameters and high sensitivity to surges. The 400/230V low voltage systems are usually affected by lightning mainly by the surges coming through the distribution transformers. In addition to that induced surges or direct strikes on load side could cause damage to distribution substations.

Through the analysis of lightning to the harmfulness of the power transmission line, puts forward the specific measures to prevent lightning accidents, improving insulation, installing controllable discharge lightning rod, reducing the tower grounding resistance, adding coupling ground wire and the proper use of send arrester electrical circuit transmission line. And take on the unit measures nearly were compared, statistics and analysis.

Power utilities are concerned about the possibility of damage to distribution transformers caused by lightning strikes leading power supply failures and other losses including transformer damage, meter equipment damage and damage to the surroundings. Assessment of such occurrences is important in the design of suitable protection schemes and mitigation strategies. The number of incoming surges, their energy content as well as the number and the amplitude of power frequency follow currents determine the level of protection required for each substation. Hence, the assessment of impacts becomes more and more important for the design of lightning protection system.

The methods used in Sri Lanka to assess the impacts of lightning are based on experience of the utility employees or the frequency of protection failures and power supply failures. Specially, when it comes to the low voltage (LV) side, the impacts are not assessed or examined, and in most of the cases, the low voltage side of a substation is not effectively protected from lightning.

At present, the measures of lightning protection of transmission line itself mainly rely on the erection of the overhead ground wire of the tower top, its operation and maintenance work is mainly on the detection and reconstruction of tower grounding resistance. Due to its single lightning protection measures, cannot well meet the requirements of lightning protection. And the installation of coupling ground wire, the implementation of the enhanced insulation level of transmission line lightning protection measures, subject to conditions, some of which cannot be effectively implemented, such as the addition or replacement of insulators for large climbing distance method of synthetic insulator to improve line insulation, to prevent the lightning strikes the tower lightning voltage effect is good, but to prevent lightning the poor effects, and to increase the insulators by the tower head insulation gap and wire of safety distance constraints, so the line insulation  enhancement is limited. And the installation of coupling ground wire is generally applicable to the hilly or mountainous crossing span, can go to the shielding effective protection function to the wire, with such striking distance principle is also reduced exposure arc wire. Effects of traffic transportation factors but the tower of strength, below the safety distance, crossing and line, thus erecting coupling ground wire for the old line is not easy to implement. So the research is not affected by the measures of lightning protection line conditions is very important, will be installing line arrester (needle), reducing tower ground resistance, a comprehensive analysis of the use of, to prevent lightning from their form of targeted starting, truly feasible and can receive the actual effect[Tan Qiong, Li jingLu, Li Zhiqiang, 2011].

In this research the impact of lightning surges particularly on low voltage side of the power distribution substation and high voltage transmission line was analyzed, and the possibilities of using protection mechanism in low voltage side of the power distribution substations were investigated in order to reduce or avoid human and installation damage caused by lightning.

Then by simulating the impact of lightning surges on a low voltage side of power distribution substation using PSCAD software, the behavior of the electrical parameters under occurrence of lightning was studied, and based on the observations and results, design parameters for the protection system were derived.

Finally, based on the findings of investigation, simulation and pilot installation, a standard protection system was deployed, and results were analyzed to check whether the implemented protection system was effective in electrical terms and monetary terms. Continuous monitoring of protected distribution substations has been carried out and the results were produced in the report.

By the results of the assessment of the impacts of lightning on LV side of power distribution substations, it was obvious that huge amount of visible and invisible losses is incurred to Ceylon Electricity Board. The results of the PSCAD simulation clearly shows that the LV side of the power distribution side is affected in the event of lightning strikes. Hence, it was concluded that the LV side of the power distribution side should be protected to eliminate the impacts of lightning strikes. Finally, this research proposes a standard protection mechanism to protect distribution substations from lightning and the effectiveness of the protection system was proved by the results obtained.

1.2                                            PROBLEM STATEMENT

Lightning accident is always an important factor affecting the reliability of the power supply of the electric line to send. Because of the randomness and complexity of lightning activity in the atmosphere, currently the world’s research on knowledge transmission line lightning and many unknown elements. Lightning accident of overhead power transmission line is always a problem of safe power supply, lightning accidents accounted for almost all the accidents of 1/2 or more line. Therefore, how to effectively prevent lightning, lightning damage reduced to more and more by transmission line of the relevant personnel to pay attention[Xu Ying, XU Shi Heng, 2006].

1.3                               AIM AND OBJECTIVES OF THE STUDY

The main aim of this study is to carry a study on Lightning strikes to overhead distribution and transmission lines which are a usual reason for unscheduled supply interruptions in the modern power systems and to create  means of  maintaining failure rates in a low level, providing high power quality and avoiding damages and disturbances, plenty of lightning performance estimation.

In order to verify the effect of lightning over voltages on an DC overhead line power system simulation software was used for understanding the effects of Lightning. With PSCAD software the above mentioned objectives was achieved and studied. The mentioned software is fast as well as accurate when it comes for the designing of high voltage systems.

OBJECTIVE

The objectives of the study are:

1.        To presents an overview of the various types of lightning over-voltages that can arise on overhead power distribution networks, as well as typical voltage waveforms.

2.        To study the effectivenesses of the most important methods for mitigating such over-voltages on MV and LV networks are also discussed

3.        To show clearly that the use of surge arresters can reduce significantly the lightning faults and their use can improve the lightning performance of them.

1.4                                              SCOPE OF THE STUDY

Protecting overhead transmission lines against lightning strokes is one of the most important tasks to safeguard electric power systems, since lightning is a usual cause of faults in overhead lines. The protection of the lines is achieved using shield wires and surge arresters. Shield wires are grounded conductors placed above phases, to intercept lightning strokes, so they cannot directly strike to phase conductors. In order to avoid back flashover, low tower footing resistance is demanded. Surge arresters installation improves the lightning performance of the lines, reducing the outage rate. A surge arrester presents a momentary path to earth, which removes the superfluous charge from the line. The most common types of arresters are the open spark gaps, the SIC arresters with spark gaps and the Metal Oxide surge arresters without gaps. The last type, which is composed of non linear resistors of metal oxide, mainly ZnO without spark gaps, is today the most common used.

The last decades several methodologies and software tools have been presented in the technical literature in order to evaluate the lightning performance of high voltage transmission lines. These are extended from analogue computer methods, Monte Carlo techniques, traveling wave methods and simulation software tools- PSCAD

1.5                                             RESEARCH METHODOLOGY

In the course of carrying this study, numerous sources were used which most of them are by visiting libraries, consulting journal and news papers and online research which Google was the major source that was used.

1.6                                     PROJECT ORGANISATION

The work is organized as follows: chapter one discuses the introductory part of the work,   chapter two presents the literature review of the study,  chapter three describes the methods applied, chapter four discusses the results of the work, chapter five summarizes the research outcomes and the recommendations.