Design And Construction Of An Underground Cable Fault Detector

ABSTRACT

The underground cable system is a common practice followed in many urban areas. While a fault occurs for some reason, at that time the repairing process related to that particular cable is difficult due to not knowing the exact location of the cable fault. The proposed system is to find the exact location of the fault. The project uses the standard concept of Ohms law i.e., when a low DC voltage is applied at the feeder end through a series resistor (Cable lines), then current would vary depending upon the location of fault in the cable. In case there is a short circuit (Line to Ground), the voltage across series resistors changes accordingly, which is then fed to inbuilt ADC of PIC controller to develop precise digital data for display in kilometers. The project is assembled with a set of resistors representing cable length in KM’s and fault creation is made by a set of switches at every known KM to cross check the accuracy of the same. The fault occurring at a particular distance and the respective phase is displayed on a LCD interfaced to the PIC controller.

TABLE OF CONTENTS

COVER PAGE

TITLE PAGE

APPROVAL PAGE

DEDICATION

ACKNOWELDGEMENT

ABSTRACT

CHAPTER ONE

INTRODUCTION

1.1      BACKGROUND OF THE PROJECT

• PROBLEM STATEMENT
• AIM AND OBJECTIVES OF THE PROJECT
• PROJECT EXPECTATION
• CAUSES OF FAULTS IN UNDERGROUND CABLES
• TYPES OF FAULT IN UNDERGROUND CABLES
• ADVANTAGES OF UNDERGROUND CABLE SYSTEM
• DISADVANTAGES OF UNDERGROUND CABLE SYSTEM

CHAPTER TWO

• LITERATURE REVIEW
• REVIEW OF THE STUDY
• REVIEW OF CABLE FAULTS
• REVIEW OF UNDERGROUND CABLE FAULTS
• DIFFERENT TYPES OF FAULT
• ELECTRICAL FAULT CALCULATION
• IMPEDANCE NOTATION OF ELECTRICAL POWER SYSTEM

CHAPTER THREE

METHODOLOGY

• SYSTEM BLOCK DIAGRAM
• BLOCK EXPLANATION
• ALGORITHM AND FLOWCHART
• SYSTEM CIRCUIT DIAGRAM
• CIRCUIT DESCRIPTION
• OPERATIONAL EXPLANATION OF THE CIRCUIT

CHAPTER FOUR

• TESTING AND RESULTS
• CONSTRUCTION PROCEDURE AND TESTING ANALYSIS
• CASING AND PACKAGING
• ASSEMBLING OF SECTIONS
• TESTING OF SYSTEM OPERATION
• INSTALLATION OF THE COMPLETED DESIGN
• OPERATING PROCEDURE
• OBSERVATION AND RESULT

CHAPTER FIVE

• CONCLUSION
• REFERENCES

CHAPTER ONE

1.1                                                        INTRODUCTION

More than 3 million miles of electrical cables are strung overhead across the country. Add to that at least 180 million telephone and cable TV lines, and it’s no wonder hurricanes, tornadoes, fires and ice storms are wreaking havoc on the electrical systems each year, causing utility outages that last days, weeks and longer. Power outages over extended periods present major health and safety concerns and economic losses. Concerns about the reliability of overhead lines, increases in their maintenance and operating costs, and issues of public safety and quality-of-life are leading more and more utilities and municipalities to the realization that converting overhead distribution lines to underground is the best way to provide high-quality service to their customers. For utility companies, undergrounding provides potential benefits through reduced operations and maintenance (O&M) costs, reduced tree trimming costs, less storm damage and reduced loss of day-to-day electricity sales when customers lose power after storms. Creative funding options are often available to make the goal of undergrounding a reality. The underground cable system is very important for distribution especially in metropolitan cities, airports and defense service.

One of the major limitations of underground cables is the fault detection. Since the cables are laid under the surface (directly or inside pressurized ducts), the visual methods of inspection don’t work effectively. This is not the case in Overhead Lines. In order to identify the faults in the cable, a device was design which does the work, which is the course of this work.

1.2                                                  PROBLEM STATEMENT

Till the last decades, a million miles of cables are threaded in the air across the country. But currently, it is laid in the underground, which is larger than an earlier method. Because, underground cables are not affected by any adverse weather conditions like pollution, heavy rainfall, snow, and storm, etc. But, when any problem occurs in cable, it is very difficult to find the exact location of the fault due to not knowing the exact location of the cable. Day by day, the world is becoming digitized so the project is proposed to find the location of the fault in a digital way. When the fault occurs, the process of repairing related to that particular cable is very difficult. The fault of the cable mainly occurs due to many reasons. They are: inconsistent, any defect, weakness of the cable, insulation failure, and breaking of the conductor. To overcome this problem, an underground cable fault distance locator, used to find the location of the fault for underground cable was built.

1.3                                          AIM AND OBJECTIVES

AIM

The objective of this project is to determine the distance of underground cable fault from base station in kilometers USING a PIC microcontroller.

OBJECTIVES

The objectives are:

• To find out the location of fault occurred in any phase in the underground cable system
• To eliminate human stress.
• To make a programmed counter to count the number of faults, respectively, occurring in each phase during the life span of the underground cable so that damaged cable can be replaced with a new cable of same length and characteristics after reaching the limit of predefined number of faults
• To study different kinds of underground cable fault
• Display the fault from kilometers apart via LCD

1.4                                                PROJECT EXPECTATIONS

The expectation of this work is to build fault sensing circuit with a low voltage regulated power supply is performed. Here, the fault sensing circuit is developed using a combination of resistors and switches for each phase that is an equivalent model of an underground cable line, is interfaced to microcontroller with the help of internally inbuilt ADC for providing the digital data to microcontroller.

1.5                          CAUSES OF FAULTS IN UNDERGROUND CABLES

Most of the faults occur when moisture enters the insulation. The paper insulation provided inside the cable is hygroscopic in nature. Other causes include mechanical injury during transportation, laying process or due to various stresses encountered by the cable during its working life. The lead sheath is also damaged frequently, usually due to the actions of atmospheric agents, soil and water or sometimes due to the mechanical damage and crystallization of lead through vibration.

1.6                            TYPES OF FAULT IN UNDERGROUND CABLES

The most common types of fault that occur in underground cables are,

1. Open circuit
2. Short circuit
3. Earth

1.                    Open circuit fault

When there is a break in the conductor of a cable, it is called open-circuit fault. The open-circuit fault can check by a megger. For this purpose, the three conductors of the 3 core cable at far end are shorted and earthed. Then resistance between each conductors and earth is measured by a megger. The megger will indicate zero resistance in the circuit of the conductor that is not broken. However if a conductor is broken the megger will indicate an infinite resistance.

2.                    Short-circuit fault

When two conductors of a multi core cable come in electrical contact with each other due to insulation failure, it is so called as short-circuit fault. Megger can also be used to check this fault. For this the two terminals of a megger are connected to any two conductors. If the megger gives a zero reading it indicates short-circuit fault between these conductors.

The same is repeated for other conductors taking two at a time.

3.                    Earth fault

When the conductor of a cable comes in contact with earth, it is called earth fault or ground fault. To identify this fault, one terminal of the megger is connected to the conductor and the other terminal connected to the earth. If the megger indicates zero reading, it means the conductor is earthed. The same procedure is repeated for other conductors of the cable.

1.6                   ADVANTAGES OF UNDERGROUND CABLE SYSTEM

This includes aesthetics, higher public acceptance, and perceived benefits of protection against electromagnetic field radiation (which is still present in underground lines), fewer interruptions, and lower maintenance costs. Failure rates of overhead lines and underground cables vary widely, but typically underground cable outage rates are about half of their equivalent overhead line types. Potentially far fewer momentary interruptions occur from lightning, animals and tree branches falling on wires which de-energize a circuit and then re- energize it a moment later.

Primary benefits most often cited can be divided into four areas:

Potentially-Reduced Maintenance and Operating Costs:

• Lower storm restoration cost
• Lower tree-trimming cost

Improved Reliability:

• Increased reliability during severe weather (wind- related storm damage will be greatly reduced for an underground system, and areas not subjected to flooding and storm surges experience minimal damage and interruption of electric
• Less damage during severe weather
• Far fewer momentary interruptions
• Improved utility relations regarding tree trimming Improved Public Safety:
• Fewer motor vehicle accidents
• Reduced live-wire contact injuries
• Fewer Fires Improved Property Values:
• Improved aesthetics (removal of unsightly poles and wires, enhanced tree canopies).
• Fewer structures impacting sidewalks

1.7                   DISADVANTAGES OF UNDERGROUND CABLE SYSTEM

The main disadvantage is that the underground cables have higher initial cost and insulation problems at high voltages. Another main drawback is that, if a fault does occur, it is difficult to locate and repair the fault because the fault is invisible.