FUNDAMENTALS OF FAULT CURRENT AND GROUNDING IN ELECTRICAL SYSTEMS
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Chapter 1 The Fundamentals of Electrical Circuits This is the foundation from which knowledge of advanced studies in electrical technology and engineering is built. In this Chapter we will explore the simple circuit, circuit protection, safety and basic electrical concepts. Chapter 2 Codes for Electrical Installation Electrical codes are a set of standards to guide the safe installation of electrical accessories, cables and equipment. These codes are prescribed by law, and all installations shall meet the minimum standards stipulated by the codes. Electrical installations incorrectly done can pose a high risk of electrocution or serious injuries. Electrical work practices must therefore follow the established electrical codes. To assure safety, all electrical installations are inspected by “Government Electrical Inspectors” or GEI’s. This activity is established to eliminate poor work practices carried out by electricians and contractors. Electrical inspections are done prior to connections to the utility's power supply or as stipulated by a manufacturer of the device(s) being installed. The chapter discuss in detail the mandate of an electrical code or regulation, minimum code requirements, code for circuit loading as well as codes for several electrical devices. Chapter 3 Circuit Protection Circuit protection is the action of isolating a circuit when unsafe operating voltages and currents are present. This involves installation of isolation mechanisms or devices such as fuses, circuit breakers or relays with predetermined specifications in circuits. These mechanisms or devices monitors the voltage, current and frequency and isolate when necessary to prevent electrocution, and or damage to property and equipment. Protective devices and monitoring equipment are designed to keep monitored values within safe operating and design limits. Fuses, circuit breakers, and protective relays are a requirement for all electrical installation to provide the primary protection listed below. a. Protect a circuit from sustained over current b. Protect a circuit from faults due to moisture c. Protection against short circuit All protective devices fall within one of the following groups: a. Fuse Protection b. Electromagnetic Protection c. Thermal Protection – Bimetallic only d. Relay Protection Chapter 4 Fault current and transformers A transformer is a unique electrical device in electrical power engineering and is the recipient and producer of all fault currents. This device is critical in the transformation and the delivery of electrical power from very small wattage to very large megawatts. Voltages of transformers vary in accordance with its design, use, purpose, and power requirements. The chapter discusses transformer windings and configurations and percent impedance. Chapter 5 Special Circuit Protection Devices Special circuit protective devices (SCPDs) are protective devices designed with microprocessors to detect and trip on micro faults. The most common type of SCPDs is the GFCIs; this device is fitted with a magnetic tripping device which activates within 4 to 35mA. The Ground Fault Circuit Interrupter (GFCI), Residual Current devices, (RCD) and Earth leakage current devices (ELCD) are devices which trip when leakage current is detected typically between 4 – 35 mA. These devices are intended to operate within 25 – 40 milliseconds to prevent electric shock. Chapter 6 Grounding Systems and Functions Grounding systems are designed to protect and provide a path for unwanted current and voltage to be dissipated to the general mass of the earth. Ground current monitoring devices constitute a significant element in electrical systems for providing protection. The systems establish set points which are used to remove undesirable currents and voltages quickly when the earth leakage set points are breached. Electronic systems such as computers or computer based controls are mostly likely to be affected by ground faults or high harmonic rich currents which are called “Noise”. Supplementary grounding systems are sometimes employed to achieve desired connection with the general mass of the earth. Chapter 7 Improper Grounding Hazards & Special Grounding Improper grounding hazards refer to conditions where damage to property and life is threatened as a result of improper grounding. In these circumstances, the earthing facility is inadequate for dissipating leakage current to the general mass of the earth. This condition can prove dangerous and in some cases fatal. Some of the conditions resulting from improper grounding such as touch potential and step potential are discussed in this chapter. Chapter 8 Earthing Configurations Earthing configurations are essential for the purposes of grounding electrical installations to reduce the risk of electric shock. Significantly, earthing configurations are also crucial for protecting domestic, commercial and industrial appliances and equipment from the destructive energy which may be created from a short circuit at any point of the installation. Earthing configurations dictate the path which fault current or transients take to dissipate to earth. The general earthing configurations used on electrical installations in some countries such as those of the Caribbean, Europe and North America are the focus of this chapter. Chapter 9 Fault Current Management Fault current management is the control of fault or unintentional voltage and current, which may be a threat to life or property. Fault current management significantly relies on three elements addressed earlier in the book, earth electrode, soil management, and equipment bonding. The use of an earth electrode is to create a low impedance path between the installation and the general mass of the earth. This plays an important role in the control or management of fault current. Chapter 10 Open Neutral Conditions (O.N.C) An Open Neutral Condition (ONC) is the separation of the main system neutral conductor from it source. The effect open neutral conditions have on appliances can be extensive and catastrophic. Further, the variation of current and voltage in the appliances while in operation during an open neutral fault could cause significant damage to sensitive appliances. The chapter further discusses the causes of ONCs and where they occur. Chapter 11 Harmonics An electrical system will generate currents or voltages with frequencies that are integer or numeric multiples of the fundamental power frequency. These voltages or currents generate magnetic waves which may cause interference to nearby communication systems. Harmonics are currents or voltages with frequencies that are integer or numeric multiples of the fundamental power frequency being 50 or 60Hz. For example, if the fundamental power frequency is 60 Hz, then the 2nd harmonic is 120 Hz. the 3rd is 180 Hz, etc. When harmonic frequencies are prevalent and excessive, domestic appliances may malfunction and electrical power panels including transformers become mechanically resonant due to the magnetic fields generated by the pollution of harmonics. The chapter discusses the implications of harmonic frequencies and how their impact can be minimized. Chapter 12 Lightning Protection Lightning protection is measures taken or implemented to preserve life and property from high discharged destructive current produced by an atmospheric phenomenon called lighting. The chapter discusses how lightening is produced and its impact.
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About the Book
This book seeks to explain in simple terms the behavior of fault current through the general mass of earth, the origin of short circuit current and its value, and how a circuit breaker operates. The drawings are unique and allow the reader to visualize the behavior of a fault current. The book clarifies common myths pertaining to a grounding electrode, short circuit, and opens neutral conditions, and provides an unambiguous understanding of the theoretical and practical explanation for an effective earthing and protective system in electrical installations. There are numerous grounding problems and unexplained fault conditions in electrical circuitry that are taken for granted and left unattended for extended periods. Potential voltage can be found on the earthing conductors in processing plants, refineries, and other industrial plants. A combination of topics in this book addresses problems that have been adversely affecting the electrical industry for years. There are a number of systems in the electrical industry that are common in the workplace but are not understood by the average workman who has to work with these systems daily. Systems such as ungrounded systems, clean earthing systems, motor controls, resistance grounding, lightning protection systems, and Intra earthing systems are all common systems; however, the knowledge base of these systems is very limited. This book highlights the basics of these topics and gives a working overview of these systems. The book also discusses the principle of operation of the ground fault circuit interrupter (GFCI). It is expected that the information provided will allow the reader to visualize various types of GFCIs and the principle of operation without necessarily having to revert to other text.
About the Author
Dr. Halden Morris is senior lecturer in the School of Education, UWI, Mona, Jamaica. He is also former principal lecturer and head of the technology division of the Technical Education Department, CAST (now UTech). He studied at Southern Illinois University, USA; the University of Western Ontario, Canada; and the University of Technology, Jamaica. Dr. Morris is a registered professional engineer (PE) in Jamaica and is a senior member of the Institute of Electrical and Electronics Engineers (IEEE). His primary areas of interest and research include workforce development, technical and vocational education, and training (TVET); information and communication technology (ICT); alternative energy; and electrical technology. Dr. Morris is married to Carlene and has two daughters, Michcah and Marsha. NORMAN CHAMBERS Mr. Norman Chambers is Jamaican but currently resides in the Turks and Caicos Islands. His professional qualifications are in electrical power engineering with expertise and concentration on power system analysis in residential, commercial, industrial designs, and construction along with grounding. Mr. Chambers worked in the Ministry of Education in Jamaica, the Jamaica Public Service Company Limited, and the Aluminum Partners of Jamaica. Norman’s empirical background also includes successful experience with Tate & Lyles refinery and the South West Trains in London. In 2006, Norman became the chief electrical inspector of the Turks and Caicos Islands. He is married to Junie Ariza and has five children, Jhonelle, Torrian, Noshar, Rose-Jeana, and Candelisa.