Physics
Electric Cables
Electric cables are conductive materials used to transmit electrical power or signals. They are typically made of copper or aluminum wires surrounded by insulation to prevent electrical leakage and protect against environmental factors. Cables are essential components in electrical circuits, providing a means for the flow of electricity from a power source to various devices and systems.
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12 Key excerpts on "Electric Cables"
eBook - PDF- SA Chuturgoon(Author)
- 2016(Publication Date)
- Troupant(Publisher)
The function of an electrical cable is to transmit electrical energy from one point to another. The conductors of cables with a cross-sectional area of less than 16 mm 2 are made of annealed copper and are tinned . Conductors with a cross-sectional area exceeding 2,5 mm 2 are stranded . This is done to ensure the cables are flexible. Note The size of a cable is actually the cross-sectional area of each conductor or core. For example, a 16 mm 2 , four-core cable means that the cable has four separate conductors (cores) and each conductor has a cross-sectional area of 16 mm 2 . Cables used in the electrical industry are generally classified according to: • The type of insulating material used. • The voltages at which they transmit electrical energy. Cables are grouped according to the following voltage categories: 1. Low voltage – up to 1 000 V. 2. Medium voltage – 1 000 V to 33 kV. 3. High voltage – 33 kV to 230 kV. 4. Extra-high voltage – greater than 230 kV. There are several critical factors that influence the design of a cable: • The size of the conductor – the cable must be capable of carrying the required current. • The type, quality and thickness of the insulation – the cable must be able to withstand the voltage at which it is expected to operate. • The type of cable protection and covering – the cable must be able to withstand the installation and the elements of nature. • All materials used must remain chemically and physically stable throughout the life of the cable.
eBook - ePub- Pradip Kumar Sadhu, Soumya Das(Authors)
- 2015(Publication Date)
- CRC Press(Publisher)
Chapter 10Underground Cables
10.1 Introduction
Cables are used for transmission and distribution of electrical energy in highly populated areas of towns and cities. Cables form the artery system for the transmission and distribution of electrical energy. A cable is basically an insulated conductor. External protection against mechanical injury, moisture entry, and chemical reaction is provided on the cable. The conductor is usually aluminum or annealed copper, while the insulation is mostly polyvinyl chloride (PVC) or other chemical compounds.Transmission line is more expensive than overhead lines, especially at high potentials. Besides increase in temperature is high in cables. However, there is limitation of raising the operating voltage. In low and medium voltage distribution in urban areas, cables are more widespread.An underground cable essentially consists of one or more conductors covered with suitable insulation and surrounded by a protecting cover. In general, a cable must fulfill the following necessary requirements:- The conductor used in cables should be tinned stranded copper or aluminum of high conductivity. Stranding is done so that conductor may become flexible and carry more current.
- The conductor size should be such that the cable carries the desired load current without overheating and causes voltage drop within permissible limit.
- The cable must have proper thickness of insulation in order to give high degree of safety and reliability at the voltage for which it is designed.
- The cable must be provided with suitable mechanical protection so that it may withstand the rough use in laying it.
- The material used in the manufacture of cables should be such that there is complete chemical and physical stability throughout.
10.2 Insulating Materials for Cables
The satisfactory operation of a cable depends to a great extent upon the characteristics of insulation used. Therefore, the proper choice of insulating material for cables is of considerable importance. In general, the insulating materials used in cables should have the following properties:
eBook - PDFHandbook of Electrical Engineering
For Practitioners in the Oil, Gas and Petrochemical Industry
- Alan L. Sheldrake(Author)
- 2016(Publication Date)
- Wiley(Publisher)
9 Cables, Wires and Cable Installation Practices Cables provide a highly reliable and compact method of transmitting power from its source to its consumer. Cables are installed in open air on racks or ladders, in the ground, or underwater as in the case of submarine cables. Power at all the voltages normally encountered in the oil industry i.e., less than 100 V and up to 33 kV, can be transmitted efficiently by single and multi-core cables. Over the last 30 years there has been a progressive improvement in the materials used in the construction of cables, especially in the non-metallic materials. This has been due to several necessary requirements e.g., a) To maximise the conductor temperature and hence the power transmitted. b) To provide high resistance to mechanical wear and tear, both during the laying of the cables, and in their on-going use when they may be disturbed in the future. c) To withstand the effects of chemical attack from their environment e.g., when laid in pol- luted ground. d) To withstand the damaging effects of steady state and transient overvoltages. e) To withstand the impact of heat from the environment when exposed to fire and high radiant temperatures. f) To withstand freezing temperatures and embrittlement. g) To be resistant to ultraviolet light when exposed to bright sunlight. Not all of the above requirements are needed for a particular plant. The specification of the cable and its materials should take account of the changes in its environment throughout a one-year cycle. The conductor current rating should be based on the worst-case conditions if the cable is to be fully utilised and expected to give a long life time of service. 9.1 ELECTRICALLY CONDUCTING MATERIALS USED IN THE CONSTRUCTION OF CABLES References 1 and 2 give detailed information about the metallic materials used in cables. Some of the more commonly used data are presented herein.
eBook - PDFMarine Electrical Practice
Marine Engineering Series
- G. O. Watson(Author)
- 2014(Publication Date)
- Butterworth-Heinemann(Publisher)
Chapter 10 Electric Cables The basic design of an electric cable consists of a metallic conductor surrounded by suitable insulation to form the core, with one or more cores being covered overall with a common sheathing to provide protection from damage and external influences. Metallic coverings are sometimes applied to give additional mechanical protection or to provide electrical screening. Cables should conform in detailed construction and test requirements to appropriate international or national standards, e.g. British Standard specifications. The majority of cable specifications throughout the world, including those in the UK, adopt the metric system of measurement, based on SI units. Conductors Cable conductors for marine fixed installations are invariably of copper except in the case of thermocouple cables for instrumentation purposes, where special metals and alloys, e.g. cupro-nickel, are used for some cores. Welding cables, associated with ship repairs and work on offshore drilling rigs, etc., may have aluminium conductors to deter pilfering. Copper conductors are metal coated in many cable designs although plain uncoated wires are used for some p.v.c.-insulated types and all mineral-insulated cables. The metal coating, generally of tin base, serves as a barrier between the core insulation and the copper, reducing adhesion of the insulation to the conductor and also considerably reducing possible chemical interaction between certain constituents of some insulants and the copper conductor. A thin non-metallic tape of suitable material is sometimes interposed between the conductor and the insulation to further facilitate easy stripping of the insulation from the core. Except for mineral-insulated cables, conductors for fixed wiring power and lighting circuits are composed of a number of wires stranded together (see Table 10.1).
eBook - PDF- J. F. Whitfield, N. Hiller(Authors)
- 2014(Publication Date)
- Pergamon(Publisher)
CHAPTER 4 CABLES 4.1. GENERAL The Regulations define a cable as a length of insulated single conductor (solid or stranded), or of two or more such conductors, each provided with its own insulation, which are laid up together. The insulated conductor or conductors may or may not be provided with an overall covering for mechanical protection.'' The purpose of the cable is to form a low resistance path for the flow of current to and from the point at which it is to be used. Insulation In a normal installation, full supply voltage exists between the live and neutral conductors and they must therefore be insulated from each other to prevent a short circuit. This same insulation also serves to prevent a leakage of current from the cables to earth. The types of insulation are discussed fully in the following sections, but it must be remembered that in almost every case certain rules have to be observed to preserve this most vulnerable part of the cable. These rules are : (1) Keep the cable dry unless it is specially designed for use in wet situations. Many insulations are hygroscopic, that is, they have a tendency to absorb moisture. When moisture is present in an insulator, its insulating properties are considerably adversely affected and they may even conduct quite large currents, when they are said to have broken down . In cases where the insulation is impervious to moisture, dampness on the surface of a cable may provide a dangerous leakage path for current. 62 CABLES 63 (2) Never compress or stretch the insulation. The effectiveness of insulation depends very greatly on its thickness, and will be reduced if deformation takes place. (3) Never puncture the insulation. Moisture, dirt, etc., may penetrate the hole and form a conducting path. (4) Always ensure that the tape, braid or sheath is stripped back at least half an inch beyond the insulation when making a connection.
eBook - PDF- G.O. Watson(Author)
- 2013(Publication Date)
- Butterworth-Heinemann(Publisher)
Electric Cables The basic design of an electric cable consists of a metallic conductor surrounded by suitable insulation to form the core with one or more cores being covered overall with a common sheathing to provide protection from damage and external influences. Metallic coverings are sometimes applied to give additional mechanical protection or to provide electrical screening. Cables should conform in detailed construction and test require-ments to appropriate international or national standards, e.g. British Standard Specifications. The majority of cable specifications throughout the world, including those in the UK, adopt the metric system of measurement, based on SI Units. Some countries are still using Imperial and similar units but most of these are in the process of changing to the metric system. CONDUCTORS Cable conductors for marine fixed installations are invariably of copper except in the case of thermocouple cables for instrumen-tation purposes where special metals and alloys, e.g. cupro-nickel, are used for some cores. Welding cables, associated with ship repairs and work on off-shore drilling rigs, etc, may have aluminium con-ductors to deter pilfering. Copper conductors are metal-coated in many cable designs although plain uncoated wires are used for some pvc-insulated types and all mineral-insulated cables. The metal coating, generally of tin base, serves as a barrier between the core insulation and the copper, reducing adhesion of the insulation to the conductor and also con-siderably reducing possible chemical interaction between certain con-stituents of some insulants and the copper conductor. A thin non-metallic tape of suitable material is sometimes interposed between the conductor and the insulation to further facilitate easy stripping of the insulation from the core. 10 164
- Paul Gill(Author)
- 2016(Publication Date)
- CRC Press(Publisher)
299 6 Cables and Accessories 6.1 Introduction The generation, transmission, and distribution of power involve electrical facilities, apparatus, and components to carry the electrical energy from its generating site to where it is utilized. An important part of this power system is the medium-voltage cable system that is used exclusively to carry power from the main substation to secondary substations at load centers. Low- voltage cable is used to distribute power from the load centers in conduits and ducts, even though other methods such as cable trays, direct burial for outdoor applications, and aerial cable are used. Electrical, mechanical, and environmental considerations are the main factors in selecting and applying cable systems for distribution and utilization of electrical power. The splices and terminations of medium-voltage cables or connections of different type of cables (such as aluminum and copper) require careful consideration and evaluation during installation, as well as throughout their service life. Correct installation and preventive maintenance of cable systems will assure contin- ued electrical power service. 6.2 Cable Construction and Classification It is difficult to select and apply cables to power systems without some knowl- edge of the cable insulation system and of cable components. Therefore, it is important to review some basic considerations and fundamentals of cables for their application to power systems. The following materials are presently used for cables. Copper conductor The copper material used in the manufacture of cable is pure electrolytic copper, which has 100% conductivity. This means that a wire 1 ft long and one circular mil (1/1000 of in.) in cross-sectional area has a resistance of 10.371 Ω at 20°C. Tinning of copper is also required for many rubber and rubber-like insulation compounds to prevent corrosion of copper due to the sulfur that is used in the vulcanizing process.
eBook - PDF- David W. Tyler(Author)
- 2013(Publication Date)
- Newnes(Publisher)
Cables with 50 or even more conductors are available. MATERIALS USED IN ELECTRONIC CIRCUITS Because of its good conductivity and mechanical strength copper is used extensively to connect electronic components either in the form of insulated stranded wires or strip bonded to an insulating board in the form of a printed circuit. The insulation used is of polythene, polystyrene, polyurethane enamel or air where conductors can be suitably spaced. Permanent connections between components and interconnecting copper are usually soldered. Where components or boards of com-ponents must be capable of removal from an equipment, possibly for repair, some form of sliding contact system is required. The plug and socket for connection of domestic electrical equipment is an example of such a system. CONDUCTOR SCREENING AND COAXIAL CABLE c^~T Steady magnetic field (a) Figure 4.12 Nickel-iron screen (b) A conductor carrying current sets up a magnetic field around it, the strength of which is proportional to that current. This magnetic field may affect other circuits in its vicinity and to prevent this circuit screening is necessary. Where a component is to be screened from a steady magnetic field it is surrounded with a material with low magnetic reluctance. In Figure 4.12 the component to be screened is marked C. Without the screen the magnetic field will affect the component. With the screen in position the magnetic lines of force take the low reluctance path which is through the nickel-iron, so leaving the component in a position of zero flux. 46 Materials and their applications in the electrical industry I A (primary) m ^ Screen (secondary) Figure 4.13 Supply Sheath C o r e Load Figure 4.14 Figure 4.15 Figure 4.16 Where alternating current is involved the conductor carrying the current, and hence producing the alternating magnetic flux, is sur-rounded by the screen.
eBook - ePub- N.H. Malik, A. A. Al-Arainy, M.I. Qureshi(Authors)
- 2018(Publication Date)
- CRC Press(Publisher)
9 High Voltage Cables 9.1 INTRODUCTIONCables have been used in transmission and distribution networks since the early days of the electrical power industry. Generally, long-distance power transmission is carried out through overhead lines. However, transmission and distribution in densely populated urban areas mostly uses underground cables. Although significantly more expensive than the overhead lines, the cables are preferred in urban areas due to safety, reliability and aesthetical considerations. As a result of developments in insulating materials and manufacturing techniques, high voltage cable technology has improved significantly over the years. With a continuous increase in the overall length of cable networks, questions regarding reliability, failure modes and diagnostics of such cables have assumed greater significance. This chapter briefly discusses various aspects of high voltage power cables with emphasis on polymeric insulated cables, which are almost exclusively being used in distribution networks in many countries. The insulation testing of high voltage cables is discussed in Chapter 12 .9.2 CABLE MATERIALS 9.2.1 ConductorsCables are constructed using a variety of materials for conductors, insulation, screening and armoring. The most common conductor materials are copper or aluminum of high purity (>99.5% pure), since the resistivity of such materials significantly increases with impurity content. Sometimes, sodium is also used as the conductor material [5 ]. In recent years, the possibility of using high-temperature superconducting materials for power applications is also being examined. The choice between aluminum and copper is normally based on resistivity (ρ), cost as well as mechanical and manufacturing considerations. Table 9.1
eBook - PDF- Tommy Ferreira, Trevor Adams, Jan Randewijk, Tommy Ferreira, Trevor Adams, Jan Randewijk(Authors)
- 2021(Publication Date)
- Future Managers(Publisher)
42 Module 2 • Conductors, insulators and cables • draw and label the following: – a PVC-insulated, wire-armoured cable – a PILCSWA cable – a PILCSTA cable – an XLPE-insulated cable; • state the functions of each part of a PVC-insulated, wire-armoured cable; • state the advantages and disadvantages of the following cables: – PVC-insulated – paper-insulated – XLPE-insulated; • state the requirements of a good cable joint; • state the basic steps that must be followed when making a cable joint; • identify low-voltage and high-voltage cable joints; • explain how a simple low-voltage resin joint is made; • state the factors to be considered when selecting a cable for a particular application; and • state the methods used to install cables and the advantages and disadvantages of each method. Introduction Working in the electrical field, you will be confronted with concepts such as conductors, insulators and cables. It is therefore important that you know the properties of conductors, insulators and cables. Part of your daily tasks might involve joining cables and conductors and installing different types of cables; therefore, knowing which cable to use for a specific application is very important. Definition Insulator – a substance that prevents the flow of electric current through it Various Acts have been promulgated to ensure the safety of employees and other people. With regard to this, reference is made throughout this book to the requirements of the South African National Standard for “The wiring of premises” (SANS 10142-1), hereinafter referred to as SANS 10142. These are often referred to as Regulations. Reference to these requirements (SANS 10142) is indicated by the symbol ▲ and the relevant number or location in bold script. Reference to the contents or an extract, interpretation or explanation of the requirement follows in italics, e.g. 43 N2 Electrical Trade Theory ▲ 6.12.3.1 The earthing terminal of a socket-outlet shall be earthed.
eBook - PDFPractical Industrial Data Communications
Best Practice Techniques
- Deon Reynders, Steve Mackay, Edwin Wright(Authors)
- 2004(Publication Date)
- Butterworth-Heinemann(Publisher)
2 Copper cable 2.1 Cable characteristics Two main types of copper cable are used in industrial communications. They are: 1. Coaxial cable, also referred to as coax 2. Twisted-pair cable, which can be shielded (STP/ScTP/FTP) or unshielded (UTP). 2.1.1 Cable structure All copper cable types have the following components in common: • One or more conductors to provide a medium for the signal • Insulation of some sort around the conductors to help keep the signal in and interference out • An outer sheath, or jacket, to encase the cable elements. The sheath keeps the cable components together, and may also help protect the cable components from water, pressure, or other types of damage. Conductor For copper cables, the conductor is known as the signal (carrier) wire and may consist of either solid or stranded wire. Solid wire is a single thick strand of conductive material, usually copper. A stranded wire consists of many thin strands of conductive material wound tightly together. The signal wire is described in terms of the following: • The type of conductive material • Whether the wire is stranded or solid • The carrier wire diameter, expressed directly (in inches, centimeters, or millimeters) or in terms of the wire gauge as specified in the AWG ( American wire gage ) • The diameter of the strands, which determines some of the wire’s electrical properties such as resistance and impedance. These properties, in turn, help determine the wire’s performance. Insulation The insulating layer keeps the signal from escaping and helps to protect the signal from outside interference. The insulation is usually made of a dielectric such as polyethylene. Copper cable 27 Some types of coaxial cable have multiple protective layers around the signal wire. The size of the insulating layer determines the spacing between the conductors in a cable and therefore its capacitance and impedance.
eBook - PDF- D.F. Warne(Author)
- 2005(Publication Date)
- Newnes(Publisher)
Chapter 9 Wires and cables V.A.A. Banks and P.H. Fraser With amendments by D. Gracias Pirelli Cables Ltd A.J. Willis Brand-Rex Ltd 9.1 Scope Thousands of cable types are used throughout the world. They are found in applications ranging from fibre-optic links for data and telecommunication purposes through to EHV underground power transmission at 275 kV or higher. The scope here is limited to cover those types of cable which fit within the general subject matter of the pocket book. This chapter therefore covers cables rated between 300/500 V and 19/33 kV for use in the public supply network, in general industrial systems and in domestic and com- mercial wiring. Optical communication cables are included in a special section. Overhead wires and cables, submarine cables and flexible appliance cords are not included. Even within this relatively limited scope, it has been necessary to restrict the cov- erage of the major metallic cable and wire types to those used in the UK in order to give the cursory appreciation which is the main aim. 9.2 Principles of power cable design 9.2.1 Terminology The voltage designation used by the cable industry does not always align with that adopted by users and other equipment manufacturers, so clarification may be helpful. A cable is given a voltage rating which indicates the maximum circuit voltage for which it is designed, not necessarily the voltage at which it will be used. For example, a cable designated 0.6/1 kV is suitable for a circuit operating at 600 V phase-to-earth and 1000 V phase-to-phase. However it would be normal to use such a cable on dis- tribution and industrial circuits operating at 230/400 V in order to provide improved safety and increased service life. For light industrial circuits operating at 230/400 V it would be normal to use cables rated at 450/750 V, and for domestic circuits operating at 230/400 V, cable rated at 300/500 V would often be used.
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