power systems loss

Steps in safeguarding wires and cables when installing it in conduits. Investigations have shown that cable failures often can be attributed to damage caused during installation due to carelessness, inexperience and inability to observe certain simple precautions. In order to eliminate such preventable causes of electrical shutdowns and loss of production, the following procedures should be followed:

Authored by: R. F. Eaton and C. J. Kmiec ABSTRACT - As coaxial cables are used at ever higher frequencies in the Gigahertz range, cable losses become extremely important. Losses are functions of both Dk, dielectric constant, Df, tangent delta, of the polymer and the geometry of the cable construction. Control of the polymer architecture and additive package can reduce electrical losses in the cables fabricated from the polymer resulting in lower cable losses. Dk of a polymer is related a variety of chemical properties of the polymer: polarity, Tg, Tm etc. Df of a polymer is related to molecular motions of polar groups either along the polymer chain or the motion of polar molecules within the polymer matrix. We will discuss the Df contributions of the alpha, beta and gamma transition in polyethylene. Dk and Df are also functions of frequency and temperature.

BUILDING WIRES TYPES AND APPLICATION GUIDE What are the common types of wires used for building wiring installation? TW (Thermoplastic Moisture-Resistant) The TW conductors are solid or stranded annealed (soft) copper, insulated with a moisture resistant and flame retardant polyvinyl compound (PVC). TW wire is used in interior wiring at circuit voltages up to 600 volts. Maximum operating temperature is 60°C in dry or wet application. Type TW building wire is used in residential, commercial and industrial buildings for generalpurpose lighting, appliance, power, control and relay panel applications. It is used for low ampacity rated circuits. This type of wire may be installed in conduits, ducts or raceways. Type TW wire is also suitable for installations in ambient temperatures down to -10°C. THW (Thermoplastic Heat and Moisture Resistant) The THW conductors are solid or stranded annealed (soft) copper, insulated with a tough heat and moisture resistant, and flame retardant polyvi

ADVANTAGES OF SHIELDED CABLES What are the known advantages of using shielded cables? Electrical insulation surrounding a conductor creates a capacitor when the conductor is electrically energized. Thus, all insulated conductors are capacitors. In the majority of non-shielded cable systems, thecable surface makes intermittent contact with an electrical ground. Where intimate contact with this ground is not made, the intervening air spaces also act primarily as capacitors in ac circuits and as resistors in dc circuits. This forms a series of cable dielectric and air dielectric. Voltage across this circuit varies along the length of the cable depending on the voltage across the air gap. The cable surface becomes a floating voltage point in a voltage divider. This floating point voltage can vary considerably, depending on the cable design and the characteristics of the air gap. If the voltage is high enough, the cable surface can experience detrimental surface tracking of arcing discha

MEDIUM AND HIGH VOLTAGE WIRES AND CABLES What are the types of conductors/cables used for power distribution? There is no consensus among standard governing bodies like (i.e., IEC, ANSI, IEEE, UL, NEC and others) concerning the classification of voltage level.Thus, for clarity of this manual we will utilize IEEE voltage level classifications wherein 601V to 69,000V is medium voltage and 69,001V to 230,000V is high voltage.Furthermore, conductors are also classified according to their degree of insulation covering (i.e. bare, covered, and insulated). Basically, construction of the wires and cables is the same or similar for medium and high voltage applications. Bare Conductors Bare conductorsare those without covering and primarily used for overhead power transmission and distribution application. Insulating medium is air wherein the conductors are spaced from each other and any grounded object based on the system voltage. Insulators (e.g. porcelain, glass, and polymers) are used to

WIRE/CABLE MANUFACTURING PROCESS What are the steps/procedures in manufacturing wires/cables? Copper and aluminum rods undergo several stages of processing beforethey become wires and cables. Below are the processes in manufacturing conductors arranged in order. Drawing Drawing is the process of pulling thecopper or aluminum rods or wires at normal temperature through a die to reduce the cross-sectional area in order to get the desired dimension. The wire is deformed due to the tapering of the die and the force exerted during pulling. Annealing Annealing is the processof "softening" the temper of the wires and improving its cold working properties and machinability through sustained heating at a pre-determined temperature followed by coolingat a defined rate.There are many ways of annealing a wire; the most common practices in annealing copper is the continuous strand or resistance annealing wherein annealing is done by means of a machine placed between the final capstan

CABLE/CONDUCTOR MATERIAL CONSIDERATIONS What are the factors considered in making electrical conductors? There are several high conductivity metals that may be used as conductor. A conductor is a metallic material which allows electric current to flow through it with less resistance. The best conductor material is silver but due to its high cost per unit weight and being one of the precious metals, it is not economical to use in the transmission and distribution of electricity. Comparatively, gold with its excellent corrosion resistance and lower resistivitythan aluminum is also a good conductor but, same as silver, is very costly. Resistance and Conductivity Resistance is the opposition of an object to the passage of electric current. For direct current, resistance isdependent on the material length, cross-sectional are and resistivity. The electrical resistance of a conductor is inverselt proportional t the cross-sectional area or diameter of a conductor. Weight Although aluminum

CABLE DESIGN AND CONSTRUCTION Major Parts of a Power Cable Design An insulated cable appears to be a relatively simple electrical device but, in fact, it can be considered an electrical system with many components. To understand it, let us examine its components and basics of operation. For simplicity, the following discussion shall be confined to a single conductor cable. However, these fundamentals also apply to multiple-conductor cables. The basic components of an insulated cable are the following: Conductor - materials that transmits electrical energy. Shielding - also referred to as screening, are used for medium to high voltage cables. Basically, the use of this stress control layers is to achieve a symmetrical dielectric fields within the cable structure. For somevoltage level, shielding may be applied over the conductor. At higher voltage levels, it is applied over the conductor and the insulation. This results in the confining of all the voltage gradients to within the

POWER CABLE AS USED IN UNDERGROUND DISTRIBUTION SYSTEM How are conductor and materials for power cables being specified? Conductor material and insulation type will be specified. Restricting extensions of existing systems to a specific conductor material and insulation type in order to match an existing cable type is permitted only when a need has been established. Neutral cables, where required, will be installed with 600V  insulation unless concentric neutral cable is used. In duct lines, neutrals will be installed in the same conduit with associated phase cables. Conductor material. Since underground conductors are continuously supported, soft-drawn copper or aluminum alloy 5005 provides adequate strength. However, the selection of copper or aluminum will be justified based upon an analysis using life, environmental, and cost factors. The need for mechanical flexibility requires that conducts be stranded, and the NEC makes this mandatory for cables larger than No. 8 AWG installed

UNDERGROUND DISTRIBUTION LINES USING POWER CABLE IN AN ELECTRIC DISTRIBUTION SYSTEM How are power cables being used in an electrical distribution system? Underground distribution lines have been a long known technology used by many electric utilities in delivering power to its customers. This set up can usually be found in highly urbanized areas where space for overhead lines can be scarce. Various pros and cons are known to be associated in using underground distribution lines in a power distribution system. Like any other construction which involves public or private area, distribution system using underground lines installation must at all times coordinate with the installation master plan of the city or with any private properties to avoid conflict with construction of future facilities. For easy access for inspection and maintenance, underground lines are normally installed adjacent to roadways in urban, housing, or industrial plant areas, but may be routed as required to meet