power systems loss

CAPACITOR FUSING APPLICATION GUIDE RULES Basic points to consider in fusing a capacitor in electric system network 1) Purpose of fusing:                 a. to isolate faulted bank from system                 b. to protect against bursting                 c. to give indication                 d. to allow manual switching (fuse control)                 e. to isolate faulted capacitor from bank 2) Recommended rating:                                a. The continuous-current capability of the fuse should be at least 165 percent of the normal capacitor-bank (for delta and floating wye banks the factor may be reduced to 150 percent if necessary).                 b. The total clearing characteristics of the fuse link must be coordinated with the capacitor "case bursting" curves. 3)  Tests have shown that expulsion fuse links will not satisfactorily protect  against violent rupture where the fault current through the capacitor is greater than 5000 amperes. 4)  The c

REA BULLETIN 160-2: MECHANICAL DESIGN MANUAL FOR OVERHEAD DISTRIBUTION LINES Overview on REA Bulletin 160-2 for overhead distribution line design guide The engineering input to an overhead line project can be divided into three principal categories; system planning, electrical design of system components, and the mechanical design of the line. This overview for the design manual deals primarily with the last mentioned of these categories. Preparation for an Overhead Distribution Line Project This part involves coordination with system planning especially in the field of route selection and acquisition. This includes securing of rights of way and permits needed for the implementation. Preparing a line project also means preparing of staking aids as well as review of existing design guides or preparation of new ones. The National Electrical Safety Code as a Basis for Distribution Line Design The second part in implementing distribution line projects is insuring that appropriate sta

SELECTION OF CONDUCTORS FOR OVERHEAD LINE DESIGN What are the guidelines to be considered in selecting conductors for overhead line design? Economically, conductors represent between 20 to 40% of the total cost of a line; consequently their selection is of prime importance. In earlier days of electrical power transmission, copper was mainly used as the material of overhead line conductors, however with the expansion of electricity networks, several factors, such as price, weight, availability and conductivity, have virtually compelled Overhead Line Design Engineers to concentrate on aluminium based conductors, eg. AAC = All Aluminium Conductor ACRS = All Aluminium Conductor Steel Reinforcement AAAC = All Aluminium Alloy Conductor Steel conductors are still widely used as overhead earth wires and also as phase conductors on rural distribution lines, eg. SC/GZ = Galvanised Steel Conductor SC/AC = Aluminium Clad Steel Conductor Phase Conductors The conductors fulfil an electromec

SELECTION OF INSULATORS FOR OVERHEAD LINE DESIGN What are the guidelines to be considered in selecting insulators for overhead line design? One of the most important and yet one of the most vulnerable links in transmission and distribution is insulators. Porcelain and toughened glass are the materials principally used for supporting conductors on overhead lines, and although these materials are relatively brittle and inelastic, they have proven service experience and are still widely used. The design of synthetic type insulators has improved both electrically and mechanically in recent times and they are being used in urban areas to minimise radio interference and in areas where gunshot or stone throwing is a problem. Insulator damage may occur due to such widely varying causes as lighting (puncture), power arcs, stone throwing, corrosion, gunshot and pollution. The following points must be considered in the selection of the appropriate insulation of an overhead line: • 50Hz perfor

STEPS IN LAYOUTING DISTRIBUTION LINE IN OVERHEAD LINE DESIGN TUTORIALS How to design overhead line especially in lay-outing distribution line? The following steps are suggested as the approach to be followed in designing a line from scratch. With experience or by reference to the tables of common applications in the Design manual section “Pole Structures” many of these steps will not be required for jobs of a standard nature. 1. Determine conductor size and type based on planning requirements and application. 2. Determine the proposed stringing tension based on the situation eg. Urban, semi urban or rural. Consideration in this decision should be given to the difficulty of staying and frequency of angles required by route restrictions. 3. Determine the Limit state design wind pressure on conductors appropriate to the location (eg 900 or 1200 pa). 4. Determine strain/angle pole locations taking into account the deviation angle limits on pin insulators as per the table in the Desig

OVERHEAD TRANSMISSION AND DISTRIBUTION LINE DESIGN GUIDELINES OVERVIEW What are the guidelines to be considered in designing overhead electrical lines? In order to minimise the risk of failure of an overhead line it is necessary to ensure that each component of an overhead line has been designed to meet all the electrical and mechanical loads likely to be experienced in service as far as reasonably practical. In order to achieve this, every line and every structure in that line could be individually designed to meet the project requirements. This would be extremely time consuming and is probably only justified for high value transmission lines. Another approach is to utilise a range of standard structures with pre-designed electrical and mechanical capabilities and apply them to a particular project. Selection of Insulators One of the most important and yet one of the most vulnerable links in transmission and distribution is insulators. Porcelain and toughened glass are the materia

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

STRANDING OF WIRES AND CABLES Various Ways of Stranding a Power Cable/Wire The conductor material may be either solid or stranded. A solid conductor is a single, solid strand of conductor for the whole length of the wire, while stranded conductor is composed of several strands of conductor concentrically wounded together over the whole length of the wire/cable. For the same cross-sectional area of a conductor, there are diameter differences between solid and various types of stranded conductors. This is an important consideration in the selection of connectors and in the methods of splicing and terminating. Largesizes ofsoild conductors are too rigid for many applications that the solution would be to aveasmaller wiresandstrand them together to form the conductor. There are several ways of stranding the wires together which is dependent of the type and temper of the metal used. The following subsections will discussthe most commonly used stranding for copper conductors.

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

WAYS AND MEASURES IN PROTECTING DISTRIBUTION LINE CONDUCTORS FROM DAMAGES  What are the ways in protecting line from damages that occur in transmission and distribution lines? Gentle Handling of Cable - Careful handling in the field to avoid scratches, cuts or kinks in the conductor is desirable during the field operations of paying out, stringing, and tying or clipping in. Follow Sag-Tension Charts - Sagging conductors at tensions higher than recommended increases susceptibility to aeolian vibration. Sagging in at tensions lower than recommended reduces the probability of aeolian vibration but increases susceptibility to galloping. The Use of Armor Rods on Conductors - Armor Rods are intended for clamp supports, but they can also be used at tied supports. Armor rods are effective in sacrificing their surface to abrasion instead of the conductor’s outside surface. In addition, they provide protection against electrical burning of the conductor from flashovers. Armor rods distr

COMMON LINE DAMAGE IN A DISTRIBUTION SYSTEM FEEDER LINE   What are the common of line damages that occur in transmission and distribution lines?  The cause of damages to transmission and distribution lines can be attributed to many potential reasons. Conductors are one of the most exposed electric company asset to many unfortunate events. The cost of conductors is one of the major expenses in any overhead power line construction. It is the primary component in the flow of revenue for a utility and the component most exposed to hazards. With the introduction of aluminum conductor, the vulnerability to damage increased due to its easily abraded surface. The four types of motion occurring on overhead power lines are (1) aeolian vibration, (2) galloping, (3) sway oscillation and (4) unbalanced loading. Each is independent in cause and effect. Insulator and conductor damage can be classified into four main points; where lines are seldom inspected, the first indication of damage may not b

CIRCUIT PROTECTION FOR DISTRIBUTION SYSTEM FEEDER LINE How an electric utility protects its distribution system line? An electric utility’s role in an electric power system does not only focus on the delivery of power to its customers. They also need to concentrate in the conservation of their assets in the network. Assets in the system like the transformers, wires, structures, etc., have an equivalent monetary value where the utility must always take care of. The ability of the electric distributor to minimize the damage during failure at the fastest time possible is very important since this means property loss can also be in the minimum. Relaying fundamentals is an important tool that protection engineers must possess in order to carefully analyse their own system. The most common form of distribution system feeder line protection which is also the most important is the overcurrent protection. Its basic application is mostly on substation protection and distribution feeder line p

DISTRIBUTION SYSTEM MODELING AND ANALYSIS BOOK By William H. Kersting This is the first book dedicated to distribution systems that is truly modern, covers computer applications, and gives a thorough grounding in modeling and analysis techniques. Assuming a basic foundation in transformers, electric machines, transmission lines, and symmetrical components, it serves as both a text for upper-level electrical engineering studies and as an essential reference for practicing engineers. CHECK OUT THIS BOOK

SPATIAL ELECTRIC LOAD FORECASTING BOOK By H.Lee Willis Containing 12 new chapters, this second edition offers increased coverage of weather correction and normalization of forecasts, anticipation of redevelopment, determining the validity of announced developments, and minimizing risk from over- or under-planning. It provides specific examples and detailed explanations of key points to consider for both standard and unusual utility forecasting situations, information on new algorithms and concepts in forecasting, a review of forecasting pitfalls and mistakes, case studies depicting challenging forecast environments, and load models illustrating various types of demand. CHECK OUT THIS BOOK

POWER DISTRIBUTION PLANNING REFERENCE BOOK By H.Lee Willis Lee (fellow, Institute of Electrical and Electronics Engineers) has doubled the total content of this second edition of a reference book and tutorial guide for the planning of electric utility power delivery systems. In addition to two new chapters on reliability, material on reliability engineering. CHECK OUT THIS BOOK