TRANSMISSION LINES DESIGN and ELECTRICAL ENGINEERING HUB

The conductivity of aluminum is not as great as that of copper for a given size. For example, checking Table 310.15(B)(16), an 8 AWG Type THHN copper conductor has an allowable ampacity of 55 amperes. An 8 AWG Type THHN aluminum or copper-clad aluminum conductor has an ampacity of 45 amperes. In 240.4(D), the maximum overcurrent protection for a 12 AWG copper conductor is 20 amperes but only 15 amperes for a 12 AWG aluminum or copper-clad aluminum conductor. Aluminum conductors have a higher resistance compared to a copper conductor of the same size. When considering voltage drop, a conductor’s resistance is a key ingredient. Common Connection Problems Some common problems associated with aluminum conductors when not properly connected may be summarized as follows: • A corrosive action is set up when dissimilar wires come in contact with one another when moisture is present. • The surface of aluminum oxidi...

The NEC is very specific about the loads permitted on branch circuits. Here is a recap of these requirements. • The load shall not exceed the branch-circuit rating. • The branch circuit must be rated 15, 20, 30, 40, or 50 amperes when serving two or more outlets, NEC 210.3. • An individual branch circuit may supply any size load. • 15- and 20-ampere branch circuits a. may supply lighting, other equipment, or both types of loads. b. for cord-and-plug-connected equipment, shall not exceed 80% of the branch-circuit rating. c. for equipment fastened in place, shall not exceed 50% of the branch-circuit rating if the branch circuit also supplies lighting, other cord-and-plug-connected equipment, or both types of loads. • The 20-ampere small-appliance circuits in homes shall not supply other loads, NEC 210.11(C)(1). • 30-ampere branch circuits may supply equipment such as dryers, cooktops, water heaters,...

Light output is measured in lumens. According to The American Heritage Dictionary of Science, a lumen is a unit of luminous flux equal to the amount of light from a source of one candela radiating equally in all directions. A candela is a unit of luminous intensity equal to 1/60 of the radiating power of one square centimeter of a black body at 1,772°C. You can draw two conclusions from this information: ➤ The higher the lumen measurement, the more light you’ll have to work with from a fixture. ➤ Authors can easily get carried away when they have too many reference books at their disposal. Illuminance, which is measured in foot-candles, is the amount of light hitting a point on a surface. A foot-candle is (easily enough) defined as the amount of light produced by one candle on a surface one foot away. We can’t see illuminance, but we do see luminance or brightness, although this is somewhat subjective. (What appears to be dim lig...

Receptacles are a little more straightforward than three- and four-way switches. With a single duplex receptacle, you’re dealing with one or two cables coming into the box.   An end-of-the-run receptacle will have one cable, and a middle-of-the-run will have two. The receptacle has two sets of terminal screws, silver for the neutral wires and brass for the hot. After shutting off the power and testing the terminal screws, remove the outlet by loosening the screws attaching it to the box. Remove the hot and neutral wires, noting their position on the outlet (hot upper, hot lower, neutral upper, neutral lower) by marking the position on an attached piece of masking tape. Reconnect to the new receptacle in the same locations, and gently push the wires back into the box while reattaching the new receptacle. Turn on the power at the service panel or fuse box and test.

The heating category may be conveniently divided into residential (small) and industrial (large) applications. Residential Heating Residential heating includes ranges for cooking; hot water heaters; toasters, irons, clothes dryers, and other such appliances; and house heating. These are all resistance loads, varying from a relatively few watts to several kilowatts, most of which operate at 120 V, while the larger ones are served at 240 V; all are single-phase. The power factor of such devices is essentially unity. The resistance of the elements involved is practically constant; hence current will vary directly as the applied voltage. The effect of reduced voltage and accompanying reduced current is merely to cause a corresponding reduction in the heat produced or a slowing down of the operation of the appliance or device. While voltage variation, therefore, is not critical, it is usually kept to small values since very often...

The NEC establishes some very important fundamentals that weave their way through the decision making process for an electrical installation. They are presented here in brief form, and are covered in detail as required throughout this text. The NEC defines a branch circuit as The circuit conductors between the final overcurrent device protecting the circuit and the outlet(s).* See Figure 3-1. In the residence discussed in this text, the wiring to wall outlets, the dryer, the range, and so on, are all examples of a branch circuit. The NEC defines a feeder as All circuit conductors between the service equipment, the source of a separately derived system, or other power supply source and the final branch-circuit overcurrent device.* In the residence discussed in this text, the wiring between Main Panel A and Subpanel B is a feeder. The ampacity (current-carrying capacity) of a conductor must not be less than the r...

The following is taken in part from the OSHA, NIOSH, NSC regulations, and the American Heart Association recommendations. These are steps that should be taken in the event of a possible electrocution (cardiac arrest). You need to refer to the actual cardiopulmonary resuscitation (CPR) instructions for complete and detailed requirements, and to take CPR training. • First of all, you must recognize that an emergency exists. Timing is everything. The time between the accident and arrival of paramedics is crucial. Call 911 immediately. Don’t delay. • Don’t touch the person if he or she is still in contact with the live circuit. • Shut off the power. • Stay with the person while someone else contacts the paramedics, who have training in the basics of life support. In most localities, telephoning 911 will get you to the paramedics. • Have the caller verify that the call was made and that help is on the way. •...

The development of nuclear-fueled steam-electric plants underwent substantial change in the 1970s.At the beginning of the decade, orders for nuclear-fueled plants were increasing to a peak of 38 per year. Following the oil crisis of 1973 to 1974, changes in the economy began to affect the cost of, and consequently the demand for, electric power. Opposition to the use of nuclear energy for electric power production increased; litigation was frequently employed. Near the end of the decade, sociopolitical aspects of nuclear-fueled plants became as involved and time-consuming as the technical aspects. In order to participate effectively in the design, construction, and operation of nuclearfueled plants, one must be familiar with the energy perspective; the concerns about the use of nuclear energy; and the functions of advocates, intervenors, and regulators. With the maturity of the nuclear-fueled plants, more emphasis was placed on project management (Pederson 1978). Siting of...

One of the most accepted expressions to determine the number of direct strikes to an overhead line in an open ground with no nearby trees or buildings, is that described by Eriksson (1987):             N = Ng (58h^06 + n)/10         eq 10.3 where h is the pole or tower height (m) — negligible for distribution lines b is the structure width (m) Ng is the Ground Flash Density (flashes/km2/year) N is the number of flashes striking the line/100 km/year. For unshielded distribution lines, this is comparable to the fault index due to direct lightning hits. For transmission lines, this is an indicator of the exposure of the line to direct strikes. (The response of the line being a function of overhead ground wire shielding angle on one hand and on conductor-tower surge impedance and footing resistance on the other hand). Note the dependence of the incidence of strikes to the line...

Included under lighting are incandescent and fluorescent lamps, neon lights, and mercury vapor, sodium vapor, and metal halide lights. Nominal voltages specified for lighting are usually 120, 240, and 277 Volts (variations may exist from the base 120-V value, e.g., 115 and 125 V). All operate with dc or single-phase ac; the discussion will be in terms of ac, with comments concerning dc operation where applicable. Incandescent Lighting Incandescent lamps operate at essentially unity power factor. Their light output drops considerably at reduced voltage, being some 16 percent less with a 5 percent lowered voltage, and decreasing at a geometrically faster rate from then on. They are also sensitive to sudden rapid voltage variations, producing a noticeable (and annoying) flicker at variations of as little as 3 Volts (on a 120-V base). Street lighting of the incandescent type can be operated in a multiple or a series fashion. The former operates as other lighting in a multiple...

Broadband PLC systems provide significantly higher data rates (more than 2 Mbps) than narrowband PLC systems. Where the narrowband networks can realize only a small number of voice channels and data transmission with very low bit rates, broadband PLC networks offer the realization of more sophisticated telecommunication services; multiple voice connections, high-speed data transmission, transfer of video signals, and narrowband services as well. Therefore, PLC broadband systems are also considered a capable telecommunications technology. The realization of broadband communications services over powerline grids offers a great opportunity for cost-effective telecommunications networks without the laying of new cables. However, electrical supply networks are not designed for information transfer and there are some limiting factors in the application of broadband PLC technology. Therefore, the distances that can be covered, as well as the dat...

Dielectric breakdown A dielectric material must possess: (a) a high insulation resistivity to avoid leakage conduction, which dissipates the capacitor energy in heat; (b) a permittivity suitable for the purpose - high for capacitors and low for insulation generally; and (c) a high electric strength to withstand large voltage gradients, so that only thin material is required. It is rarely possible to secure optimum properties in one and the same material. A practical dielectric will break down (i.e. fail to insulate) when the voltage gradient exceeds the value that the material can withstand. The breakdown mechanism is complex. Gases With gaseous dielectrics (e.g. air and hydrogen), ions are always present, on account of light, heat, sparking, etc. These are set in motion, making additional ionisation, which may be cumulative, causing glow discharge, sparking or arcing unless the field strength is below a critical value. Field strength of the order of 3MV/m...

A celluloid template, shaped to the form of the suspended conductor, is used to scale the distance from the conductor to the ground and to adjust structure locations and heights to (1) provide proper clearance to the ground; (2) equalize spans; and (3) grade the line. The template is cut as a parabola on the maximum sag (usually at 49#C) of the ruling span and should be extended by computing the sag as proportional to the square of the span for spans both shorter and longer than the ruling span. By extending the template to a span of several thousand feet, clearances may be scaled on steep hillsides. The form of the template is based on the fact that, at the time when the conductor is erected, the horizontal tensions must be equal in all spans of every length, both level and inclined, if the insulators hang plumb. This is still very nearly true at the maximum temperature. The template, therefore, must be cut to a catenary or, approximately, a parabola. The parabola is accu...

Overhead transmission of electric power remains one of the most important elements of today’s electric power system. Transmission systems deliver power from generating plants to industrial sites and to substations from which distribution systems supply residential and commercial service. Those transmission systems also interconnect electric utilities, permitting power exchange when it is of economic advantage and to assist one another when generating plants are out of service because of damage or routine repairs. Total investment in transmission and substations is approximately 10% of the investment in generation. Since the beginning of the electrical industry, research has been directed toward higher and higher voltages for transmission. As systems have grown, higher-voltage systems have rarely displaced existing systems, but have instead overlayed them. Economics have typically dictated that an overlay voltage should be between 2 and 3 times the voltage of the system it is r...

PV is best suited for remote site applications that have small to moderate power requirements, or small power consuming applications even where the grid is in existence. A few power companies are also promoting limited grid-connected PV systems, but the large market for this technology is for stand-alone (off-grid) applications. Some common PV applications are as follows: Water Pumping . Pumping water is one of the most competitive arenas for PV power since it is simple, reliable, and requires almost no maintenance. Agricultural watering needs are usually greatest during sunnier periods when more water can be pumped with a solar system. PV-powered pumping systems are excellent for small to medium scale pumping needs (e.g., livestock tanks) and rarely exceed applications requiring more than a 2 hp motor. There are thousands of agricultural PV water pumping systems in the field today throughout Texas. PV pumping systems’ main advantages are that no fuel is required and little ma...

According to Faraday’s law, in any closed linear path in space, when the magnetic flux φ surrounded by the path varies with time, a voltage is induced around the path equal to the negative rate of change of the flux in webers per second.                         V = - ∂φ/ ∂t     Eq. (2-2) The minus sign denotes that the direction of the induced voltage is such as to produce a current opposing the flux. If the flux is changing at a constant rate, the voltage is numerically equal to the increase or decrease in webers in 1 s. The closed linear path (or circuit) is the boundary of a surface and is a geometric line having length but infinitesimal thickness and not having branches in parallel. It can vary in shape or position. If a loop of wire of negligible cross section occupies the same place and has the same motion as the path just considered, the v...

Kh - Kh is the meter disk watt-hour constant representing the number of watt-hours per revolution of the disk. Rr - Rr is the register ratio. This is the relationship between the first take off gear on the meter’s register and the far right hand dial on the front of the register. Rs - Rs represents the first shaft reduction. This is the relationship between the worm wheel on the disk shaft and the first take off gear on the meter’s register. Rg - Rg is the relationship between the worm wheel on the disk shaft and the far right hand dial on the meter. It may be calculated by multiplying Rs times Rr. Kr - The term "Kr" is used to represent the dial multiplier for the meter. CT - Current Transformer. VT - Voltage Transformer. TF - Transformer Factor may be determined from the turns ratio of the CT’s and VT’s. The transformer factor is VT ratio times CT ratio or simply CT ratio if VT’s are not being used. RF - Rating Factor is the overload factor ...

The historical evolution of electrical engineering can be attributed, in part, to the work and discoveries of the people in the following list. You will find these scientists, mathematicians, and physicists referenced throughout the text. William Gilbert (1540–1603), English physician, founder of magnetic science, published De Magnete, a treatise on magnetism, in 1600. Charles A. Coulomb (1736–1806), French engineer and physicist, published the laws of electrostatics in seven memoirs to the French Academy of Science between 1785 and 1791. His name is associated with the unit of charge. JamesWatt (1736–1819), English inventor, developed the steam engine. His name is used to represent the unit of power. Alessandro Volta (1745–1827), Italian physicist, discovered the electric pile. The unit of electric potential and the alternate name of this quantity (voltage) are named after him. Hans Christian Oersted (1777–1851), Danish physic...

We usually think of an electric power system in terms of its more impressive parts the big generating stations, transformers, high-voltage lines, etc. While these are some of the basic elements, there are many other necessary and fascinating components. Protective relaying  is one of these. The role of protective relaying in electric-power-system design and operation is explained by a brief examination of the over-all background. There are three aspects of a power system that will serve the purposes of this examination. These aspects are as follows: A. Normal operation B. Prevention of electrical failure. C. Mitigation of the effects of electrical failure. The term "normal operation" assumes no failures of equipment, no mistakes of personnel, nor "acts of God." It involves the minimum requirements for supplying the existing load and a certain amount of anticipated future load. Some of the considerations are: A. Choice between hydro, steam, ...

There are numerous different mixtures of elements that work as semiconductors. The two most common materials are silicon and a compound of gallium and arsenic known as gallium arsenide (often abbreviated GaAs). In the early years of semiconductor technology, germanium formed the basis for many semiconductors; today it is seen occasionally, but not often. Other substances that work as semiconductors are selenium, cadmium compounds, indium compounds, and various metal oxides. Many of the elements found in semiconductors can be mined from the earth. Others are “grown” as crystals under laboratory conditions. Silicon Silicon (chemical symbol Si) is widely used in diodes, transistors, and integrated circuits. Generally, other substances, or impurities, must be added to silicon to give it the desired properties. The best quality silicon is obtained by growing crystals in a laboratory. The silicon is then fabricated into wafers or chips. Ga...

Charge carriers, particularly electrons, can build up, or become deficient, on things without flowing anywhere. You’ve probably experienced this when walking on a carpeted floor during the winter, or in a place where the humidity was very low. An excess or shortage of electrons is created on and in your body. You acquire a charge of static electricity. It’s called “static” because it doesn’t go anywhere. You don’t feel this until you touch some metallic object that is connected to earth ground or to some large fixture; but then there is a discharge, accompanied by a spark that might well startle you. It is the current, during this discharge, that causes the sensation that might make you jump. If you were to become much more charged, your hair would stand on end, because every hair would repel every other. Like charges are caused either by an excess or a deficiency of electrons; they repel. The spark might jump an inch, two inche...

The application of engineering principles and technology to medicine and biology has had an increasing influence on the practice of medicine. The most visible of these contributions is in the form of medical devices. This article, however, describes the engineering introduction of quantitative methods in the field of bioelectricity. When such contributions first be- came evident, in the early 1950s many physiology researchers were already employing modern quantitative methods to develop and utilize governing equations and suitable models of bioelectric phenomena. Today it appears that systems physiology lives on as biomedical engineering, while physiology has become more concerned with cell and molecular biology. On the other hand, biomedical engineering is also currently involved in efforts to develop and apply quantitative approaches in cellular and molecular levels. This article, which is concerned with the electr...

CANADIAN STANDARDS ASSOCIATION The Canadian Standards Association is a not-for-profit membership-based association serving business, industry, government and consumers in Canada and the global marketplace. As a solutions-oriented organization, we work in Canada and around the world to develop standards that address real needs, such as enhancing public safety and health. Advancing the quality of life. Helping to preserve the environment. Facilitating trade. We help people understand standards through education and information products and services. Each year, thousands of people benefit from the training materials, workshops and seminars offered by the CSA Education & Training. Electrical standards are part of our everyday lives. From the products you buy to make your life more enjoyable to the systems of lines and towers that deliver the electricity to power these products, Canadian Standards Associations (CSA) offers over 700 CSA electrical standards and application tools t...

ANSI=IEEE Std 80-1986: IEEE Guide for Safety in AC Substation Grounding Presents essential guidelines for assuring safety through proper grounding at AC substations at all voltage levels. Provides design criteria to establish safe limits for potential differences within a station, under fault conditions, between possible points of contact. Uses a step-by-step format to describe test methods, design and testing of grounding systems. Provides English translations of three fundamental papers on grounding by Rudenberg, Laurent, and Zeitschrift that are not available in Std 80-2000. ANSI=IEEE Std 80-2000: IEEE Guide for Safety in AC Substation Grounding Provides an improved methodology for interpreting two-layer soil resistivity and using the values in the design of AC substations. Provides methods for determining the maximum grid current at substations,= some of which also predict the maximum fault currents available on lines close by. Provides a number of new worked-examples in a...

Surges associated with switching transmission lines (overhead, SF6, or cable) include those that are generated by line energizing, reclosing (three phase and single phase operations), fault initiation, line dropping (deenergizing), fault clearing, etc. During an energizing operation, for example, closing a circuit breaker at the instant of crest system voltage results in a 1 pu surge traveling down the transmission line and being reflected at the remote, open terminal. The reflection interacts with the incoming wave on the phase under consideration as well as with the traveling waves on adjacent phases. At the same time, the waves are being attenuated and modified by losses. Consequently, it is difficult to accurately predict the resultant waveshapes without employing sophisticated simulation tools such as a transient network analyzer (TNA) or digital programs such as the Electromagnetic Transients Program (EMTP). Transmission line overvoltages can also be influenced...