TRANSMISSION LINES DESIGN and ELECTRICAL ENGINEERING HUB

The capacitor motor is slightly different from a split-phase motor. A capacitor is placed in the path of the electrical current in the start winding (see Fig. 12-13). (A) Single-phase diagram for the AH air conditioner and heat-pump compressor. (Tecumseh) (B) Terminal box showing the position of the terminals on the AH series of compressors. (Courtesy of Tecumseh) Except for the capacitor, which is an electrical component that slows any rapid change in current, the two motors are the same electrically. A capacitor motor can usually be recognized by the capacitor can or housing that is mounted on the stator (see Fig. 12-14). Adding the capacitor to the start winding increases the effect of the two-phase field described in connection with the split-phase motor. The capacitor means that the motor can produce a much greater twisting force when it is started. It also reduces the amount of electrical current required during starting to about 1....

Capacitance switching currents may include part or all of the operating duty of a circuit breaker, such as the charging current of an unloaded transmission line or cable or the load current of a shunt capacitor bank. The rating of a circuit breaker for capacitance current switching shall include, where applicable, a) Rated line-charging breaking current applicable to all outdoor circuit breakers b) Rated cable-charging breaking current applicable to all indoor circuit breakers c) Rated single capacitor bank breaking current d) Rated back-to-back capacitor bank breaking current e) Rated back-to-back capacitor bank inrush making current and frequency Preferred values of rated capacitance switching currents are given in Table 1A, Table 2A, and Table 3A of ANSI C37.06-2000. The recovery voltage related to capacitance current switching depends on — The grounding of the system — The grounding of the capacitive load, e.g., shielded cable, capacitor bank, transmission li...

A GFCI monitors the current balance between the ungrounded “hot” conductor and the grounded conductor. As soon as the current flowing throughthe “hot” conductor is in the range of 4 to 6 milliamperes more than the current flowing in the “return” grounded conductor, the GFCI senses this unbalance and trips (opens) the circuit off. The unbalance indicates that part of the current flowing in the circuitis being diverted to some path other than the normal return path along the grounded return conductor. If the “other” path is through a human body, as , the outcome could be fatal. UL Standard No. 943 covers ground-fault circuit interrupters. • Class “A” GFCI devices are the most common. They are designed to – trip when current to ground is 6 milliamperes (6/1000 of an ampere) or greater. – not trip when the current to ground is less than 4 milliamperes (4/1000 of an ampere). – may or may not trip when the current to...

A voltage regulator is used to hold the voltage of a circuit at a predetermined value, within a band which the control equipment is capable of maintaining and within accepted tolerance values for distribution purposes. Regulators may be installed at substations or out on distribution feeders on poles, pads, or platforms or in vaults. Voltage regulators are essentially autotransformers, with the secondary (or series) portion of the coil arranged so that all or part of its induced voltage can be added to or subtracted from the line or incoming primary voltage (across which the primary or exciting portion of the winding is connected). The voltage variations are accomplished by changing the ratio of transformation automatically without deenergizing the unit. Types There are two types of voltage regulators in use in distribution systems: the induction regulator and the tap-changing-under-load (TCUL), or step-type, regulator. The fi...

Lightning or surge arresters consist basically of an air gap in series with another element which has the special characteristic of providing a relatively low resistance or impedance to the current produced by a high voltage surge, and a high resistance or impedance to the flow of power current at the relatively low operating voltage of the distribution line to which it is connected. In some later units, the air gap may be omitted. Pellet Type In the pellet type of arrester, the second element is made up of a tube full of lead pellets. The lead pellets are actually lead peroxide coated with lead oxide. The pellets normally act as insulation preventing current from flowing to ground. When a high-voltage surge is impressed on them, a current will flow that heats them and turns the lead oxide (a poor conductor) into lead peroxide (a good conductor). After the surge is discharged to ground, the surface of the pellets is changed by ...

The Canadian Electrical Code is significantly different from the National Electrical Code. It is considered Part 1 of the Canadian Electrical Code. Part 2 of the Canadian Electrical Code consists of electrical product safety standards similar to the standards produced in the United States by Underwriters Laboratories. Canadian product safety standards are produced by the Canadian Standards Association (CSA). In fact, many of the Canadian and U.S. standards have been harmonized. This allows a product to be evaluated and listed to the same requirements in both countries. Efforts are continuing to harmonize U.S. and Canadian standards with those from Mexico. CSA also serves as a third-party independent electrical products testing laboratory. Manufacturers are permitted to use a listing mark to identify products that have been found by examination and testing to comply with the Canadian Elec...

Numerous types of structure are used for supporting transmission line conductors, for example, self-supporting steel towers, guyed steel towers, self-supporting aluminum towers, guyed aluminum towers, self-supporting steel poles, flexible and semiflexible steel towers and poles, rope suspension, wood poles, wood H frames, and concrete poles. The type of supporting structure to use depends on such factors as the location of the line, importance of the line, desired life of the line, money available for initial investment, cost of maintenance, and availability of material. Because of the wide conductor spacing required for electrical clearances and insulation, the high tensile stresses used in conductors and ground cables to pull these cables up to a sag which will keep the heights of the structures within reason, the long spans necessary for crossing ravines in mountainous country, and the reliance to be placed on a major trunk line, lines...

Wake-induced oscillation is limited to lines having bundled conductors and results from aerodynamic forces on the downstream conductor of the bundle as it moves in and out of the wake of the upstream conductor. Wake-induced oscillation is controlled by maintaining sufficiently large conductor spacing in the bundle, unequal subspan lengths, and tilting the bundles. Bundled conductors are subject to wake-induced oscillations with amplitudes and frequencies typically between that of eolian vibration and galloping. The frequencies of oscillation are normally in the range of 1 to 10 Hz, and the amplitudes are in the range of 10 conductor diameters. The modes in which such vibration occurs are considerably more complex than the modes exhibited during either galloping or the almost invisible eolian vibrations. The source of wind energy for wake-induced oscillation is, as the name suggests, the wake from the windward conductor of the bundle wh...

Eolian vibration can occur when conductors are exposed to a steady low-velocity wind. If the amplitude of such vibration is sufficient, it can result in strand fatigue and/or fatigue of conductor accessories. The amplitude of vibration can be reduced by reducing the conductor tension, adding damping by using dampers (or clamps with damping characteristics), or by the use of special conductors which either provide more damping than standard conductors or are shaped so as to prevent resonance between the tensioned conductor span and the wind-induced vibration force. Eolian Vibration. As wind blows across a conductor, vortices are shed from the top and bottom of the conductor. The vortex shedding is accompanied by a varying pressure on the top and bottom of the conductor that encourages cyclic vibration of the conductor perpendicular to the direction of wind flow. The frequency at which this alternating pressure occurs is given by the expressi...

Color Coding (Cable Wiring) The conductors in nonmetallic-sheathed cable (Romex) are color coded with insulation as follows: 2-wire: one black (“hot” phase conductor)one white (grounded “identified” conductor)one bare, covered, or insulated (equipment grounding conductor) 3-wire: one black (“hot” phase conductor) one white (grounded “identified” conductor) one red (“hot” phase conductor) one bare, covered, or insulated (equipment grounding conductor) 4-wire: one black (“hot” phase conductor) one white (grounded “identified” conductor) one red (“hot” phase conductor) one blue (“hot” phase conductor) one bare, covered, or insulated (equipment grounding conductor) Four-wire nonmetallic-sheathed cable is also available with two ungrounded (“hot”) and two neutral conductors. This cable is designed for wiring two 120-volt branch circuits without using a common neutral. This avoids the requirem...

Design of any system should always be preceded by a formal determination of the business and corresponding technical requirements that drive the design. Such a formal statement is known as a “functional requirements specification.” Functional requirements capture the intended behavior of the system. This behavior can be expressed as services, tasks, or functions the system is required to perform. In the case of SCADA, the specification contains such information as system status points to be monitored, desired control points, and analog quantities to be monitored. It also includes identification of acceptable delays between when an event happens and when it is reported, required precision for analog quantities, and acceptable reliability levels. The functional-requirements analysis will also include a determination of the number of remote points to be monitored and controlled. It should also include identification of communication stakeholders other than the control center,...

The insulation of the cable must be able to withstand the voltage stresses experienced during normal and abnormal operating conditions. Therefore the selection of the cable insulation should be made on the basis of the applicable phase-to-phase voltage and the general system category which are classified as either 100%, 133%, or 173% insulation levels. These insulation levels are discussed as follows: 1. 100% level: Cables in this category may be applied where the system is provided with relay protection which normally clears ground faults within 1 min. This category is usually referred to as the grounded systems. 2. 133% level: Cables in this category may be applied where the system is provided with relay protection which normally clears ground faults within 1 h. This category is usually referred to as the low resistance grounded, or ungrounded systems. 3. 173% level : Cables in this category may be applied where the time needed to de-energize the ground fault is in...

A wide variety of finishes are used; they are referred to as jackets, sheaths, armors, and braids. These coverings are required primarily because of the physical or chemical characteristics of the particular insulation involved and the required mechanical protection. Finishes can be divided into two categories: (1) metallic finishes and (2) nonmetallic finishes. Metallic Finishes Metallic armor should be applied where a high degree of mechanical protection is required along with protection from rodents, termites, and the like. All metallic sheaths are subject to electrolytic damage. Metallic finishes are subdivided into the following: 1. Lead sheaths: One of the earliest types of metallic sheaths still in use. 2. Flat-band armor: Consists of jute bedding, two helical tape wraps, and a protective jute covering over the tapes. The tape may be either galvanized or plain steel. 3. Interlocked armor: Consists of galvanized steel, aluminum, or bronze strip (0.750 in. w...

This type of cable can be classified as follows: 1. NEC compounds 2. Elastomers 3. Thermoplastics 4. Thermosettings The rubber and rubber-like insulated cables enjoy their popularity owing to moisture resistance, ease of handling, ease of splicing, and extreme flexibility. Elastomers are materials that can be compressed, stretched, or deformed like rubber and yet retain their original shape. The thermoplastics materials soften when they are reheated, whereas thermosetting-type insulation has very little tendency to soften upon reheating after vulcanization. The earlier oil-based natural rubber compounds have been replaced by synthetic materials, which have better electrical and mechanical characteristics. The following synthetic rubber-like compounds are in use today: Ethylene propylene rubber (EPR) , an elastomer compound: EPR is commonly used in power cables, but is also gaining use in telecommunications and other types of cables. EPR possesses good chemical,...

The concentric stranding is most commonly used for power cable conductors. The construction of concentric-type cable consists of a central core surrounded by one or more layers of helically applied wires. The first layer has six wires and each subsequent layer has six more wires than the preceding layer. In this type of cable construction, the core consists of single wire and all of the strands have the same diameter. The first layer over the core contains 6 wires, the second contains 12 wires, the third 18, and so on. The following types of strandings are used in this application. Class B: This class of stranding is used exclusively for industrial power cables for application in 600 V, 5 kV, and 15 kV power systems. The cable stranding usually consists of 7 (#2 AWG), 19 (#4/0 AWG), 37 (500 kcmil), or 61 (750 kcmil) strands. Classes C and D: These classes are used where a more flexible cable is required. Class C uses 19, 37, 61, or 91 strands and class D uses 37, 61, 9...

Power cables at voltages above 2000 V usually have shielding and semiconducting tape. Cable shielding system consists of “strand shield” and “ insulation shield system.” Insulation shield system The insulation shield system is comprised of two conductive components: a semi-conductive layer called “semi-con” and metallic (conductive) layer. The insulation shield system is installed on the outer surface of the insulation and hence is called “the outer shield.” The purpose of the semi-con is to remove air voids between the metallic shield and the insulation. Shielding is accomplished by wrapping a thin (0.005 in.) copper tape spirally around the insulation to form a continuous shield along the entire length of the cable. This tape may or may not be perforated to reduce losses and is held to ground potential by suitable grounding. Shielding is necessary on medium and HV cables to 1. Prevent damage from corona. 2. Confi ne dielectric fi eld to the inside of cables...

The NESC recommends limits on the tension of bare overhead conductors as a percentage of the conductor’s rated breaking strength. The tension limits are: 60% under maximum ice and wind load, 33.3% initial unloaded (when installed) at 60°F, and 25% final unloaded (after maximum loading has occurred) at 60°F. It is common, however, for lower unloaded tension limits to be used. Except in areas experiencing severe ice loading, it is not unusual to find tension limits of 60% maximum, 25% unloaded initial, and 15% unloaded final. This set of specifications could easily result in an actual maximum tension on the order of only 35 to 40%, an initial tension of 20% and a final unloaded tension level of 15%. In this case, the 15% tension limit is said to govern. Transmission-line conductors are normally not covered with ice, and winds on the conductor are usually much lower than those used in maximum load calculations. Under such everyday conditions, tension limits are specified to l...

Insulator Washing Another common practice is to utilize helicopters for insulator washing. Again, this is a method that allows for the line to remain energized during the process. The helicopter carries a water tank that is refilled at a staging area near the work location. A hose and nozzle are attached to a structure on the helicopter and are operated by a qualified line worker who directs the water spray and adequately cleans the insulator string. Again, with the ease of access afforded by the helicopter, the speed of this operation can result in a typical three-phase tower being cleaned in a few minutes. Inspections Helicopters are invaluable for tower line and structure inspections. Due to the ease of the practice and the large number of inspections that can be accomplished, utilities have increased the amount of maintenance inspections being done, thus promoting system reliability. Helicopters typically carry qualified line workers who utilize stabilizing bin...

The short answer to the question “What is electricity?” is the transfer of energy through the motion of charge-carrying electrons. Lightning is an example of electricity and of electrons — lots and lots of them — in motion. Electricians are generally concerned with a much more controlled situation where electricity flows through a given path in a safe, predictable manner, but the electricity we use in shows is no different than that in a lightning strike, a static discharge, or a flashlight battery. Each is an example of the transfer of energy through the motion of electrons. But from where do these electrons come? The answer can be found in one of the most basic building blocks of the universe, the atom. For thousands of years, the nature of electricity puzzled and mystified some of the most brilliant minds. It wasn’t until scientists such as Benjamin Franklin, André-Marie Ampère, Alessandro Volta, and Michael Faraday contributed to our understanding of electricity that w...

In electrical parlance, certain terms relating to grounding are commonly confused. The neutral (the white or gray wire in North America, the blue wire in Europe, the black wire in India and Australia, and the light blue wire in China) is grounded at the panelboard, so it is referred to as a grounded conductor. None of the phase conductors are grounded, so they are referred to as ungrounded conductors. The grounding conductor is usually the green or green/yellow striped wire, or it can be a bare copper wire in the United States and Canada. Grounding is a continual process — the system is constantly kept at zero potential — so the green wire is called the grounding wire as opposed to the neutral, which is the grounded conductor. Bonding is the physical connection between metallic conducting materials in the system such as metal enclosures, conduit, and water pipes. The components of a power distribution system are bonded to ensure that they remain at ground potential...

In North America, getting an occasional shock by the 120-volt household mains supply is almost a rite of passage. In Europe, where the mains supply is 230V or 240V, getting “bit” by the mains supply might lead to your last rites. The higher voltage is much more dangerous because it produces more current given the same impedance. In some parts of Europe, the situation is exacerbated by the fact that the utility companies use a T-T (terra-terra) earthing system whereby the electrical service is grounded at the service entrance or utility pole and at the point of consumption as well. The ground fault return path is taken to be the earth, and if it happened to be a less than ideal conductor, then so be it. The problem is that if the impedance of the return path for fault currents is high enough, then the current is proportionately lower. Since the circuit breakers that are supposed to protect the circuit from large short circuit currents have an inverse-time relationship w...

Ancillary services support the basic electrical services and are essential for the reliability and operation of the electric power system. The electrical services that are supported include generating capacity, energy supply, and the power delivery system. FERC requires six ancillary services, including system control, regulation (frequency), contingency reserves (both spinning and supplemental), voltage control, and energy imbalance. In addition, load following, backup supply, network stability, system ‘‘black-start’’, loss replacement, and dynamic scheduling are necessary for the operation of the system. Utilities have been performing these functions for decades, but as vertically integrated regulated monopoly organizations. As these begin to disappear, and a new structure with multiple competing parties emerges, distributed utilities might be able to supply several of these. The distributed utilities providing these services could be owned by the former traditional u...

The electrolyte defines the key properties, particularly the operating temperature, of the fuel cell. Consequently, fuel cells are classified based on the types of electrolyte used as described below. 1. Polymer Electrolyte Membrane (PEM) 2. Alkaline Fuel Cell (AFC) 3. Phosphoric Acid Fuel Cell (PAFC) 4. Molten Carbonate Fuel Cell (MCFC) 5. Solid Oxide Fuel Cell (SOFC) These fuel cells operate at different temperatures and each is best suited to particular applications. Polymer Electrolyte Membrane (PEM) The PEM cell is one in a family of fuel cells that are in various stages of development. It is being considered as an alternative power source for automotive application for electric vehicles. The electrolyte in a PEM cell is a type of polymer and is usually referred to as a membrane, hence the name. Polymer electrolyte membranes are somewhat unusual electrolytes in that, in the presence of water, which the membrane readily absorbs, the negative ions are rigi...

The fuel cell works by processing a hydrogen-rich fuel—usually natural gas or methanol—into hydrogen, which, when combined with oxygen, produces electricity and water. This is the reverse electrolysis process. Rather than burning the fuel, however, the fuel cell converts the fuel to electricity using a highly efficient electrochemical process. A fuel cell has few moving parts, and produces very little waste heat or gas. A fuel cell power plant is basically made up of three subsystems or sections. In the fuel-processing section, the natural gas or other hydrocarbon fuel is converted to a hydrogen-rich fuel. This is normally accomplished through what is called a steam catalytic reforming process. The fuel is then fed to the power section, where it reacts with oxygen from the air in a large number of individual fuel cells to produce direct current (DC) electricity, and by-product heat in the form of usable steam or hot water. For a power plant, the number of fuel cells ca...

The gas-insulated transmission line (GIL) was invented in 1974 to connect the electrical generator of a hydro pump storage plant in Schluchsee, Germany. The GIL went into service in 1975 and has remained in service without interruption since then, delivering peak energy into the southwestern 420 kV network in Germany. With 700 m of system length running through a tunnel in the mountain, this GIL is still the longest application at this voltage level in the world. Today, at high-voltage levels ranging from 135 to 550 kV, a total of more than 100 km of GILs have been installed worldwide in a variety of applications, e.g., inside high-voltage substations or power plants or in areas with severe environmental conditions. Typical applications of GIL today include links within power plants to connect high-voltage transformers with high-voltage switchgear, links within cavern power plants to connect high-voltage transformers in the cavern with overhead lines on the outside, links to connect ...

The gas-insulated transmission line (GIL) is a system for the transmission of electricity at high power ratings over long distances. In cases where overhead lines are not possible, the GIL is a viable technical solution to bring the power transmitted by an overhead line underground without a reduction of power transmission capacity. As a gas-insulated system, the GIL has the advantage of electrical behavior similar to that of an overhead line, which is important to the operation of the complete network. Because of the large cross section of the conductor, the GIL has low electrical losses compared with other transmission systems (overhead lines and cables). This reduces the operating and transmission costs, and it contributes to reduction of global warming because less power needs to be generated. Safety of personnel in the vicinity of a GIL is very high because the solid metallic enclosure provides reliable protection. Even in the rare case of an internal failure, the met...

There are usually many factors that impact on the selection of the structure type for use in an OHTL. Some of the more significant are briefly identified below. Erection Technique: It is obvious that different structure types require different erection techniques. As an example, steel lattice towers consist of hundreds of individual members that must be bolted together, assembled, and erected onto the four previously installed foundations. A tapered steel pole, on the other hand, is likely to be produced in a single piece and erected directly on its previously installed foundation in one hoist. The lattice tower requires a large amount of labor to accomplish the considerable number of bolted joints, whereas the pole requires the installation of a few nuts applied to the foundation anchor bolts plus a few to install the crossarms. The steel pole requires a large-capacity crane with a high reach which would probably not be needed for the tower. Therefore, labor needs to be b...

Impact of corona discharges on the design of high-voltage lines has been recognized since the early days of electric power transmission when the corona losses were the limiting factor. Even today, corona losses remain critical for HV lines below 300 kV. With the development of EHV lines operating at voltages between 300 and 800 kV, electromagnetic interferences become the designing parameters. For UHV lines operating at voltages above 800 kV, the audible noise appears to gain in importance over the other two parameters. The physical mechanisms of these effects—corona losses, electromagnetic interference, and audible noise—and their current evaluation methods are discussed below. Corona Losses The movement of ions of both polarities generated by corona discharges, and subjected to the applied field around the line conductors, is the main source of energy loss. For AC lines, the movement of the ion space charges is limited to the immediate vicinity of the line conductors, ...

The onset of important power system problems can be assessed in part by experience from contemporary geomagnetic storms. At geomagnetic field disturbance levels as low as 60–100 nT=min (a measure of the rate of change in the magnetic field flux density over the Earth’s surface), power system operators have noted system upset events such as relay misoperation, the offline tripping of key assets, and even high levels of transformer internal heating due to stray flux in the transformer from GIC-caused half-cycle saturation of the transformer magnetic core. Reports of equipment damage have also included large electric generators and capacitor banks. Power networks are operated using what is termed as ‘‘N– 1’’ operation criterion. That is, the system must always be operated to withstand the next credible disturbance contingency without causing a cascading collapse of the system as a whole. This criterion normally works very well for the well-understood terrestrial environment chall...