TRANSMISSION LINES DESIGN and ELECTRICAL ENGINEERING HUB

Cranes or hoists having adequate lifting capacities should be available for handling material during installation. Nylon web slings provide an ideal means for lifting equipment without damaging it. Gas is handled through commercially available gas-processing trailers that contain vacuum pumping equipment, gas storage tanks, compressors, filters, and dryers. The size of the individual gas compartments and the evacuating and storage capacity of the gas-handling equipment is especially important in large stations. Suitable evacuating GAS equipment and a heat source to counteract the chilling effect of the expanding gas may permit filling directly from gas cylinders or gas-handling equipment. High-voltage test equipment is required for checking the quality of the insulation after installation. Adapters for high voltage testing may be required. These include a suitable entrance bushing for connecting the high voltage to the gas insulated conductor and a termination for closi...

A deliberate and complete installation plan, including the future addition of similar equipment, is essential so that all aspects of construction can be reviewed. The preassembled sections of the equipment and the manufacturer’s instructions dictate the assembly sequence and, in most instances, follow a series of steps categorized as follows: a) Preconstruction meeting between the user and the manufacturer b) Site preparation including grading; installation of drainage, foundations, and grounding mats; access roads; and auxiliary power c) Staging of construction equipment required during the installation d) Final alignment and leveling of foundation supports e) Receiving, unloading, and storing GIS equipment f) On-site assembly g) Leak testing h) Connection of control wires i) Purging and filling with insulating gas j) Mechanical or operational testing k) Dielectric testing l) Cleanup in accordance with applicable regulations m) Energization Other ...

PD measurements are an ideal method for evaluating switchgear apparatus with non-self-restoring insulation. During a temporary overvoltage, during a high-voltage test, or under transient voltage conditions during operation, PDs may occur on insulation of this type, which includes gas, liquid, and solid materials. If these PDs are sustained due to poor materials, design, and/or foreign inclusions in the insulation, degradation and possible failure of the insulation structure may occur. Due to the variability of performance of dielectric materials and system designs, it is recommended that partial discharge tests be made as design tests in conjunction with the other dielectric tests on new switchgear equipment designs. The partial discharge test should be performed both before and after the impulse and normal frequency dielectric tests. Once performance is established, partial discharge tests on the switchgear equipment design need only be performed following the normal fre...

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 sp...

High-voltage and extra-high-voltage (EHV) transmission lines interconnect power plants and loads, and form an electric network. This system contains 500-kV, 345-kV, 230-kV, and 115-kV lines. T Presently, synchronous ties (AC lines) interconnect all networks in the eastern U.S. and Canada. Synchronous ties also (AC lines) interconnect all networks in the western U.S. and Canada. Several nonsynchronous ties (DC lines) connect the East and the West. These interconnections increase the reliability of the electric supply systems. In the U.S., the nominal voltage of the high-voltage lines is between 100 kV and 230 kV. The voltage of the extra-high-voltage lines is above 230 kV and below 800 kV. The voltage of an ultra-high-voltage line is above 800 kV. The maximum length of high-voltage lines is around 200 miles. Extra-high-voltage transmission lines generally supply energy up to 400–500 miles without intermediate switching and var support. Transmission lines are term...

The figure below shows the concept of typical energy transmission and distribution systems. The generating station produces the electric energy. The generator voltage is around 15 to 25 kV. This relatively low voltage is not appropriate for the transmission of energy over long distances. At the generating station a transformer is used to increase the voltage and reduce the current. In Fig. 4.3 the voltage is increased to 500 kV and an extra-high-voltage (EHV) line transmits the generator-produced energy to a distant substation. Such substations are located on the outskirts of large cities or in the center of several large loads. As an example, in Arizona, a 500-kV transmission line connects the Palo Verde Nuclear Station to the Kyrene and Westwing substations, which supply a large part of the city of Phoenix. The voltage is reduced at the 500 kV/220 kV EHV substation to the high-voltage level and high voltage lines transmit the energy to high-voltage substations locat...

The excitation system provides the DC voltage to the field winding of the generator and modulates this voltage for control purposes. There are many different configurations and designs of excitation systems. Stability programs usually include a variety of models capable of representing most systems. These models normally include the IEEE standard excitation system models, described in IEEE Standard 421.5 (1992). Reference should be made to that document for a description of the various models and typical data for commonly used excitation system designs. The excitation system consists of several subsystems, as shown in Fig. 11.33. The excitation power source provides the DC voltage and current at the levels required by the generator field. The excitation power may be provided by a rotating exciter, either a DC generator or an AC generator (alternator) and rectifier combination, or by rectifiers supplied from the generator terminals (or other AC source). Excitation ...

The implementation of “distribution automation” within the continental U.S. is as diverse and numerous as the utilities themselves. Particular strategies of implementation utilized by various utilities have depended heavily on environmental variables such as size of the utility, urbanization, and available communication paths. The current level of interest in distribution automation is the result of: • The maturation of technologies within the past 10 years in the areas of communication and RTUs/PLCs. • Increased performance in host servers for the same or lower cost; lower cost of memory. • The threat of deregulation and competition as a catalyst to automate. • Strategic benefits to be derived (e.g., potential of reduced labor costs, better planning from better information, optimizing of capital expenditures, reduced outage time, increased customer satisfaction). While not meant to be all-inclusive, this section on distribution automation attempts to provide some...

This instrument is an extremely stable and linear integrator that integrates the voltage induced in a flux coupling coil or sensor, usually called a search coil, connected to the input terminals of the fluxmeter. The voltage, V, induced in a coil that is placed in a time varying magnetic field is V = NAdB/dt where N is the number of turns in the coil and A is the area of this coil. This relationship can be rewritten to yield òVdt = NA(DB). From this equation it can be seen that the time integral of the voltage induced in the coil is proportional to the change in B at its location. The leads from the flux coupling coil should be twisted to eliminate the effect of stray magnetic flux linking these leads and producing errors. The plane of the coil should be positioned to obtain the maximum reading, which yields the correct value. Because a fluxmeter measures the change in B, one way that a dc measurement can be made is by turning on and off the magnetic device under test, which ...

Preservative Treatment. Pole decay is due to a fungus which requires air, moisture, warmth, and food for its subsistence; the wood of the pole constitutes its food. The conditions most favorable to the growth of the fungus are found at the ground line. The preservative has toxic or antiseptic properties which make the wood either poisonous or unfit food for the fungus. Preservatives and preserving methods conforming to the standards of the American Wood Preservers Association (AWPA)85 should be used in the treatment of poles. There are many wood preservatives, including those using poisonous salts such as copper, mercury, zinc, and arsenic compounds. However, only two are included in AWPA recommendations for poles, Standard C-4-74-C: 1. Coal-tar creosote, AWPA Standard P1-65 2. A 5% solution of pentachlorophenol in a petroleum distillate, AWPA Standard P8 (commonly called “penta”) By AWPA Standard M1-70, pentachlorophenol is not recommend...

Creep is Permanent Elongation at Everyday Tensions. Conductors permanently elongate under tension even if the tension level never exceeds everyday levels. This permanent elongation caused by everyday tension levels is called creep. Creep can be determined by long-term laboratory creep tests. The results of the tests are used to generate creep-versus-time curves. On the stress-strain graphs, creep curves are often shown for 6-month, 1-year, and 10-year periods. Figure 14-27 shows these typical creep curves for a 37-strand 250- to 1033.5-kcmil AAC. In Fig. 14-27, assume that the conductor tension remains constant at the initial stress of 4450 lb/in2. At the intersection of this stress level and the initial elongation curve, 6-month, 1-year, and 10-year creep curves, the conductor elongation from the initial elongation of 0.062% increases to 0.11%, 0.12%, and 0.15%, respectively. Because of creep elongation, the resulting final sags a...

Blondel’s theorem of polyphase metering describes the measurement of power in a polyphase system made up of an arbitrary number of conductors. The theorem provides the basis for correctly metering power in polyphase circuits. In simple terms, Blondel’s theorem states that the total power in a system of (N) conductors can be properly measured by using (N) wattmeters or watt-measuring elements. The elements are placed such that one current coil is in each of the conductors and one potential coil is connected between each of the conductors and some common point. If this common point is chosen to be one of the (N) conductors, there will be zero voltage across one of the measuring element potential coils. This element will register zero power. Therefore, the total power is correctly measured by the remaining (N – 1) elements. In application, this means that to accurately measure the power in a four-wire three-phase circuit (N = 4), the m...

The electromechanical watthour meter is basically a very specialized electric motor, consisting of • A stator and a rotor that together produce torque • A brake that creates a counter torque • A register to count and display the revolutions of the rotor Single Stator Electromechanical Meter A two-wire single stator meter is the simplest electromechanical meter. The single stator consists of two electromagnets. One electromagnet is the potential coil connected between the two circuit conductors. The other electromagnet is the current coil connected in series with the load current. Figure 7.1 shows the major components of a single stator meter. The electromagnetic fields of the current coil and the potential coil interact to generate torque on the rotor of the meter. This torque is proportional to the product of the source voltage, the line current, and the cosine of the phase angle between the two. Thus, the torque is also proportional to the power...

Distance relays respond to the voltage and current, i.e., the impedance, at the relay location. The impedance per mile is fairly constant so these relays respond to the distance between the relay location and the fault location. As the power systems become more complex and the fault current varies with changes in generation and system configuration, directional overcurrent relays become difficult to apply and to set for all contingencies, whereas the distance relay setting is constant for a wide variety of changes external to the protected line. There are three general distance relay types as shown in Fig. 9.32. Each is distinguished by its application and its operating characteristic. Impedance Relay The impedance relay has a circular characteristic centered at the origin of the R-X diagram. It is nondirectional and is used primarily as a fault detector. Admittance Relay The admittance relay is the most commonly used distance relay. It is...

The ability of a pole to be self-supporting depends on the class of the pole and the load it must carry (ignoring for the present the characteristic of the soil). Classes of Poles All wood poles are divided into classes based on thickness and circumference. One system uses five classes: 5, 4, 2, 0, and 00, ranging from moderately thin (class 5) to extra heavy (class 00). Knowing the load, it is possible then to select the proper class of pole for each location and degree of loading. If the number of units of loading is greater than the number of units the pole can support by itself, either the pole must be guyed or the conductors slackened to reduce the tension. Heavier-class Poles Poles one class heavier than the class specified by the tables should be used for each of the following purposes: 1. Junction poles 2. Poles supporting alley or side arms 3. Poles supporting line disconnects (except in-line types) or fuse cutouts...

Connections made between conductors, in joining two ends together or in making a tap off the other, should be electrically and mechanically sound. They not only should introduce no additional resistance (and associated heating) at the points of contact, but they should also not be subject to corrosion or conductor stresses or movements. In earlier times, such connections usually consisted of wires wrapped together and soldered. Later, twisted sleeves were employed in which the two ends of the conductor were inserted in a sleeve and the whole assembly twisted. Stranded conductors had each strand serviced separately before soldering. Many of these connections still exist. The later development of “solderless” or mechanical connectors made obsolete the wrapped and soldered splices. Parallel-groove clamps, split-bolt connectors, and crimped sleeves made splicing more simple and more uniform, with substantial reduction in labor costs. ...

Since it is impractical to manufacture an infinite number of wire sizes, standards have been adopted for an orderly and simple arrangement of such sizes for manufacturers and users. The American Wire Gauge (AWG), formerly known as the Browne and Sharpe Gauge (B&S), is the standard generally employed in this country and where American practices prevail. In defining conductor sizes, the circular mil (cmil) is usually used as the unit of measurement. It is the area of a circle having a diameter of 0.001 in, which works out to be 0.7854 × 10–6 in2. In the metric system, these figures are a diameter of 0.0254 mm and an area of 506.71 × 10–6 mm2. Wire sizes are given in gauge numbers, which, for distribution system purposes, range from a minimum of no. 12 to a maximum of no. 0000 (or 4/0) for solid-type conductors. Solid wire is not usually made in sizes larger than 4/0, and stranded wire for sizes larger than no. 2 is gener...

Cross arms are the most common means of supporting distribution conductors on poles. Although they are being used less frequently, their use will persist for some time. Standard Arms Standard cross-section dimensions for wood cross arms (width by height) are: 3-1/4 in by 4-1/4 in 3-1/2 in by 4-1/2 in 3-3/4 in by 4-3/4 in 4 in by 5 in Of these, the first two are most commonly used for distribution purposes, and usually only one of these will be stocked by an individual utility. The larger size finds greater use in the harsher northern and western climates, while the smaller finds use in the south and southwest. The rectangular cross section is slightly rounded or “roofed” on the top surface to shed rain and snow. The length of the cross arm depends on the number of conductors it is to support and the spacing between them. Standard cross arms include two-, four-, six-, and eight-pin arms, although the four- and six-pin arms, 8...

Concrete are at present not used extensively for distribution purposes in the United States. They are, however, used extensively in Europe and other lands where woods suitable for poles are not readily or economically available. Concrete poles are usually used where great strength and appearance are paramount requirements; concrete poles are made in several colors and finishes. Concrete poles come in cross sections that are circular, square, or polygonal (usually six- or eight-sided). Both allow electrical risers to be installed in the hollow space within them. Concrete poles are manufactured with hollow cores to reduce their weight, which has been (and still is) a disadvantage, especially when they are handled in the field.  Reinforcing steel strands are installed longitudinally for the full length of the pole and prestressed before the concrete is placed; reinforcing steel strands are also installed, essentially...

Watthour meters are customarily calibrated by determining the percentage registration, that is, the percentage of the energy passed through the meter in a short time interval. This may be done by two methods: 1) By precise timing of a number of revolutions of a meter while holding the watt input constant during the period, or 2) By operating the meter for a preselected number of revolutions simultaneously with a calibrated portable watthour standard of higher accuracy than the meter. For the first method, the watthours registered in a given time are noted while the average power is simultaneously measured during the same period with a standard wattmeter. Since the energy represented by one revolution, or the watthour constant, has been marked on the nameplate, the watthours registered by the meter on a given period will be Kh ´ R, where Kh is the watthour constant and R is the number of revolutions. The accuracy of the gear ratio between the rotating element and the first dia...

Induction-type watthour meters are basically induction motors with the following essential parts: The rotor, which consists of an aluminum disk mounted on a shaft that is free to rotate; The stator, which consists of voltage coil and a current coil wound on laminated iron cores; A braking magnet, which generates a torque that opposes disk rotation; and A revolution counter. The voltage and current coils produce fluxes that induce eddy currents in the aluminum disk. With proper space and phase displacement the interaction between these fluxes and the eddy currents will generate a rotational torque on the disk. The space displacement is achieved by a suitable arrangement of the coils and laminations. A 90° phase displacement is realized in part by the fact that the voltage coil is highly inductive. The remaining phase shift is obtained by a compensating coil and resistor that is magnetically coupled to the voltage coil. Induction watthour meters are frequency dependent an...