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106-515: The aluminium alloy and temper used for the outer strands in the United States and Canada is normally 1350-H19 and elsewhere is 1370-H19, each with 99.5+% aluminium content. The temper of the aluminium is defined by the aluminium version's suffix, which in the case of H19 is extra hard. To extend the service life of the steel strands used for the conductor core they are normally galvanized, or coated with zinc to prevent corrosion. The diameters of

212-454: A diode bridge . A "delta" (Δ) connected transformer winding is connected between phases of a three-phase system. A "wye" (Y) transformer connects each winding from a phase wire to a common neutral point. A single three-phase transformer can be used, or three single-phase transformers. In an "open delta" or "V" system, only two transformers are used. A closed delta made of three single-phase transformers can operate as an open delta if one of

318-415: A high-leg delta supply is sometimes used where one winding of a delta-connected transformer feeding the load is center-tapped and that center tap is grounded and connected as a neutral as shown in the second diagram. This setup produces three different voltages: If the voltage between the center tap (neutral) and each of the top and bottom taps (phase and anti-phase) is 120  V (100%), the voltage across

424-404: A change in ductility and hardness. As the material cools it recrystallizes. For many alloys, including carbon steel, the crystal grain size and phase composition, which ultimately determine the material properties, are dependent on the heating rate and cooling rate. Hot working or cold working after the annealing process alters the metal structure, so further heat treatments may be used to achieve

530-516: A defined set of assumptions. Individual utilities normally apply different ratings due to using varying assumptions (which may be a result in higher or lower amperage ratings than those the manufacturers provide). Significant variables include wind speed and direction relative to the conductor, sun intensity, emissivity, ambient temperature, and maximum conductor temperature. In three phase electrical power distribution , conductors must be designed to have low electrical impedance in order to assure that

636-445: A failure of just one splice can cause an outage that affects a large amount of electrical load. Most splices are compression-type splices ( crimps ). These splices are inexpensive and have good strength and conductivity characteristics. Some splices, called automatics, use a jaw-type design that is faster to install (does not require the heavy compression equipment) and are often used during storm restoration when speed of installation

742-420: A four-wire secondary and a three-wire primary, while allowing unbalanced loads and the associated secondary-side neutral currents. Wiring for three phases is typically identified by colors that vary by country and voltage. The phases must be connected in the correct order to achieve the intended direction of rotation of three-phase motors. For example, pumps and fans do not work as intended in reverse. Maintaining

848-461: A given amount of electrical power. Three-phase power is mainly used directly to power large induction motors , other electric motors and other heavy loads. Small loads often use only a two-wire single-phase circuit, which may be derived from a three-phase system. The conductors between a voltage source and a load are called lines, and the voltage between any two lines is called line voltage . The voltage measured between any line and neutral

954-456: A grounding transformer (usually a zigzag transformer ) may be connected to allow ground fault currents to return from any phase to ground. Another variation is a "corner grounded" delta system, which is a closed delta that is grounded at one of the junctions of transformers. There are two basic three-phase configurations: wye (Y) and delta (Δ). As shown in the diagram, a delta configuration requires only three wires for transmission, but

1060-428: A longer and larger-diameter splice for the aluminium portion. The outer splice must be threaded on first and slid along the conductor and the steel splice compressed first and then the outer splice is slid back over the smaller splice and then compressed. This complicated process can easily result in a poor splice. Splices can also fail partially, where they have higher resistance than expected, usually after some time in

1166-444: A low absorption of sunlight. As the conductor ages the color becomes dull gray due to the oxidation reaction of the aluminium strands. In high pollution environments, the color may turn almost black after many years of exposure to the elements and chemicals. For aged conductor, the emissivity for heat radiation and the absorption of sunlight increases. Conductor coatings are available that have a high emissivity for high heat radiation and

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1272-497: A low absorption of sunlight. These coatings would be applied to new conductor during manufacture. These types of coatings have the ability to potentially increase the current rating of the ACSR conductor. For the same amount of amperage, the temperature of the same conductor will be lower due to the better heat dissipation of the higher emissivity coating. Annealing (metallurgy) In metallurgy and materials science , annealing

1378-422: A lower yield strength and a lower tensile strength . This process is also called LP annealing for lamellar pearlite in the steel industry as opposed to a process anneal , which does not specify a microstructure and only has the goal of softening the material. Often the material to be machined is annealed, and then subject to further heat treatment to achieve the final desired properties. Short cycle annealing

1484-713: A paper to the Royal Academy of Sciences in Turin . Two months later Nikola Tesla gained U.S. patent 381,968 for a three-phase electric motor design, application filed October 12, 1887. Figure 13 of this patent shows that Tesla envisaged his three-phase motor being powered from the generator via six wires. These alternators operated by creating systems of alternating currents displaced from one another in phase by definite amounts, and depended on rotating magnetic fields for their operation. The resulting source of polyphase power soon found widespread acceptance. The invention of

1590-413: A set of three AC electric currents , one from each coil (or winding) of the generator. The windings are arranged such that the currents are at the same frequency but with the peaks and troughs of their wave forms offset to provide three complementary currents with a phase separation of one-third cycle ( 120° or 2π ⁄ 3 radians ). The generator frequency is typically 50 or 60 Hz , depending on

1696-425: A specific conductor version when various versions of the same amount of aluminum to avoid issues related to different size hardware (such as splices). Due to the numerous different sizes available, utilities often skip over some of the sizes to reduce their inventory. The various stranding versions result in different electrical and mechanical characteristics. Manufacturers of ACSR typically provide ampacity tables for

1802-523: A waterfall at a distance was explored at the Grängesberg mine. A 45  m fall at Hällsjön, Smedjebackens kommun, where a small iron work had been located, was selected. In 1893, a three-phase 9.5  kV system was used to transfer 400 horsepower (300 kW) a distance of 15 km (10 miles), becoming the first commercial application. In a symmetric three-phase power supply system, three conductors each carry an alternating current of

1908-414: A wye (star) configuration may have a fourth wire. The fourth wire, if present, is provided as a neutral and is normally grounded. The three-wire and four-wire designations do not count the ground wire present above many transmission lines, which is solely for fault protection and does not carry current under normal use. A four-wire system with symmetrical voltages between phase and neutral is obtained when

2014-455: Is 3 = 1.732 … {\displaystyle {\sqrt {3}}=1.732\ldots } times the amplitude of the voltage of the individual phases. The symmetric three-phase systems described here are simply referred to as three-phase systems because, although it is possible to design and implement asymmetric three-phase power systems (i.e., with unequal voltages or phase shifts), they are not used in practice because they lack

2120-417: Is √ 3 times greater than the line-to-neutral voltage delivered to a load in the wye configuration. As the power transferred is V / Z , the impedance in the delta configuration must be 3 times what it would be in a wye configuration for the same power to be transferred. Except in a high-leg delta system and a corner-grounded delta system, single-phase loads may be connected across any two phases, or

2226-441: Is a heat treatment that alters the physical and sometimes chemical properties of a material to increase its ductility and reduce its hardness , making it more workable. It involves heating a material above its recrystallization temperature, maintaining a suitable temperature for an appropriate amount of time and then cooling. In annealing, atoms migrate in the crystal lattice and the number of dislocations decreases, leading to

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2332-411: Is a common type of alternating current (AC) used in electricity generation , transmission , and distribution . It is a type of polyphase system employing three wires (or four including an optional neutral return wire) and is the most common method used by electrical grids worldwide to transfer power. Three-phase electrical power was developed in the 1880s by several people. In three-phase power,

2438-487: Is a constant, V is the voltage applied, r is the number of rotations of the pulleys per minute, and t a is the ambient temperature , The constant K depends on the diameter of the pulleys and the resistivity of the copper. Purely in terms of the temperature of the copper wire, an increase in the speed of the wire through the pulley system has the same effect as a decrease in resistance. Three phase power Three-phase electric power (abbreviated 3ϕ )

2544-400: Is a heat treatment cycle that restores some of the ductility to a product being cold-worked so it can be cold-worked further without breaking. The temperature range for process annealing ranges from 260 °C (500 °F) to 760 °C (1400 °F), depending on the alloy in question. This process is mainly suited for low-carbon steel. The material is heated up to a temperature just below

2650-565: Is also done in forming gas , a mixture of hydrogen and nitrogen. The magnetic properties of mu-metal (Espey cores) are introduced by annealing the alloy in a hydrogen atmosphere. Typically, large ovens are used for the annealing process. The inside of the oven is large enough to place the workpiece in a position to receive maximum exposure to the circulating heated air. For high volume process annealing, gas fired conveyor furnaces are often used. For large workpieces or high quantity parts, car-bottom furnaces are used so workers can easily move

2756-441: Is called phase voltage . For example, for a 208/120-volt service, the line voltage is 208 volts, and the phase voltage is 120 volts. Polyphase power systems were independently invented by Galileo Ferraris , Mikhail Dolivo-Dobrovolsky , Jonas Wenström , John Hopkinson , William Stanley Jr. , and Nikola Tesla in the late 1880s. Three phase power evolved out of electric motor development. In 1885, Galileo Ferraris

2862-406: Is called "aluminium conductor steel supported" (ACSS) is also available. Trapezoidal-shaped wire (TW) can be used in lieu of round wire in order to "fill in the gaps" and have a 10–15% smaller overall diameter for the same cross-sectional area or a 20–25% larger cross-sectional area for the same overall diameter. Ontario Hydro (Hydro One) introduced trapezoidal-shaped wire ACSR conductor designs in

2968-559: Is classified as High Strength steel. The equivalent material per the ASTM standards is the GA2 strength grade and called Regular Strength steel. The CSA S3A strength grade is classified as Extra High Strength steel. The equivalent material per the ASTM standards is the GA3 strength grade called High Strength. The present day CSA standards for overhead electrical conductor do not yet officially recognize

3074-536: Is galvanized steel, but zinc, 5% or 10% aluminium alloy and trace mischmetal coated steel (sometimes called by the trade-names Bezinal or Galfan ) and aluminium-clad steel (sometimes called by the trade-name Alumoweld) are also available. Higher strength steel may also be used. In the United States the most commonly used steel is designated GA2 for galvanized steel (G) with class A zinc coating thickness (A) and regular strength (2). Class C zinc coatings are thicker than class A and provide increased corrosion protection at

3180-441: Is generally purchased that the reel can accommodate to avoid more splices than are absolutely necessary. Splices are designed to run cooler than the conductor. The temperature of the splice is kept lower by having a larger cross-sectional area and thus less electrical resistance than the conductor. Heat generated at the splice is also dissipated faster due to the larger diameter of the splice. Failures of splices are of concern, as

3286-536: Is more important than the long term performance of the splice. Causes for splice failures are numerous. Some of the main failure modes are related to installation issues, such as: insufficient cleaning (wire brushing) of the conductor to eliminate the aluminium oxide layer (which has a high resistance {is a poor electrical conductor}), improper application of conducting grease, improper compression force, improper compression locations or number of compressions. Splice failures can also be due to Aeolian vibration damage as

Aluminium-conductor steel-reinforced cable - Misplaced Pages Continue

3392-540: Is not considered in these cases. For ACSR conductors with an odd number of aluminium layers however, a magnetization factor is used to accurately calculate the AC resistance. The correction method for single-layer ACSR is different than that used for three-layer conductors. Due to applying the magnetization factor, a conductor with an odd number of layers has an AC resistance slightly higher than an equivalent conductor with an even number of layers. Due to higher hysteresis losses in

3498-410: Is not necessarily 0 and depends on the type of load impedance, Z y . Inductive and capacitive loads will cause current to either lag or lead the voltage. However, the relative phase angle between each pair of lines (1 to 2, 2 to 3, and 3 to 1) will still be −120°. By applying Kirchhoff's current law (KCL) to the neutral node, the three phase currents sum to the total current in the neutral line. In

3604-441: Is possible with any number of phases greater than one. However, two-phase systems do not have neutral-current cancellation and thus use conductors less efficiently, and more than three phases complicates infrastructure unnecessarily. Additionally, in some practical generators and motors, two phases can result in a less smooth (pulsating) torque. Three-phase systems may have a fourth wire, common in low-voltage distribution. This

3710-458: Is result of a changing magnetic field which influences the distribution of an electric current flowing within an electrical conductor due to electromagnetic induction. When an alternating current (AC) flows through an isolated conductor, it creates an associated alternating magnetic field around it. The alternating magnetic field induces eddy currents in adjacent conductors, altering the overall distribution of current flowing through them. The result

3816-436: Is termed stress relief . The relief of internal stresses is a thermodynamically spontaneous process ; however, at room temperatures, it is a very slow process. The high temperatures at which annealing occurs serve to accelerate this process. The reaction that facilitates returning the cold-worked metal to its stress-free state has many reaction pathways, mostly involving the elimination of lattice vacancy gradients within

3922-422: Is that the current is concentrated in the areas of the conductor furthest away from nearby conductors carrying current in the same direction. Hysteresis in an ACSR conductor is due to the atomic dipoles in the steel core changing direction due to induction from the 60 or 50 Hertz AC current in the conductor. Hysteresis losses in ACSR are undesirable and can be minimized by using an even number of aluminium layers in

4028-403: Is the neutral wire. The neutral allows three separate single-phase supplies to be provided at a constant voltage and is commonly used for supplying multiple single-phase loads. The connections are arranged so that, as far as possible in each group, equal power is drawn from each phase. Further up the distribution system , the currents are usually well balanced. Transformers may be wired to have

4134-404: Is the phase of delta impedance ( Z Δ ). Inspection of a phasor diagram, or conversion from phasor notation to complex notation, illuminates how the difference between two line-to-neutral voltages yields a line-to-line voltage that is greater by a factor of √ 3 . As a delta configuration connects a load across phases of a transformer, it delivers the line-to-line voltage difference, which

4240-419: Is to originate a uniform and stable microstructure that most closely resembles the metal's phase diagram equilibrium microstructure, thus letting the metal attain relatively low levels of hardness, yield strength and ultimate strength with high plasticity and toughness. To perform a full anneal on a steel for example, steel is heated to slightly above the austenitic temperature and held for sufficient time to allow

4346-408: Is used as a medium for quenching usually in the form of brine (salt water). Brine provides faster cooling rates than water. This is because when an object is quenched in water steam bubbles form on the surface of the object reducing the surface area the water is in contact with. The salt in the brine reduces the formation of steam bubbles on the object's surface, meaning there is a larger surface area of

Aluminium-conductor steel-reinforced cable - Misplaced Pages Continue

4452-468: Is used for turning normal ferrite into malleable ferrite. It consists of heating, cooling and then heating again from 4 to 8 hours. Resistive heating can be used to efficiently anneal copper wire ; the heating system employs a controlled electrical short circuit . It can be advantageous because it does not require a temperature -regulated furnace like other methods of annealing. The process consists of two conductive pulleys ( step pulleys ), which

4558-582: The UK may supply one phase and neutral at a high current (up to 100  A ) to one property, while others such as Germany may supply 3 phases and neutral to each customer, but at a lower fuse rating, typically 40–63 A per phase, and "rotated" to avoid the effect that more load tends to be put on the first phase. Based on wye (Y) and delta (Δ) connection. Generally, there are four different types of three-phase transformer winding connections for transmission and distribution purposes: In North America,

4664-425: The austenite transform into bainite or martensite , but rather have it completely transform to pearlite and ferrite or cementite . This means that steels that are very hardenable (i.e. tend to form martensite under moderately low cooling rates) have to be furnace cooled. The details of the process depend on the type of metal and the precise alloy involved. In any case the result is a more ductile material but

4770-508: The "neutral" and either of the center-tapped phase points. In the perfectly balanced case all three lines share equivalent loads. Examining the circuits, we can derive relationships between line voltage and current, and load voltage and current for wye- and delta-connected loads. In a balanced system each line will produce equal voltage magnitudes at phase angles equally spaced from each other. With V 1 as our reference and V 3 lagging V 2 lagging V 1 , using angle notation , and V LN

4876-403: The 1980s to replace existing round-wire ACSR designs (they called them compact conductors; these conductor types are now called ACSR/TW). Ontario Hydro's trapezoidal-shaped wire (TW) designs used the same steel core but increased the aluminium content of the conductor to match the overall diameter of the former round-wire designs (they could then use the same hardware fittings for both the round and

4982-524: The ASTM equivalent GA4 or GA5 grades. The present day CSA standards do not yet officially recognize the ASTM "M" family of zinc alloy coating material. Canadian utilities are using conductors built with the higher strength steels with the "M" zinc alloy coating. Lay of a conductor is determined by four extended fingers; "right" or "left" direction of the lay is determined depending if it matches finger direction from right hand or left hand respectively. Overhead aluminium (AAC, AAAC, ACAR) and ACSR conductors in

5088-447: The TW conductors). Hydro One's designs for their trapezoidal ACSR/TW conductors only use even numbers of aluminium layers (either two layers or four layers). They do not use designs which have odd number of layers (three layers) due to that design incurring higher hysteresis losses in the steel core. Also in the 1980s, Bonneville Power Administration (BPA) introduced TW designs where the size of

5194-473: The USA are always manufactured with the outer conductor layer with a right-hand lay. Going toward the center, each layer has alternating lays. Some conductor types (e.g. copper overhead conductor, OPGW , steel EHS) are different and have left-hand lay on the outer conductor. Some South American countries specify left-hand lay for the outer conductor layer on their ACSR, so those are wound differently than those used in

5300-697: The USA. ACSR conductors are available in numerous specific sizes, with single or multiple center steel wires and generally larger quantities of aluminium strands. Although rarely used, there are some conductors that have more steel strands than aluminum strands. An ACSR conductor can in part be denoted by its stranding, for example, an ACSR conductor with 72 aluminium strands with a core of 7 steel strands will be called 72/7 ACSR conductor. Cables generally range from #6 AWG ("6/1" – six outer aluminum conductors and one steel reinforcing conductor) to 2167 kcmil ("72/7" – seventy two outer aluminum conductors and seven steel reinforcing conductors). To help avoid confusion due to

5406-521: The aluminium strands are fully annealed. Annealing the aluminium strands reduces the composite conductor strength, but after installation, permanent elongation of the aluminium strands results in a much larger percentage of the conductor tension being carried in the steel core than is true for standard ACSR. This in turn yields reduced composite thermal elongation and increased self-damping. The major advantages of ACSS are: The major disadvantages of ACSS are: Twisted pair (TP) conductor (sometimes called by

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5512-472: The aluminium wires in the first two layers are trapezoidal shaped and sized so that each aluminium layer forms a stranded tube which does not collapse onto the layer beneath when under tension, but maintains a small annular gap between layers. The trapezoidal wire layers are separated from each other and from the steel core by the two smaller annular gaps that permit movement between the layers. The round aluminium wire layers are in tight contact with each other and

5618-409: The appearance of new strain-free grains. The grain size and shape do not change. The second stage is recrystallization , where new strain-free grains nucleate and grow to replace those deformed by internal stresses. If annealing is allowed to continue once recrystallization has completed, then grain growth (the third stage) occurs. In grain growth, the microstructure starts to coarsen and may cause

5724-531: The balanced case: In the delta circuit, loads are connected across the lines, and so loads see line-to-line voltages: (Φ v1 is the phase shift for the first voltage, commonly taken to be 0°; in this case, Φ v2 = −120° and Φ v3 = −240° or 120°.) Further: where θ is the phase of delta impedance ( Z Δ ). Relative angles are preserved, so I 31 lags I 23 lags I 12 by 120°. Calculating line currents by using KCL at each delta node gives and similarly for each other line: where, again, θ

5830-461: The body of the metal. The creation of lattice vacancies is governed by the Arrhenius equation , and the migration/diffusion of lattice vacancies are governed by Fick's laws of diffusion. In steel, there is a decarburization mechanism that can be described as three distinct events: the reaction at the steel surface, the interstitial diffusion of carbon atoms and the dissolution of carbides within

5936-458: The conductor contributes significantly to the overall current that needs to travel through the line, and thus contributes to resistive losses in the line. For more information on transmission line inductance and capacitance, see electric power transmission and overhead power line . The skin effect decreases the cross sectional area in which the current travels through the conductor as AC frequency increases. For alternating current, most (63%) of

6042-417: The conductor. Due to the cancelling effect of the magnetic field from the opposing lay (right-hand and left-hand) conductors for two aluminium layers there is significantly less hysteresis loss in the steel core than there would be for one or three aluminium layers where the magnetic field does not cancel out. The hysteresis effect is negligible on ACSR conductors with even numbers of aluminium layers and so it

6148-399: The country. At the power station, transformers change the voltage from generators to a level suitable for transmission in order to minimize losses. After further voltage conversions in the transmission network, the voltage is finally transformed to the standard utilization before power is supplied to customers. Most automotive alternators generate three-phase AC and rectify it to DC with

6254-452: The crystal lattice, which allows these dopant atoms to function properly as dopants in the semiconducting material. Normalization is an annealing process applied to ferrous alloys to give the material a uniform fine-grained structure and to avoid excess softening in steel. It involves heating the steel to 20–50 °C above its upper critical point, soaking it for a short period at that temperature and then allowing it to cool in air. Heating

6360-461: The distribution network so the loads are balanced as much as possible, since the same principles that apply to individual premises also apply to the wide-scale distribution system power. Hence, every effort is made by supply authorities to distribute the power drawn on each of the three phases over a large number of premises so that, on average, as nearly as possible a balanced load is seen at the point of supply. For domestic use, some countries such as

6466-414: The distribution of current within each conductor will be constrained to smaller regions. The resulting current crowding is termed as the proximity effect. This crowding gives an increase in the effective AC resistance of the circuit, with the effect at 60 Hertz being greater than at 50 Hertz. Geometry, conductivity, and frequency are factors in determining the amount of proximity effect. The proximity effect

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6572-404: The effect of redistributing and eradicating the dislocations in metals and (to a lesser extent) in ceramics. This alteration to existing dislocations allows a metal object to deform more easily, increasing its ductility. The amount of process-initiating Gibbs free energy in a deformed metal is also reduced by the annealing process. In practice and industry, this reduction of Gibbs free energy

6678-417: The electric current flows between the surface and the skin depth, δ, which depends on the frequency of the current and the electrical (conductivity) and magnetic properties of the conductor. This decreased area causes the resistance to rise due to the inverse relationship between resistance and conductor cross sectional area. The skin effect benefits the design, as it causes the current to be concentrated towards

6784-407: The expense of reduced tensile strength. A regular strength galvanized steel core with Class C coating thickness would be designated GC2. Higher strength grades of steel are designated high-strength (3), extra-high-strength (4), and ultra-high-strength (5). An ultra-high-strength galvanized steel core with class A coating thickness would be designated GA5. The use of higher strength steel cores increases

6890-516: The expense of reduced tensile strength. Aluminium-clad steel is commonly specified for coastal applications. IEC and CSA use a different naming convention. The most commonly used steel is S1A for S1 regular strength steel with a class A coating. S1 steel has slightly lower tensile strength than the regular strength steel used in the United States. Per the Canadian CSA standards the S2A strength grade

6996-431: The field. These can be detected using thermal camera, thermal probes, and direct resistance measurements, even when the line is energized. Such splices usually require replacement, either on deenergized line, by doing a temporary bypass to replace it, or by adding a big splice over the existing splice, without disconnecting. When ACSR is new, the aluminium has a shiny surface which has a low emissivity for heat radiation and

7102-399: The geometry of the conductor as differentiated by the conductor name, these phenomena have varying degrees of affecting the overall resistance in the conductor at AC vs DC frequency. Often not tabulated with ACSR conductors is the electrical reactance of the conductor, which is due largely to the spacing between the other current carrying conductors and the conductor radius. The reactance of

7208-553: The growth of power-transmission network grids on continents around the globe. Mikhail Dolivo-Dobrovolsky developed a three-phase electrical generator and a three-phase electric motor in 1888 and studied star and delta connections . His three-phase three-wire transmission system was displayed in 1891 in Germany at the International Electrotechnical Exhibition , where Dolivo-Dobrovolsky used

7314-528: The identity of phases is required if two sources could be connected at the same time. A direct connection between two different phases is a short circuit and leads to flow of unbalanced current. As compared to a single-phase AC power supply that uses two current-carrying conductors (phase and neutral ), a three-phase supply with no neutral and the same phase-to-ground voltage and current capacity per phase can transmit three times as much power by using just 1.5 times as many wires (i.e., three instead of two). Thus,

7420-418: The length of conductor which can be contained on one reel. As a result, splicing is often necessary to join conductors to provide the desired length. It is important that the splice not be the weak link. A splice (joint) must have high physical strength along with a high electrical current rating. Within the limitations of the equipment used to install the conductor from the reels, a sufficient length of conductor

7526-611: The low-resistivity aluminum on the outside of the conductor. To illustrate the impact of the skin effect, the American Society for Testing and Materials (ASTM) standard includes the conductivity of the steel core when calculating the DC and AC resistance of the conductor, but the IEC and CSA Group standards do not. In a conductor (ACSR and other types) carrying AC current, if currents are flowing through one or more other nearby conductors

7632-446: The lower critical temperature of steel. Cold-worked steel normally tends to possess increased hardness and decreased ductility, making it difficult to work. Process annealing tends to improve these characteristics. This is mainly carried out on cold-rolled steel like wire-drawn steel, centrifugally cast ductile iron pipe etc. A full annealing typically results in the second most ductile state a metal can assume for metal alloy. Its purpose

7738-424: The material to fully form austenite or austenite-cementite grain structure. The material is then allowed to cool very slowly so that the equilibrium microstructure is obtained. In most cases this means the material is allowed to furnace cool (the furnace is turned off and the steel is let cool down inside) but in some cases it is air cooled. The cooling rate of the steel has to be sufficiently slow so as to not let

7844-450: The metal is softened and prepared for further work such as shaping, stamping, or forming. Many other materials, including glass and plastic films , use annealing to improve the finished properties. Annealing occurs by the diffusion of atoms within a solid material, so that the material progresses towards its equilibrium state. Heat increases the rate of diffusion by providing the energy needed to break bonds. The movement of atoms has

7950-405: The metal to lose a substantial part of its original strength. This can however be regained with hardening . The high temperature of annealing may result in oxidation of the metal's surface, resulting in scale. If scale must be avoided, annealing is carried out in a special atmosphere , such as with endothermic gas (a mixture of carbon monoxide , hydrogen gas , and nitrogen gas ). Annealing

8056-441: The most important advantages of symmetric systems. In a three-phase system feeding a balanced and linear load, the sum of the instantaneous currents of the three conductors is zero. In other words, the current in each conductor is equal in magnitude to the sum of the currents in the other two, but with the opposite sign. The return path for the current in any phase conductor is the other two phase conductors. Constant power transfer

8162-426: The neutral (which is common to the three phases). When a group of customers sharing the neutral draw unequal phase currents, the common neutral wire carries the currents resulting from these imbalances. Electrical engineers try to design the three-phase power system for any one location so that the power drawn from each of three phases is the same, as far as possible at that site. Electrical engineers also try to arrange

8268-550: The neutral is connected to the "common star point" of all supply windings. In such a system, all three phases will have the same magnitude of voltage relative to the neutral. Other non-symmetrical systems have been used. The four-wire wye system is used when a mixture of single-phase and three-phase loads are to be served, such as mixed lighting and motor loads. An example of application is local distribution in Europe (and elsewhere), where each customer may be only fed from one phase and

8374-404: The number of aluminium strands is different between Grosbeak and Egret, differing sizes of the aluminium strands are used to offset the change in the number of strands such that the total amount of aluminium remains the same. Differences in the number of steel strands result in varying weights of the steel portion and also result in different overall conductor diameters. Most utilities standardize on

8480-565: The numerous combinations of stranding of the steel and aluminium strands, code words are used to specify a specific conductor version. In North America bird names are used for the code words while animal names are used elsewhere. For instance in North America, Grosbeak is a 322.3 mm (636 kcmil) ACSR conductor with 26/7 Aluminium/Steel stranding whereas Egret is the same total aluminium size ( 322.3 mm , 636 kcmil conductor) but with 30/19 Aluminium/Steel stranding. Although

8586-464: The object in contact with the water, thus facilitating better conduction of heat from the object to the surrounding water. Quench hardening is generally applicable to some ferrous alloys, but not copper alloys. In the semiconductor industry, silicon wafers are annealed to repair atomic level disorder from steps like ion implantation . In the process step, dopant atoms, usually boron , phosphorus or arsenic , move into substitutional positions in

8692-419: The other conductors and one third of a cycle before the remaining conductor. This phase delay gives constant power transfer to a balanced linear load. It also makes it possible to produce a rotating magnetic field in an electric motor and generate other phase arrangements using transformers (for instance, a two-phase system using a Scott-T transformer ). The amplitude of the voltage difference between two phases

8798-503: The parts in and out. Once the annealing process is successfully completed, workpieces are sometimes left in the oven so the parts cool in a controllable way. While some workpieces are left in the oven to cool in a controlled fashion, other materials and alloys are removed from the oven. Once removed from the oven, the workpieces are often quickly cooled off in a process known as quench hardening. Typical methods of quench hardening materials involve media such as air, water, oil, or salt. Salt

8904-401: The phase and anti-phase lines is 240 V (200%), and the neutral to "high leg" voltage is ≈ 208 V (173%). The reason for providing the delta connected supply is usually to power large motors requiring a rotating field. However, the premises concerned will also require the "normal" North American 120 V supplies, two of which are derived (180 degrees "out of phase") between

9010-531: The polyphase alternator is key in the history of electrification, as is the power transformer. These inventions enabled power to be transmitted by wires economically over considerable distances. Polyphase power enabled the use of water-power (via hydroelectric generating plants in large dams) in remote places, thereby allowing the mechanical energy of the falling water to be converted to electricity, which then could be fed to an electric motor at any location where mechanical work needed to be done. This versatility sparked

9116-433: The power grid and use a split-phase system to the panelboard from which most branch circuits will carry 120 V. Circuits designed for higher powered devices such as stoves, dryers, or outlets for electric vehicles carry 240 V. In Europe, three-phase power is normally delivered to the panelboard and further to higher powered devices. At the power station , an electrical generator converts mechanical power into

9222-443: The power lost in the distribution of power is minimal. Impedance is a combination of two quantities: resistance and reactance. The resistances of ASCR conductors are tabulated for different conductor designs by the manufacturer at DC and AC frequency assuming specific operating temperatures. The reasons that resistance changes with frequency are largely due to the skin effect , the proximity effect , and hysteresis loss . Depending on

9328-499: The properties required. With knowledge of the composition and phase diagram , heat treatment can be used to adjust from harder and more brittle to softer and more ductile. In the case of ferrous metals , such as steel , annealing is performed by heating the material (generally until glowing) for a while and then slowly letting it cool to room temperature in still air. Copper , silver and brass can be either cooled slowly in air, or quickly by quenching in water. In this fashion,

9434-566: The ratio of capacity to conductor material is doubled. The ratio of capacity to conductor material increases to 3:1 with an ungrounded three-phase and center-grounded single-phase system (or 2.25:1 if both use grounds with the same gauge as the conductors). That leads to higher efficiency, lower weight, and cleaner waveforms. Three-phase supplies have properties that make them desirable in electric power distribution systems: However, most loads are single-phase. In North America, single-family houses and individual apartments are supplied one phase from

9540-399: The same frequency and voltage amplitude relative to a common reference, but with a phase difference of one third of a cycle (i.e., 120 degrees out of phase) between each. The common reference is usually connected to ground and often to a current-carrying conductor called the neutral. Due to the phase difference, the voltage on any conductor reaches its peak at one third of a cycle after one of

9646-402: The small vibrations of the conductor over time cause damage (breakage) of the aluminium strands near the ends of the splice. Special splices (two-piece splices) are required on SD-type conductors as the gap between the trapezoidal aluminium layer and the steel core prevents the compression force on the splice to the steel core to be adequate. A two-piece design has a splice for the steel core and

9752-564: The special properties they offer which provide sufficient advantage to justify their added expense. Special conductors may be more economic, offer increased reliability, or provide a unique solution to an otherwise difficult, of impossible, design problem. The main types of special conductors include "trapezoidal wire conductor" (TW) - a conductor having aluminium strands with a trapezoidal shape rather than round) and "self-damping" (SD), sometimes called "self-damping conductor" (SDC). A similar, higher temperature conductor made from annealed aluminium

9858-535: The steel and associated heating of the core, an odd-layer design will have a lower ampacity rating (up to a 10% de-rate) than an equivalent even-layer design. All standard ACSR conductors smaller than Partridge ( 135.2 mm {266.8 kcmil} 26/7 Aluminium/Steel) have only one layer due to their small diameters so the hysteresis losses cannot be avoided. ACSR is widely used due to its efficient and economical design. Variations of standard (sometimes called traditional or conventional) ACSR are used in some cases due to

9964-621: The steel core was increased to maintain the same Aluminium/Steel ratio. Self-damping (ACSR/SD) is a nearly obsolete conductor technology and is rarely used for new installations. It is a concentric-lay stranded, self-damping conductor designed to control wind induced ( Aeolian-type ) vibration in overhead transmission lines by internal damping. Self-damping conductors consists of a central core of one or more round steel wires surrounded by two layers of trapezoidal shaped aluminium wires. One or more layers of round aluminium wires may be added as required. SD conductor differs from conventional ACSR in that

10070-601: The steel just above its upper critical point creates austenitic grains (much smaller than the previous ferritic grains), which during cooling, form new ferritic grains with a further refined grain size. The process produces a tougher, more ductile material, and eliminates columnar grains and dendritic segregation that sometimes occurs during casting. Normalizing improves machinability of a component and provides dimensional stability if subjected to further heat treatment processes. Process annealing, also called intermediate annealing , subcritical annealing , or in-process annealing ,

10176-437: The steel. The three stages of the annealing process that proceed as the temperature of the material is increased are: recovery , recrystallization , and grain growth . The first stage is recovery , and it results in softening of the metal through removal of primarily linear defects called dislocations and the internal stresses they cause. Recovery occurs at the lower temperature stage of all annealing processes and before

10282-536: The strands used for both the aluminum and steel strands vary for different ACSR conductors. ACSR cable still depends on the tensile strength of the aluminium; it is only reinforced by the steel. Because of this, its continuous operating temperature is limited to 75 °C (167 °F), the temperature at which aluminium begins to anneal and soften over time. For situations where higher operating temperatures are required, aluminium-conductor steel-supported ( ACSS ) may be used. The standard steel core used for ACSR

10388-440: The system to transmit electric power at the distance of 176 km (110 miles) with 75% efficiency . In 1891 he also created a three-phase transformer and short-circuited ( squirrel-cage ) induction motor . He designed the world's first three-phase hydroelectric power plant in 1891. Inventor Jonas Wenström received in 1890 a Swedish patent on the same three-phase system. The possibility of transferring electrical power from

10494-495: The tensile strength of the conductor allowing for higher tensions which results in lower sag. Zinc-5% aluminium mischmetal coatings are designated with an "M". These coatings provide increased corrosion protection and heat resistance compared to zinc alone. Regular strength Class "A" mischmetal thickness weight coated regular strength steel would be designated MA2. Aluminium-clad steel is designated as "AW". Aluminium-clad steel offers increased corrosion protection and conductivity at

10600-567: The trade-names T-2 or VR) has the two sub-conductors twisted (usually with a left-hand lay) about one another generally with a lay length of approximately three meters (nine feet). The conductor cross-section of the TP is a rotating "figure-8". The sub-conductors can be any type of standard ACSR conductor but the conductors need to match one another to provide mechanical balance. The major advantages of TP conductor are: The major disadvantages of TP conductor are: Many electrical circuits are longer than

10706-456: The transformers has failed or needs to be removed. In open delta, each transformer must carry current for its respective phases as well as current for the third phase, therefore capacity is reduced to 87%. With one of three transformers missing and the remaining two at 87% efficiency, the capacity is 58% ( 2 ⁄ 3 of 87%). Where a delta-fed system must be grounded for detection of stray current to ground or protection from surge voltages,

10812-532: The underlying trapezoidal wire layer. Under vibration, the steel core and the aluminium layers vibrate with different frequencies and impact damping results. This impact damping is sufficient to keep any Aeolian vibration to a low level. The use of trapezoidal strands also results in reduced conductor diameter for a given AC resistance per mile. The major advantages ACSR/SD are: The major disadvantages ACSR/SD are: Aluminium-conductor steel supported (ACSS) conductor visually appears to be similar to standard ACSR but

10918-501: The voltage between the line and the neutral we have: These voltages feed into either a wye- or delta-connected load. The voltage seen by the load will depend on the load connection; for the wye case, connecting each load to a phase (line-to-neutral) voltages gives where Z total is the sum of line and load impedances ( Z total = Z LN + Z Y ), and θ is the phase of the total impedance ( Z total ). The phase angle difference between voltage and current of each phase

11024-479: The voltage on each wire is 120 degrees phase shifted relative to each of the other wires. Because it is an AC system, it allows the voltages to be easily stepped up using transformers to high voltage for transmission and back down for distribution, giving high efficiency. A three-wire three-phase circuit is usually more economical than an equivalent two-wire single-phase circuit at the same line-to-ground voltage because it uses less conductor material to transmit

11130-408: The wire passes across after it is drawn. The two pulleys have an electrical potential across them, which causes the wire to form a short circuit. The Joule effect causes the temperature of the wire to rise to approximately 400 °C. This temperature is affected by the rotational speed of the pulleys, the ambient temperature, and the voltage applied. Where t is the temperature of the wire, K

11236-426: Was doing research on rotating magnetic fields . Ferraris experimented with different types of asynchronous electric motors . The research and his studies resulted in the development of an alternator , which may be thought of as an alternating-current motor operating in reverse, so as to convert mechanical (rotating) power into electric power (as alternating current). On 11 March 1888, Ferraris published his research in

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