SM30 is a Polish series of diesel shunting locomotives used by PKP and industry, built by Fablok , Chrzanów (factory designation Ls300E ). They were also used for a local traffic.
103-667: SM30 locomotive is the first Polish diesel locomotive equipped with electrical transmission . A design was worked out by the Central Rolling Stock Industry Construction Bureau in Poznań. The prototype was constructed in Fablok , Chrzanów in 1957. 909 items were built in 1957-1970, 302 of them found place in PKP , the rest worked in the industry (with designations Ls300 or SM30). The locomotive
206-639: A flashover and loss of supply. Oscillatory motion of the physical line is termed conductor gallop or flutter depending on the frequency and amplitude of oscillation. Electric power can be transmitted by underground power cables . Underground cables take up no right-of-way, have lower visibility, and are less affected by weather. However, cables must be insulated. Cable and excavation costs are much higher than overhead construction. Faults in buried transmission lines take longer to locate and repair. In some metropolitan areas, cables are enclosed by metal pipe and insulated with dielectric fluid (usually an oil) that
309-430: A galvanometer , but this method involves breaking the electrical circuit , which is sometimes inconvenient. Current can also be measured without breaking the circuit by detecting the magnetic field associated with the current. Devices, at the circuit level, use various techniques to measure current: Joule heating, also known as ohmic heating and resistive heating , is the process of power dissipation by which
412-453: A rectifier . Direct current may flow in a conductor such as a wire, but can also flow through semiconductors , insulators , or even through a vacuum as in electron or ion beams . An old name for direct current was galvanic current . Natural observable examples of electric current include lightning , static electric discharge , and the solar wind , the source of the polar auroras . Man-made occurrences of electric current include
515-411: A circuit, as an equal flow of negative charges in the opposite direction. Since current can be the flow of either positive or negative charges, or both, a convention is needed for the direction of current that is independent of the type of charge carriers . Negatively charged carriers, such as the electrons (the charge carriers in metal wires and many other electronic circuit components), therefore flow in
618-405: A common lead-acid electrochemical cell, electric currents are composed of positive hydronium ions flowing in one direction, and negative sulfate ions flowing in the other. Electric currents in sparks or plasma are flows of electrons as well as positive and negative ions. In ice and in certain solid electrolytes, the electric current is entirely composed of flowing ions. In a metal , some of
721-416: A definition of current independent of the type of charge carriers, conventional current is defined as moving in the same direction as the positive charge flow. So, in metals where the charge carriers (electrons) are negative, conventional current is in the opposite direction to the overall electron movement. In conductors where the charge carriers are positive, conventional current is in the same direction as
824-1096: A few centimetres in diameter), much of the current flow is concentrated near the surface due to the skin effect . The center of the conductor carries little current but contributes weight and cost. Thus, multiple parallel cables (called bundle conductors ) are used for higher capacity. Bundle conductors are used at high voltages to reduce energy loss caused by corona discharge . Today, transmission-level voltages are usually 110 kV and above. Lower voltages, such as 66 kV and 33 kV, are usually considered subtransmission voltages, but are occasionally used on long lines with light loads. Voltages less than 33 kV are usually used for distribution . Voltages above 765 kV are considered extra high voltage and require different designs. Overhead transmission wires depend on air for insulation, requiring that lines maintain minimum clearances. Adverse weather conditions, such as high winds and low temperatures, interrupt transmission. Wind speeds as low as 23 knots (43 km/h) can permit conductors to encroach operating clearances, resulting in
927-447: A localized high current. These regions may be initiated by field electron emission , but are then sustained by localized thermionic emission once a vacuum arc forms. These small electron-emitting regions can form quite rapidly, even explosively, on a metal surface subjected to a high electrical field. Vacuum tubes and sprytrons are some of the electronic switching and amplifying devices based on vacuum conductivity. Superconductivity
1030-428: A metal wire is connected across the two terminals of a DC voltage source such as a battery , the source places an electric field across the conductor. The moment contact is made, the free electrons of the conductor are forced to drift toward the positive terminal under the influence of this field. The free electrons are therefore the charge carrier in a typical solid conductor. For a steady flow of charge through
1133-404: A millimetre per second. To take a different example, in the near-vacuum inside a cathode-ray tube , the electrons travel in near-straight lines at about a tenth of the speed of light . Any accelerating electric charge, and therefore any changing electric current, gives rise to an electromagnetic wave that propagates at very high speed outside the surface of the conductor. This speed is usually
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#17327764238391236-575: A much smaller benefit than the squared reduction provided by multiplying the voltage. Long-distance transmission is typically done with overhead lines at voltages of 115 to 1,200 kV. At higher voltages, where more than 2,000 kV exists between conductor and ground, corona discharge losses are so large that they can offset the lower resistive losses in the line conductors. Measures to reduce corona losses include larger conductor diameter, hollow cores or conductor bundles. Factors that affect resistance and thus loss include temperature, spiraling, and
1339-444: A network might otherwise result in synchronization problems and cascading failures . Electricity is transmitted at high voltages to reduce the energy loss due to resistance that occurs over long distances. Power is usually transmitted through overhead power lines . Underground power transmission has a significantly higher installation cost and greater operational limitations, but lowers maintenance costs. Underground transmission
1442-408: A particular band called the valence band . Semiconductors and insulators are distinguished from metals because the valence band in any given metal is nearly filled with electrons under usual operating conditions, while very few (semiconductor) or virtually none (insulator) of them are available in the conduction band , the band immediately above the valence band. The ease of exciting electrons in
1545-426: A practice that later became known as distributed generation using large numbers of small generators. Transmission of alternating current (AC) became possible after Lucien Gaulard and John Dixon Gibbs built what they called the secondary generator, an early transformer provided with 1:1 turn ratio and open magnetic circuit, in 1881. The first long distance AC line was 34 kilometres (21 miles) long, built for
1648-475: A significant fraction of the speed of light, as can be deduced from Maxwell's equations , and is therefore many times faster than the drift velocity of the electrons. For example, in AC power lines , the waves of electromagnetic energy propagate through the space between the wires, moving from a source to a distant load , even though the electrons in the wires only move back and forth over a tiny distance. The ratio of
1751-405: A surface, the current I (in amperes) can be calculated with the following equation: I = Q t , {\displaystyle I={Q \over t}\,,} where Q is the electric charge transferred through the surface over a time t . If Q and t are measured in coulombs and seconds respectively, I is in amperes. More generally, electric current can be represented as
1854-412: A tram system. Traction motors can be powered in series connection , parallel connection and parallel connection with field reduction of 40 to 60%. Traction motors are series devices with 60 kW (80 hp) hour power. Main generator (PABOM-186a type) is a DC machine with 600 V and 367 A . Its power rating whilst working with 1500 rpm . is 220 kW (300 hp). During engine starting
1957-537: A transformer and alternating current lighting system led Westinghouse to begin installing AC systems later that year. In 1888 the first designs for an AC motor appeared. These were induction motors running on polyphase current, independently invented by Galileo Ferraris and Nikola Tesla . Westinghouse licensed Tesla's design. Practical three-phase motors were designed by Mikhail Dolivo-Dobrovolsky and Charles Eugene Lancelot Brown . Widespread use of such motors were delayed many years by development problems and
2060-591: A wide area reduced costs. The most efficient plants could be used to supply varying loads during the day. Reliability was improved and capital costs were reduced, because stand-by generating capacity could be shared over many more customers and a wider area. Remote and low-cost sources of energy, such as hydroelectric power or mine-mouth coal, could be exploited to further lower costs. The 20th century's rapid industrialization made electrical transmission lines and grids critical infrastructure . Interconnection of local generation plants and small distribution networks
2163-603: Is I , which originates from the French phrase intensité du courant , (current intensity). Current intensity is often referred to simply as current . The I symbol was used by André-Marie Ampère , after whom the unit of electric current is named, in formulating Ampère's force law (1820). The notation travelled from France to Great Britain, where it became standard, although at least one journal did not change from using C to I until 1896. The conventional direction of current, also known as conventional current ,
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#17327764238392266-496: Is 1500 rpm. Electrical transmission Electric power transmission is the bulk movement of electrical energy from a generating site, such as a power plant , to an electrical substation . The interconnected lines that facilitate this movement form a transmission network . This is distinct from the local wiring between high-voltage substations and customers, which is typically referred to as electric power distribution . The combined transmission and distribution network
2369-578: Is a Bo′Bo′ locomotive, what means it runs on two bogies , each equipped with two axles . The general construction of this engine is relatively simple. Being the pioneer machine in the Polish railway industry, it incorporated many solutions from other branches of industry, i.e. the first engine to be mounted, Wola V-300, was taken from tank construction, main DC current generator was in fact stationery generator and traction motors were taken from trams . As
2472-490: Is a network of power stations , transmission lines, and substations . Energy is usually transmitted within a grid with three-phase AC . Single-phase AC is used only for distribution to end users since it is not usable for large polyphase induction motors . In the 19th century, two-phase transmission was used but required either four wires or three wires with unequal currents. Higher order phase systems require more than three wires, but deliver little or no benefit. While
2575-523: Is a phenomenon of exactly zero electrical resistance and expulsion of magnetic fields occurring in certain materials when cooled below a characteristic critical temperature . It was discovered by Heike Kamerlingh Onnes on April 8, 1911 in Leiden . Like ferromagnetism and atomic spectral lines , superconductivity is a quantum mechanical phenomenon. It is characterized by the Meissner effect ,
2678-411: Is arbitrarily defined as the direction in which positive charges flow. In a conductive material , the moving charged particles that constitute the electric current are called charge carriers . In metals, which make up the wires and other conductors in most electrical circuits , the positively charged atomic nuclei of the atoms are held in a fixed position, and the negatively charged electrons are
2781-683: Is current. Magnetic fields can also be used to make electric currents. When a changing magnetic field is applied to a conductor, an electromotive force (EMF) is induced, which starts an electric current, when there is a suitable path. When an electric current flows in a suitably shaped conductor at radio frequencies , radio waves can be generated. These travel at the speed of light and can cause electric currents in distant conductors. In metallic solids, electric charge flows by means of electrons , from lower to higher electrical potential . In other media, any stream of charged objects (ions, for example) may constitute an electric current. To provide
2884-668: Is either static or circulated via pumps. If an electric fault damages the pipe and leaks dielectric, liquid nitrogen is used to freeze portions of the pipe to enable draining and repair. This extends the repair period and increases costs. The temperature of the pipe and surroundings are monitored throughout the repair period. Underground lines are limited by their thermal capacity, which permits less overload or re-rating lines. Long underground AC cables have significant capacitance , which reduces their ability to provide useful power beyond 50 miles (80 kilometres). DC cables are not limited in length by their capacitance. Commercial electric power
2987-473: Is improved at higher voltage and lower current. The reduced current reduces heating losses. Joule's first law states that energy losses are proportional to the square of the current. Thus, reducing the current by a factor of two lowers the energy lost to conductor resistance by a factor of four for any given size of conductor. The optimum size of a conductor for a given voltage and current can be estimated by Kelvin's law for conductor size, which states that size
3090-423: Is in a nanowire , for every energy there is a state with electrons flowing in one direction and another state with the electrons flowing in the other. For a net current to flow, more states for one direction than for the other direction must be occupied. For this to occur, energy is required, as in the semiconductor the next higher states lie above the band gap. Often this is stated as: full bands do not contribute to
3193-482: Is known as the base load and is generally served by large facilities with constant operating costs, termed firm power . Such facilities are nuclear, coal or hydroelectric, while other energy sources such as concentrated solar thermal and geothermal power have the potential to provide firm power. Renewable energy sources, such as solar photovoltaics, wind, wave, and tidal, are, due to their intermittency, not considered to be firm. The remaining or peak power demand,
PKP class SM30 - Misplaced Pages Continue
3296-468: Is low, gases are dielectrics or insulators . However, once the applied electric field approaches the breakdown value, free electrons become sufficiently accelerated by the electric field to create additional free electrons by colliding, and ionizing , neutral gas atoms or molecules in a process called avalanche breakdown . The breakdown process forms a plasma that contains enough mobile electrons and positive ions to make it an electrical conductor. In
3399-420: Is more common in urban areas or environmentally sensitive locations. Electrical energy must typically be generated at the same rate at which it is consumed. A sophisticated control system is required to ensure that power generation closely matches demand. If demand exceeds supply, the imbalance can cause generation plant(s) and transmission equipment to automatically disconnect or shut down to prevent damage. In
3502-455: Is opposite that of the chosen reference direction. Ohm's law states that the current through a conductor between two points is directly proportional to the potential difference across the two points. Introducing the constant of proportionality, the resistance , one arrives at the usual mathematical equation that describes this relationship: I = V R , {\displaystyle I={\frac {V}{R}},} where I
3605-658: Is opposite to the velocity of the charges. In SI units , current density (symbol: j) is expressed in the SI base units of amperes per square metre. In linear materials such as metals, and under low frequencies, the current density across the conductor surface is uniform. In such conditions, Ohm's law states that the current is directly proportional to the potential difference between two ends (across) of that metal (ideal) resistor (or other ohmic device ): I = V R , {\displaystyle I={V \over R}\,,} where I {\displaystyle I}
3708-401: Is optimal when the annual cost of energy wasted in resistance is equal to the annual capital charges of providing the conductor. At times of lower interest rates and low commodity costs, Kelvin's law indicates that thicker wires are optimal. Otherwise, thinner conductors are indicated. Since power lines are designed for long-term use, Kelvin's law is used in conjunction with long-term estimates of
3811-617: Is part of electricity delivery , known as the electrical grid . Efficient long-distance transmission of electric power requires high voltages . This reduces the losses produced by strong currents . Transmission lines use either alternating current (AC) or direct current (DC). The voltage level is changed with transformers . The voltage is stepped up for transmission, then reduced for local distribution. A wide area synchronous grid , known as an interconnection in North America, directly connects generators delivering AC power with
3914-406: Is partially dependent on the physical orientation of the lines with respect to each other. Three-phase lines are conventionally strung with phases separated vertically. The mutual inductance seen by a conductor of the phase in the middle of the other two phases is different from the inductance seen on the top/bottom. Unbalanced inductance among the three conductors is problematic because it may force
4017-998: Is produced at a relatively low voltage between about 2.3 kV and 30 kV, depending on the size of the unit. The voltage is then stepped up by the power station transformer to a higher voltage (115 kV to 765 kV AC) for transmission. In the United States, power transmission is, variously, 230 kV to 500 kV, with less than 230 kV or more than 500 kV as exceptions. The Western Interconnection has two primary interchange voltages: 500 kV AC at 60 Hz, and ±500 kV (1,000 kV net) DC from North to South ( Columbia River to Southern California ) and Northeast to Southwest (Utah to Southern California). The 287.5 kV ( Hoover Dam to Los Angeles line, via Victorville ) and 345 kV ( Arizona Public Service (APS) line) are local standards, both of which were implemented before 500 kV became practical. Transmitting electricity at high voltage reduces
4120-472: Is sometimes used in railway electrification systems . DC technology is used for greater efficiency over longer distances, typically hundreds of miles. High-voltage direct current (HVDC) technology is also used in submarine power cables (typically longer than 30 miles (50 km)), and in the interchange of power between grids that are not mutually synchronized. HVDC links stabilize power distribution networks where sudden new loads, or blackouts, in one part of
4223-405: Is stepped down before the current is sent to smaller substations. Subtransmission circuits are usually arranged in loops so that a single line failure does not stop service to many customers for more than a short time. Electric current An electric current is a flow of charged particles , such as electrons or ions , moving through an electrical conductor or space. It is defined as
PKP class SM30 - Misplaced Pages Continue
4326-666: Is supplied by peaking power plants , which are typically smaller, faster-responding, and higher cost sources, such as combined cycle or combustion turbine plants typically fueled by natural gas. Long-distance transmission (hundreds of kilometers) is cheap and efficient, with costs of US$ 0.005–0.02 per kWh, compared to annual averaged large producer costs of US$ 0.01–0.025 per kWh, retail rates upwards of US$ 0.10 per kWh, and multiples of retail for instantaneous suppliers at unpredicted high demand moments. New York often buys over 1000 MW of low-cost hydropower from Canada. Local sources (even if more expensive and infrequently used) can protect
4429-411: Is swapped at specially designed transposition towers at regular intervals along the line using various transposition schemes . Subtransmission runs at relatively lower voltages. It is uneconomical to connect all distribution substations to the high main transmission voltage, because that equipment is larger and more expensive. Typically, only larger substations connect with this high voltage. Voltage
4532-433: Is the current through the conductor in units of amperes , V is the potential difference measured across the conductor in units of volts , and R is the resistance of the conductor in units of ohms . More specifically, Ohm's law states that the R in this relation is constant, independent of the current. In alternating current (AC) systems, the movement of electric charge periodically reverses direction. AC
4635-400: Is the current, measured in amperes; V {\displaystyle V} is the potential difference , measured in volts ; and R {\displaystyle R} is the resistance , measured in ohms . For alternating currents , especially at higher frequencies, skin effect causes the current to spread unevenly across the conductor cross-section, with higher density near
4738-441: Is the form of electric power most commonly delivered to businesses and residences. The usual waveform of an AC power circuit is a sine wave , though certain applications use alternative waveforms, such as triangular or square waves . Audio and radio signals carried on electrical wires are also examples of alternating current. An important goal in these applications is recovery of information encoded (or modulated ) onto
4841-461: Is the rate at which charge passes through a chosen unit area. It is defined as a vector whose magnitude is the current per unit cross-sectional area. As discussed in Reference direction , the direction is arbitrary. Conventionally, if the moving charges are positive, then the current density has the same sign as the velocity of the charges. For negative charges, the sign of the current density
4944-403: Is zero net current within the metal. At room temperature, the average speed of these random motions is 10 metres per second. Given a surface through which a metal wire passes, electrons move in both directions across the surface at an equal rate. As George Gamow wrote in his popular science book, One, Two, Three...Infinity (1947), "The metallic substances differ from all other materials by
5047-465: The I 2 R {\displaystyle I^{2}R} losses are still reduced ten-fold using the higher voltage. While power loss can also be reduced by increasing the wire's conductance (by increasing its cross-sectional area), larger conductors are heavier and more expensive. And since conductance is proportional to cross-sectional area, resistive power loss is only reduced proportionally with increasing cross-sectional area, providing
5150-858: The International System of Units (SI), electric current is expressed in units of ampere (sometimes called an "amp", symbol A), which is equivalent to one coulomb per second. The ampere is an SI base unit and electric current is a base quantity in the International System of Quantities (ISQ). Electric current is also known as amperage and is measured using a device called an ammeter . Electric currents create magnetic fields , which are used in motors, generators, inductors , and transformers . In ordinary conductors, they cause Joule heating , which creates light in incandescent light bulbs . Time-varying currents emit electromagnetic waves , which are used in telecommunications to broadcast information. The conventional symbol for current
5253-405: The electrical conductivity . However, as a semiconductor's temperature rises above absolute zero , there is more energy in the semiconductor to spend on lattice vibration and on exciting electrons into the conduction band. The current-carrying electrons in the conduction band are known as free electrons , though they are often simply called electrons if that is clear in context. Current density
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#17327764238395356-528: The international electricity exhibition in Frankfurt . A 15 kV transmission line, approximately 175 km long, connected Lauffen on the Neckar and Frankfurt. Transmission voltages increased throughout the 20th century. By 1914, fifty-five transmission systems operating at more than 70 kV were in service. The highest voltage then used was 150 kV. Interconnecting multiple generating plants over
5459-458: The reference direction of the current I {\displaystyle I} . When analyzing electrical circuits , the actual direction of current through a specific circuit element is usually unknown until the analysis is completed. Consequently, the reference directions of currents are often assigned arbitrarily. When the circuit is solved, a negative value for the current implies the actual direction of current through that circuit element
5562-712: The resistance define the impedance ) constitute reactive power flow, which transmits no power to the load. These reactive currents, however, cause extra heating losses. The ratio of real power transmitted to the load to apparent power (the product of a circuit's voltage and current, without reference to phase angle) is the power factor . As reactive current increases, reactive power increases and power factor decreases. For transmission systems with low power factor, losses are higher than for systems with high power factor. Utilities add capacitor banks, reactors and other components (such as phase-shifters ; static VAR compensators ; and flexible AC transmission systems , FACTS) throughout
5665-399: The resistive losses . For example, raising the voltage by a factor of 10 reduces the current by a corresponding factor of 10 and therefore the I 2 R {\displaystyle I^{2}R} losses by a factor of 100, provided the same sized conductors are used in both cases. Even if the conductor size (cross-sectional area) is decreased ten-fold to match the lower current,
5768-506: The skin effect . Resistance increases with temperature. Spiraling, which refers to the way stranded conductors spiral about the center, also contributes to increases in conductor resistance. The skin effect causes the effective resistance to increase at higher AC frequencies. Corona and resistive losses can be estimated using a mathematical model. US transmission and distribution losses were estimated at 6.6% in 1997, 6.5% in 2007 and 5% from 2013 to 2019. In general, losses are estimated from
5871-418: The watt (symbol: W), is equivalent to one joule per second. In an electromagnet a coil of wires behaves like a magnet when an electric current flows through it. When the current is switched off, the coil loses its magnetism immediately. Electric current produces a magnetic field . The magnetic field can be visualized as a pattern of circular field lines surrounding the wire that persists as long as there
5974-528: The 1884 International Exhibition of Electricity in Turin, Italy . It was powered by a 2 kV, 130 Hz Siemens & Halske alternator and featured several Gaulard transformers with primary windings connected in series, which fed incandescent lamps. The system proved the feasibility of AC electric power transmission over long distances. The first commercial AC distribution system entered service in 1885 in via dei Cerchi, Rome, Italy , for public lighting. It
6077-519: The AC grid. These stopgaps were slowly replaced as older systems were retired or upgraded. The first transmission of single-phase alternating current using high voltage came in Oregon in 1890 when power was delivered from a hydroelectric plant at Willamette Falls to the city of Portland 14 miles (23 km) down river. The first three-phase alternating current using high voltage took place in 1891 during
6180-401: The AC signal. In contrast, direct current (DC) refers to a system in which the movement of electric charge in only one direction (sometimes called unidirectional flow). Direct current is produced by sources such as batteries , thermocouples , solar cells , and commutator -type electric machines of the dynamo type. Alternating current can also be converted to direct current through use of
6283-401: The ability to link all the loads. These included single phase AC systems, poly-phase AC systems, low voltage incandescent lighting, high-voltage arc lighting, and existing DC motors in factories and street cars. In what became a universal system, these technological differences were temporarily bridged via the rotary converters and motor-generators that allowed the legacy systems to connect to
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#17327764238396386-412: The charge carriers, free to move about in the metal. In other materials, notably the semiconductors , the charge carriers can be positive or negative, depending on the dopant used. Positive and negative charge carriers may even be present at the same time, as happens in an electrolyte in an electrochemical cell . A flow of positive charges gives the same electric current, and has the same effect in
6489-402: The charge carriers. In a vacuum , a beam of ions or electrons may be formed. In other conductive materials, the electric current is due to the flow of both positively and negatively charged particles at the same time. In still others, the current is entirely due to positive charge flow . For example, the electric currents in electrolytes are flows of positively and negatively charged ions. In
6592-534: The complete ejection of magnetic field lines from the interior of the superconductor as it transitions into the superconducting state. The occurrence of the Meissner effect indicates that superconductivity cannot be understood simply as the idealization of perfect conductivity in classical physics . In a semiconductor it is sometimes useful to think of the current as due to the flow of positive " holes " (the mobile positive charge carriers that are places where
6695-544: The correct voltages within radio antennas , radio waves are generated. In electronics , other forms of electric current include the flow of electrons through resistors or through the vacuum in a vacuum tube , the flow of ions inside a battery , and the flow of holes within metals and semiconductors . A biological example of current is the flow of ions in neurons and nerves, responsible for both thought and sensory perception. Current can be measured using an ammeter . Electric current can be directly measured with
6798-551: The discrepancy between power produced (as reported by power plants) and power sold; the difference constitutes transmission and distribution losses, assuming no utility theft occurs. As of 1980, the longest cost-effective distance for DC transmission was 7,000 kilometres (4,300 miles). For AC it was 4,000 kilometres (2,500 miles), though US transmission lines are substantially shorter. In any AC line, conductor inductance and capacitance can be significant. Currents that flow solely in reaction to these properties, (which together with
6901-410: The energy of the ground state, the state in which electrons are tightly bound to the atomic nuclei of the material, and the free electron energy, the latter describing the energy required for an electron to escape entirely from the material. The energy bands each correspond to many discrete quantum states of the electrons, and most of the states with low energy (closer to the nucleus) are occupied, up to
7004-458: The fact that the outer shells of their atoms are bound rather loosely, and often let one of their electrons go free. Thus the interior of a metal is filled up with a large number of unattached electrons that travel aimlessly around like a crowd of displaced persons. When a metal wire is subjected to electric force applied on its opposite ends, these free electrons rush in the direction of the force, thus forming what we call an electric current." When
7107-515: The first Polish locomotive with diesel-electric transmission it proved the high efficiency of that solution and was quite successful. The locomotive frame is constructed of steel rolled formers . Ball stub-axles are mounted to strend girders, that make welded box construction. A power unit, composed of a diesel engine and main generator , is mounted on parallel girders. The engine is connected to main generator with an elastic clutch . Four traction motors (two on each bogie) are mounted with
7210-582: The first practical series AC transformer in 1885. Working with the support of George Westinghouse , in 1886 he demonstrated a transformer-based AC lighting system in Great Barrington, Massachusetts . It was powered by a steam engine-driven 500 V Siemens generator. Voltage was stepped down to 100 volts using the Stanley transformer to power incandescent lamps at 23 businesses over 4,000 feet (1,200 m). This practical demonstration of
7313-459: The flow of conduction electrons in metal wires such as the overhead power lines that deliver electrical energy across long distances and the smaller wires within electrical and electronic equipment. Eddy currents are electric currents that occur in conductors exposed to changing magnetic fields. Similarly, electric currents occur, particularly in the surface, of conductors exposed to electromagnetic waves . When oscillating electric currents flow at
7416-409: The fraction of energy lost to Joule heating , which varies by conductor type, the current, and the transmission distance. For example, a 100 miles (160 km) span at 765 kV carrying 1000 MW of power can have losses of 0.5% to 1.1%. A 345 kV line carrying the same load across the same distance has losses of 4.2%. For a given amount of power, a higher voltage reduces the current and thus
7519-410: The heavier positive ions, and hence carry the bulk of the current. The free ions recombine to create new chemical compounds (for example, breaking atmospheric oxygen into single oxygen [O 2 → 2O], which then recombine creating ozone [O 3 ]). Since a " perfect vacuum " contains no charged particles, it normally behaves as a perfect insulator. However, metal electrode surfaces can cause a region of
7622-440: The length of the wire he deduced that the heat produced was proportional to the square of the current multiplied by the electrical resistance of the wire. P ∝ I 2 R . {\displaystyle P\propto I^{2}R.} This relationship is known as Joule's Law . The SI unit of energy was subsequently named the joule and given the symbol J . The commonly known SI unit of power,
7725-424: The main generator serves as electric starter , powered from the battery . For the purposes of lighting the locomotive and charging batteries an additional generator (Pw-114a type) is used. SM30 locomotives had two types of diesel engine mounted. Wola V-300 and 2DVSa-350 (from 1962) 12-cylinder engines had powers, respectively: 300 and 350 hp (220 and 260 kW). Neutral gear rotation is 600 rpm. and rated rev
7828-400: The maximum reliable capacity of each line (ordinarily less than its physical or thermal limit) to ensure that spare capacity is available in the event of a failure in another part of the network. High-voltage overhead conductors are not covered by insulation. The conductor material is nearly always an aluminum alloy, formed of several strands and possibly reinforced with steel strands. Copper
7931-424: The metal into the vacuum. Externally heated electrodes are often used to generate an electron cloud as in the filament or indirectly heated cathode of vacuum tubes . Cold electrodes can also spontaneously produce electron clouds via thermionic emission when small incandescent regions (called cathode spots or anode spots ) are formed. These are incandescent regions of the electrode surface that are created by
8034-451: The middle line to carry a disproportionate amount of the total power transmitted. Similarly, an unbalanced load may occur if one line is consistently closest to the ground and operates at a lower impedance. Because of this phenomenon, conductors must be periodically transposed along the line so that each phase sees equal time in each relative position to balance out the mutual inductance seen by all three phases. To accomplish this, line position
8137-424: The moving electrons in metals. In certain electrolyte mixtures, brightly coloured ions are the moving electric charges. The slow progress of the colour makes the current visible. In air and other ordinary gases below the breakdown field, the dominant source of electrical conduction is via relatively few mobile ions produced by radioactive gases, ultraviolet light, or cosmic rays. Since the electrical conductivity
8240-462: The net rate of flow of electric charge through a surface. The moving particles are called charge carriers , which may be one of several types of particles, depending on the conductor . In electric circuits the charge carriers are often electrons moving through a wire . In semiconductors they can be electrons or holes . In an electrolyte the charge carriers are ions , while in plasma , an ionized gas, they are ions and electrons. In
8343-400: The opposite direction of conventional current flow in an electrical circuit. A current in a wire or circuit element can flow in either of two directions. When defining a variable I {\displaystyle I} to represent the current, the direction representing positive current must be specified, usually by an arrow on the circuit schematic diagram . This is called
8446-403: The opposite direction of the electric field. The speed they drift at can be calculated from the equation: I = n A v Q , {\displaystyle I=nAvQ\,,} where Typically, electric charges in solids flow slowly. For example, in a copper wire of cross-section 0.5 mm , carrying a current of 5 A, the drift velocity of the electrons is on the order of
8549-502: The outer electrons in each atom are not bound to the individual molecules as they are in molecular solids , or in full bands as they are in insulating materials, but are free to move within the metal lattice . These conduction electrons can serve as charge carriers , carrying a current. Metals are particularly conductive because there are many of these free electrons. With no external electric field applied, these electrons move about randomly due to thermal energy but, on average, there
8652-413: The passage of an electric current through a conductor increases the internal energy of the conductor, converting thermodynamic work into heat . The phenomenon was first studied by James Prescott Joule in 1841. Joule immersed a length of wire in a fixed mass of water and measured the temperature rise due to a known current through the wire for a 30 minute period. By varying the current and
8755-528: The power supply from weather and other disasters that can disconnect distant suppliers. Hydro and wind sources cannot be moved closer to big cities, and solar costs are lowest in remote areas where local power needs are nominal. Connection costs can determine whether any particular renewable alternative is economically realistic. Costs can be prohibitive for transmission lines, but high capacity, long distance super grid transmission network costs could be recovered with modest usage fees. At power stations , power
8858-467: The price of copper and aluminum as well as interest rates. Higher voltage is achieved in AC circuits by using a step-up transformer . High-voltage direct current (HVDC) systems require relatively costly conversion equipment that may be economically justified for particular projects such as submarine cables and longer distance high capacity point-to-point transmission. HVDC is necessary for sending energy between unsynchronized grids. A transmission grid
8961-514: The price of generating capacity is high, energy demand is variable, making it often cheaper to import needed power than to generate it locally. Because loads often rise and fall together across large areas, power often comes from distant sources. Because of the economic benefits of load sharing, wide area transmission grids may span countries and even continents. Interconnections between producers and consumers enables power to flow even if some links are inoperative. The slowly varying portion of demand
9064-468: The process, it forms a light emitting conductive path, such as a spark , arc or lightning . Plasma is the state of matter where some of the electrons in a gas are stripped or "ionized" from their molecules or atoms. A plasma can be formed by high temperature , or by application of a high electric or alternating magnetic field as noted above. Due to their lower mass, the electrons in a plasma accelerate more quickly in response to an electric field than
9167-401: The rate at which charge flows through a given surface as: I = d Q d t . {\displaystyle I={\frac {\mathrm {d} Q}{\mathrm {d} t}}\,.} Electric currents in electrolytes are flows of electrically charged particles ( ions ). For example, if an electric field is placed across a solution of Na and Cl (and conditions are right)
9270-559: The same relative frequency to many consumers. North America has four major interconnections: Western , Eastern , Quebec and Texas . One grid connects most of continental Europe . Historically, transmission and distribution lines were often owned by the same company, but starting in the 1990s, many countries liberalized the regulation of the electricity market in ways that led to separate companies handling transmission and distribution. Most North American transmission lines are high-voltage three-phase AC, although single phase AC
9373-628: The scarcity of polyphase power systems needed to power them. In the late 1880s and early 1890s smaller electric companies merged into larger corporations such as Ganz and AEG in Europe and General Electric and Westinghouse Electric in the US. These companies developed AC systems, but the technical difference between direct and alternating current systems required a much longer technical merger. Alternating current's economies of scale with large generating plants and long-distance transmission slowly added
9476-501: The semiconductor crystal is missing a valence electron). This is the case in a p-type semiconductor. A semiconductor has electrical conductivity intermediate in magnitude between that of a conductor and an insulator . This means a conductivity roughly in the range of 10 to 10 siemens per centimeter (S⋅cm ). In the classic crystalline semiconductors, electrons can have energies only within certain bands (i.e. ranges of levels of energy). Energetically, these bands are located between
9579-503: The semiconductor from the valence band to the conduction band depends on the band gap between the bands. The size of this energy band gap serves as an arbitrary dividing line (roughly 4 eV ) between semiconductors and insulators . With covalent bonds, an electron moves by hopping to a neighboring bond. The Pauli exclusion principle requires that the electron be lifted into the higher anti-bonding state of that bond. For delocalized states, for example in one dimension – that
9682-419: The sodium ions move towards the negative electrode (cathode), while the chloride ions move towards the positive electrode (anode). Reactions take place at both electrode surfaces, neutralizing each ion. Water-ice and certain solid electrolytes called proton conductors contain positive hydrogen ions (" protons ") that are mobile. In these materials, electric currents are composed of moving protons, as opposed to
9785-443: The surface, thus increasing the apparent resistance. The mobile charged particles within a conductor move constantly in random directions, like the particles of a gas . (More accurately, a Fermi gas .) To create a net flow of charge, the particles must also move together with an average drift rate. Electrons are the charge carriers in most metals and they follow an erratic path, bouncing from atom to atom, but generally drifting in
9888-409: The system help to compensate for the reactive power flow, reduce the losses in power transmission and stabilize system voltages. These measures are collectively called 'reactive support'. Current flowing through transmission lines induces a magnetic field that surrounds the lines of each phase and affects the inductance of the surrounding conductors of other phases. The conductors' mutual inductance
9991-405: The vacuum to become conductive by injecting free electrons or ions through either field electron emission or thermionic emission . Thermionic emission occurs when the thermal energy exceeds the metal's work function , while field electron emission occurs when the electric field at the surface of the metal is high enough to cause tunneling , which results in the ejection of free electrons from
10094-500: The worst case, this may lead to a cascading series of shutdowns and a major regional blackout . The US Northeast faced blackouts in 1965 , 1977 , 2003 , and major blackouts in other US regions in 1996 and 2011 . Electric transmission networks are interconnected into regional, national, and even continent-wide networks to reduce the risk of such a failure by providing multiple redundant , alternative routes for power to flow should such shutdowns occur. Transmission companies determine
10197-474: Was also known under its project designation 1D or early PKP designation Lwe55 (until 1960). In the 1970s, 109 items of SM30 locomotive were modified for heating passenger wagons with 500 V electric heaters, and as a result their class designation was changed to SP30 (able to pull passenger trains). Those machines remained in regular service until the late 1980s. In 2000 all of them were again, after dismounting heating systems, returned to SM30 series. SM30
10300-452: Was initially transmitted at the same voltage used by lighting and mechanical loads. This restricted the distance between generating plant and loads. In 1882, DC voltage could not easily be increased for long-distance transmission. Different classes of loads (for example, lighting, fixed motors, and traction/railway systems) required different voltages, and so used different generators and circuits. Thus, generators were sited near their loads,
10403-648: Was powered by two Siemens & Halske alternators rated 30 hp (22 kW), 2 kV at 120 Hz and used 19 km of cables and 200 parallel-connected 2 kV to 20 V step-down transformers provided with a closed magnetic circuit, one for each lamp. A few months later it was followed by the first British AC system, serving Grosvenor Gallery . It also featured Siemens alternators and 2.4 kV to 100 V step-down transformers – one per user – with shunt-connected primaries. Working to improve what he considered an impractical Gaulard-Gibbs design, electrical engineer William Stanley, Jr. developed
10506-464: Was sometimes used for overhead transmission, but aluminum is lighter, reduces yields only marginally and costs much less. Overhead conductors are supplied by several companies. Conductor material and shapes are regularly improved to increase capacity. Conductor sizes range from 12 mm (#6 American wire gauge ) to 750 mm (1,590,000 circular mils area), with varying resistance and current-carrying capacity . For large conductors (more than
10609-426: Was spurred by World War I , when large electrical generating plants were built by governments to power munitions factories. These networks use components such as power lines, cables, circuit breakers , switches and transformers . The transmission network is usually administered on a regional basis by an entity such as a regional transmission organization or transmission system operator . Transmission efficiency
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