93-505: The Karnataka Power Transmission Corporation Limited , also known as KPTCL , is the sole electricity transmission and distribution company in state of Karnataka . Its origin was in Karnataka Electricity Board. Until 2002, the Karnataka Electricity Board (KEB) handled electricity transmission and distribution across the state. It was then broken up, with Karnataka Power Transmission Corporation Ltd (KPTCL) established to manage
186-423: A chordal resistance or static resistance , since it corresponds to the inverse slope of a chord between the origin and an I – V curve . In other situations, the derivative d V d I {\textstyle {\frac {\mathrm {d} V}{\mathrm {d} I}}} may be most useful; this is called the differential resistance . In the hydraulic analogy , current flowing through
279-639: 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
372-410: A linear approximation is typically used: R ( T ) = R 0 [ 1 + α ( T − T 0 ) ] {\displaystyle R(T)=R_{0}[1+\alpha (T-T_{0})]} where α {\displaystyle \alpha } is called the temperature coefficient of resistance , T 0 {\displaystyle T_{0}}
465-532: A circuit element is characterized not only by the ratio of their magnitudes, but also the difference in their phases . For example, in an ideal resistor , the moment when the voltage reaches its maximum, the current also reaches its maximum (current and voltage are oscillating in phase). But for a capacitor or inductor , the maximum current flow occurs as the voltage passes through zero and vice versa (current and voltage are oscillating 90° out of phase, see image below). Complex numbers are used to keep track of both
558-406: A circuit is called a resistor . Conductors are made of high- conductivity materials such as metals, in particular copper and aluminium. Resistors, on the other hand, are made of a wide variety of materials depending on factors such as the desired resistance, amount of energy that it needs to dissipate, precision, and costs. For many materials, the current I through the material is proportional to
651-420: A conductor of uniform cross section, therefore, can be computed as R = ρ ℓ A , G = σ A ℓ . {\displaystyle {\begin{aligned}R&=\rho {\frac {\ell }{A}},\\[5pt]G&=\sigma {\frac {A}{\ell }}\,.\end{aligned}}} where ℓ {\displaystyle \ell }
744-1096: 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
837-575: 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
930-444: 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
1023-426: 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
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#17328548368741116-432: A straight line through the origin with positive slope . Other components and materials used in electronics do not obey Ohm's law; the current is not proportional to the voltage, so the resistance varies with the voltage and current through them. These are called nonlinear or non-ohmic . Examples include diodes and fluorescent lamps . The resistance of a given object depends primarily on two factors: what material it
1209-537: 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
1302-457: A voltage drop that interferes with the measurement, so more accurate devices use four-terminal sensing . Many electrical elements, such as diodes and batteries do not satisfy Ohm's law . These are called non-ohmic or non-linear , and their current–voltage curves are not straight lines through the origin. Resistance and conductance can still be defined for non-ohmic elements. However, unlike ohmic resistance, non-linear resistance
1395-591: 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
1488-415: A wire (or resistor ) is like water flowing through a pipe, and the voltage drop across the wire is like the pressure drop that pushes water through the pipe. Conductance is proportional to how much flow occurs for a given pressure, and resistance is proportional to how much pressure is required to achieve a given flow. The voltage drop (i.e., difference between voltages on one side of the resistor and
1581-404: Is electrical conductance , measuring the ease with which an electric current passes. Electrical resistance shares some conceptual parallels with mechanical friction . The SI unit of electrical resistance is the ohm ( Ω ), while electrical conductance is measured in siemens (S) (formerly called the 'mho' and then represented by ℧ ). The resistance of an object depends in large part on
1674-465: Is a fixed reference temperature (usually room temperature), and R 0 {\displaystyle R_{0}} is the resistance at temperature T 0 {\displaystyle T_{0}} . The parameter α {\displaystyle \alpha } is an empirical parameter fitted from measurement data. Because the linear approximation is only an approximation, α {\displaystyle \alpha }
1767-490: 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
1860-453: Is different for different reference temperatures. For this reason it is usual to specify the temperature that α {\displaystyle \alpha } was measured at with a suffix, such as α 15 {\displaystyle \alpha _{15}} , and the relationship only holds in a range of temperatures around the reference. The temperature coefficient α {\displaystyle \alpha }
1953-668: 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
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#17328548368742046-414: Is exactly -90° or +90°, respectively, and X and B are nonzero. Ideal resistors have an angle of 0°, since X is zero (and hence B also), and Z and Y reduce to R and G respectively. In general, AC systems are designed to keep the phase angle close to 0° as much as possible, since it reduces the reactive power , which does no useful work at a load. In a simple case with an inductive load (causing
2139-437: Is governed under the purview of Ministry of Energy. Department is headed by a cabinet grade minister. Currently Siddaramaiah is the minister under the chief ministership of him. The Bangalore Electricity Supply Company (Bescom) came under intense criticism with its telephonic helpline number 1912, due to rampant power cuts, after which Bescom added mobile numbers to its existing call answering facilities for different regions in
2232-452: Is higher than expected. Similarly, if two conductors near each other carry AC current, their resistances increase due to the proximity effect . At commercial power frequency , these effects are significant for large conductors carrying large currents, such as busbars in an electrical substation , or large power cables carrying more than a few hundred amperes. The resistivity of different materials varies by an enormous amount: For example,
2325-473: 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
2418-482: 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,
2511-411: Is made of metal, usually platinum, while a thermistor is made of ceramic or polymer.) Resistance thermometers and thermistors are generally used in two ways. First, they can be used as thermometers : by measuring the resistance, the temperature of the environment can be inferred. Second, they can be used in conjunction with Joule heating (also called self-heating): if a large current is running through
2604-435: Is made of, and its shape. For a given material, the resistance is inversely proportional to the cross-sectional area; for example, a thick copper wire has lower resistance than an otherwise-identical thin copper wire. Also, for a given material, the resistance is proportional to the length; for example, a long copper wire has higher resistance than an otherwise-identical short copper wire. The resistance R and conductance G of
2697-420: 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
2790-459: Is not always true in practical situations. However, this formula still provides a good approximation for long thin conductors such as wires. Another situation for which this formula is not exact is with alternating current (AC), because the skin effect inhibits current flow near the center of the conductor. For this reason, the geometrical cross-section is different from the effective cross-section in which current actually flows, so resistance
2883-506: Is not constant but varies with the voltage or current through the device; i.e., its operating point . There are two types of resistance: Also called chordal or DC resistance This corresponds to the usual definition of resistance; the voltage divided by the current R s t a t i c = V I . {\displaystyle R_{\mathrm {static} }={V \over I}.} Also called dynamic , incremental , or small-signal resistance It
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2976-399: Is often undesired, particularly in the case of transmission losses in power lines . High voltage transmission helps reduce the losses by reducing the current for a given power. On the other hand, Joule heating is sometimes useful, for example in electric stoves and other electric heaters (also called resistive heaters ). As another example, incandescent lamps rely on Joule heating:
3069-438: Is only true in the special cases of either DC or reactance-free current. The complex angle θ = arg ( Z ) = − arg ( Y ) {\displaystyle \ \theta =\arg(Z)=-\arg(Y)\ } is the phase difference between the voltage and current passing through a component with impedance Z . For capacitors and inductors , this angle
3162-401: 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
3255-610: 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
3348-406: 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
3441-991: 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
3534-417: Is related to their microscopic structure and electron configuration , and is quantified by a property called resistivity . In addition to geometry and material, there are various other factors that influence resistance and conductance, such as temperature; see below . Substances in which electricity can flow are called conductors . A piece of conducting material of a particular resistance meant for use in
3627-1012: Is resistance, G is conductance, X is reactance , and B is susceptance . These lead to the complex number identities R = G G 2 + B 2 , X = − B G 2 + B 2 , G = R R 2 + X 2 , B = − X R 2 + X 2 , {\displaystyle {\begin{aligned}R&={\frac {G}{\ G^{2}+B^{2}\ }}\ ,\qquad &X={\frac {-B~}{\ G^{2}+B^{2}\ }}\ ,\\G&={\frac {R}{\ R^{2}+X^{2}\ }}\ ,\qquad &B={\frac {-X~}{\ R^{2}+X^{2}\ }}\ ,\end{aligned}}} which are true in all cases, whereas R = 1 / G {\displaystyle \ R=1/G\ }
3720-422: Is shining on them. Therefore, they are called photoresistors (or light dependent resistors ). These are a common type of light detector . Superconductors are materials that have exactly zero resistance and infinite conductance, because they can have V = 0 and I ≠ 0 . This also means there is no joule heating , or in other words no dissipation of electrical energy. Therefore, if superconductive wire
3813-472: 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
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3906-401: 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. Electrical resistance and conductance The electrical resistance of an object is a measure of its opposition to the flow of electric current . Its reciprocal quantity
3999-666: 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
4092-411: 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
4185-548: Is that the resistivity itself may depend on frequency (see Drude model , deep-level traps , resonant frequency , Kramers–Kronig relations , etc.) Resistors (and other elements with resistance) oppose the flow of electric current; therefore, electrical energy is required to push current through the resistance. This electrical energy is dissipated, heating the resistor in the process. This is called Joule heating (after James Prescott Joule ), also called ohmic heating or resistive heating . The dissipation of electrical energy
4278-406: Is the derivative of the voltage with respect to the current; the slope of the current–voltage curve at a point R d i f f = d V d I . {\displaystyle R_{\mathrm {diff} }={{\mathrm {d} V} \over {\mathrm {d} I}}.} When an alternating current flows through a circuit, the relation between current and voltage across
4371-462: Is the length of the conductor, measured in metres (m), A is the cross-sectional area of the conductor measured in square metres (m ), σ ( sigma ) is the electrical conductivity measured in siemens per meter (S·m ), and ρ ( rho ) is the electrical resistivity (also called specific electrical resistance ) of the material, measured in ohm-metres (Ω·m). The resistivity and conductivity are proportionality constants, and therefore depend only on
4464-409: Is typically +3 × 10 K−1 to +6 × 10 K−1 for metals near room temperature. It is usually negative for semiconductors and insulators, with highly variable magnitude. Just as the resistance of a conductor depends upon temperature, the resistance of a conductor depends upon strain . By placing a conductor under tension (a form of stress that leads to strain in the form of stretching of
4557-465: 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
4650-519: 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
4743-712: 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
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#17328548368744836-399: 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,
4929-506: 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
5022-524: 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
5115-512: 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
5208-401: 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
5301-444: The article: Electrical resistivity and conductivity . For the case of electrolyte solutions, see the article: Conductivity (electrolytic) . Resistivity varies with temperature. In semiconductors, resistivity also changes when exposed to light. See below . An instrument for measuring resistance is called an ohmmeter . Simple ohmmeters cannot measure low resistances accurately because the resistance of their measuring leads causes
5394-491: The city. Electricity 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
5487-400: The conductance G is the reciprocal: R = V I , G = I V = 1 R . {\displaystyle R={\frac {V}{I}},\qquad G={\frac {I}{V}}={\frac {1}{R}}.} For a wide variety of materials and conditions, V and I are directly proportional to each other, and therefore R and G are constants (although they will depend on
5580-468: The conductivity of teflon is about 10 times lower than the conductivity of copper. Loosely speaking, this is because metals have large numbers of "delocalized" electrons that are not stuck in any one place, so they are free to move across large distances. In an insulator, such as Teflon, each electron is tightly bound to a single molecule so a great force is required to pull it away. Semiconductors lie between these two extremes. More details can be found in
5673-589: The conductor), the length of the section of conductor under tension increases and its cross-sectional area decreases. Both these effects contribute to increasing the resistance of the strained section of conductor. Under compression (strain in the opposite direction), the resistance of the strained section of conductor decreases. See the discussion on strain gauges for details about devices constructed to take advantage of this effect. Some resistors, particularly those made from semiconductors , exhibit photoconductivity , meaning that their resistance changes when light
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#17328548368745766-551: 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
5859-401: The filament is heated to such a high temperature that it glows "white hot" with thermal radiation (also called incandescence ). The formula for Joule heating is: P = I 2 R {\displaystyle P=I^{2}R} where P is the power (energy per unit time) converted from electrical energy to thermal energy, R is the resistance, and I is the current through
5952-569: 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
6045-409: 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
6138-422: The material it is made of. Objects made of electrical insulators like rubber tend to have very high resistance and low conductance, while objects made of electrical conductors like metals tend to have very low resistance and high conductance. This relationship is quantified by resistivity or conductivity . The nature of a material is not the only factor in resistance and conductance, however; it also depends on
6231-399: The material the wire is made of, not the geometry of the wire. Resistivity and conductivity are reciprocals : ρ = 1 / σ {\displaystyle \rho =1/\sigma } . Resistivity is a measure of the material's ability to oppose electric current. This formula is not exact, as it assumes the current density is totally uniform in the conductor, which
6324-400: 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
6417-451: 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
6510-409: The other), not the voltage itself, provides the driving force pushing current through a resistor. In hydraulics, it is similar: the pressure difference between two sides of a pipe, not the pressure itself, determines the flow through it. For example, there may be a large water pressure above the pipe, which tries to push water down through the pipe. But there may be an equally large water pressure below
6603-1245: The phase and magnitude of current and voltage: u ( t ) = R e ( U 0 ⋅ e j ω t ) i ( t ) = R e ( I 0 ⋅ e j ( ω t + φ ) ) Z = U I Y = 1 Z = I U {\displaystyle {\begin{array}{cl}u(t)&=\operatorname {\mathcal {R_{e}}} \left(U_{0}\cdot e^{j\omega t}\right)\\i(t)&=\operatorname {\mathcal {R_{e}}} \left(I_{0}\cdot e^{j(\omega t+\varphi )}\right)\\Z&={\frac {U}{\ I\ }}\\Y&={\frac {\ 1\ }{Z}}={\frac {\ I\ }{U}}\end{array}}} where: The impedance and admittance may be expressed as complex numbers that can be broken into real and imaginary parts: Z = R + j X Y = G + j B . {\displaystyle {\begin{aligned}Z&=R+jX\\Y&=G+jB~.\end{aligned}}} where R
6696-491: The phase to increase), a capacitor may be added for compensation at one frequency, since the capacitor's phase shift is negative, bringing the total impedance phase closer to 0° again. Y is the reciprocal of Z ( Z = 1 / Y {\displaystyle \ Z=1/Y\ } ) for all circuits, just as R = 1 / G {\displaystyle R=1/G} for DC circuits containing only resistors, or AC circuits for which either
6789-409: The pipe, which tries to push water back up through the pipe. If these pressures are equal, no water flows. (In the image at right, the water pressure below the pipe is zero.) The resistance and conductance of a wire, resistor, or other element is mostly determined by two properties: Geometry is important because it is more difficult to push water through a long, narrow pipe than a wide, short pipe. In
6882-528: 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
6975-467: 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
7068-514: 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
7161-404: The reactance or susceptance happens to be zero ( X or B = 0 , respectively) (if one is zero, then for realistic systems both must be zero). A key feature of AC circuits is that the resistance and conductance can be frequency-dependent, a phenomenon known as the universal dielectric response . One reason, mentioned above is the skin effect (and the related proximity effect ). Another reason
7254-411: The resistance of wires, resistors, and other components often change with temperature. This effect may be undesired, causing an electronic circuit to malfunction at extreme temperatures. In some cases, however, the effect is put to good use. When temperature-dependent resistance of a component is used purposefully, the component is called a resistance thermometer or thermistor . (A resistance thermometer
7347-435: The resistor, the resistor's temperature rises and therefore its resistance changes. Therefore, these components can be used in a circuit-protection role similar to fuses , or for feedback in circuits, or for many other purposes. In general, self-heating can turn a resistor into a nonlinear and hysteretic circuit element. For more details see Thermistor#Self-heating effects . If the temperature T does not vary too much,
7440-409: The resistor. Near room temperature, the resistivity of metals typically increases as temperature is increased, while the resistivity of semiconductors typically decreases as temperature is increased. The resistivity of insulators and electrolytes may increase or decrease depending on the system. For the detailed behavior and explanation, see Electrical resistivity and conductivity . As a consequence,
7533-559: 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
7626-555: The same way, a long, thin copper wire has higher resistance (lower conductance) than a short, thick copper wire. Materials are important as well. A pipe filled with hair restricts the flow of water more than a clean pipe of the same shape and size. Similarly, electrons can flow freely and easily through a copper wire, but cannot flow as easily through a steel wire of the same shape and size, and they essentially cannot flow at all through an insulator like rubber , regardless of its shape. The difference between copper, steel, and rubber
7719-621: 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
7812-420: The size and shape of an object because these properties are extensive rather than intensive . For example, a wire's resistance is higher if it is long and thin, and lower if it is short and thick. All objects resist electrical current, except for superconductors , which have a resistance of zero. The resistance R of an object is defined as the ratio of voltage V across it to current I through it, while
7905-409: The size and shape of the object, the material it is made of, and other factors like temperature or strain ). This proportionality is called Ohm's law , and materials that satisfy it are called ohmic materials. In other cases, such as a transformer , diode or battery , V and I are not directly proportional. The ratio V / I is sometimes still useful, and is referred to as
7998-409: 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
8091-503: The transmission business. This electricity transmission and distribution entity was corporatised to provide efficient and reliable electric power supply to the people of Karnataka state. KPTCL scope of work includes the handling of large projects in the field of energy. KPTCL buys power from power generating companies like Karnataka Power Corporation Limited (KPCL) and other IPPs (Independent Power Producers) like GMR, Jindal, Lanco(UPCL) etc., and sell them to their respective ESCOMS. Company
8184-481: The voltage V applied across it: I ∝ V {\displaystyle I\propto V} over a wide range of voltages and currents. Therefore, the resistance and conductance of objects or electronic components made of these materials is constant. This relationship is called Ohm's law , and materials which obey it are called ohmic materials. Examples of ohmic components are wires and resistors . The current–voltage graph of an ohmic device consists of
8277-500: 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
8370-452: 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,
8463-648: 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
8556-464: 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
8649-426: 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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