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46th ISTE Annual National Convention & National Conference 2017 International Journal of Advance Research and Innovation (ISSN 2347 – 3258) Review Paper of Use of Supercondutor in Electricity Transmission Ravneet kaur Nirbhai Singh Applied physics department Gulzar group of institutes Khanna punjab, India [email protected] EEE department Gulzar group of institutes Khanna Punjab, India [email protected] Abstract—— Radical developments have recently taken place in the field of superconductors. More specifically, high temperature superconductors have been a focal point, and therefore many modifications are being made in the types and varieties of products which employ such devices. In order to better appreciate and understand this field and its implications, it is necessary to attain knowledge of the history and basic principles of superconductivity. This review paper explains how high temperature superconductors (HTS) can contribute to the resolution of electricity transmission problem. Secondly, it describes HTS cable architectures and explains the effects of superconductor cables on power grid flows. Concluding with economic, financial and environment benefits. In 1986, it was discovered that some cuprateperovskite ceramic materials have a critical temperature above 90 K (−183 °C). Such a high transition temperature is theoretically impossible for a conventional superconductor, leading the materials to be termed high-temperature superconductors. Liquid nitrogen boils at 77 K, and superconduction at higher temperatures than this facilitates many experiments and applications that are less practical at lower temperatures. II. HISTORY The field of superconductivity began with the discovery by H. Kameriingh-Onnes in 1911 that mercury wire at 4.2 K had zero electrical resistance. Zero resistance implied transmission of current at any distance with no losses, the production of large magnetic fields, or because a superconducting loop could carry current indefinitely storage of energy. These applications were not realized because, as was quickly discovered, the superconductors reverted to normal conductors at a relatively low current density, called the critical current density Jc , or in a relatively low magnetic field, called the critical field, He- In 1916, Silsbee, at the National Bureau of Standards, hypothesized that the critical current for a superconducting wire was equal to that current which gave the critical field at the surface of the wire. The reason for this behavior was not made clear until the Meissner effect came into light in 1933. The discovery and development, in the 1950s and 1960s, of superconductors which can remain superconducting at much higher fields and currents made practical the production of useful superconducting magnets (see table 1). Such high-field superconductors, which exhibit two critical fields designated Hci and Ha, are called type-II. In 1950, another NBS scientist, E. Maxwell, was the discoverer of the isotope effect, which was also independently discovered by Serin et al.. This experimental observation was an important key to theoretical explanations of the mechanism of superconductivity. In the isotope effect, the critical temperature for many superconductors depends on the isotopic mass, indicating that lattice vibrations are involved in the superconductivity, and Keywords— superconductor, HTC, VLI. I. INTRODUCTION Superconductivity is a phenomenon of exactly zero electrical resistance and exclusion of magnetic flux fields occurring in certain materials when cooled below a characteristic critical temperature. It was discovered by Dutch physicist 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, the complete expulsion 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. The electrical resistance of a metallic conductor decreases steadily as temperature is lowered. In ordinary conductors, such as copper or silver, this decrease is limited by impurities and other defects. Even near absolute zero, a real sample of a normal conductor shows some resistance. In a superconductor, the resistance drops abruptly to zero when the material is cooled below its critical temperature. An electric current flowing through a loop of superconducting wire can persist indefinitely with no power source. 1 Gulzar Group of Institutes, Ludhiana, Punjab-141401 (INDIA) 46th ISTE Annual National Convention & National Conference 2017 International Journal of Advance Research and Innovation (ISSN 2347 – 3258) that the attractive coupling between electrons is through the lattice vibrations (i.e., phonon-mediated). The discovery of the Josephson effect in 1962 opened up exciting potential for the use of superconductors III. TYPES OF SUPERCONDUCTORS A. Type I superconductor. High magnetic fields demolish superconductivity and restore the normal conducting state. Depending on the character of this transition, we may differentiate between type I and II superconductors. The graph shown i illustrates the internal magnetic field strength, Bi, with increasing applied magnetic field. It is found that the internal field is zero (as expected from the Meissner effect) until a critical magnetic field, Bc, is reached where a sudden transition to the normal state occurs. This results in the penetration of the applied field into the interior. Superconductors that undergo this abrupt transition to the normal state above a critical magnetic field are known as type I superconductors. Most of the pure elements tend to be type I superconductors. Fig 2 behavior of type II superconductor IV.THE LONDON EQUATIONS Developed by brothers Fritz and Heinz London in 1935, relate current to electromagnetic fields in and around a superconductor. Questionably the simplest meaningful description of superconducting phenomena, they form the origins of almost any modern introductory text on the subject. A major success of the equations is their capability to explain the Meissner effect, wherein a material exponentially expels all internal magnetic fields as it crosses the superconducting threshold. There are two London equations when expressed in terms of measurable fields j nse 2 E t m J S Fig 1 behavior of type I superconductor. ns e2 B m (1) (2) B.Type II superconductor Where E and B are electric and magnetic field with in the super conductor. J S is superconducting current density. e, m are the charge and mass of electron respectively Type II superconductors are the most technologically useful because the second critical field can be quite high, enabling high field electromagnets to be made out of superconducting wire. Wires made from say niobium-tin (Nb3Sn) have a Bc2 as high as 24.5 Tesla – in practice it is lower. This makes them useful for applications require high magnetic fields, such as Magnetic Resonance Imaging (MRI) machines. The benefit of using superconducting electromagnets is that the current only has to be applied once to the wires, which are then formed into a closed loop and allow the current (and field) to persist indefinitely – as long as the superconductor stays below the critical temperature. That is, the external power supply can be switched off. As a comparison, the strongest permanent magnets today may be able to produce a field close to 1 Tesla. However, it is possible to obtain up to 24.5 Tesla from a niobium–tin superconductor. There is a delusion amongst some non-specialists that the term "Type II" refers to the copper oxide based high temperature superconductors discovered in the late 1980s. While these are type II superconductors, so are many superconductors discovered before that time London penetration depth London's equations is manipulated by applying Ampere's law * B O j 2B 1 2 B m o s e 2 The London equations imply a characteristic length scale over which external magnetic fields are exponentially suppressed. This value is the London penetration depth For an example, consider a superconductor within free space where the magnetic field outside the superconductor is a constant value pointed parallel to the superconducting boundary plane in the z direction. If x leads perpendicular to the boundary then the solution inside the superconductor may be shown to be 2 Gulzar Group of Institutes, Ludhiana, Punjab-141401 (INDIA) 46th ISTE Annual National Convention & National Conference 2017 International Journal of Advance Research and Innovation (ISSN 2347 – 3258) x BZ ( x) B0e Table of different cable V.NEED OF SUPER CONDUCTORS The electric power grid looms large in America’s energy future. It delivers clean energy at low cost and connects conveniently too many sources and end users. For decades, the grid has been the invisible backbone of energy accessibility, enabling increases in productivity and quality of life with the flick of a switch. Although we hardly ever notice it, it ranks first on the list of great engineering achievements of the 20th century, according to the National Academy of Engineering. Yet this preferential form of energy distribution is increasingly compromised by its limited capacity and reliability. By 2030, demand for electricity will grow by 50% in India and 100% globally. The power grid struggles to provide this increased capacity, especially in packed full urban and suburban areas where demand is strongest and access for new power lines is tightest. Beyond capacity, the grid is effective only if it delivers energy constantly, keeping voltage and frequency tightly controlled within narrow windows. As we add more nodes to accommodate more generators and users, and as we send more power over the links connecting these nodes, we increase the potential for dynamic instabilities of voltage, current, and frequency. The sheer complexity of the electricity network precludes predicting these unstable modes in advance. Instead, we discover unstable behavior in the form of frequency fluctuations, overloaded transmission lines, brownouts, and blackouts B.VLI superconductor cables Compared to conventional overhead lines, underground copper cables, or unshielded HTS cables, the most distinctive capability of VLI cable is their controllability. When inserted into networks consisting of conventional elements with higher impedances, VLI cables will act as "current hogs", naturally attracting current or power flows. In fact, if not modified, insertion of these cables into networks that already have existing parallel paths with higher impedance ratings will sharply reduce the amount of flow that would otherwise be borne by these other conventional network elements From a transmission planning perspective, this "current hogging" attribute is a double-edged sword. To the extent planners have considered low impedance in the past, they have tended to view it as a potential liability because of its results in large system normal and contingency power flows. In fact, the full capacity of a VLI cable upgrade may not initially be usable because the cable can immediately represent the single largest contingency on the system. Viewed from a different perspective, however, low impedance can offer important advantages. Under some circumstances, it can be much easier and less expensive to "pull" power onto high-capacity pathways that flow directly into a congested load pocket, through a low-impedance cable, than to site, construct and "push" comparable quantities of power to the same spot on the grid using conventional approaches. In addition, impedance may be added to a VLI circuit, simply and inexpensively, by installing conventional substation equipment, e.g., inductors or phase angle regulators (PARs), yielding effective and economical control of flows over "current hogging" VLI cables. Thus, VLI superconductor cables can be configured to function like fully controllable DC circuits, while operating in the synchronous AC environment -- thereby avoiding the cost of AC/DC converter stations. In addition, small and less expensive PARs can achieve the same degree of control over a VLI circuit as the larger, costlier phase shifting equipment needed for a conventional circuit. Moreover, it would be feasible to develop compact, integrated HTS PARs that could fit into the congested areas of a power grid. In short, VLI cable introduces the prospect of an unobtrusive, low-impact and fully controllable transmission solution, operating at HV transmission voltages or distribution voltages within the existing AC environment. The introduction of VLI cable into the transmission planner's arsenal also suggests a potent new strategy for expanding grid capacity. As thermal transfer limits are reached on power grids, congestion bottlenecks appear. Historically, utilities have preferred to relieve these bottlenecks, when possible, by constructing overhead lines which are typically the least-cost solution. However, this VI.TYPE OF SUPERCONDUCTOR CABLE A.HTS cable Interest in the field of superconducting power cable dates back to the 1960’s, but because conventional metallic superconductors required cooling with liquid helium, these cable system designs were overly complex and costprohibitive. Interest in the field was renewed following the discovery of ceramic-based high-temperature superconductors in the late 1980’s, which enabled the use of liquid nitrogen as a cooling medium at about -200°C. Liquid nitrogen is widely used in a variety of industrial applications and is recognized as a cheap, abundant and environmentally kind coolant. Nitrogen is an inert gas that constitutes 79% of the atmosphere. At present there are two principal types of HTS cable. The simpler design is based on a single conductor, consisting of HTS wires trapped around a flexible core in a channel filled with liquid nitrogen coolant. This cable design employs an outer dielectric insulation layer at room temperature, and is normally referred to as a "warm dielectric" design. It offers high power density and uses the least amount of HTS wire for a given level of power transfer. Drawbacks of this design relative to other superconductor cable designs include higher electrical losses (and therefore a requirement for cooling stations at closer intervals), higher inductance, required phase separation to limit the effects of eddy current heating and control the production of stray electromagnetic fields (EMF) in the area of the cable. 3 Gulzar Group of Institutes, Ludhiana, Punjab-141401 (INDIA) 46th ISTE Annual National Convention & National Conference 2017 International Journal of Advance Research and Innovation (ISSN 2347 – 3258) approach is becoming increasingly difficult, particularly in urban areas, because of sitting restrictions. Moreover, recent experience has shown that bottlenecks often arise in and around urban areas where the combination of short distances and high real estate costs make HTS cable a viable alternative solution. In such situations, power flow problems could be solved by overlaying the existing, conventional network of lines and cables with relatively short, strategic insertions of VLI cable across these congested interfaces. This approach would draw currents away from other conventional grid elements operating at or near their limits. By reducing high current flows and associated overheating on existing lines, VLI cables can slow or prevent the dielectric aging, annealing and other processes that often cause conventional cable or lines to age and fail. Employing such a strategy judiciously will increase grid capacity, extend the useful life of conventional network elements, and improve overall asset utilization -- all at lower cost and with much less environmental impact than would result from a conventional strategy of wide-area network upgrades. High-current VLI cables at 115 kV or even 69 kV may solve problems that would ordinarily require a 230 kV or 345 kV conventional solution. In the long run, VLI may obviate the much higher system costs (e.g., transformer and breaker replacement) associated with wide-area voltage up-ratings. B. Greater controllability VLI cable offers the ability to control power flows with conventional series reactors or PARs, yielding market and reliability benefits typically associated with other "controllable" forms of transmission − e.g., FACTS (Flexible AC Transmission Systems) or DC transmission. Yet this control at the termini of a line would be achieved with much less expense and complexity than is typically required using conventional technologies (e.g., large, inflexible DC converter stations or the large-scale power electronic devices often associated with conventional FACTS devices). Whereas DC lines are limited to point-to-point flows, VLI cable systems could be expanded to provide controllability to many points in a network. This inherent controllability has important regulatory implications. For example, VLI could form the basis for private, at-risk investment in merchant transmission projects with assignable property rights in transmission capacity, outside of the rate base framework, in situations where DC and conventional FACTS solutions are not costcompetitive. The cost of DC systems is highly impacted by the cost of converter stations. For short runs of DC transmission, system costs are dominated by the cost of converter stations; VLI cables face no such penalty. D. Life extension and improved asset utilization. VLI cable represents a new weapon to attack the principal enemy of congested urban transmission systems: heat. Over time, thermal overload ages and degrades cable insulation. By drawing flow away from overtaxed cables and lines, strategic insertions of VLI cable can "take the heat off" urban power delivery networks that are increasingly prone to overheating, the inevitable result of increased loadings and acute siting difficulties associated with siting conventional (copper or aluminum-based) system expansions. Reducing the burden on existing electrical pathways will extend the life of conventional system elements. This approach also improves overall asset utilization, and defers the need for the large-scale capital investment required for the replacement of aging and worn-out grid infrastructure. Fig 3 superconductor underground cable VII.ECONOMIC AND FINANCIAL BENEFITS Using VLI cables in new solutions for power flow problems can translate into significant cost savings. As described above, the factors that lead to lower costs on an installed system basis may be summarized as follows: A.Shorter length Short, strategic insertions of VLI cable could achieve the same power flow benefit as lengthier circuits of overhead line. VLI cable need not be cost-competitive with conventional cable or overhead line technology on a stand-alone basis for it to offer a lower total cost solution. For example, with VLI, cable utilities may solve power flow problems with shorter circuit lengths, e.g., connecting to the more pervasive 115/138/161 kV system rather than tying back to the more distant EHV backbone transmission system. E. Expanded generator sitting options Because it greatly reduces voltage drop, low impedance VLI cable has the ability to "shrink electrical distance". This means that new generators could be located at greater distance from urban loads (where land, labor and other costs are lower), while providing the same degree of voltage support as if they were located in or adjacent to the city center. Thus, HTS transmission lines could be deployed as "virtual generators" to solve both power supply and reactive power problems. B.Lower voltage Because of the higher capacity of VLI cable (approximately three to five times higher capacity than conventional circuits), utilities may employ lower-voltage equipment, avoiding both the electrical (I²R) losses typical of high-current operation and the capital costs of step-up and step-down transformers (as well as the no-load losses within the transformers themselves). F. Reduced electrical losses In specially optimized designs, VLI cable can result in lower net energy losses than occur in either conventional lines and cables or unshielded HTS cables with a single conductor per phase, offering a transmission path with high electrical 4 Gulzar Group of Institutes, Ludhiana, Punjab-141401 (INDIA) 46th ISTE Annual National Convention & National Conference 2017 International Journal of Advance Research and Innovation (ISSN 2347 – 3258) efficiency. Because VLI circuits tend to attract power flow, they will naturally operate at a high capacity factor, reducing the losses on other circuits and further magnifying their efficiency advantage. could ultimately help to resolve. It is important, therefore, to undertake all appropriate steps to speed the commercialization of this promising technology. A series of demonstration projects to illustrate the power flow attributes of VLI cables, to develop a reliability record for the technology, and to resolve system integration and other issues, should be a top priority of public officials responsible for transmission-related policy. G.Reduced regional congestion costs . Finally, and perhaps most significantly, the ability to complete grid upgrade projects more quickly will translate into the earlier elimination or relaxation of grid bottlenecks. Solving physical bottleneck problems will sharply reduce the grid congestion costs that, in today's unsettled, imperfectly competitive marketplace, can impose huge penalties on consumers and the economy at large. IX. FUTURE SCOPE OF SUPERCONDUCTIVITY As we know superconductor have approximate zero resistance this property of superconductor can be utilized in different fields that can improve the efficiency of any system which is related to electrical field VIII. CONCLUSION Given today's acute level of concern about system reliability and new competitive pressures, policymakers and market participants recognize that strategies to control and redirect transmission flows have greater value than ever before. HTS cables and fault current limiters constitute new tools to develop these strategies. By taking advantage of their outstanding features, utilities and regional transmission operators will find new and less expensive ways to tackle grid congestion problems, reduce grid security violations, improve overall asset utilization and extend the life of their existing systems. The widespread commercial adoption of these superconducting devices for power networks has great potential to generate a range of economic, environmental and reliability benefits, many of which are discussed herein. Yet, as is often the case with many “breakthrough” technologies that are initially high-cost, early developers, and users face high risks. These risks are compounded by the very uncertainties and regulatory complications that VLI cable Increase the load ability of electrical transmission line Nitrogen based superconductor can be used for short and long transmission line High temperature conductor can be distribution system Superconductor can be used in highly efficient super computers Levitation can be used for super speed electrical trains 5 Gulzar Group of Institutes, Ludhiana, Punjab-141401 (INDIA) used in