HVDC Light Technology Essay Example for Free

HVDC come Technology EssayAbstractThis document reveals theHVDC fair DC transmittance technology.It is apply in underground transmittal and moreover provides point to point transmission.HVDC Light requires only two elements namely a converter transport and a correspond of ground cables. The new HVDC Light cable is an extruded, single-pole cable. It is ideally suited for feeding indicant into growing metropolitan areas from a suburban substation. HVDC Light is inwrought environmentally friendly cables instead of OH transmission declensions. Virtually no magnetic field. The environmental gains would be substantial, since the provide supplied via the DC cables will be transmitted from efficacious power plants in the main AC grid. 1. INTRODUCTIONA hundred years ago, the transformer and a new transmission and distributionbe controlled precisely and independently shadower replace overhead lines at no costcontrol capabilities that are not present oreconomically feasible to connect smallscale,Equally important, HVDC Light hasfor inefficient, polluting local anaesthetic generationfrequency, participating and reactive power canislands, mining districts and drilling consigns from a main AC-gridof each(prenominal) other. This technology also relieson a new type of underground cable which penalty platforms can be supplied with power from realistic even in the most forward-looking ACrenewable power generation. Renewable power generation plantssuch as diesel units.The potentiality, .Connect small scaleFeeding remote isolatedFlexible transmission placement technology, HVDC Light, makes it the main grid, on that pointby eliminating the needto the main AC grid. Vice versa,using thevery same technology, remote locations asthe three phase system made it possible totransmit AC power efficiently and economically over vast distances and todistributethe power toamultitude ofusers.Since then all aspects of transmission anddistribution have developed by means ofte chnical improvement and evolution. This AC transmission and distributiontechnology has made it possible to locategeneratingplants in optimum locations, andtoutilize them efficiently. This has alsoresulted in great environmental gains.Thermal plants have been located wherethey can be supplied with fuel through anefficient transportation system, therebyreducing waste and pollution.Hydro plantshave been located where the hydroresources can be used at the greatestadvantage. And bulky generating plantshave meant fewer overhead lines than amultitude of smaller generating plantswould have required.However, todays AC transmission anddistribution systems are, at least inprinciple, base on ideas that haventchanged much since a hundred years ago. To transmit power, step up the voltage withtransformers, transmit power, step downthe voltage and distribute power.Despitetheir turn out advantages, it is difficult andexpensive to adapt AC transmission anddistribution systems to the numerous small scalegenerating plants that are being built,or to the increasingly complex and variableproduction and load demands.Environmental concerns and regulationsalso vagabond heavy restrictions on shape uping right-of-ways and on small-scale, fossilfuelledgenerating plants, such as dieselgenerating plants.These new trends require networks that are tractile. The networks must be able to copewith large variations in load and frequentchanges in productions patterns with tougher environmental regulations.Also, in such flexible networks, the powerflow and the voltages require precisecontrol in order to make the grids stable and economic.2. TECHNOLOGYAs its name implies, HVDC Light is a DCtransmission technology. However, it isdifferent from the classic HVDCtechnology used in a large number oftransmission schemes. Classic HVDCtechnology is mostly used for large point-to-point transmissions, often over vastdistances across land or under water. It requires fast communications channels among the t wo stations, and there mustbe large rotating units generators orsynchronous condensers present in theAC networks at both ends of thetransmission.HVDC Light consists of only two elements a converter station and a pair ofground cables. The converters are voltagesource converters, VSCs. The siding from the VSCare determined by the controlsystem, which does not require anycommunications bear ons between the differentconverter stations. Also, they dont need torely on the AC networks ability to keepthe voltage and frequency stable. Thesefeatures make it possible to connect theconverters to the points bests suited for theAC system as a whole.Power range up to 100 MWIndependent control of active and reactive powerCan feed power to AC network without ownGeneration DCThe converter station is designed for apower range of 1-100 MW and for a DCvoltage in the 10-100 kV range. One suchstation occupies an area of less than 250sq. m. (2 700 sq. ft.), and consists ofjust a few elements two contai ners for theconverters and the control system, threesmall AC air-core reactors, a simpleharmonics filter and some cooling fans. 20MW18x12mThe converters are using a set of six valves,two for each phase, equipped with highpowertransistors, IGBT (Insulated GateBipolar Transistor). The valves arecontrolled by a computerized controlsystem by pulse width modulation, PWM.Since the IGBTs can be switched on or off, the output voltages and currents onthe AC side can be controlled precisely.The control system automatically adjuststhe voltage, frequency and flow of activeand reactive power according to the needsof the AC system.The PWM technology has been tried andtested for two decades in switched powersupplies for electronic equipment ascomputers.Due to the new, high powerIGBTs, the PWM technology can now beused for high power applications as electricpower transmission.HVDC Light can be used with regularoverhead transmission lines, but it reachesits full potential when used with a new kindof DC cable. The new HVDC Light cable isan extruded, single-pole cable. As anexample a pair of cables with a conductorof 95 sq mm aluminum can carry a load of30 MW at a DC voltage of +/-100KV.Handling the cable is easy. Despite its large power-carrying facultyit has a special weight of just over 1 kg/m.Contrary to the case with AC transmissiondistance is not the factor that determinesthe line voltage. The only limit is the costof the line losses, which whitethorn be lowered bychoosing a cable with a conductor with alarger cross section. Thus, the cost of apair of DC cables is linear with distance.Insulation 5.5 mm triple extruded disguise Copper wireSheath HDPEWeight 1.05 kg/mVoltage 100 kV DCCurrent 300 APower 30 MWConductor 95 mm2AluminumA DC cable partnership could be more costefficientthan even a medium distance ACoverhead line, or local generating unitssuch as diesel generators.The converter stations can be used indifferent grid configurations. A singlestation can connect a DC load or generatingunit, such as a photo-voltaic power plant,with an AC grid. Two converter stationsand a pair of cables make a point-to pointDC transmission with AC connections ateach end. trio or more converter stationsmake up a DC grid that can be connected toone or more points in the AC grid or todifferent AC grids.An HVDCLight network can be configured radial or meshed,like any network.The DC grids can be radial with multi-dropconverters, meshed or a combination ofboth. In other words, they can beconfigured, changed and expanded in muchthe same way AC grids are.3. APPLICATIONS3.1 OVERHEAD LINESIn general, it is getting increasingly difficultto build overhead lines. Overhead lineschange the landscape, and the constructionof new lines is often met by public resentment and political resistance. Peopleare often concerned about the possiblehealth hazards of living close to overheadlines. In addition, a right-of-way for a high voltage line occupant valuable land. The subroutine o f obtaining permissions forbuilding new overhead lines is alsobecoming time-consuming and expensive.Laying an underground cable is a mucheasier process than building an overheadline.A cable doesnt change the landscapeand it doesnt need a wide right-of-way.Cables are rarely met with any publicopposition, and the electromagnetic fieldfrom a DC cable pair is very low, and also a tranquil field. Usually, the process ofobtaining the rights for laying anunderground cable is much easier, quickerand cheaper than for an overhead line.A pair of HVDC Light cables can beplowed into the ground. Despite their largepower capacity, they can be put in placewith the same equipment as ordinary, AChigh voltage distribution cables. Thus,HVDC Light is ideally suited for feedingpower into growing metropolitan areasfrom a suburban substation.3.2 REPLACING LOCAL extensionRemote locations often need localgeneration if they are situated far-off awayfrom an AC grid. The distance to the gridmakes it technical ly or economicallyunfeasible to connect the area to the maingrid. Such remote locations may be islands,mining areas, bollocks up and petroleum fields or drillingplatforms. Sometimes the local generators use gas turbines, but diesel generators aremuch more common.An HVDC Light cable connection could bea better choice than building a local powerplant based on fossil fuels.Theenvironmental gains would be substantial,since the power supplied via the DC cableswill be transmitted from efficient powerplants in the main AC grid. Also, thepollution and noise produced when thediesel fuel is transported will be completelyeliminated by an HVDC line, as the needfor frequent maintenance of the diesels.Since the cost of building an HVDC Lightline is a linear unravel of the distance, abreak-even might be reached for as shortdistances as 50- 60 km.HVDC Light lowest costAC + Overhead lineHVDC Light + cableCost inner(a)AC gridDistance from the AC grid eliminate local diesel Cost/kWh3.3 CONNECTING P OWER GRIDSRenewable power sources are often builtfrom scratch, scratch on a small scaleand gradually expanded. Wind turbine farms is the typical case, but this is alsotrue for photovoltaic power generation.These power sources are usually locatedwhere the conditions are particularlyfavorable, often far away from the mainAC network. At the beginning, such aslowly expanding energy resource cannotsupply a remote community with enoughpower.An HVDC Light bind could be anideal solution in such cases.First, the link could supply the communitywith power from the main AC grid,eliminating the need for local generation.The HVDC Light link could also supply thewind turbine farm with reactive power for the generators, and keeping the powerfrequency stable.When the power output from the windgenerators grows as more units are added,they may supply the community with asubstantial share of its power needs. Whenthe output exceeds the needs of theCommunity, the power flow on the HVDCLight link is rev ersed automatically, and thesurplus power is transmitted to the mainAC grid.Wind powerSmall scale hydropowerHVDC LightExtruded cableDistant ac- gridWaste gas is usually burnt-out at offshoredrillingplatforms, since it is too expensive,or technically difficult, to use the gas for power generation and transmit it by an ACcable to the main grid on the shore. Thus,the energy content of the gas is wasted, andthe primitive burning process is source ofpollution. With an HVDC Lightunderwater cable transmission, the gas canbe used as gas turbine fuel, supplying boththe platform and the main AC grid withpower. The process of burning the gas ingas turbines would also produce much acleaner exhaust than simple burning woulddo.The DC underwater cable network could easily be widen to other offshoreplatforms.3.4 ASYNCRONOUS LINKSTwo AC grids, adjacent to each other butrunning asynchronously with respect toeach other, cannot exchange any powerbetween each other. If there is a surplus ofgenerating c apacity in one of the grids itcannot be utilized in the other grid. Each ofthe networks must have its own capacity of peak power generation, usually in the formof older, inefficient fuel fossil plants, ordiesel or gas turbine units. Thus, peakpower generation is often a source ofsubstantial pollution, and their fueleconomy is frequently bad.A DC link, connecting two such networks,can be used for combining the generationcapacities of both networks. Cheap surpluspower from one network can replace peakpower generation in the other. This willresult in both reduced pollution levels andincreased fuel economy. The powerexchange between the networks is alsovery easy to measure accurately.4. ADVANTAGES* Transmission by HVDC Light saves the environment by replacing local fossil-fueled generation withtransmission from main AC-grid. * Connecting small scale renewable power to main AC grid. * HVDC Light is inherent environmentally friendlycables instead of OH transmission lines. * Virtually no m agnetic field. * No ground currents because of bipolar transmission.5. CONCLUSIONHVDC Light technology saves theenvironment by replacing remote fossilfuelledgenerators with cost-efficienttransmission of power from efficient andclean, large-scale generation productionunits. The efficiency of a modern, largescale, thermal generating plant is usually 25percent higher than that for a modernsmall or moderate scale diesel generatorplant,Vice versa, HVDC Light provides aconvenient and cost-effective way forconnecting renewable and non-pollutingenergy sources as wind power farms andphotovoltaic power plants to a main grid.The HVDC Light technology in itself hasstrong environmental benefits.Since poweris transmitted via a pair of underground cables, the electromagnetic fields from thecables cancel each other. Any residual fieldis a static field, as opposed to the powerfrequencyfields radiated from AC cables.Since HVDC Light transmissions arebipolar, they do not inject any currents intothe gr ound. Ground currents can disturbcommunications systems or causecorrosion on gas or oil pipelines.A pair of light-weight DC cables can beeasily plodded into the ground at a costthat is comparable to or less than for acorresponding AC overhead line. Asopposed to an overhead line, anunderground cable pair has no visualimpact at all on the landscape. Usually itsalso much easier to obtain permissions andpublic approval for a cable transmissionthan for an overhead line, especially inresidential areas.ACKNOWLEDGEMENTOur sincere thanks to HOD and FACULTIES for promote us to prepare the above document. A special thanks to IEEE.orgREFERNCES1 K. Eriksson, HVDC Light and development of Voltage SourceConverters, IEEE TD 2002 Latin America, So Paulo, Brazil, March. 2 L. Carlsson, G. Asplund, H. Bjrklund, M. berg, Present trends inHVDC converter station design IV SEPOPE Conference, Foz doIguacu, Brazil. 3IEEE explorer.org