HVDC Light Technology Essay

tweetThis document reveals theHVDC cleverness DC contagion technology.It is used in underground transmission system and moreover provides evidence to point transmission.HVDC lightness requires only twain elements namely a convertor station and a duplicate of ground strains. The unseasoned HVDC timid crinkle is an extruded, single-pole line of reasoning. It is ideally suited for feeding office staff into growing metropolitan atomic bod 18as from a suburban substation. HVDC Light is inherent milieually friendly credit lines instead of OH transmission lines. Virtually no magnetic field. The environmental gains would be substantial, since the provide supplied via the DC cables will be impartted from cost-effective force-out plants in the briny AC control grid.1. INTRODUCTIONA hundred years ago, the transformer and a new transmission and distributionbe controlled precisely and independently hind end replace crash lines at no pricecontrol capabilities that are n ot present oreconomically feasible to unite smallscale,Equally important, HVDC Light hasfor inefficient, polluting local anaesthetic generationfrequency, active and unstable power canislands, mining districts and drillingloads from a master(prenominal) AC-gridof each other. This technology also relieson a new type of underground cable which penalty platforms can be supplied with power from possible even in the most sophisticated ACrenewable power generation. renewable power generation plants such as diesel engine units.The voltage, .Connect small scaleFeeding remote isolatedFlexible transmissionSystem technology, HVDC Light, turn overs it the briny grid,thereby 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 de veloped by means oftechnical 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 by means of anefficient transportation system, therebyreducing waste and pollution.Hydro plantshave been located where the hydroresources can be used at the greatestadvantage. And large generating plantshave meant fewer budget items 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 proven advantages, it is difficult andexpensive to adapt AC transmission anddistribution sy stems to the numerous smallscalegenerating plants that are being built,or to the increasingly complex and variableproduction and load demands.Environmental concerns and regulationsalso put heavy restrictions on building right-of-ways and on small-scale, fossilfuelledgenerating plants, such as dieselgenerating plants.These new trends require networks that areflexible. 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. engineeringAs 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 cha nnelsbetween the two stations, and there mustbe large rotating units generators orsynchronous condensers present in theAC networks at some(prenominal) ends of thetransmission.HVDC Light consists of only two elements a converter station and a agree ofground cables. The converters are voltagesource converters, VSCs. The sidetrack from the VSCare goaded by the controlsystem, which does not require anycommunications links 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 knowing 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 ofj ust a few elements two containers for theconverters and the control system, threesmall AC air-core reactors, a simpleharmonics filter and some cooling fans. 20MW18x12mThe converters are using a coiffure 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 mechanically adjuststhe voltage, frequency and flow of activeand reactive power according to the needof 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 pot ential 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 qualificationit has a specific weight of just over 1 kg/m.Contrary to the end with AC transmissiondistance is not the factor that determinesthe line voltage. The only limit is the costof the line losses, which may be lowered bychoosing a cable with a conductor with alarger cross section. Thus, the cost of apair of DC cables is additive with distance.Insulation 5.5 mm triple extrudedScreen Copper wireSheath HDPEWeight 1.05 kg/mVoltage 100 kV DCCurrent 300 APower 30 MW film director 95 mm2AluminumA DC cable connection 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 configur ations. 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. Three 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 expand 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 occu pant semiprecious land. Theprocess of 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 astatic 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 GENERATIONRemote locations often need localgeneration if they are situated far away(p)from an AC grid. The dista nce to the gridmakes it technically or economicallyunfeasible to connect the area to the maingrid. Such remote locations may be islands,mining areas, fumble and oil 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 function of the distance, abreak-even might be reached for as shortdistances as 50- 60 km.HVDC Light lowest costAC + Overhead lineHVDC Light + cableCost insideAC gridDistance from the AC grid eliminate local diesel Cost/ kWh3.3 CONNECTING POWER GRIDSRenewable power sources are often builtfrom scratch, beginning on a small scaleand gradually expanded. Wind turbine farms is the typic 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 link 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 HVD CLight link is reversed automatically, and thesurplus power is transmitted to the mainAC grid.Wind power miniscule scale hydropowerHVDC LightExtruded cableDistant ac- gridWaste gas is usually burned 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 combustion 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 extended 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 i s a surplus ofgenerating capacity 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 corporate trust 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 tran smission lines. * Virtually no magnetic 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 no t inject any currents intothe ground. 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, in particular inresidential areas.ACKNOWLEDGEMENTOur sincere thank to HOD and FACULTIES for encouraging us to prepare the above document. A special thanks to IEEE.orgREFERNCES1 K. Eriksson, HVDC Light and development of Voltage SourceConverters, IEEE T&D 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