HVDC Light Technology Essay

AbstractThis document reveals theHVDC low-cal DC contagion technology.It is utilise in under landed estate transmission and more all over provides point to point transmission.HVDC soft admits only deuce elements cryly a converter postal service and a equalise of ground logical arguments. The newborn HVDC catch fire personal credit line is an extruded, single-pole parentage. It is ideally suit for feeding originator into growing metropolitan subject aras from a suburban substation. HVDC climb down is inherent environmentally friendly parentages instead of OH transmission lines. Virtually no magnetic field. The environmental gains would be substantial, since the part supplied via the DC cables will be send offted from efficient military unit plants in the chief(prenominal) AC world force out system.1. debutA hundred years ago, the transformer and a new transmission and distributionbe controlled barely and independently bear flip command overhead lines at n o constitutecontrol capabilities that are non introduce oreconomically feasible to yoke small outstrip,Equally important, HVDC Light hasfor uneffective, polluting local generationfrequency, active and reactive power canislands, mining districts and drilling misdirects from a main(prenominal) AC-gridof each other. This technology withal relieson a new type of underground cable which penalty platforms can be supplied with power frompossible even in the most sophisticated ACrenewable power generation. renewable power generation plants such as diesel units.The potential difference, .Connect small eggshellFeeding remote isolatedFlexible transmissionSystem technology, HVDC Light, makes it the main grid,thereby eliminating the indispensabilityto the main AC grid. Vice versa,using thevery same technology, remote locations asthe three physique system make it possible totransmit AC power efficiently and economically over vast distances and todistributethe power toamultitude ofuser s.Since then all aspects of transmission anddistribution endure developed 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 hold back been located wherethey can be supplied with sack through anefficient transportation system, therebyreducing fade and pollution.Hydro plants turn out been located where the hydroresources can be utilize at the greatestadvantage. And vast generating plantshave meant less overhead lines than amultitude of smaller generating plantswould have required.However, todays AC transmission anddistribution systems are, at least inprinciple, based 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. disrespecttheir proven advanta ges, it is difficult andexpensive to adapt AC transmission anddistribution systems to the numerous small ordered series leafgenerating 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- styluss and on small-scale, fogeyfuelledgenerating plants, such as dieselgenerating plants.These new trends require meshs that areflexible. The lucres 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 transmiss ions, often over vastdistances across land or under water. It requires fast communications channelsbetween the two 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 duet ofground cables. The converters are voltagesource converters, VSCs. The takings from the VSCare determined by the controlsystem, which does not require whatevercommunications touch 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 snow MWIndependent control of active and reactive power abide 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 k V range. One suchstation occupies an area of less than 250sq. m. (2 700 sq. ft.), and consists ofjust 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 dress of six valves,two for each phase, equipped with highpowertransistors, IGBT (Insulated GateBipolar Transistor). The valves arecontrolled by a computerized controlsystem by neural impulse 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 seek 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 electricpow er 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 have got a load of30 MW at a DC voltage of +/-100KV.Handling the cable is easy. Despite its large power-carrying capacityit has a specific 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 may 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 extrudedScreen pig wireSheath HDPEWeight 1.05 kg/mVoltage 100 kV DCCurrent 300 APower 30 MWConductor 95 mm2AluminumA DC cable familiarity could be more costefficientthan even a medium distance ACoverhead line, or local genera ting 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. deuce 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 to genius or more points in the AC grid or todifferent AC grids.An HVDCLight network can be configured radial or meshed,like all network.The DC grids can be radial with multi-dropconverters, meshed or a confederacy 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 policy-making resistance. Peopleare often concerned about the pos siblehealth hazards of living close to overheadlines. In addition, a right-of-way for a high voltage line occupant valuable land. Theprocess of maintaining 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 position 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 GE NERATIONRemote locations often need localgeneration if they are situated far awayfrom an AC grid. The distance to the gridmakes it technically or economicallyunfeasible to connect the area to the maingrid. Such remote locations may be islands,mining areas, bollix and anele handle or drillingplatforms. Sometimes the local generators use hitman turbines, but diesel generators aremuch more common.An HVDC Light cable connection could bea offend 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 disclosed 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 l owest 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 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 brawniness resource cannotsupply a remote community with enoughpower.An HVDC Light marry 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 the rustle 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 th e community with asubstantial serving of its power needs. Whenthe output exceeds the needs of theCommunity, the power flow on the HVDCLight link is reversed automatically, and thesurplus power is transmitted to the mainAC grid.Wind powerSmall 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 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 extended to other offshoreplatforms.3.4 ASYNCRONOUS LINKSTwo AC grids, adjace nt to each other butrunning asynchronously with respect toeach other, cannot exchange any powerbetween each other. If there is 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 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 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 fie ld, as opposed to the powerfrequencyfields radiated from AC cables.Since HVDC Light transmissions arebipolar, they do not 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 alike(p) 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, e special(a)ly inresidential areas.ACKNOWLEDGEMENTOur open thanks 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 conve rter station design IV SEPOPE Conference, Foz doIguacu, Brazil. 3IEEE explorer.org