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U ovom završnom radu objašnjeno je što je HVDC prijenos električne energije, navedene su i definirane mogućnosti koje HVDC pruža s fokusom na usporedbu s HVAC-om. Također definirani su i dijelovi te tehnologije koje se koriste u radu HVDC sustava. Primjena HVDCa je prikazana kroz primjere u svijetu za: kabelski podmorski prijenos električne energije, nadzemni prijenos električne energije, te za primjene kod povezivanja elektroenergetskih sustava različitih frekvencija. U završnom radu prikazana je i usporedba gubitaka izmjeničnog i istosmjernog prijenosa po pojedinim elementima svakog sustava pri kabelskom prijenosu. Dokazano je da, gledajući na gubitke, HVDC ima prednost koja je izraženija povećanjem duljine prijenosa. In this undergraduate thesis it is explained what HVDC is, the possibilities that HVDC provides with a focus on comparison with HVAC which are listed and defined. Parts and technology used in the operation of the HVDC system have also been defined. The application of HVDC is presented through these examples: subsea cable transmission of electricity, overhead transmission of electricity, and for applications in the connection of power systems with different frequencies. The thesis also compares the losses of alternating and direct transmission by individual elements of each system in cable transmission. It has been shown that, looking at losses, HVDC has an advantage that is more pronounced by the increase of the transmission length.

U diplomskom radu opisan je visokonaponski istosmjerni prijenos energije (HVDC). Osnova HVDC prijenosa su pretvarače stanice koje mogu biti ispravljačke (izmjenična struja u istosmjernu) i izmjenjivačke (istosmjerna struja u izmjeničnu). Veza između dvije pretvaračke stanice su DC vodovi ili kabeli. Usporedbom AC i DC sustava možemo vidjeti kako su kod DC sustava veći početni troškovi zbog cijene pretvaračkih stanice no manji su gubici te su DC sustavima te su znatno isplativiji na veće udaljenosti. Pretvaračke stanice možemo povezati na različite načine. HVDC mreže možemo primijeniti u različitim slučajevima npr. kada je potreban prijenos energije na velike udaljenosti, zatim ukoliko imamo dva sustava različitih frekvencija te kada je potrebno spojiti kopno i more. U DigSilet programu analizirana je jedna tipična HVDC mreža. Izvršena je analiza tokova snaga te više vrsta kvarova u sustavu. The master thesis describes high voltage direct current transmission (HVDC). The basics of HVDC transmission are converter stations that can be rectifier (alternating current in direct current) and alternating current (direct current in alternating current). The connection between the two converter stations is DC lines or cables. Comparing AC and DC systems, we can see that in a DC system, the initial costs are higher due to the prices of converter stations, but the losses are smaller and DC systems are significantly increased over longer distances. Converter stations can be connected in different ways. HVDC networks can be applied in different cases, eg. when long distance energy transmission is required, then if we have two systems of different frequencies and off-shore connection. One typical HVDC network was analyzed in the DigSilet program. An analysis of power flows and several types of failures in the system was performed.

Based on completely mastering ±800 kV transmission technologies, the first ±1100 kV direct current (DC) transmission demonstration project is being constructed in China. Combining theoretical analysis and a large number of experiments, the margin of switching overvoltage in converter stations, the configuration scheme and performance of lightning arresters, the shielding angles of ground lines under different geographical conditions, and the maximum air gap of lines have been determined. The switching impulse flashover characteristics of equipotential sphere and typical rod-plane air gaps are also provided. The external insulation is designed differently for light, medium, and heavy pollution areas. For the ±1100 kV project, if the 8 × 1250 mm^2 conductors are applied, the pole gap is 26 m and the height of the line is 25 m, all the electromagnetic parameters will meet the requirement of international electromagnetic standards. The key design points of ±1100 kV converter transformers, smoothing reactors, converter valves, and wall bushings are researched and the 75 mH smoothing reactors, ±1100 kV/5000 A converter valves, and ±1100 kV/5523 A wall bushings are successfully made. The optimised hierarchical connection modes and coordination control measure of the ±1100 kV project are studied and the results can provide sufficient technical support for the demonstration project.

This Technical Brochure 836 (CIGRE WG C4.45) presents 6 transient measuring techniques in their working principles, key technical features as well as advantages and disadvantages. A series of performance requirements as well as their testing methods for the transient measuring system are specified. A series of field measurement cases on switching transient voltage, lightning transient voltage and VFFO from seven countries are introduced in detail.

Considering the negative resistance effect of power electronic equipment, unstable resonance problems may occur between wind farms and converter stations. This paper focuses on the resonance stability problem of a wind power base coupling with a multi-level converter−high-voltage direct-current transmission (MMC–HVDC) system. Firstly, the s-domain impedance models of the doubly-fed induction wind generator, the permanent magnet synchronous wind generator, and the modular MMC are built, through the theoretical derivation and simulation test. Secondly, based on the s-domain nodal admittance matrix method, the resonance structure of the wind power base coupling with an MMC–HVDC system is analysed, including the resonance mode frequencies, the resonance mode damping factors, the nodal participation factors, and the nodal voltage mode shapes. Thirdly, the main factors influencing the resonance structure are studied, including the topology of the wind power base, the capacity of the wind turbines, and the operation mode of the MMC station. Finally, a brief conclusion ends the paper.

In this study, direct current (DC) voltage margin control strategy and droop control strategy of voltage source converter multi-terminal direct current (VSC-MTDC) are introduced firstly, and according to the characteristics of two control strategies, an adaptive droop control strategy of DC voltage margin is proposed. When the power fluctuation of DC grid is relatively smaller, some of converter stations which connect to the power generations systems are involved in power coordination to balance the power margin of the entire DC grid. When the power of DC grid suddenly changes and the power fluctuation is relatively larger, the converter stations that adopt the adaptive droop control strategy adjust power and can avoid some of them to lose the adjust ability due to full load and power huge fluctuation as far as possible. Finally, the simulation based on MATLAB validates the effectiveness of the strategy.

U ovom diplomskom radu opisana je visokonaponska istosmjerna tehnologija prijenosa električne energije (HVDC). HVDC sustavi počeli su se instalirati zbog velikog napretka elektronike, pomoću koje se smanjila cijena pretvaračkih stanica, a time i samih sustava. Princip rada istosmjernog prijenosa je da se električna energija pomoću AC mreže dovodi do pretvaračkih stanica, zatim se ispravlja, prenosi se DC prijenosim vodom ili kabelom, i opet pretvara u izmjeničnu struju, te zatim se dovodi do krajnjih korisnika. Postoji više vrsta povezivanja pretvaračkih stanica. HVDC prijenos se koristi na velike udaljenosti, podzemni i podmorski prijenos, prijenos na otvoreno more, prijenos u urabana područja i asinkrono povezivanje. Usporedbom troškova HVDC i AC prijenosa može se vidjeti da su u HVDC sustavima veći početni troškovi, zbog visokih cijena pretvaračkih stanica, ali su manji gubici prijenosa, što dovodi do veće isplativosti HVDC sustava na velike udaljenosti. Također kritična udaljenost kabela ne dozvoljava veliku duljinu prijenosa, što je još jedan nedostatak izmjeničnog prijensa. Pomoću simulatora PowerWorld moguće je modelirati HVDC sustav sa svim njegovim elementima, te pomoću tokova snaga analizirati i usporediti s AC prijenosom. U simulaciju je modeliran HVDC kabelski prijenos s Italijom, prijenosne snage 200 MW, te je zatim izvršena analiza tokova snaga za dva slučaja u kojemu je modelirana mreža spojena s susjednim sustavima. This diploma thesis describes high voltage direct current transmission (HVDC). HVDC systems started to instal beacuse of big progress in electonics, which reduced the cost of converter stations, and thus the whole systems. Basic princip of DC transmission is that electric energy is being carried with AC network to converter stations, then the current is being rectified, then its being transmitted with DC lines, and then its being converted back to AC current and delivered to consumers. There are multiple modes of connecting converter stations. HVDC transmission is used to transmit bulk power over long distances, offshore transmission, power delivery to large urban areas, underground and submarine cabel transmission and asynchronous ties. Comparating the expenses of HVDC and AC transmission one can see that inital costs are bigger in HVDC systems, beacuse of the big price of converter stations, but there are less loses in HVDC transmissions, which makes HVDC transmission more profitable over long distances. Also critical longitude of AC cabels don't let power transmission over long distances, which is one more negative side of alternating transmission. Using the PowerWorld simulator it's possible to make HVDC system with basic elements, and then using power flow analyse and compare with AC transmission. In simulation HVDC cabel transmission is connected with Italy, transmission power is 200 MW, and then the power flow has been done, for two cases, in which simulator network is being connected with neighborhood systems.

U ovom diplomskom radu opisan je istosmjerni visokonaponski prijenosni sustav i njegovi dijelovi, a naglasak je stavljen na pretvarače i primjenu energetske elektronike u takvom prijenosu. Rad nadalje opisuje sve prednosti i mane istosmjernog prijenosnog sustava u odnosu na izmjenični, te je utvrđeno u kojim prilikama je istosmjerni sustav superiorniji od izmjeničnog. Glavne topologije istosmjernog sustava također su obrađene, te je objašnjen problem interakcije između ta dva sustava. Sadržaj je popraćen odgovarajućim skicama, slikama i shemama koje daju viziju ovakvog sustava. This thesis describes the DC high-voltage transmission system and its components, and the emphasis is placed on inverters and application of power electronics in such transfer. The paper furthermore describes the advantages and disadvantages of DC transmission system in relation to the AC transmission system and is determined in what circumstances the DC system is superior to the AC system. The main topology of DC systems is also processed, and is explained the problem of interaction between the two systems. Content is accompanied by appropriate drawings, pictures and diagrams that provide a vision of this system

Master's thesis in Industrial economics Electrification of offshore installations has been an evaluated option for several platforms on the Norwegian Continental shelf (NCS). Offshore installations consume huge quantities of energy and for the majority of the installations the energy is made from burning natural gas in gas turbines locally. Electrification or Power From Shore solution, also called PFS-solution, is a technically complex system of components like submarine cables, offshore cable installation, transformer stations/converter stations, all which requires manufacturers and contractors with high competence and expertise. The PFS-solution must be safe, reliable and long lasting. Every meter of the submarine cable must work; only one weak spot in the cable will bring the whole power supply out of work, leaving the offshore platform without electricity. There are limited number of qualified suppliers available in the market to deliver such type of solution, and the research aim is to focus on how the procurement strategy can be developed to achieve a technical viable and cost effective PFS-solution in a market with limited competition. Methods used: Transporting electrical power over long distances by cables is a technical challenge that is not being dealt with in detail in this report, but knowledge from other studies and projects are used to describe a feasible PFS-solution similar to other systems already built to date. The aim for this thesis is to develop a procurement strategy that best suits a technical solution, reduces the costs and gives an acceptable quality for the offshore electrification. HSE (Health Safety and Environment) is also a high priority factor in today’s projects and will be part of the award criteria in tender evaluation. To realize PFS-solution for an offshore platform is to a large degree depending on the total cost. If the cost can be kept down, chances for the implementation is much higher. PFS-solution is depending on both a technical viable solution, the supplier market must be large enough to give competition and sufficient manufacturing capacity and experience to deliver in time, with reliable quality to a competitive cost. If the procurement strategy is able to join all these factors the probability for a successful project will be high. Findings of the research: Procurement strategy determines how the project in the best possible way can be specified and tendered to achieve the best possible and optimal result. By joining technical and contract knowledge with input from market situation and supplier competition, the probability for a successful project increases. Project of this size might have impact on competition between suppliers. The technical specification, cable manufacturing capacity, limited available capacity from few suppliers are key points to investigate as part of the procurement strategy development. Limited competition is a challenge and to create competition between the few suppliers the scope needs to be split in packages. The cost influence curve illustrates that the success of the projcect is decided in an early phase. By trying not to limit the technical PFS-alternatives and to keep both HVDC and HVAC solutions open until procurement phase, will give competition and alternatives for the developing company. Also allowing extruded DC cables as well as MI DC cables will give more competition. Utsira selected as example PFS-project (200 km from shore to field center): (Example is based on open published references and documentation. There has been no contact with Statoil or other partners in the Utsira development project. All assumptions except from the ones in the reference list are writer’s own opinion based on experience). Objective and goal is to supply the four offshore platforms at Utsira with up to 250-300 MW of electrical power from shore. Technically feasible with both DC-solution and AC solution. (AC solution is limited to about 240 to 250 MW). Limited number of suppliers/contractors available in market. Important to involve as many suppliers as possible to create competition and urge for cost effective solutions. Definition of lots: Lot 1: HVDC Converters (one onshore and one offshore), Lot 2: Submarine HVDC cable(s) – approx. 200 km single core x 2. Voltage 200 kV. Lot 3: Submarine AC cable(s) – approx. 82 km three core 66 kV. Lot 4: HVDC Converters + Submarine HVDC cable and AC cable(s). Lot 5: AC substations (one onshore 300 kV to 230 kV and one offshore 230 kV to 66 kV). Lot 6: Submarine HVAC cable – approx. 200 km three core 230 kV. Cost estimate of FPS-solution for Utsira example project is about 3500 MNOK for HVAC solution and about 4500 MNOK for HVDC solution. Estimated implementation time is about 4 years. AC solution is somewhat more cost effective that DC solution. Conclusions and recommendations: Electrification of offshore platforms with power from shore requires a complex and costly system of submarine cables and transformer stations/converter stations. By applying specification allowing for more competition will bring down cost and provide for cost effective PFS-solution. Enough time needs to be allocated to secure a proper prequalification, tender and contract negotiation phase. By splitting the contract packages in Lots suitable for the contractors in the market, will allow focus on their core business, but also create interfaces. Company need experienced personnel to handle these complex interfaces. Target is to establish these interfaces where they are logic and clear, for example at the end of the submarine cable, connection to substation or converter station.