The size of offshore wind generators is increasing, and the trend is moving towards full converter gear-less solutions with permanent magnet synchronous generators (PMSG). The nacelle weight reduction is a key design criterion for offshore wind turbines. To overcome the weight challenge, a transformer-less concept is under development. This concept employs a special PMSG with an innovative high insulation level between the groups of windings. The generator supplies nine series connected converter modules, which results in a high voltage DC output of 100 kV, reducing the total weight of the system.Conventional three phase 2-level voltage source converters, each with 11.1 kV output, are utilized in concept studies and simulations. However, other voltage source converter topologies are assumed to be more beneficial in terms of efficiency, voltage quality and reliability issues. This work compares multilevel converter topologies with regards to their suitability for the proposed concept.The result of an initial study is that the modular multilevel converter (MMC) is the most promising candidate. The MMC adds more components and complexity to an already intricate system, but gives benefits that are in line with many of the ideas behind the proposed concept. A modular structure grants the easiest expansion to a high number of levels, providing a high-quality voltage with less demand for filters to save both volume and weight. The MMC also offers redundancy possibilities for higher reliability, which is important in offshore wind power installations. PSCAD/EMTDC simulation models have been built, implementing voltage balancing and redundancy control. The simulations have also investigated the functionality of the converter in the proposed system. The results show that the MMC performs well in the full system, and is therefore considered as a viable candidate. The number of levels needed is at least five to avoid series connection of IGBTs. Further studies should find an optimal number of levels, depending on the generator specifications, the desired level of losses, voltage quality and a weighting of reliability versus complexity.

This thesis is centered around the design of a grid-connected photovoltaic (PV) roof installation at a specific location in Oslo, Norway. The motivating factor in this study has been the growth of the solar industry globally, while there has been little to none larger PV investments in Norway. The objective is to investigate how much renewable PV energy that can be produced from the designed system, with an electrical focus. Factors such as the suns position during each day of the year, the shadings on modules, the electrical effect of shading and bypass diodes, and other factors influence the production of a PV installation. Due to the complexity of power production in a PV system, the simulation software PVsyst was used as support. A 3D representation of the building and shading elements was constructed in the simulation program for shading calculation purposes. Meteorological data from local weather stations in Lier, Ås and Blindern was compared with meteorological data provided by interpolation and satellite images. The distance between modular rows was dimensioned after a shading criterion so that there would be no shading from other modular rows during spring equinox (March 21st). The modular tilt was adjusted (from the optimal tilt angle of 40 degrees) in order to reduce shading loss and improve the performance ratio of the system. The number of module and inverter types and manufacturers was limited to three different module types, and four different inverter series. The simulated production from the three best alternatives, based on performance ratio and production were compared with the energy consumption in the building. Simple economical evaluations of the three best alternatives have been performed using the simple payback method and life cycle costing. As a result of the limited area on the roof, the shading objects and the dimensioning criteria (maximize performance ratio and production of the system) it was found that the module tilt was 20 degrees. The modules in the system are directed towards geographical south, and there is a pitch distance of 2 meters between the module rows. The resulting three final alternatives were two polycrystalline alternatives and one monocrystalline alternative. The polycrystalline alternatives used the same REC modules and different inverters, one from Eltek and the other from SMA. The monocrystalline alternative was simulated with SunPower modules and SMA inverters. The installations have a simulated energy production of 22.4, 22.9 and 31.0 MWh/year, which would cover the average energy consumption of a household in Norway (20.4 MWh/year). However, the installation will only contribute to reduce the energy consumption in the six storey commercial building by approximately 1 % per year. Comparing the simulated productions and the consumption in 2011, it is found that the installation will not result in a surplus of energy which could have been injected into the grid. The installation will therefore not change the buildings customer status to a surplus customer (plusskunde). With the simplified economical evaluation it is found that the energy from the PV installation will cost more than the energy agreement of today and it is triple the yearly average market price of electricity the last three years. The polycrystalline alternative with SMA inverters was the least expensive alternative of the three and the polycrystalline alternative with highest production. The monocrystalline alternative gave best simulated production and performance ratio of the three alternatives, but was the most expensive alternative.

The purpose of the experiments conducted in this Master's thesis is to predict and explain the change in breakdown voltage when insulating barriers are introduced in a rod-plane gap arrangement. The experiments have been conducted with positive lightning impulse voltage, using the up and down method to determine the 50 % breakdown voltage. A cylindrical rod with rounded tip and radius 3.5 mm was used as the high voltage electrode above a plane grounded electrode. The polycarbonate barriers used were 1 mm thick and of different sizes (4x4 cm, 6x6 cm, 8x8 cm, 16x16 cm, 30x30 cm and 40x40 cm). They were placed at various positions in the 80 mm rod-plane gap to find the optimal combination.The results show that the breakdown voltage of the gap could be increased by the use of barriers, strongly dependent upon their size and position. The largest barrier offered the highest breakdown voltage, an increase of 98.0 % versus the barrier-less rod-plane gap. With the two largest barriers, the optimal position was found to be in the upper part of the gap, 0-10 mm from the high voltage rod tip. The four smaller barriers perform their best around 20 mm from the tip. Literature has suggested that the optimal position is in the range 12-24 mm for this gap [Lebedev et al. 2005], where the breakdown voltage can be over tripled.It has been discovered that placing the smallest barriers close to the high voltage rod tip drops the breakdown voltage to levels below that of the barrier-less gap. A suggested explanation is the strong tangential field present on the barrier surface under these conditions, quickly building up charge on the barrier and leading to breakdown. Streamer inception on the underside of the barrier has not been observed despite the high field strength directly under the rod tip. This is possibly caused by the slightly higher field on the upper side of the barrier, leading to streamer inception which weakens the field under the rod tip. As the barrier size is increased, the voltage drop in the longer streamer path is the dominating factor behind the rise in breakdown voltage. It is recommended to employ barriers of considerable cross-sectional length, preferably twice the gap distance or longer, to ensure satisfactory breakdown performance improvement. An empirical equation for predicting breakdown voltage in barrier insulated rod-plane gaps has been constructed on the basis of the conducted experiments.

This thesis is written in cooperation with Fred Olsen's Wave Energy Project Bolt2 which is a Wave Energy Converter (WEC) recently deployed outside of Falmouth Bay in the UK. After the initial phases of testing, the device is to be grid connected to the local distribution network. The purpose of this thesis is to develop a model that can serve as a useful starting point for investigating grid connection issues for Wave Energy Converters or as a part of a complete wave-to-wire modelling of a WEC. The Bolt2 project will be used as a framework for the thesis. Measurements from the testing of Bolt2 have been provided and strengthen the project by applying real life conditions to the model.The work emphasizes on the challenges of grid connecting wave energy devices as motivation for the work. As a first step, the design of the grid side converter and its control system is carried out with the main criterion being a constant DC-link voltage. In addition, the control circuit ensures no reactive power exchange at the converter output that the currents are injected at the grid frequency. The control strategy applied is based on vector control due to its well documented performance in a variety of applications.One of the main barriers for wave energy developers are the large power variations that are inherent to most WECs since the produced wave power goes through zero twice in each wave period. An effective way of reducing the power fluctuations is by disposing several point absorbers in an array configuration which is one of the advantages of Fred Olsen's Bolt2.To further smooth out the power, an Energy Storage System (ESS) is considered. After a short discussion, the energy storage device was chosen to be a supercapacitor (SC) bank. Initially, the possibility to provide a constant power to the grid was investigated but was rejected as being unrealistic for a practical case. Instead, an alternative power management strategy of the ESS was developed. It was decided to chop off only the largest power peaks and to discharge whenever any amount of energy remained in the SCs for the storage system to be completely discharged and prepared for any incoming power peak. A bi-directional DC-DC converter was used to interface the SCs with the DC-link and the described power management strategy was realized through current control of the switching devices. Two similar but separate control schemes were necessary in order to perform both buck charging and boost discharging.Finally, simulations of power data from a design sea state were performed in order to prove the validity of the developed model. The peak-to-average power ratio was demonstrated to be reduced with the integration of the energy storage system. However, the expenses of including a storage would have to be justified by reduced costs for the developer in order for the scenario to be economically viable.

På grunn av den økende alderen på mye av distribusjonsnettet og den økte ressursbruken dette medfører, har nettselskap satt fokus på hvordan vedlikehold og reinvestering kan planlegges og utføres på en best mulig måte. HelgelandsKraft(HK) er et nettselskap med ansvar for mye distribusjonsnett. For å planlegge vedlikeholdet har HK laget en database, Prelib, der tilstanden til komponenter registreres etter tilstandsbefaringer omtrent hvert tiende år. Tidligere resultat fra tilstandsbefaringer lagres også, og dette gir muligheten til å undersøke utviklingen av tilstanden. Bakgrunnsdata som grunnforhold og korrosivitet er også registrert i databasen. Bakgrunnen for oppgaven var å undersøke hvordan tilstandsdataene i Prelib kan brukes i planleggingen av vedlikehold og reinvestering og på den måten være et ledd i overgangen fra en tidsstyrt til en risikobasert vedlikeholdsstrategi. Oppgavens mål var å foreslå en prosedyre for hvordan planleggingen kan utføres med de ressursene, både økonomisk og tidsmessig, som er tilgjengelige.HelgelandsKraft ble besøkt ved flere anledninger. Oppholdet ga innsikt i hvordan bedriften jobber med planlegging av vedlikehold og hvordan de har brukt Prelib. Det ble dannet et godt grunnlag for oppgaven gjennom innføring i dagens situasjon i nettet og hvordan tilstanden til komponenter bestemmes.Oppgaven har gått gjennom teori knyttet til tilstandsbasert og risikobasert vedlikehold. Teorien ga eksempel på hvordan man kan bruke risiko i planleggingen av vedlikehold av kraftnett. Den ga også en innføring i hvordan informasjon om teknisk tilstand kan brukes til å estimere sannsynlighet for svikt og tilhørende risiko. Dette ble brukt i analysen av casene og i prosedyren som ble satt opp på bakgrunn av disse. Siden arbeidet som allerede var gjort i HK stemte godt overens med teorien, kunne mye av teorien brukes i praksis. Gjennom analysen av tre konkrete case, har det blitt foreslått en prosedyre for å analysere vedlikeholds- og reinvesteringsbehovet i en nettdel. Prosedyren tar utgangspunkt i tilstandsdata som er registrert i Prelib. Først ble informasjonen brukt til å danne seg et bilde av tilstanden på nettdelen. Videre ble den brukt til å beregne økonomisk risiko for ulike tiltak i nettet. Risikoen ble satt inn i lønnsomhetsberegninger av alternative handlingsplaner. Det ble undersøkt hvordan endringer i sannsynlighet for svikt, tiltakets kostnad og tidspunkt for iverksetting av tiltak påvirker lønnsomheten til et alternativ. Med å gjennomføre tilsvarende analyse, vil bedriften ha et bedre beslutningsgrunnlag i vedlikeholdsarbeidet. Selv om prosedyren har en enkel framgangsmåte og ikke er spesielt tidkrevende, vil den kreve mer tid til å planlegge vedlikeholdet enn det som er tilfelle i dag. Før prosedyren kan implementeres i bedriften, er det nødvendig å enten etablere levetidskurver for komponentene i nettet eller å estimere sannsynligheten for svikt for komponenter i gitte tilstander.

Kravene til å redusere energiforbruk i eksisterende og ny bygningsmasse øker stadig. Det er derfor viktig å se på hvordan disse kravene kan oppnås uten at det går på bekostning av inneklimaet. I byggprosjektering benyttes simuleringsprogram i økende grad til å stadfeste byggets energiytelse og til å vurdere inneklima og termisk komfort. Derfor er det viktig med god kompetanse ved bruk av simuleringsprogrammer. Det benyttes i dag en rekke standarder som setter kriterier for prosjektering av bygg. For passivhus er det allerede utarbeidet en standard for bolighus, mens en standard for yrkesbygg er på god vei og er forventet innført fra høsten 2012. Fra 2015 skal det i Norge innføres passivhusnivå i byggforskriftene. Det er nødvendig for en hver bruker av disse å være kritisk til hvordan man benytter seg av disse i simuleringer og byggprosjektering generelt.Rapporten beskriver innledningsvis momenter rundt vurdering av energiytelse og termisk komfort. Deretter velges en rekke systemløsninger og parametere som er aktuelle å analysere. Disse er av både passiv og aktiv art. Av passiv art vurderes to ulike fasadeutforminger. Av aktiv art er det hovedfokus på sammenlikning av romkjøling og ventilasjonskjøling, med eller uten nattventilasjon og ved ulike settpunkter for kjøling.Bygget som simuleres er et kontorbygg i Oslo som skal stå ferdig rundt årsskiftet 2012/2013. Det opprettes så simuleringsmodeller for dette bygget i simuleringsverktøyet IDA ICE 4.2. Modellene som er utarbeidet varierer mellom utsnitt av ytre og indre soner av bygget, med den hensikt å studere termiske forhold innad i bygget. Det er også gjennomført års-simuleringer av en representativ etasje for bygget for å gi et inntrykk av byggets energiytelse.Rapporten anbefaler ventilasjonskjøling og nattkjøling som en systemløsning som gir tilfredsstillende termisk komfort samtidig som det gir bygget god energiytelse. Resultatene som har blitt utarbeidet viser også hvordan ulike fasadeutforminger med ulik glassandel påvirker byggets termiske inneklima og energiytelse. Et rom i kjernen av bygget har også blitt studert med tanke på tilførsel av luftmengder til rom som står tomme i lengre tid. Årssimuleringene viser at byggets energiytelse påvirkes av minimumsluftmengdene som er satt for ventilasjonskjøling. Dersom disse er for høye om vinteren vil det kjøle ned bygget unødvendig, og kompensasjon må til med oppvarming. Riktig valg av minimumsmengder gjør ventilasjonskjøling til det beste valget energimessig. Dette avhenger selvsagt også av riktig tilluftstemperatur og reelle komponenter som tilrettelegger stor variasjon i luftmengder og lave tilluftstemperaturer.Ved bruk av effektiv solavskjerming som aktiveres ved 50 W/m2 innstrålt effekt på innsiden av glasset er det funnet at ulike soneinndelinger av bygget har mindre å si for resultatet av en energiberegning.

The title of the thesis - "Offshore Rankine Cycles" - is very general and cover a large range of engineering fields, e.g. thermodynamic cycles (Rankine, ORC, Brayton, Kalina, etc.), mechanical equipment (gas/steam turbine, heat exchangers and additional equipment) and safety concerns (flammable and/or toxic fluids, high temperature and pressures), to name the most important.The thesis try to give a brief overview of all critical points and alternatives, concerning employment of a waste heat recovery machine on offshore facilities, although focus has been on three more specified cases, namely:1. Comparison of a steam cycle vs. an organic Rankine cycle for high temperature operating conditions.2. Study of heat exchanger parameters on total cycle performance.3. Investigation of a modular expander setup versus a single expander.To compare a steam cycle to an organic cycle, a choice of working fluid for the organic cycle had to be made. After some investigation, toluene was chosen as it is a "common" fluid with known properties and was found to be a viable option for high temperature heat sources, both for subcritical and supercritical operation. Due to water being constricted to subcritical operation a CO2 cycle was implemented as a comparison to the supercritical toluene cycle. The main focus of the comparison was exergy losses during heat transfer and power output.The heat exchanger parameter study was conducted with a printed circuit heat exchanger as an example. The study of overall cycle performance has close connections to the heat exchanger size, since it is an important parameter concerning offshore employment due to costly "footprint". The cycle's dependency on the heat exchanger is mainly by the heat transfer rate, or heat load, which the heat exchanger applies to the cycle. The heat transfer rate is given by the heat exchanger`s ability to reduce the temperature of the exhaust gases. This ability depends on the two fluids involved and the geometry of the heat exchanger. While the choice in working fluid and pinch points sets the amount of heat transferred, the remaining analysis rest on the overall heat transfer coefficient (UA) to balance the heat load. When fluid properties are determined, the UA - value is again dependent on heat exchanger geometry and further variation of these parameters will in turn reveal the size of the heat exchanger. When imposing a working fluid to the cold side of the heat exchanger an optimization in heat exchanger volume could be found at specified heat load.A VBA macro has been made where expander parameters (rated power and efficiency vs. volumetric flow rate values) could be used as inputs to calculate the power output of two expanders in a modular setup relative to a single expander as reference.

As a consequence of increased government efforts to reduce local Norwegian CO_2-emissions the development of small distributed generators have increased. This development is assumed to continue, but at an increasing incremental cost due to the inferior profitability of remaining prospects. To maintain profitability of smaller and high cost distributed generators, cost savings must be implemented. Quality of supply is a significant factor in determining potential profitability. Hence, a significant potential in cost reduction lies in increasing quality of supply. This can be achieved by utilizing the decentralized nature of these power producers by enabling intended island operation. By enabling these generators to run in intended island mode, they are able to supply their local grid with power when fallout of the main grid or other components occurs. This increases the uptime for local customers and therefore increases quality of supply. Five different grids are modeled in PowerFactory based on collected empirical data for the evaluation of the potential for islanding in Norway. With these models different cases utilizing islanding schemes are simulated and the reliability of these configurations compared to a base case representing normal operations. The results from this analysis suggest big reductions in the reliability indices “Energy Not Supplied” and “System Average Interruption Frequency” are possible. In the thesis the reductions achieved are in the 10%-60% range of the base case. The estimated savings earned from increased reliability of supply does not justify the assumed investment needed, but the numbers are not conclusive. Better estimates of expenses and assessing other grids with better prerequisites for islanding could indicate to be profitability.

I denne oppgaven er det sett på hvordan energibehov og lys i bygninger påvirkes av solavskjerming.Solavskjermingens oppgave er ikke bare å skjerme for sjenerende lys. Økt fokus på passivhus fører til at solavskjerming i større grad enn tidligere også må skjerme for varme. Det vil være ønskelig å stenge ute varme samtidig som en slipper inn lys.Ved hjelp av simuleringer er det sett på hvilke utslag endring av ulike egenskaper i glasset gir på energibehov og belysningsstyrke i bygninger. Det er også sett på ulike glassbelegg, bygningsutspring og himmelretning. Av aktive solavskjerminger er det sett på persienner, da både utvendig, mellomliggende og innvendig persienne og styring av disse. Simuleringene er gjennomført med tanke på skolebygg, men er overførbare til andre bygningskategorier.De viktigste resultatene av simuleringene er: •Glassets egenskaper: o g-verdi virker inn på  energibehovet til oppvarming og kjøling  effektbehovet til kjøling o u-verdi virker inn på  energibehovet til oppvarming o t_v-verdien virker inn på  belysningsstyrke  energibehov til belysning •Bygningsutspring virker inn på o belysningsstyrke o energi og effektbehov til kjøling • Himmelretning virker inn på o energibehov til både oppvarming, kjøling og belysning o belysningsstyrken • Persienne: o Utvendig persienne gir  høyere energibehov til oppvarming enn innvendig persienne  lavere energi og effektbehov til kjøling enn innvendig persienneKonklusjon: • Rom med kjølebehov bør o ha lav g-verdi o ha utvendig persienne o legges mot nord •Rom uten kjølebehov bør o ha lav u-verdi o ha høy g-verdi o ha innvendig persienne o legges mot sør • Rom med ønske om høy belysningsstyrke bør o ha høy t_v-verdi o legges mot sør

An analysis incorporating different principles for determination of the electricity mix and the subsequent environmental characteristic.