Experimental studies as well as simulations have been performed on the Back-to-Back starting schemes low frequency-, partial frequency-, and soft -start-up. A Back-to-Back configuration of two synchronous machines has been established in the laboratory, upon which parameter estimation and start-up experiments have been performed. Extensive parameter estimation was conducted in order to replicate the laboratory machines in the simulation model as accurately as possible. This was done in order to verify the validity of the simulation model. Studies into the effects of inductance interconnecting the machines were made in the laboratory and in the simulation model. Effects of resistance and inertia were studied in the simulation model. It is concluded that the simulation model appears to be as reliable as is its input parameters. Discrepancies were found in line voltages, due to faulty implementation of field current replication. Full scale simulations using Motorformer parameters were performed in the simulation model, featuring low frequency- and soft -staring. The effects of an interconnecting cable were studied. It is concluded that low frequency starting appears to be most reliable and least violent starting method. However, it might be limited by the availability of a turbine. This is not the case for soft starting, which has a lower starting capability and is more violent to the motor damper- and field windings. Low frequency startig is the recommended starting method of the ones studied. Dynamic short circuit simulations were done on a fixed speed LNG-facility. The fixed speed alternative appears to be more stable when responding to a short circuit. This is because the motors contribute to upholding the voltage during a fault by delivering reactive power to the short circuit, and because the motors do not loose all torque as is the case for LCI drives when the voltage dip exceeds 20$%$. Further work is needed in up-scaling the experiments. A sophisticated simulation model should be established and its validity tested on the up-scaled experiments. Preliminary custom design of machines should be initiated depending on what starting scheme is chosen. Custom machine parameters should then be used in full scale simulation using the more sophisticated model.

As part of the energy recovery part of the ROMA (Resource Optimization and recovery in the Materials industry) project, a laboratory prototype power production system is being built and completed in 2009. The laboratory prototype is based on a new technology for power production from low to medium temperature heat sources (the off gas from electrolysis cells in the aluminum industry) where CO2 is used as a working medium in a trans-critical Rankine cycle. The laboratory rig consists of the power cycle with a prototype expander as the core unit, an air loop to provide the heat, and an ethylene glycol loop to provide condensation of the working fluid in the power cycle. As a preparation to the assembling and instrumentation of the prototype rig, a simulation and an uncertainty analysis were conducted for the prototype rig in the autumn of 2008. This report focuses on the continuation of that work by an experimental investigation of the individual loops and the components of the prototype rig. The emphasis of this investigation has been put on the air loop and the expander unit of the power cycle. This is basically because these are of great importance to the performance of the power production prototype rig. The air loop was thoroughly tested, and from the investigations it was discovered that there was an unfavorable temperature distribution of the air going into the air-to-CO2 heat exchanger. This is the heat exchanger where heat is provided to the power cycle. The source for this temperature maldistribution was identified, and solutions were investigated to improve on the problem without results. The reduced performance of the air loop was incorporated in a new simulation of the power cycle in order to quantify the consequences for the optimization of the power cycle. The simulation was carried out for warm air temperature of 80 °C. The new calculations showed a reduction in maximum net work output of 27 % compared to the original simulation. The optimal conditions for the power cycle were also changed as a consequence of the reduced air loop performance. The investigation of the expander unit revealed that the expander isentropic efficiency was a strong function of the pressure difference across the expander, and a weak function of the expander inlet pressure. It also revealed that overall the isentropic efficiency was much less than the value of 80 % which was used in the original simulation. A new simulation of the power cycle was carried out where the expander isentropic efficiency was incorporated as a function of the pressure difference across the expander. This function was based on the data from the expander testing. The simulation showed a reduction in maximum net work output from 225 W to about 60 W, for warm air temperature of 80 °C. The new expander characteristics also affected the optimization of the power cycle. The simulation results and the results from the prototype investigation will be important in the optimization and control procedures of the assembled prototype power production system.

1. Initial problem formulation 2. Iterative approach building for one reservoir 3. Testing for two cascaded reservoirs 4. Testing for four cascaded reservoirs 5. Further work

This report is the results of the work on a master thesis concerning intelligent monitoring of hydro power stations. In the report two different types of computer software is investigated to find out whether they are suitable to make out a monitoring system capable of giving the user information about faults and unwanted operating conditions at an early stage. It is also investigated whether the software has proven the capability to detect faults and unwanted operating conditions. The different advantages and disadvantages of the two software products are commented and the two software products are compared. This report shows that the two software products are quite different. The software from Volve is software meant to construct an expert system capable of recognising faults from previous cases of faults. The software from SKF is software that gives intelligent machine diagnostics from analysis of vibration measurements in addition to measuring and trending of other variables. It also gives the user tools for analysing the root cause of faults influencing the bearing system of different industry machinery. This means that the software from SKF demands some involvement from the user to produce the best and most precise results. The expert system developed from the Volve software on the other hand is meant to present only results and advice to the user. The results from tests and simulations of the expert system developed by the Volve software are very limited. It is not possible to conclude which of the two software products is better before more tests of the Volve system is performed. In addition to the investigation of these two monitoring software products two different types of sensors are investigated. The sensors that are investigated are smoke sensors and sensors for detection of ultrasonic sound. Both types are commonly used in monitoring of industry processes similar to those in hydro power stations. These two sensors are capable of giving additional information to the monitoring system making it possible to detect faults that it is difficult to detect today. This is because the two sensor types perform measurements that the normal measuring equipment of today is incapable of. This will increase the information flow to the monitoring systems of hydro power stations making it possible to perform better and more precise monitoring.

Lowering the cost of wave energy conversion is an essential task for it to succeed as a future energy resource. In this work a converter, assumed cheaper than the regular back to back converter setting, have been investigated for a electric direct drive point absorber. Both experimental work and simulations are used in the analysis. In the experimental work, a permanent magnet generator with a 6-pulse diode rectifier, a DC-link and a DC/DC converter equivalent, was used. Steady state, dynamic and transient measurements were preformed and a simulation model was compared to the measurements. Good results were obtained and deviations were in general small, mostly +-3% for voltage and current measurements and +-8% for torque measurements. Based on transient measurements and simulations a general linearization of the system was made in order to obtain useful information about the system. A step up converter was used in the simulation and it demonstrated stable passive loading control. By using the information obtained by the linearization, the performance of the simulation model was improved by decreasing the DC-link capacitance. The modified simulation model had significant less torque ripple than the initial. The linearization model also can been used to identify time delay represented by the power take off unit in a wave energy converter. This will be done for a commercial size wave energy converter summer 2009.

In this master thesis the wake of a hydrofoil have been investigated using PIV. The main goal of this work have been to investigate how vortex generators can create mixing and smoothing of the velocity deficit in hydrofoil wakes. This study is motivated by the rotor stator interactions in Francis turbines with the idea that smoother wakes from the stator can reduce the forces on the rotor and hence increase the life span of Francis turbines. A literature survey of foil theory and wake flows have been carried out. This survey motivated the use of a normalization of the velocity in the wake. Experimental work was carried out at the water tunnel facility at Saint Anthony Falls Laboratory at the University of Minnesota. Tests were performed on a NACA0015 hydrofoil with four different vortex generator configurations, for a range of different angles of attack and velocities. Lift and drag forces on the hydrofoil was measured using a force balance. Because the drag measurement had poor accuracy, it could not be used to compare the different vortex generator configurations in terms of drag. As a result the drag was investigated using the velocity deficit in the wakes. The quality of this analysis have been discussed with the use of CFD. CFD is also used to gain insight into how pressure and velocity is distributed in the water tunnel. The PIV images from the tests have been processed into vector fields with the commercial PIV software DaVis7. For analyzing the PIV data further, different post-processing schemes in DaVis7 was investigated together with programs developed in Matlab. In order to compare the wakes resulting from the use of different vortex generators with measurable quantities, the use of a standard wake profile has been investigated. The standard wake profile is symmetrical and could hence only describe wake measurements done at an angle of attack close to $0^{circ}$. Furthermore it turned out that most vortex generators resulted in a wake that could not be described with the standard wake profile. The vortex generator configurations that gave the best smoothing of the hydrofoil wake for the investigated operation points turned out to be a $1unit{mm}$ V-shaped vortex generator. This vortex generator also caused less drag than than the other vortex generators tested. However, the use of vortex generators resulted in increased drag compared to the plain hydrofoil for the analyzed operating points. The velocity deficit in the wake is shown to get so well smoothed out for some tested cases that it is considered worth while to continue the investigation on vortex generators capability to increase the lifespan of Francis turbines.

Compression and purification processes are considered for CO2 coming from the three different capture methods. By using the simulation tool Pro/II these processes are further optimized.

This Master thesis analyzes the optimal use of the hydro resources in Albania. Albania is a country totally dependent on hydro power. More than 90% of the electricity today comes from hydro power, mainly from the Drin river system. There are three hydro power plants located in the Drin river system: Fierze (500 MW), Koman (600 MW) and Vau Dejes (250 MW). Only one third of Albania’s hydro power potential is today exploited, and Albania is a net importer of energy. The main objective with this study is to analyze the utilization of the hydro resources in Albania and look at potential improvements in the short term (next years) and the long term (after Albania joins the regional market). Two scenarios were worked out. The first scenario focuses on the present market situation in Albania. Investigations are done through simulations with the EOPS model. The results were analyzed and compared with historical data to discover potential upgrades of the utilization of water in Fierze, Koman and Vau Dejes. In the simulations the production in Drin river system is increased with 1.3 TWh in an average year. Fierze power plant has the highest potential with 25% more production in the simulation than what is shown through historical data. Under the process towards a liberalized market, the optimizing problem regarding the production planning will change. Today the main task is cost minimization given an expected demand. In a free market it will be profit maximizing given a price expectation. A second scenario dealing with the potential market situation in Albania in 2020 was worked out. In addition to the new market situation four new power plants were included in the EOPS model. With new plants in the Drin and a functioning market it is possible to achieve 1 TWh more production during an average year compared with the simulation for the present market situation in Albania. If the implementation of the market, new power plants and transmission lines are accomplished, the supply situation in Albania will improve substantially through more secure power delivery. However a participation in a regional market forces the production company to plan each day like the participants in the Nordic market, both in the long and short the term, to be able to exploit the technical and financial opportunities and develop their country.

Wet gas compression technology is of great value to the oil and gas industry for boosting of unprocessed well stream and to reduce investment costs related to equipment and personnel. The growing interest in wet gas compression leads to a general request for accurate performance calculation procedures and proper measurement techniques for multiphase flow metering in compressors. An impeller rig for examination of single-phase and multiphase performance and aerodynamic stability is under construction at the test facility at NTNU. The construction of the compressor rig is behind time due to late deliveries of the compressor components and instrumentation. The performance calculations are therefore based upon one compressor test conducted with dry gas at part-load. The thermodynamic equation of state for ambient air is verified to be consistent with the ideal gas law in the compressor pressure and temperature range. The calculated polytropic performance is calculated with ideal gas assumptions and compared to values estimated by PRO/II. By analyzing the results the sensitivity of the calculation procedures is identified and the suitability for the ideal polytropic performance calculations is validated for the actual compressor test and operating range. A sensitivity analysis is conducted in order to determine the effect of measurement uncertainties on performance calculations. Due to the low pressures involved for the compressor test, the performance calculation procedures are highly sensitive to uncertainties in the pressure measurements. Uncertainties in the temperature measurements will only slightly influence the polytropic head, but have great influence on the polytropic efficiency. The efficiency and operating range of a compressor are constrained by aerodynamic instabilities. This thesis describes the different flow phenomena associated with compressor instability and presents recommendations for suitable instrumentation and measuring techniques. Various visualization techniques are in addition evaluated to determine the suitability for multiphase compressors. Dynamic pressure transducers installed in the inlet and discharge piping are recommended for detection of pressure pulsation throughout the compressor system. Unsteady internal pressure measurements can be obtained from circumferentially distributed pressure transducers at various locations within the compressor components. Vibration probes installed at each end of the rotor are recommended for the vibration measurements. By analyzing the frequency spectrum for the pressure fluctuation and radial vibrations one can identify the type of instability phenomenon that occur. Laser measurement techniques are recommended for the flow visualization in order to obtain information on the main features of the multiphase flow field.

Gas turbines in offshore power systems contribute to about 23% of Norway’s total emissions of CO2. One method for reducing these emissions could be the addition of wind turbines to the offshore utility grids. Power from shore is another alternative, but has been proven costly due to long cables and expensive HVDC converter stations. In this thesis work, the behaviours of different wind turbine technologies during transient fluctuations in an offshore utility grid have been studied. For this purpose, a dynamic model for an offshore oil platform was developed. Models of squirrel cage and doubly fed induction generator based turbines were developed as well. None of the modelled generators experienced problems with the disturbances caused by the electromechanical transient fluctuations. Based on the behaviour of the DFIG’s grid side converter, it is believed that the result would be the same for a wind turbine with full frequency conversion. Variable speed wind turbines are expected to remain controllable throughout electromechanical transient fluctuations such as for the simulated case. However, the controllers, converters and equipment have to be designed while bearing these fluctuations in mind. The controllability of the variable speed wind turbines could be used to contribute to voltage control by production and consumption of reactive power. A controller scheme with the purpose of stabilising the voltage at the gas turbine generators’ terminal was developed, but had low impacts on the power system behaviour. A stator flux feed forward term for the speed controller was developed. The term stabilised the power output of the doubly fed induction generator. However, the impact on the power system’s frequency response was minimal, and there is probably no material value of such an addition to the control loop.