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- Alvarez, Manuel, 1980-
(författare)
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Distribution Network Planning Considering Capacity Mechanisms and Flexibility
- 2019
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The increasing penetration of distributed energy resources (DERs) has posed challenges to the distribution system operator (DSO) from the operation and regulatory point of view. High penetration of DERs could have negative impacts on the performance of the distribution grid, and depending on the regulatory framework, the DSO's remuneration as well. In liberalized electrical systems, the focus on promoting eciency has led to the implementation of an incentive-based regulation that exerts additional pressure on the DSOs to reduce costs. Additionally, the European Parliament Directive 2009/72/EC establishes a regulatory unbundling among the distribution, production, and retailing activities within the same vertically integrated electric utility.A way of helping the DSO to cope with the posed challenges is by providing it with exibility. This exibility can be acquired from the planning stage, and later be used during the system operation. This exibility can stem from the DSO's ability to exert control on the demand and the supply side to balance the system and correct its operational state.Based on the European DSOs' current situation at facing the increasing penetration of DERs, this thesis investigates in non-wired exible grid tools to solve the distribution network expansion problem. The investigation focuses on exibility providers, in particular on energy storage systems and hydropower, and also on capacity mechanisms to translate the capacity from DERs into the grid's capacity for planning purposes.Given that the share of renewable sources among the DERs is increasing, and considering the importance of energy storage systems in providing exibility to balance renewable energy production, the eort has been turned on to developing a hydropower model and a generic storage model that t both planning and operational studies.Given the need for gearing the DERs' behavior into the DSO's decision making process during the planning and operational timescales, the design and implementation of a distribution capacity mechanism have been developed. The design of the capacity mechanism has been conceived considering its integration within the distribution network expansion problem.The outcomes of this thesis can be synthesized as follows: 1) A generic hydraulic/storage model provided with an equivalent marginal cost that aids in considering the impact of present decisions in the future costs. 2) A market oriented distribution capacity mechanism that gears DERs and the DSOs to benefit mutually. 3) A distribution network expansion planning formulation that integrates the capacity resource from DERs through the distribution capacity mechanism.
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| 2. |
- Nasri, Amin, 1984-
(författare)
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On the Dynamics and Statics of Power System Operation : Optimal Utilization of FACTS Devicesand Management of Wind Power Uncertainty
- 2014
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Nowadays, power systems are dealing with some new challenges raisedby the major changes that have been taken place since 80’s, e.g., deregu-lation in electricity markets, significant increase of electricity demands andmore recently large-scale integration of renewable energy resources such aswind power. Therefore, system operators must make some adjustments toaccommodate these changes into the future of power systems.One of the main challenges is maintaining the system stability since theextra stress caused by the above changes reduces the stability margin, andmay lead to rise of many undesirable phenomena. The other important chal-lenge is to cope with uncertainty and variability of renewable energy sourceswhich make power systems to become more stochastic in nature, and lesscontrollable.Flexible AC Transmission Systems (FACTS) have emerged as a solutionto help power systems with these new challenges. This thesis aims to ap-propriately utilize such devices in order to increase the transmission capacityand flexibility, improve the dynamic behavior of power systems and integratemore renewable energy into the system. To this end, the most appropriatelocations and settings of these controllable devices need to be determined.This thesis mainly looks at (i) rotor angle stability, i.e., small signal andtransient stability (ii) system operation under wind uncertainty. In the firstpart of this thesis, trajectory sensitivity analysis is used to determine themost suitable placement of FACTS devices for improving rotor angle sta-bility, while in the second part, optimal settings of such devices are foundto maximize the level of wind power integration. As a general conclusion,it was demonstrated that FACTS devices, installed in proper locations andtuned appropriately, are effective means to enhance the system stability andto handle wind uncertainty.The last objective of this thesis work is to propose an efficient solutionapproach based on Benders’ decomposition to solve a network-constrained acunit commitment problem in a wind-integrated power system. The numericalresults show validity, accuracy and efficiency of the proposed approach.
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| 3. |
- Shirzadegan, Shahin
(författare)
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Development of a Methodology for Dynamic Testing of Rock Support : Field Tests and Numerical Analysis
- 2020
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The increasing mining depth in the Luossavaara-Kiirunavaara Aktiebolag (LKAB) mine located in the northern part of Sweden leads to higher stress magnitudes, resulting in increased seismic activity and more seismically-induced damage. The effectiveness of various ground support systems under dynamic loading conditions has therefore become of prime interest to LKAB for successful and safe mining at deep levels. The problems of mining-induced seismicity have necessitated the use of ground support systems which are capable of withstanding strong dynamic loads. Within this respect, a series of seven large-scale dynamic tests of rock support were conducted at LKAB Kiirunavaara mine. Explosives were detonated in boreholes in the pillar between two cross-cuts in order to generate dynamic loads on the rock support system installed on the cross-cut wall. This was done to evaluate the response of rock support subjected to strong dynamic loading. The tests included ground motion measurements, fracture investigation, ground and support motion imaging, as well as the deformation measurements. The design and the results of field Tests 1 to 7 and their associated numerical analysis are presented in this thesis. Field Tests 3 and 7 are excluded from detailed analysis in this study since the burden condition in these tests were different from the rest of the tests. The performance and energy absorption by the support system comprising Swellex Mn 24, 100 mm fibre reinforced shotcrete (40 kg/m3 steel fibre) and 75 mm * 75 mm weld mesh with 5.5 mm diameter is estimated and compared to the large-scale and laboratory test results conducted in different countries. The field tests results indicated that the relation between the burden and the used amount of explosive material and number of blastholes has a vital role in either reducing or involving the effect of detonation gases in test results. Results from field Tests 1, 2, 4 and 5 (considered in this study) showed that in Tests 1 and 2 minimum damage was created on the surface of the wall despite high PPVs were measured on the test wall. In Tests 4 and 5 complete damage of the burden was occurred despite the burden was in the range of Tests 1 and 2. Results from Tests 1 – 5 were used to design an improved burden in Test 6. The evidence of the damage to the test wall in Test 6 showed that the design in Test 6 was successful in terms of minimising the effect of gas in the burden and generating a sub-planar stress wave. The large amount of data recorded during these tests was used to develop the numerical models, and to study the field tests in more detail. The aim was to study the behaviour and response of the burden, free surface of the opening, and the installed rock support to the dynamic loading generated by a nearby blast numerically. A combination of two numerical methods, including the Finite Element code LS-DYNA and the Discrete Element code UDEC was used in the numerical analyses. The LS-DYNA model was used to calculate the dynamic input for the UDEC analysis. This was done by identifying the crushed zone boundary (CZB) developed around the blasthole. The velocity at the CZB (at the moment when it was fully developed) was applied as an internal boundary condition in the UDEC model. The geological conditions of the test site and the installed rock support were modelled in UDEC. The peak particle velocities, the velocity – time graphs, the maximum displacement generated on the surface of the wall, and the ejected thickness of the rock from the wall computed in the UDEC models were studied, and compared to the data obtained from field tests. This was done to identify the models that well represent the field tests behaviour. The identified models were used to study the failure mechanism in the burden and the rock support response to dynamic loading. Results indicated that, the numerical models were able to mimic the behaviour of the jointed rock mass and the rock support fairly well. The difference in behaviour between the numerical models and the field Tests 1 – 5, appeared to be caused by the gas expansion in the field tests, especially Tests 4 and 5. The numerical analysis results confirmed that the design of the burden in Test 6 limited the development of tensile yielded zones and as a result, complete failure of the burden was avoided. Furthermore, the ejection experienced from the wall was similar to that in actual seismic event. Numerical analysis results indicated that the geological structure of the burden and in particular the formed wedges near the opening have a significant role on the damage developed on the surface of the test wall. The presented testing method has the potential to be used in all similar large-scale testing of the rock support. Performing numerical analysis can significantly save time and energy while searching for an optimum design of the burden. By using a calibrated numerical model, it is possible to test the performance of different support systems using the same boundary conditions, in future studies.
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| 5. |
- Zhang, Pimin, 1990-
(författare)
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Performance of MCrAlX coatings : Oxidation, Hot corrosion and Interdiffusion
- 2019
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- MCrAlY coatings (M=Ni and/or Co) are widely used for the protection of superalloy components against oxidation and hot corrosion in the hot sections of gas turbines. The drive for coating systems to bestow adequate oxidation and corrosion resistance upon the components becomes urgent as an inevitable result of the necessary improvement in engine combustion efficiency and service lifetime. Through the careful design of the composition, MCrAlY coating performance can be optimized to meet the needs under different service conditions and component materials, therefore, “MCrAlX”, with “X” stands for the minor alloying elements, is used to highlight the effect. In the present thesis, the performance of new MCrAlX coatings is investigated with respect to oxidation, hot corrosion and interactions between coating-superalloy substrates.Oxidation of MCrAlX coatings can be generally categorized into initial, steady and close-to-end stages. Coating performance can be affected by various factors at different stages, therefore, experiments were designed by targeting the oxidation stages. Investigation on the initial stage oxidation behavior of MCrAlY coatings with post-deposition surface treatments reveals the different growth mechanisms of alumina scales. Surface treatments significantly reduce the alumina growth rate by suppressing transient alumina development and aiding the early formation of α-Al2O3, which improves the long-term oxidation performance of the coating. Similarly, the modification of minor alloy elements in MCrAlX coatings also serves the purpose. The oxidation behavior of new MCrAlX coatings was investigated at the steady oxidation stage, followed by the microstructure observation, thermodynamic and kinetic simulations. As an alternative reactive element addition of Y, Ce shows a negative effect on the formation of columnar alumina scales of high strain tolerance. In comparison, Fe or Ru addition shows no influence on alumina growth, rather than strengthening the phase stability in the coating and reducing the interdiffusion between coating-substrate through different mechanisms. As the oxidation proceeds to the close-to-end stage, a reliable criterion to estimate the capability of coating to form α-Al2O3 is of great importance to accurately evaluate coating lifetime. A temperature-dependent critical Al-activity criterion was proposed to better predict the formation of a continuous α-Al2O3 scale based on correction of elemental activity using thermodynamic database to replace the empirical Al-concentration based criterion.Severe interdiffusion occurs between coating-substrate during high temperature oxidation, accelerating the degradation of the system. Interdiffusion behavior of diffusion couples of superalloys-MCrAlX coatings were examined. It is highlighted that the recrystallization of superficial layer of the substrate contributes to the secondary reaction zone formation and element interdiffusion controls subsequent zone thickening.Study on Type I hot corrosion behavior of new MCrAlX coatings shows that the addition of Fe has no influence on basic fluxing reactions before severe Al depletion from the coating occurs. Instead, it boosts the “effective” Al supply of coating by shifting the equilibrium concentration of Al in the γ phase to a low Al level. Besides, the pre-mature coating degradation at the coating-substrate interface was due to the fast growth of corrosion products from substrate induced large local volume expansions, resulting in early coating spallation.
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