Proximity-Aware Calculation of Cable Series Impedance for Systems of Solid and Hollow Conductors

Wide-band cable models for the prediction of electromagnetic transients in power systems require the accurate calculation of the cable series impedance as function of frequency. A surface current approach was recently proposed for systems of round solid conductors, with inclusion of skin and proximity effects. In this paper we extend the approach to include tubular conductors, allowing to model realistic cables with tubular sheaths, armors and pipes. We also include the effect of a lossy ground. A noteworthy feature of the proposed technique is the accurate prediction of proximity effects, which can be of major importance in three-phase, pipe type, and closely-packed single-core cables. The new approach is highly efficient compared to finite elements. In the case of a cross-bonded cable system featuring three phase conductors and three screens, the proposed technique computes the required 120 frequency samples in only six seconds of CPU time.Comment: Update: This paper has been accepted for publication in the IEEE Transactions on Power Delivery. DOI: 10.1109/TPWRD.2014.233099

Variable Transmission Voltage for Loss Minimization in Long Offshore Wind Farm AC Export Cables

Connection of offshore wind farms to shore requires the use of submarine cables. In the case of long HVAC connections, the capacitive charging currents limit the transfer capability and lead to high losses. This paper shows that the losses can be substantially reduced by continuously adjusting the cable operating voltage according to the instantaneous wind farm power production.Calculations for a 320 MW windfarm connected to shore via a 200 km cable at 220 kV nominal voltage shows that an annual loss reduction of 9 percent is achievable by simply using a 15 percent tap changer voltage regulation on the two transformers. Allowing a larger voltage regulation range leads to further loss reduction (13 percent for 0.4-1.0 p.u. voltage range). If the windfarm has a low utilization factor, the loss reduction potential is demonstrated to be as high as 21 percent . The methodology can be applied without introducing new technology that needs to be developed or qualified.Comment: To be submitted to IEEE Transactions on Power Deliver

Industrial Relations in Norway

The Norwegian industrial relations system is marked by close co-operation between the state, the employers and the unions and by the high degree of institutionalization of labour relations in general and conflict resolution in particulilr. This co-operation arises partly from industrialisation at a time when democratic attitudes and processes were already established and from the need for national unity in the post-war reconstruction. This co-operation and institutionalization is illustrated by the highly centralised trade union movement and in the formal aspects of the bargaining and conflict resolution system such as the Labour Court and the committees and other bodies associated with the incomes policy and tripartite bargaining system

Passive Macromodeling: Theory and Applications

Offers an overview of state of the art passive macromodeling techniques with an emphasis on black-box approaches This book offers coverage of developments in linear macromodeling, with a focus on effective, proven methods. After starting with a definition of the fundamental properties that must characterize models of physical systems, the authors discuss several prominent passive macromodeling algorithms for lumped and distributed systems and compare them under accuracy, efficiency, and robustness standpoints. The book includes chapters with standard background material (such as linear time-invariant circuits and systems, basic discretization of field equations, state-space systems), as well as appendices collecting basic facts from linear algebra, optimization templates, and signals and transforms. The text also covers more technical and advanced topics, intended for the specialist, which may be skipped at first reading. Provides coverage of black-box passive macromodeling, an approach developed by the authors. Elaborates on main concepts and results in a mathematically precise way using easy-to-understand language. Illustrates macromodeling concepts through dedicated examples. Includes a comprehensive set of end-of-chapter problems and exercises. Passive Macromodeling: Theory and Applications serves as a reference for senior or graduate level courses in electrical engineering programs, and to engineers in the fields of numerical modeling, simulation, design, and optimization of electrical/electronic systems

Fast Computation of the Series Impedance of Power Cables with Inclusion of Skin and Proximity Effects

We present an efficient numerical technique for calculating the series impedance matrix of systems with round conductors. The method is based on a surface admittance operator in combination with the method of moments and it accurately predicts both skin and proximity effects. Application to a three-phase armored cable with wire screens demonstrates a speed-up by a factor of about 100 compared to a finite elements computation. The inclusion of proximity effect in combination with the high efficiency makes the new method very attractive for cable modeling within EMTP-type simulation tools. Currently, these tools can only take skin effect into account.Comment: Submitted for publication to IEEE Transactions on Power Delivery. Update: Published in IEEE Transactions on Power Delivery with the revised title of "An Equivalent Surface Current Approach for the Computation of the Series Impedance of Power Cables with Inclusion of Skin and Proximity Effects

Industrial Relations in Norway

The Norwegian industrial relations system is marked by close co-operation between the state, the employers and the unions and by the high degree of institutionalization of labour relations in general and conflict resolution in particulilr. This co-operation arises partly from industrialisation at a time when democratic attitudes and processes were already established and from the need for national unity in the post-war reconstruction. This co-operation and institutionalization is illustrated by the highly centralised trade union movement and in the formal aspects of the bargaining and conflict resolution system such as the Labour Court and the committees and other bodies associated with the incomes policy and tripartite bargaining system

Developing Low-Conductance Window Frames: Capabilities and Limitations of Current Window Heat Transfer Design Tools

While window frames typically represent 20-30% of the overall window area, their impact on the total window heat transfer rates may be much larger. This effect is even greater in low-conductance (highly insulating) windows that incorporate very low-conductance glazing. Developing low-conductance window frames requires accurate simulation tools for product research and development. Based on a literature review and an evaluation of current methods of modeling heat transfer through window frames, we conclude that current procedures specified in ISO standards are not sufficiently adequate for accurately evaluating heat transfer through the low-conductance frames. We conclude that the near-term priorities for improving the modeling of heat transfer through low-conductance frames are: (1) Add 2D view-factor radiation to standard modeling and examine the current practice of averaging surface emissivity based on area weighting and the process of making an equivalent rectangular frame cavity. (2) Asses 3D radiation effects in frame cavities and develop recommendation for inclusion into the design fenestration tools. (3) Assess existing correlations for convection in vertical cavities using CFD. (4) Study 2D and 3D natural convection heat transfer in frame cavities for cavities that are proven to be deficient from item 3 above. Recommend improved correlations or full CFD modeling into ISO standards and design fenestration tools, if appropriate. (5) Study 3D hardware short-circuits and propose methods to ensure that these effects are incorporated into ratings. (6) Study the heat transfer effects of ventilated frame cavities and propose updated correlations

Experimental and Numerical Examination of the Thermal Transmittance of High Performance Window Frames

While window frames typically represent 20-30percent of the overall window area, their impact on the total window heat transfer rates may be much larger. This effect is even greater in low-conductance (highly insulating) windows which incorporate very low conductance glazings. Developing low-conductance window frames requires accurate simulation tools for product research and development. The Passivhaus Institute in Germany states that windows (glazing and frames, combined) should have U-values not exceeding 0.80 W/(m??K). This has created a niche market for highly insulating frames, with frame U-values typically around 0.7-1.0 W/(m2 cdot K). The U-values reported are often based on numerical simulations according to international simulation standards. It is prudent to check the accuracy of these calculation standards, especially for high performance products before more manufacturers begin to use them to improve other product offerings. In this paper the thermal transmittance of five highly insulating window frames (three wooden frames, one aluminum frame and one PVC frame), found from numerical simulations and experiments, are compared. Hot box calorimeter results are compared with numerical simulations according to ISO 10077-2 and ISO 15099. In addition CFD simulations have been carried out, in order to use the most accurate tool available to investigate the convection and radiation effects inside the frame cavities. Our results show that available tools commonly used to evaluate window performance, based on ISO standards, give good overall agreement, but specific areas need improvement

Eliminating Measurement Cable Effects From Transformer Admittance Measurements

-Admittance frequency-sweep measurements is an accepted procedure for characterizing transformer terminal behavior for the purpose of frequency-dependent black-box modeling. The errors introduced by the measurement cables is with one existing practice mitigated by removal of the associated shunt capacitance effect. In this paper, it is shown that the accuracy can be greatly improved by using transmission-line representation of the measurement cables with parameters obtained from standard cable data or from S-parameter measurements. The procedure is demonstrated for the modeling of a 45 MVA generator step-up transformer requiring cable lengths of six meters and an upper frequency limit of 10 MHz