This review describes induction coil sensors, which are also known as search coils, pickup coils or magnetic loop sensors. The design methods for coils with air and ferromagnetic cores are compared and summarized. The frequency properties of coil sensors are analysed and various methods for output signal processing are presented. Special kinds of induction sensors, such as Rogowski coil, gradiometer sensors, vibrating coil sensors, tangential field sensors and needle probes are described. The applications of coil sensors as magnetic antennae are also presented.

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Induction coil sensors—a review

Wind power is going through a very rapid development. It is among the fastest growing power sources in the world, the technology is being developed rapidly and wind power is supplying significant shares of the energy in large regions. The integration of wind power in the power system is now an issue in order to optimize the utilization of the resource and to continue the high rate of installation of wind generating capacity, which is necessary so as to achieve the goals of sustainability and security of supply. This paper presents the main technical challenges that are associated with the integration of wind power into power systems. These challenges include effects of wind power on the power system, the power system operating cost, power quality, power imbalances, power system dynamics, and impacts on transmission planning. The main conclusion is that wind power's impacts on system operating costs are small at low wind penetrations (about 5% or less). At higher wind penetrations, the impact will be higher, although current results suggest the impact remains moderate with penetrations approaching 20%. In addition, the paper presents the technology and expectations of wind forecasting as well as cases where wind power curtailment could arise. Future research directions for a better understanding of the factors influencing the increased integration of wind power into power systems are also provided.

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Technical challenges associated with the integration of wind power into power systems

With the fast-paced changing technologies in the power industry, new references addressing new technologies are coming to the market. Based on this fact, there is an urgent need to keep track of international experiences and activities taking place in the field of modern transformer design. The complexity of transformer design demands reliable and rigorous solution methods. A survey of current research reveals the continued interest in application of advanced techniques for transformer design optimization. This paper conducts a literature survey and reveals general backgrounds of research and developments in the field of transformer design and optimization for the past 35 years, based on more than 420 published articles, 50 transformer books, and 65 standards.

Transformer Design and Optimization: A Literature Survey

We report an investigation and theoretical assessment of the DC magnetic properties of high-permeability grain-oriented (GO) Fe-Si laminations under variously directed applied fields. We verified that normal magnetization curves, hysteresis loops, and energy losses depend on the field direction according to the sample geometry. This is explainable in terms of specific 180/spl deg/ and 90/spl deg/ domain wall processes and magnetization rotations. We present a novel phenomenological theory of the magnetization curves and hysteresis losses in GO laminations, excited along a generic direction; the theory is based on the single crystal approximation and pre-emptive knowledge of the magnetic behavior of the material along the rolling (RD) and the transverse (TD) directions. This approach is consistent with the general structure of Neel's phase theory, with the additional consideration of hysteresis and losses. Epstein and cross-stacked sheet testing methods are the two base measuring configurations; all the other testing geometries (single sheet, disk, square) are expected to display intermediate behavior. The devised model provides, through a direct procedure, thorough and accurate prediction of magnetization curves and quasi-static losses in these two basic cases. Its application to the other geometries is equally possible, with only a limited amount of supplementary information.

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Comprehensive model of magnetization curve, hysteresis loops, and losses in any direction in grain-oriented Fe-Si

Multiscale modeling of the magneto-mechanical behavior of grain-oriented silicon steels

Because the performance of power transformers is by various distinct parameters of the magnetic core, the prediction of relevant characteristics such as no-load losses P by analytical methods is impractical. This paper reports first attempts to predict the dependence of P on several parameters of core design by means of artificial neural networks (ANN's). Investigations of several ANN versions showed good results for simple backpropagation networks equipped with several output neurons for an adaptive version of Gaussian coarse coding. A main problem arises from the fact that an increase of input parameters is linked with a large increase in training batches established by time-consuming model core experiments. As a compromise, first ANN's were trained for the prediction of the losses P/sub J/ of "linearized" joint regions as a function of the most relevant parameters, including the number of overlap steps and the mean air-gap length of joints. This yields rough estimations of the joint's contribution to the building factor for small cores. For larger cores, an ANN cascade structure was tested. It includes a second ANN that considers indirect effect of joint designs on the global distribution of losses. The major problem with an ANN-based prediction system is establishing representative training data. Modified versions of the ANN method can be applied to various tasks, including the prediction of losses and noises of full-sized cores.

N. Baumgartinger

Papers

Neural networks for the prediction of magnetic transformer core characteristics

Relevance of multidirectional magnetostriction for the noise generation of transformer cores

A hand-held sensor for analyses of local distributions of magnetic fields and losses

On the practical relevance of rotational magnetisation for power losses of transformer cores

Stress effects on the multidirectional magnetic behaviour of grain-oriented silicon iron sheets