Practical Aspects of the Skin Effect in Low Frequencies in Rectangular Conductors

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A physical model for low-frequency electromagnetic induction in the near field based on direct interaction between transmitter and receiver electrons

A physical model of electromagnetic induction is developed which relates directly the forces between electrons in the transmitter and receiver windings of concentric coaxial finite coils in the near-field region. By applying the principle of superposition, the contributions from accelerating electrons in successive current loops are summed, allowing the peak-induced voltage in the receiver to be accurately predicted. Results show good agreement between theory and experiment for various receivers of different radii up to five times that of the transmitter. The limitations of the linear theory of electromagnetic induction are discussed in terms of the non-uniform current distribution caused by the skin effect. In particular, the explanation in terms of electromagnetic energy and Poynting’s theorem is contrasted with a more direct explanation based on variable filament induction across the conductor cross section. As the direct physical model developed herein deals only with forces between discrete current elements, it can be readily adapted to suit different coil geometries and is widely applicable in various fields of research such as near-field communications, antenna design, wireless power transfer, sensor applications and beyond

Frequency-Dependent Pi Model of a Three-Core Submarine Cable for Time and Frequency Domain Analysis

In this paper, a Frequency-Dependent Pi Model (FDPi) of a three-core submarine cable is presented. The model is intended to be used for the representation of submarine cables in an Offshore Wind Power Plant (OWPP) scenario for both time and frequency domain analysis. The frequency-dependent variation of each conductive layer is modeled by a Foster equivalent network whose parameters are tuned by means of Vector Fitting (VF) algorithm. The complete formulation for the parameterization of the model is presented in detail, which allows an easy reproduction of the presented model. The validation of the model is performed via a comparison with a well-established reference model, the Universal Line Model (ULM) from PSCAD/EMTDC software. Two cable system case studies are presented. The first case study shows the response of the FDPi Model for a three-core submarine cable. On the other hand, the second case study depicts the response of three single-core underground cables laying in trefoil formation. This last case shows the applicability of the FDPi Model to other types of cable systems and indirectly validates the response of the aforementioned model with experimental results. Additionally, potential applications of the FDPi model are presented

A new approach to the fault location problem: using the fault's transient intermediate frequency response

The fault location problem has been tackled mainly through impedance-based techniques, the travelling wave principle and more recently by machine learning algorithms. These techniques require both current and voltage measurements. In the case of impedance-based methods they can provide multiples solutions. In the case of the travelling wave approach it usually requires high sampling and synchronized frequency measurements together with sophisticated identification algorithms. Machine learning techniques require training data and re-tuning for different grid topologies. In this work we propose a new fault location method based on the fault's transient intermediate frequency response of the system immediately after a fault occurs. The transient response immediately after the occurrence of a fault is characterized by the travelling wave phenomenon together with intermediate frequencies of oscillation in the range of 5 to 500 kHz. These intermediate frequencies of oscillations are associated with the natural response of the cable/line system to the fault event. Their frequencies of oscillation are dependent on the faulted section and the fault location within that section. The proposed fault location methodology aims to leverage on that dependency, by firstly identifying these intermediate frequencies for different fault location scenarios for a given network. This process is performed offline using a linear time invariant (LTI) representation of the network. To compute this LTI representation, as part of this work an impedance representation in the modal domain is established for cable/line sections, which is able to capture the frequency-dependence and distributed nature of its electrical parameters. The offline methodology identifies these intermediate frequencies for different fault location scenarios, and then proceeds to fit the fault location dependence of each intermediate frequency using a polynomial regression. An online methodology is also proposed to perform the fault location in real time by solving the polynomial regressions computed during the offline methodology using measurements of the intermediate frequencies present in the frequency spectrum of transient signals. The fault location is thus solved by using voltage or current measurements of the fault’s transient response at different locations in the network, together with simple signal processing techniques such as the Fast Fourier Transform. The full method is tested with an EMT simulation in PSCAD, using the detailed frequency dependent model for underground cables, together with realistic load models in a low voltage distribution network test system.Open Acces

Harmonics and unbalanced load compensation by a modular multilevel cascaded converter active power conditioner

This paper presents a novel control scheme for a modular multilevel cascaded converter (MMCC) functioning as an active power conditioner (APC) to control the reactive power, eliminate the current harmonics, and compensate unbalanced load current simultaneously. This combines a modified predictive current controller with the inter-cluster and intra-cluster voltage balance control for MMCC sub-module capacitors. Simulation studies of this MMCC-APC for a power network containing both an unbalanced thyristor controlled rectifier and a reactive load are performed and results verifying its performance under varying degrees of load current distortion measured by THD levels are presented

Equivalent circuit models for package level discontinuities and chip-package intersonnects

Equivalent circuit models with closed form expressions, in conjunction with a segmentation technique, have been derived to study three different aspects related to chip-package co-design issues. This technique has been successfully applied to package level discontinuities, chip-package interconnects, and the modeling of transients that affect the performance of an integrated microstrip antenna placed at the RF front end. In each case, circuit models have been developed to include coupling by the use of coupling capacitance and mutual inductance. All circuit elements are defined by closed form expressions. To analyze package level discontinuities various microstrip transmission lines placed in close proximity to each other have been considered. Typical via structures such as the single via connecting signal lines placed on either side of a ground plane, and two-via structures between transmission lines placed on different layers have also been modeled. In each case the S-matrix from the equivalent circuit model compared to that obtained using a full wave simulator shows excellent agreement, thereby establishing the validity of the model. To address chip-package co-design issues associated with RF front end a test bed consisting of a microstrip antenna with an embedded matching network has been implemented in a Multi-Layered Organic (MLO) material. The impact on the antenna\u27s input and radiation characteristics due to neighboring circuitry is found to be significant in both the frequency and time domains. Using the equivalent circuit model the coupling has been characterized and compared with that obtained from a full wave simulator

SIMULATION AND MITIGATION OF POWER QUALITY DISTURBANCES ON A DISTRIBUTION SYSTEM USING DVR

Voltage sag is the most important power quality problem faced by many industrial customers. Equipment such as process controllers, programmable logic controllers, adjustable speed drives, robotics, etc used in modern industrial plants are actually becoming more sensitive to voltage sags. Voltage sags are normally described by the magnitude variation and duration, and also characterized by unbalance, non-sinusoidal wave shape and phase angle shift. One of the most common mitigation solution is installing uninterrupted power supply (UPS). To meet the demand for more efficient mitigation solution, the Dynamic Voltage Restorer (DVR) will be deployed. When a fault occurs, either at the high voltage source end or at the consumer end, the DVR injects active and reactive power for the restoration of the voltage sags in the network. This thesis presents the power quality problems faced by the power distribution systems in general and then concentrates on analyzing an important and specific distribution system in particular. A dynamic voltage restorer (DVR) is connected on the 11KV of an utility feeder to Ipoh hospital, in reducing the voltage sags, that affect the operation of sensitive loads to the hospital. Case studies were conducted at four industrial sites (Hitachi plant and Nihoncanpack at Bemban, Filrex at Bercham and Ipoh Hospital) by monitoring and taking physical sag measurements for a period of one month. The real time measurements were carried out to identify the types power quality disturbances that exits in the various plants before providing the custom power device as a mitigation tool. The Ipoh Hospital is taken for a special case study since the hospital has to maintain high quality power supply to the medical equipments such as CT Scan, Magnetic Resonance Imaging (MRI), Magnetic Scanner, X-ray unit, and other life savingequipment. For simulation study, PSS/ADEPT and PSCAD/EMTDC software packages were used in modeling of the power distribution system. With the PSS/ADEPT simulation tool, the voltage severity is studied by introducing different types of faults. The PSCAD/EMTDC is a graphical user interface simulation tool to simulate sag waveforms for various types of faults. A DVR was modeled using the PSCAD/EMTDC software and simulated for voltage sag mitigation. The recorded waveform shows the DVR as a potential custom power solution provider. The DVR can improve the overall voltage regulation. The results obtained from the DVR show that the voltage sags are reduced by bringing the supply voltage level to 100%. The simulated results were verified for selected faults theoretically. v

Verification of a computer simulator for digital transmission over twisted pairs.

A dissertation submitted to the Faculty of Engineering, University of the Witwatersrand, Johannesburg, in fulfilment of the requirements for the degree of Master of Science in EngineeringThis dissertation verifies a Computer Simulation Package for modeling pulse transmission over digital subscriber loops. Multigauge sections on subscriber cables can be studied. The model used for each section incorporates skin, proximity and eddy current effects. The model allows important quantities such as near end echo and overall transmission distortion of pulses to be.predicted. An experimental facility has been established in the laboratory for the purpose of validating the results produced by the simulator with results obtained over real cables. The experimental facility has as far as possible been automated by making use of computer controlled equipment for direct setup or the experiment, data transfer, and analysis. The results obtained from the pulse propagation program and that obtained from measurements are in close. agreement, rendering the Computer Simulation Package useful for analysing the performance of multi gauge digital subscriber loops.AC 201

Stabilised Control of Converter Interfaced DERs for Reliable Operation of Microgrid and Microgrid Clusters

This thesis aims to achieve a stabilised control of converter interfaced DER for the reliable and resilient operation of microgrid and microgrid clusters. The suitability of voltage and current control for VSCs is evaluated and corrective measures are proposed to stabilise converter operation. Furthermore, the accurate power demand distribution in islanded MGs and interconnected MGs are ensured by advanced control strategies. The proposal presented in the thesis is verified both through simulation and experimental work