Magnetic behavior of a laminated magnetic core in the presence of interlaminar faults: A simulation method based on fractional operators

Stacks of grain-oriented silicon steel (GO FeSi) laminations play a crucial role as magnetic cores of power transformers. These cores undergo degradation over time due to corrosion, thermal cycles, etc. Geometrical abnormalities and residual stress from manufacturing processes exacerbate these degradation processes. Edge burrs can form around cut edges and lead to InterLaminar Faults (ILFs). In a recent work, we described an innovative method for simulating dynamical GO FeSi lamination hysteresis cycles. This method can be applied without any change to a stack of electrically isolated laminations, like in a magnetic core. It is especially easy when the working conditions impose a homogeneous behavior (B-imposed conditions). The simulation technique combines the resolution of the magnetic diffusion equation and a fractional differential equation as material law, yielding excellent simulation results across a broad frequency range with only two parameters accounting for the dynamic contribution. This new article outlines the successful extension of this simulation method to consider ILFs and predict their impact on the performances. For this, lamination stacks were initially simulated under full short-circuit conditions. Then, we used linear combinations between responses from these stacks and flawless ones. The simulation successfully reproduced the experimental data obtained for one or three aligned ILFs on several conditions. Then it was used to predict the behavior of additional aligned ILFs and/or different numbers of laminations in the simulated stack

Earthing requirements for HVDC systems

Following the recent developments in the field of power electronic valves, High Voltage Direct Current (HVDC) systems have become more attractive in power systems, and are widely recognised as a suitable tool for future power systems, especially in bulk power transmission over long distances. Grounding electrodes are an important part with significant roles in the operation of the HVDC systems. In this paper, first a brief review of different types of HVDC configuration is presented. Essential requirements in the design and operation of the HVDC grounding system are then presented and discussed. In the relevant studies, environmental impacts of HVDC electrodes, e.g. step voltage, effect on the buried metallic structures, DC magnetic bias of power transformers and mitigation methods are highlighted. Finally, a basic modelling of different physical configurations of HVDC electrode resistance is performed

A Novel Dynamic Hysteresis Model for Grain-Oriented Electrical Steels Based on Magnetic Domain Theory

A novel approach is adopted to model the hysteresis phenomenon of grain-oriented electrical steels (GOESs), by incorporating a variation of the domain patterns associated with ferromagnetic materials during magnetization and demagnetization. The ensuing model treats the anisotropic and isotropic components separately, together with the coupling effect of the excitation field. Its ability to replicate experimentally obtained dynamic hysteresis loops (DHLs) for Epstein size laminations of GO 3% SiFe electrical steels, for different magnetizing frequencies and peak flux densities, and facilitate the straightforward evaluation of the energy loss in GOESs is demonstrated for the case of controlled sinusoidal magnetic induction. Close agreement is found to exist between the predicted energy loss and corresponding bulk measurements, with the maximum difference being less than 2%

Application of an analysis technique to characterise impulse response of grounding systems

Transient response plays a key role in the evaluation of the performance of grounding systems and for the protection of electrical installations under lightning strikes. The frequency spectrum of the lightning impulse contains harmonics components up to the megahertz range. The measured transient response of grounding systems under test may be distorted by spurious high frequency interference in the acquired signals, which presents challenges for the accurate analysis of high frequency performance of such systems. In this paper, the high frequency performance of a rod electrode is investigated based on measurements of its transient response under impulse energisation. A practical method is implemented to eliminate the high frequency noise in the measured voltage and current shapes, which allows a frequency domain analysis based Fast Fourier Transforms

Characterization of horizontal earth electrodes: Variable frequency and impulse responses

Grounding systems such as vertical and horizontal electrodes, and grids are installed in the soil to mitigate against the effects of system faults and lightning surges. Their main function is to dissipate lightning and fault currents into the earth without generating any hazardous potential differences between different contacts points of grounded structures and the earth that may be bridged by people or sensitive electrical equipment. In this investigation, field tests applying both low voltage impulse and variable frequency energisations to a horizontal earth electrode installed in a low resistivity soil medium have been carried out. The frequency response is determined from the AC variable frequency test over frequency (50Hz up to 1MHz). Numerical models of the tested electrodes were simulated considering the effect of soil parameters and the results were compared with field tests measurements

Characterization of horizontal earth electrodes: variable frequency and impulse responses

Grounding systems such as vertical and horizontal electrodes, and grids are installed in the soil to mitigate against the effects of system faults and lightning surges. Their main function is to dissipate lightning and fault currents into the earth without generating any hazardous potential differences between different contacts points of grounded structures and the earth that may be bridged by people or sensitive electrical equipment. In this investigation, field tests applying both low voltage impulse and variable frequency energisations to a horizontal earth electrode installed in a low resistivity soil medium have been carried out. The frequency response is determined from the AC variable frequency test over frequency (50Hz up to 1MHz). Numerical models of the tested electrodes were simulated considering the effect of soil parameters and the results were compared with field tests measurements