Purpose The prompt measurements of variation in phase, amplitude and frequency of a sinusoidal signal are crucial in a complex electrical network system. A Phasor measurement unit (PMU) uses a phasor estimation technique to estimate the phasor of the voltage and current signals, frequency and rate-of-change of frequency. The phasor estimation technique must adhere to the compliance requirements mentioned in the IEC/IEEE 60255-118-1 Standard. It is observed that fulfilling the IEEE compliance is a challenging task with a low sampling rate. This paper aims to develop a phasor estimation technique fulfilling the performance criteria at low sampling frequency. Design/methodology/approach To provide high accuracy during off-nominal frequency estimation, this work attempts to enrich the attenuation level at the side-lobe using a five-term cosine function, namely, an enriched side-lobe suppressor (ESS). It enhances the phasor estimation in the interpolation discrete Fourier transform (IpDFT) technique to achieve the performance requirements at a low sampling rate. Findings The performance of the proposed ESS-IpDFT technique is evaluated under the static and dynamic compliance specified in the IEC/IEEE 60255-118-1 Standard. The ESSIpDFT complies with the M-class performance requirements by maintaining the performance indices within the limits specified in the Standard. In addition, the performance of the ESSIpDFT approach is compared with the recently reported studies and found to offer better performance in most of the test indices. Originality/value A five-term cosine function-based ESS is designed to enrich the DFT interpolation for phasor estimation. The ESS-IpDFT based phasor estimation has been validated rigorously according to the IEC/IEEE 60255-118-1 Standard and compared with recently reported works.
Purpose This paper aims to investigate how to achieve a balance between high torque density and low vibration noise for the spoke-type permanent magnet (STPM) machine with a slotted rotor. Design/methodology/approach First, an analytical model (AM) of the radial electromagnetic force (REF) and electromagnetic torque for the STPM machine with a slotted rotor is proposed, and the influence of rotor slotting on the REF and electromagnetic torque is analyzed in combination with the finite element method. Then, the multi-physics model is established to analyze the electromagnetic torque and vibration noise with different rotor slotting structures to identify the optimal slotting configuration. Finally, the vibration noise is further optimized to achieve a balance between electromagnetic torque and vibration noise. Findings An appropriate rotor slotting structure can effectively enhance torque density and optimize electromagnetic noise. The optimized machine has higher torque density and lower vibration noise. Finally, two STPM prototypes with initial and optimized machines are manufactured and tested to verify the accuracy of the simulation results. Originality/value In this paper, the spatial order generation principle for REF density in the STPM machine with different rotor structures is revealed and analyzed. In addition, the electromagnetic torque and vibration noise of the STPM machine with different key parameters are analyzed and optimized to improve torque and reduce vibration noise.
PurposeThe application of high voltage direct current (DC) gas insulated lines in the power grid is expected to increase in the near future, due to its advantages considering safety, compactness and high voltage capacity. However, there are challenges in the design of the system which need to be addressed, such as space charge accumulation and high electric field stress. Therefore, precise simulation models of the gas insulated line need to be developed for examination purposes. One important aspect is the accurate representation of the conduction behavior of the insulating gas. Factors influencing the electrical conductivity, such as electric field strength, temperature, gas pressure and gas humidity, must be considered. In addition, an accurate determination of the temperature is essential for precise simulation results, since practical applications show different temperature distributions in the gas, depending on a horizontally or vertically arrangement of the gas insulated line. This study aims to develop a simulation model, which incorporates such phenomena. Design/methodology/approachA three dimensional model of a high voltage DC gas insulated line is developed, with the application of a nonlinear electrical conductivity model for the insulation gas, sulphur hexalfluoride. The conductivity model is derived from experimental measurements. The electric field distribution is investigated with a focus on the humidity content of the gas. For the determination of the temperature distribution, heat conduction is considered in the solid domain of the system and heat convection and heat radiation is considered in the gaseous domain, where the dynamic gas flow is explicitly modeled. FindingsThe simulation results reveal distinct electric field distributions for dry (2% humidity) or humid gas (30% humidity), where the difference of the maximum electric field value is up to 35%. The inclusion of heat convection and thermal radiation in the gaseous domain allows to consider the effect of a vertical or horizontal arrangement of the gas insulated line, where higher temperature values are seen on the upper parts in a horizontal construction, compared to a vertical arrangement. However, the consideration of such physical phenomena increases the complexity of the model and results in up to 12 times longer computation times. Originality/valueIn most scientific studies, the electrical conductivity of the sulphur hexalfluoride gas is assumed to be constant, and heat conduction is considered the dominant heat transfer mechanism throughout the system. In contrast, the present work describes the conduction behaviour of the gas by a nonlinear electrical conductivity model, e.g. enabling a comparative analysis of dry and humid gas conditions. In addition, heat convection and thermal radiation is considered as a heat transfer mechanism in the gaseous domain, to account for the influence of the geometrical configuration of the system on the temperature and electric field distributions.
PurposeThis paper aims to develop and experimentally validate a three-dimensional (3D) multiphysics model for predicting the transient magneto-thermal behavior of an axial-flux permanent-magnet (PM) braking system. Design/methodology/approachA coupled 3D finite element model is proposed, combining electromagnetic and transient thermal analyses to account for eddy-current losses, temperature rise and torque reduction. The model includes full geometry and armature reaction effects. A prototype is designed and experimentally tested to validate the approach. FindingsThe proposed coupled 3D magneto-thermal FEM model shows very good agreement with experimental results, accurately predicting both the transient magnetic field distribution and the temperature-dependent reduction in braking torque. The results confirm the capability of the model to reliably reproduce the real operating behavior of axial-flux PM braking systems. Practical implicationsThe proposed approach provides an efficient tool for the design and optimization of PM braking systems, reducing development time while improving performance prediction. Originality/valueThe contribution lies in a coupled 3D magneto-thermal framework experimentally validated on a dedicated prototype and integrating full 3D geometry, armature reaction and temperature-dependent effects within a unified multiphysics model.
Purpose Distortion of the magnetotelluric response is an obstacle that prevents the full use of numerous advantages of the method. Current approaches to removing distortion from measured data depend largely on favourable circumstances and the subjective assessment of their processor. The purpose of this study is to present a correction method that only requires a more precise approach to measurement and data storage. Design/methodology/approach The method is based on the physical interpretation of response distortion, according to which the disturbances that cause it are generically associated with the primary electromagnetic field. It assumes a simple source of disturbances. In the first step, the resistivity of the near-surface layer is determined using the response for the highest frequencies and equations valid only for the impedance of the first layer. This knowledge is also associated with determining the position of the distortion source. The obtained values are then used to identify and numerically remove the disturbance effect from the response for the entire measured spectrum. Findings Testing on synthetic data has shown that with a reasonable initial estimate, the method is able to remove not only the static shift in apparent resistivity caused by charge induction on the surface of the inhomogeneity, but also the spurious layers resulting from induction processes within it. Thus, it can almost accurately restore the intact response and provide reliable information about the subsurface structure. Originality/value Consistent elimination of the impact of disturbances from the response based on understanding the mechanism of their occurrence represents an original approach to the problem.
