This study describes a technique for evaluating partial discharges at fast impulse voltages. Fast transient voltages are increasingly present in power equipment and industrial environments due to the ubiquitous application of power electronics switching devices. Special attention should be paid to the dangers caused by the accumulative effect of repetitive impulse voltages on electrical insulation. This study describes a method of analysing partial discharges occurring during impulse voltage stimuli. A repetitive train of pulses is applied to a dielectric specimen and the accumulated PD pattern is obtained. This study focuses on the reverse discharges which occur during the tail part of the impulse voltage waveform acquired in time-resolved mode. Investigations of the partial discharges in the wave tail can potentially lead to greater degradation of the insulation due to the formation of longer, repetitive sequence occurring along the decaying impulse voltage tail. Experiments were performed which investigated the influence of rise time, fall time and peak voltage on discharge pattern reshaping, intensity and time to inception on the tail. In the future, such an approach might be further developed for diagnostic applications and for extended factory tests.

This study presents an analysis and the design of a new flat-type position sensor with an external armature. One excitation coil and two antiserially connected pickup coils are used in the stationary part. Solid iron segments or steel lamination segments are used for the moving armature. The proposed position sensor was modelled using linear movement. A two-dimensional finite-difference method was developed and was used for fast analysis for optimising the sensor. The induced eddy currents in the solid armature were taken into account in the finite-difference analysis. The finite-difference calculations were compared with 2D and 3D finite-element method simulations and with experimental results. The sensor has a total error of 0.23 mm root-mean-square for 36 mm range without any compensation. Unlike previous designs, the authors’ new sensor has no moving coil.

To effectively improve the computation efficiency in the strapdown inertial navigation system (SINS) alignment process, the authors propose a marginalised adaptive sparse-grid quadrature filter (MASGQF). The filtering method combines the virtues of marginalisation technique and accuracy level switching structure to decrease the computational burden and improve the filtering precision simultaneously. With the adaptation criterion and the predefined tolerance value, different integration rules corresponding to the different accuracy levels nested in the proposed filtering method can be adjusted autonomously. It is proved that the MASGQF is exponentially bounded by theoretical analysis. The performance comparison of different filtering methods is demonstrated by the numerical results of the simulation and offline experiment. On the basis of the data performance of the online test, the validity of the proposed MASGQF is verified in the SINS alignment application.

During the recursive calculate process of the cubature Kalman filter (CKF), the covariance matrix tends to lose positive definiteness and noise statistical characteristics are inaccurate, which results in inaccurate filtering or even filter divergence. This study presents an improved algorithm based on the CKF. The algorithm combines the square root filter algorithm and the Sage–Husa maximum a posterior noise estimator, which can ensure the non-negative determination and symmetry of the covariance matrix and has the ability to deal with unknown and time-varying noise statistical characteristics in the filtering process adaptively. In the multi-dimension system, the noise covariance matrix may dissatisfy non-negative definiteness and result in filter divergence, and then the noise covariance matrix estimator is improved. The analysis is verified by state estimation example of the non-linear system, compared with the standard CKF, the accuracy of the adaptive square root CKF (ASRCKF) state estimation is increased by 63.13, 63.88, and 42.71%, respectively. Finally, the effectiveness of the ASRCKF is verified by the state estimation of the permanent magnet linear synchronous motor.

The inverse problem of electromagnetic (EM) non-destructive testing (NdT) consists of reconstructing material defect parameters invoking EM field measurements. Uncertainties of the configuration (e.g. imprecise constitutive and geometrical parameters) are inevitably present; hence, the reconstructed defect parameters are also uncertain. In this study, the different sources of uncertainty are ranked by means of sensitivity analysis. The model-based inversion (involving EM simulation) is computationally demanding; moreover, sensitivity analysis usually requires a vast number of repeated runs of the inversion. To overcome the computational complexity, surrogate models are applied at different levels. Interpolation on a sparse grid is used as a surrogate model of the EM simulation. The sensitivity of the reconstructed defect parameters concerning configuration uncertainties is characterised by means of Sobol indices. The Sobol indices are obtained from a polynomial chaos expansion surrogate model of the entire inversion scheme. A numerical example drawn from eddy-current NdT is thoroughly analysed to illustrate the proposed methodology and to demonstrate its performance.

With the rapid development of the vehicle navigation system (VNS), the functions of VNS are improved, while the design becomes very complicated. The conventional field-circuit simulation method is not precise enough to evaluate the VNS design. It is difficult to ensure that the electromagnetic compatibility index of VNS meets the GMW 3097 standard, resulting in electromagnetic interference (EMI) testing in an absorber lined shielded enclosure (ALSE). If the VNS does not comply with the GMW 3097 standard, it needs to be debugged repeatedly in the expensive ALSE. Therefore, a more accurate simulation method is highly desired, which can be used for improving the designed system to avoid using the expensive ALSE solution. In this study, an advanced field-circuit simulation method utilising actual parameters of the working printed circuit board is proposed to improve the simulation accuracy. The system is debugged by the proposed simulation method. Meanwhile, the optimisation method is proposed to enhance the EMI performance. Finally, by suppressing noise on the transmission path, the emission level of the VNS at 1.6 GHz is reduced from 5.9 dBμV to below−4 dBμV, which is ∼8 dBμV lower than the GMW 3097 standard.

This study presents a probabilistic approach, based on the finite element method (FEM), to model insulator flashover and calculate the failure risk of insulators under contaminated conditions. In the proposed method, the voltage distribution along the insulator surface is estimated by FEM and the random turn wheel is utilised to describe the stochastic propagation of arc along the insulator surface as well as in the air. This basis is used to obtain the probability of insulator flashover for different contaminations, separately. Then, from the simulation results, the probability density function of flashover in terms of pollution can be determined based on the Kolmogorov–Smirnov test. The proposed model is verified by comparing the associated results with those of the literature, in which the reliability and accuracy of the presented method are approved. Finally, having the cumulative distribution function of insulation strength and probability density function of pollution stress, the failure risk is calculated, in which the results can be used to predict the annual outage rate of transmission lines.

Service unavailability of transmission lines, particularly in mountain areas due to the direct and indirect lightning strikes, is considered as a challenging issue within electric companies. Therefore, the efforts to mitigate the power outages caused by this phenomenon have been introduced. In this study, an attempt has been made to study the different types of externally gapped line arresters (EGLAs) considering the Pinceti model and discharge voltage curve. Based on the best selected EGLA, the installation effect of EGLA on the possibility of instance back-flashover in different phases of the transmission line is investigated in the presence of downstream shield wire. For assessment, a double-circuit 400 kV transmission line in a mountainous area is modelled in EMTP-RV software. Then, an extensive analysis is carried out to verify the effectiveness of this method. The obtained results show the acceptable transmission line direct lightning protection can be achieved by four EGLAs in upper and middle phases with downstream shield wire. Although employing the downstream shield wires in the transmission line imposes more costs, but by using them, the scale and capability of EGLAs can be reduced.

Nomex insulation paper has been widely used in mining dry type transformer insulation because of its excellent performance. However, the injection of space charge can affect the electrical properties of the Nomex paper and accelerate the ageing process of the insulation system, which causes the insulation system failure or even breakdown. Therefore, it is of great practical value to study the space charge characteristics of Nomex insulation paper in different hygrothermal ageing conditions. The accelerated hygrothermal ageing tests of Nomex insulation specimens with different initial moisture contents were conducted. The space charge distribution of specimens impregnated by varnish were measured by the pulsed electro-acoustic method at different ageing stages. Simultaneously, the space charge characteristics during polarising and depolarising phases were deeply analysed. Experimental results show that negative charges accumulate between the varnish-paper interface in specimens near the anode. The number of negative charges gradually decreases with the increase of ageing degree. Under the influence of humidity, Nomex paper can be hydrolysed, which increases the trap density and trap level. Finally, a large amount of positive and negative charges in aged specimens would result in the distortion of the local electric field, which could decrease the breakdown strength of Nomex insulation specimens and be a threat to transformer insulation.

Studying the influence of electric field on the icing process of insulators with various dielectric surfaces is of great importance to the design of external insulation. This study established a finite element model to simulate the distribution of electric field around various insulator strings. Energised and non-energised icing tests were conducted to obtain the influence rules of electric field on the insulator icing process. The results of water droplets freeze experiment provided microscopic explanation of icing tests. Research results indicate that electric field and surface dielectrics have influence on the appearance, density and mass of ice on insulators. In microcosmic view, water droplets on super-hydrophobic surface correspond to longer freezing time and smaller average diameters, which leads to the better anti-icing character of super-hydrophobic insulator. Different types of ice branches appear in the water droplets freezing process on various dielectric surfaces. Owing to the polarisation effect, electric field can inhibit the formation and growth of ice branch, which contributes to different anti-icing characters of various dielectric surfaces in electric field. The effect of dielectric surface on insulator icing process mainly act at the initial period, surface coatings of insulators are not suggested to be applied in heavily icing area.

Here, a new fault detection and isolation (FDI) method based on linear optimisation is proposed for stochastic linear systems with unknown inputs. The stochastic system is discrete and its state and output equations are dependent on unknown inputs. Both stochastic/deterministic unknown inputs (external disturbances) and measurement noise are considered in the dynamic model; therefore, a simple and complete formulation of the robust FDI scheme is presented for stochastic systems. According to the proposed method, first an observable and controllable subsystem is found such that it is independent of the effect of unknown inputs. Then an innovation filter is used for the FDI task. Sufficient conditions to guarantee the stability and observability of the new subsystem are presented based on linear matrix inequalities. Simulation results demonstrate the effectiveness and capability of the proposed method for FDI in stochastic systems with unknown inputs.

Position signal faces several weak oscillations due to mechanical flaw and faults occurred in the systems. These oscillations can be identified by the encoders that determine the performance and health condition of the machine. Nevertheless, also the concerned oscillation, rotary encoder signal also includes some measurement noise and a significant trend. These trends are typically of several orders, greater in activities than the involved amplitude oscillations, making it tough to detect the small oscillations except deformation of the signal. In addition, the oscillations can be problematic, and magnitude adjusted in unstable conditions. Singular spectrum analysis (SSA) is proposed to overcome this issue. A numerical emulation is demonstrated to show the efficiency of the approach. It indicates that SSA outperforms ensemble empirical mode decomposition (EEMD), empirical mode decomposition, and complete EEMD with adaptive noise in ability and accuracy. Moreover, during the movement of the robotic arm, encoder signals from the robot are analysed to determine the sources of oscillations in joints. The suggested technique is proven to be reliable and feasible for an industrial robot.

This study presents the comparative analysis of earthing grid configurations to determine the optimum design in terms of safety parameters and cost for 66/11 kV substation. For different grid configurations, a fixed earthing area of 9000 m² was considered. Rectangular, triangular, L-shaped and T-shaped grids buried in two-layer soil model were considered for this study. Three methods, i.e. ANSI/IEEE standard 80-2000, finite element method and genetic algorithm, were used to design the grids. All safety constraints as mentioned in the IEEE standard were followed for designing the earthing grid. A new mathematical cost function (CF) was proposed for designing an effective and economic L-shaped, T-shaped and triangular earthing systems. The CFs used in this study include grid depth, dimensions of earthing rod and horizontal conductor, number of rods and conductors, revetment and excavation area. The economic earthing grid obtained through the proposed method reduces the total cost related to grid materials, installation and excavation. Analysis also showed that the rectangular grid showed preferred results in terms of safety parameters while the triangular grid showed optimum cost design for the earthing system under study. Good agreements were found with the rectangular earthing grid in comparison with triangular, T-shape and L-shape configurations.

This study examines the sustainability of uniform as well as an optimal grounding grid (GG) design for the microgrid (MG), in terms of variations in the top layer (TL), middle layer (ML), and bottom layer (BL) soil resistivities (, , and , respectively) along with change in a thickness of TL and ML. GG design is highly dependent on , as it helps in determining the density of conductors at grid extremities. With an increase in , touch voltage (TV) crosses its tolerable limit, but step voltage (SV) remains within its limit. However, with a simultaneous increase in the thickness of ML (MLT), SV also crosses its limit. For higher than , with an increase in MLT, TV, and SV increase, while in the reverse case, they decrease. For the given MLT, is crucial in determining GG burial depth. Validation of results is done by comparing them with the IEEE standard. Also, the optimal compression ratio of GG with an increase in MLT is analysed. TVs can be reduced to a great extent, with the application of distinctive methods of earthing (TT-GG system, TN-S-GG system, and TN-C-S-GG system) in MG. This study also reveals that an increase in GG resistance leads to a reduction in TV.

In the study, in the title of this comment, a ring conductor with rectangular cross-section excited by ramped potentials at one end, with the other end grounded, has been considered. Analytical series solutions have been derived to describe the diffusing field transients in a few milliseconds in the ring conductor. This comment indicates the weaknesses of the study and presents an improved and much simpler analytical approach to the problem.