Iet Science Measurement & Technology最新文献

The authors propose an innovative technique for dealing with optimal shape design problems that exploits the flexibility of the virtual element method in generating meshes composed of general polygonal and polyhedral elements. Virtual element method and finite element method can coexist on the same discretized domain; therefore, the possibility of dealing with hanging nodes and gluing sub-domain meshes is ensured. Accordingly, the shape synthesis of a magnetic pole is considered as the case study. It is shown that the proposed technique is effective in handling the shape variations dictated by an algorithm of evolutionary optimisation.

Higher time resolution imaging is vital for exploring the microscopic mechanisms of the discharge process. The transient processes of discharge phenomena occur in a short time, and the onset cannot be predicted in advance, thus not providing a trigger mechanism for conventional high-speed imaging methods. Here, the authors propose a high-time-resolution imaging method with 55-ps time resolution and single-photon detection sensitivity. First, the current signal generated by the discharge itself with a rising edge of only a few tens of nanoseconds combined with a high-speed sensing and signal-processing device is used to solve the high-speed triggering problem, and then the single-photon avalanche detector array operating in time-correlated single-photon counting mode combined with computational imaging techniques is used to obtain the evolution of the negative corona discharge at atmospheric pressure in air on the ps time scale, and finally, the time-dependent curves of the discharge photon number at different experimental voltages with different curvature radii are analysed. The method opens up new possibilities for imaging other high-speed dynamic processes without a fixed trigger signal.

The directional multiple signal classification (Dir-MUSIC) algorithm based on antenna gain array manifold has been proposed to find the direction of the partial discharge source successfully in substations, however, a non-linear optimisation problem in this algorithm is usually time-consuming. To achieve real-time feature, a data-driven Dir-MUSIC method based on the multilayer perception model is proposed to speed up the computing process and simultaneously guarantee the accuracy. Pre-trained the multilayer perception model, the non-linear optimisation problem can be treated as a function can be calculated directly. Input of the model is the noise matrix which can be uniquely calculated with a certain matrix measurement, and output is the estimated direction of the partial discharge source. Simulation results demonstrate that the proposed method has an excellent efficiency and relatively high accuracy, and the computing time can match the real-time demand. Additionally, two effective improvements are proposed to raise the direction accuracy and stability. Specifically, mean error is reduced from 2.58° to 2.22° with the first improvement, and from 2.58° to 1.00° with the second improvement.

Perfectly matched layer has been used for solving anchor-loss limited quality factor in the Micro electromechanical systems. However, setting up a well-behaved perfectly matched layer requires users to change the parameters of a perfectly matched layer to give correct results, while the current existing methods for choosing the right parameters are vague and lack theoretical support. Based on the mathematical theory of perfectly matched layer and simulation results of a beam structure's quality factor, this paper proposes a method for choosing the parameter to optimise the performance of perfectly matched layer in COMSOL. The accuracy of the proposed method is proved by matching the effect of substrate height on beam's quality factor with theory prediction. The author also studies the effect of beam height and beam width on the quality factor of the beam. The results demonstrate that simulated quality factors are in agreement with analytical values when the ratio of height over length is small but will show great divergence when height equals the length. This trend can be observed for the beam width as well. Especially for larger ratio of beam width over beam length, instead of decreasing monotonously as analytical equitation would expect, the simulated quality factor will converge into a stable value of 1700, which matches the result of two-dimensional model for the same beam structure. This means that a three-dimensional model has to be used for estimating the quality factor of a beam structure.

This paper deals with the utilization of printed circuit board Rogowski coils (PCBRCs) for differential protection of electric arc furnace (EAF) transformers in Mobarakeh Steel Company (MSC), Isfahan, Iran. Because of a high level of current (in the range of 100 kA) in the EAF transformers in the MSC, employment of differential protection is quite challenging. Conventional current transformers (CTs) cannot offer reliable performance for very high current levels. The PCBRCs are a branch of Rogowski coils (RCs) that can be manufactured with high precision using computer-aided design approaches and have the capability for the measurement of very large currents. In this study, we have designed and manufactured two sets of PCBRCs to measure current in the primary and secondary sides of the EAF's transformers in the MSC. The PCBRCs are followed by a signal condition circuit (SCC) which includes a low-pass filter, amplifier, and voltage-to-current (V-to-I) converter block. Thanks to the SCC, the high current of the transformers can be properly sensed and transmitted over a long cable that connects the PCBRCs to the relay. Furthermore, a novel model is suggested for the EAF that includes characteristics of both time and frequency domain models. The suggested model is developed using a large number of recorded data from the MSC and can model the non-linear and time-variant behaviours of the EAF. The proposed PCBRCs, SCC, and EAF modelling are evaluated by some simulations and experiments in the MSC.

The electrical performance of transmission line insulators will decrease dramatically under ice-covered conditions, and ice flashover may occur under operating voltage. There is no direct and effective monitoring method for ice cover on insulators of transmission lines. In this paper, the interface quasi-distributed fibre Bragg grating (FBG) is used to study the positioning detection of glaze icing loads on composite insulators, and a mechanical lever model of single glaze icing load on single umbrella detection with three FBGs is established. Based on this model, a multi-glaze location detection method on multiple umbrella skirts is proposed. Six optical fibres with 13 quasi-distributed FBGs each are implanted into the interface of a 110 kV composite insulator. The minimum load test of FBG for detecting glaze icing load, the FBG axial/circumferential sensing rule test for the glaze, and the weight simulation test and laboratory icing verification test for multi-glazes on multi-umbrellas location detection method are carried out. The results show that the positioning of glaze simulated by weights is accurate, and the positioning of icing in the laboratory is basically correct.

To investigate partial discharge-induced deterioration characteristics of ethylene-propylene rubber (EPR) cable insulation under repeated alternating current (AC) voltage on high-speed trains, an experimental platform with a column-plate EPR insulation model is established. The surface condition and breakdown voltage of insulation samples after discharge treatment are observed and measured. In addition, a fitting formula to evaluate the deterioration extent of EPR samples is proposed. The results show that under repeated discharge pretreatments, the volume resistivity increases first and decreases afterwards when discharge magnitude is low. When partial discharge (PD) intensity increases to 100 pC, the volume and surface resistivity decrease monotonously, and the decreasing rate is positively correlated with PD intensity. During PD pre-treatment, a white circle appears near the electrode and turns to pale yellow with PD intensity. For PD pretreatments of 50 and 100 pC, withstand voltage of EPR insulation increase first and decrease afterwards, and the downward trend is slow. For PD pre-treatments of 200 and 400 pC, the withstand voltage decreases significantly with the degradation time. The fitting formula model shows that under the action of a strong electric field, the relationship between the reliability of EPR insulation samples, the probability and rate of molecular chain breakage, and the intensity of discharge activity is not linear.

Series multi-break mechanical switch is one of the critical components of high-voltage hybrid DC circuit breakers. However, due to the existence of distributed capacitance, the voltage distribution between the breaks is not balanced. This paper proposed a voltage sharing configuration method of the mechanical switch of hybrid DC circuit breaker, and carried out the static DC voltage and the transient voltage distribution characteristics tests to verify its effectiveness. Considering the influence of whole structure of the circuit breaker, this paper established the electrostatic field model and circuit simulation model of a typical ±535-kV hybrid DC circuit breaker. And it analyzed the influence of single break's opening fault, breaking open distance, and the shielding fitting on the voltage distribution characteristics of series six break mechanical switch. According to the simulation results based on the Zhangbei voltage source converter-based high-voltage direct current project type test parameters, the parameters design of the voltage sharing components of the mechanical switch are obtained, which can meet the voltage sharing coefficient requirement of 95%.

To study the influence of the arrangement of glass fibres on the growth morphology of electric dendrites, this paper conducted experiments on the initiation and cultivation of electric dendrites on insulation specimens with different glass fibre arrangements. The experimental results show that when the electric field is parallel to the glass fibres, the electric dendrites show linear growth with multiple branches; when the electric field is perpendicular to the glass fibres, the electric dendrites show aggregated growth. The analysis suggests that when the applied electric field is parallel to the glass fibre, to release the discharge energy in the main channel of the dendrite, the discharge in the track of the electric dendrite will drive the electric dendrite to grow along the interface area between the glass fibre and the epoxy resin. When the externally applied electric field is perpendicular to the glass fibre, the discharge within the electric dendrite discharge channel is high. To release the energy in the electrical tree channel, the blast in the electrical tree track induces the electrical tree branch to grow along the interface area and forward.

Soil ionisation has an important influence on impulse characteristics of grounding conductor. This paper introduced improvements to an existing soil ionisation model considering the influence of electric field on the change of soil resistivity, while soil resistivity is not directly dependent on soil electric field. The validity of improved soil ionisation model was verified by surge response of vertical conductor in uniform soil and horizontally stratified soil. Furthermore, the impulse experiment was carried out on horizontal conductor in soil with finite volumes. Based on experimental configuration, the corresponding calculation model was built, and calculated results were in good agreement with experimental results.