Partial discharge is one of the main reasons for insulation degradation in high‐voltage apparatuses. Partial discharge is an ineluctable phenomenon that happens when a high electrical field is ...adjacent to an insulator. High‐frequency current transformers are widely used for detecting partial discharge current in high‐voltage equipment. Determination of the apparent charge in pico coulombs is essential for having a common understanding of results and verifying that the measuring system can obtain specified partial discharge magnitude correctly. To this end, a high‐frequency current transformer sensor and a partial discharge calibrator have been prepared to measure the current of the partial discharge (PD) pulses inside mineral oil. The constructed PD calibrator has been evaluated. The high‐frequency current transformer (HFCT) sensor has been simulated using a mathematical model‐based AC analysis and has been characterized and then calibrated using a calibration technique to measure the apparent charge of the PD pulses. Experimental results show the effectiveness of the HFCT sensor and the proposed calibration method.
• In this paper, a PD calibrator, an HFCT sensor, and a transformer insulation oil breakdown voltage (BDV) test cell have been built and presented in detail. Also, we gave guidance for their manufacturing in the article.
• Also, a discharge calibration method for the HFCT has been presented.
•The test verification on distribution transformers is given, which shows obvious guiding significance for engineering and can be helpful for both academic researchers and engineers. The survey of the research is of great help to readers in understanding the state of the art in this field because of the detailed work.
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FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SBCE, SBMB, UL, UM, UPUK
In order to reduce the cogging torque of a symmetrical V-type line-start permanent magnet synchronous (LSPMS) motor, this paper proposes a multi-objective optimization method based on the combination ...of design parameter stratification and response surface methodology (RSM). The optimal solution to the RSM model is acquired using the max–min ant algorithm. The permanent magnet width, pole opening angle, stator slot width, rotor axial length, and rotor tooth width are selected as optimization variables. The cogging torque and average torque are the optimization objectives. Finite element method (FEM) results show that the cogging torque is reduced by 71.5%, the torque ripple is reduced by 65.6%, and the average torque is improved by 12%. Finally, the effectiveness of the algorithm is verified with simulation results.
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EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
Networked control systems which transfer data over communication networks may suffer from malicious cyber attacks by injecting false data to the transferred information. Such attacks can cause ...performance degradation of the closed-loop system and the filtering problem. The sequential importance sampling (SIS) particle filtering (PF) methods employ the sequential Monte Carlo approach to estimate the generally non-Gaussian posterior probability density function (pdf) for Bayesian estimation of generally non-linear non-Gaussain systems. In this paper, it is firstly shown that with the normal SIS PF, the injected false data to the networked systems remains stealthy and therefore it is not possible to reduce the degrading effect of the attack on the estimation. However, with a modification in the proposal pdf, a modified SIS PF is then proposed which guarantees the attack detectability where the attacked measurements are incorporated in the particle generation process and thus the particles are updated and make the attack detectable. Using the derived thresholds and under small enough measurement noises, it is also proved that no false alarm occurs. After estimation of the attack value, the posterior pdf conditioned on truly detected attack leads to an estimation equivalent to the attack free SIS PF in terms of estimation bias and estimation covariance error. Finally, the accuracy of the presented concepts is demonstrated for a networked interconnected four-tank system.
Partial Discharge (PD) is one of the symptoms of an electrical insulation problem, and its permanence can lead to the complete deterioration of the electrical insulation in high-voltage equipment ...such as power transformers. The acoustic emission (AE) method is a well-known technique used to detect and localize PD activity inside oil-filled transformers. However, the commercially available monitoring systems based on acoustic sensors still have a high cost. This paper analyses the ability of low-cost piezoelectric sensors to identify PDs within oil-filled power transformers. To this end, two types of low-cost piezoelectric sensors were fully investigated using time-domain, frequency-domain, and time-frequency analysis, separately. Thereafter, the effectiveness of these sensors for PD detection and monitoring was studied. A three-phase distribution transformer filled with oil was examined. PDs were produced inside an oil-immersed transformer by applying a high voltage over two copper electrodes, and the AE sensors were coupled to the housing of the transformer. By extracting typical features from the AE signals, the PD signals were differentiated from on-site noise and interference. The AE signals were analyzed using acoustic signal metrics such as peak value, energy criterion, and other statistical parameters. The obtained results indicated that the used low-cost piezoelectric sensors have the capability of PD monitoring within power transformers.
This paper addresses the localization of Partial Discharge through a 3D Finite Element Method analysis of acoustic wave propagation inside a 3-phase 35kV transformer with the help of COMSOL ...Multiphysics software. Due to the complexity inside transformers, acoustic waves generated by PDs cannot simply be detected with typical acoustic sensors, especially when PDs happen inside inner windings. These waves are distorted and attenuated along with their propagation. The type, number, and position of sensors are essential factors in PD localization inside a transformer. A new installation arrangement of fiber-optic acoustic sensors inside the transformers is proposed with this information. This array of acoustic sensors has significant effects on PD localization accuracy and has immunity from on-site noise and interference; more importantly, they can be installed after transformer manufacturing. They are reachable if needed to be repaired or replaced. Several numerical studies have been carried out considering different PD source positions, and the Levenberge-Marquardt algorithm is employed for solving localization equations.
In recent years, PM-assisted synchronous reluctance machines simplicity, robustness, efficiency, and temperature capacity (SynRMs) make them a viable alternative in various applications. The poor ...power factor (PF) and high torque ripple are the main challenges of SynRMs, which necessitate robust optimization improving the mentioned demerits. However, the optimization algorithms usually rely on complex analytical models; in this paper, in order to optimize, the design of experiments with the Taguchi method has been used. Taguchi is a simple and effective optimization method and requires a small number of experiments and experience. Also, to select the best combination in multi-objective optimization, the TOPSIS method has been utilized to prioritize the optimal solutions. The proposed method is evaluated by finite element analysis (FEA).
Aim and Background: Because the deficiency of communication skills in children with autism spectrum disorder (ASD) has a negative effect on the relationship between them and their parents, it seems ...necessary to use early interventions to improving the communication skills of these children. Therefore, the purpose of this study was to investigate the effectiveness of Hanen parent program on the parent-child relationship of families with children with ASD. Methods and Materials: This study was pre- test/ post- test and follow up with control group design. The Statistical population of this study included all children with ASD (ages 3 to 7) that lived in Isfahan county. The research sample included 22 children and their parents that were selected by convenience sampling. These participants assigned in two groups of 11 people, the experimental group and the control group. Then, parents of the experimental group received Hanen parent program for 3 months and 2 sessions per week. At this time, the control group did not receive any intervention. The study data collected by the child- parent relationship scale- CPRS (Pianta, 1994). The repeated measures MANCOVA analysis was used to analysis of data. Findings: The results showed efficiency of Hanen parent program on child- parent relationship and Subscales (conflicts, closeness and dependence) is significant in α= 0/05 level. Conclusions: According to the results of the present study, Hanen parent program can be used to improve the quality of child- parent relationship in children with ASD and their parent by providing opportunities for parent training.
Methods of contactless electrical power transfer technologies have been surveyed and results are presented here. In this among, the inductive based contactless electrical power transfer systems are ...investigated in more detail. The principles, structures and operations of the systems as well as their methods presented in the literature are reviewed and their applications are explored. Also, current challenges and opportunities and future trends are noted. An effective index is proposed to compare different contactless power transfer systems describing their present statuses and the future trends. Finally, some remarks and recommendations regarding future studies are proposed.
Due to the widespread impact of renewable energy resources on high power
density grids, transmission at the DC regime has been considered more useful
than AC transmission systems. The findings of ...this study suggest the
application of a ripple-free input current resonant DC-DC converter
possessing high voltage gain and high efficiency as being more suitable for
renewable energy systems. Applying variable switching frequency control
systems, the proposed converter discussed here is generally operated at the
critical conduction mode for soft switching of the semiconductor switches.
Using the resonance mechanism, the proposed converter causes a decrease in
the turn-on loss of the power switch without needing additional
semiconductor gadgets. It leads to a reduction in the reverse-recovery
losses of the rectifying diodes. Also, analysis and design consideration of
the proposed converter are presented with excellent performance.
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IZUM, KILJ, NUK, PILJ, PNG, SAZU, UL, UM, UPUK
There are several ways to reduce and compensate for voltage disturbances. One of the methods is to use a Multilevel STATCOM. Multilevel inverters are widely used in various parts of the power system ...and industry due to advantages, such as appropriate output waveform (voltage and current). There are numerous controllers for multilevel STATCOM control. One of the simple and economy controllers is the one-cycle controller, which is usually used in DC / DC and DC / AC converters. In this paper, a new structure is proposed to improve the performance of the one-cycle controller. Improvements include voltage sag and swell, voltage disturbances, harmonics, and short-term outages. To demonstrate the performance of the proposed controller, the multilevel STATCOM is also tested and compared with conventional PWM control. The simulation results show that multilevel STATCOM will correct the disturbances. Among the advantages of the proposed method are its simplicity, robustness, and flexibility, so that with one adjustment, the parameters of the control system can compensate for all the defects.
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