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Repeated impulses have long been considered to affect the insulation properties of electrical equipment. This interesting but rarely studied phenomenon may pose great risks to the reliable operation of power equipment. Therefore, in this work, we focus on the accumulative effect of repeated lightning impulses on the oil-impregnated paper (OIP) used in power transformers. Specifically, we study the effect of space charge on the accumulative characteristics of OIP. A repetitive impulse accumulating test platform was set up, and the tests were conducted to obtain the accumulative characteristics of OIP under repeated lightning impulses. The accumulative characteristics of OIP with various interval time were experimentally identified to study the influence of interval time on the accumulative effect. Then, space charge in OIP samples were investigated using the pulsed electro-acoustic technique. Charge behavior in OIP was analyzed under different conditions, i.e., changing the applied times, amplitude and interval time of the applied lightning impulses. Charge injection and transport occurred during lightning impulse accumulation. The increased application of lightning impulses, high applied voltage, and short interval time contributed to the accumulation and transport of space charges. At last, the possible mechanisms of the accumulative effect are discussed in this article based on the experimental results. [ABSTRACT FROM AUTHOR]

Sheet tension control is crucial in the paper winding process in order to get properly formed shipping roll(s) produced in the winder. Typically, the tension loop uses load cells as tension sensors, which are expensive and require frequent maintenance and calibration. This paper develops two new tension estimators for a two-drum electric-braking-generator production winder, based on unwinding and rewinding variables, respectively. The estimators consider all the essential dynamic, friction, and inertial variation effects. Both estimators are evaluated in typical trapezoidal winder operating cycles. Multiple sensitivity analyses show that the proposed estimators are robust to normal parameter variations, and give stable and precise sheet tension control without the use of load cell tension loops. [ABSTRACT FROM AUTHOR]

Presents a study on deterioration diagnostic techniques for applying to oil-impregnated paper film capacitors. Information on power capacitors; Methodology used in the various tests involving accelerated deterioration; Main causes of deterioration of power capacitors; Investigation of the degree of the deterioration of insulating oil power capacitors; Findings of the investigations.

This paper presents a technique for circuit breaker radiometric monitoring using broadband plana monopole antennas (PMA). Considering that this work represents the continuity of a previous research, the antenna has been miniaturized using a bioinspired geometry based on the Acer Macrophyllum leaf. The monitoring system consists in measuring the signal radiated by electric arcs in circuit breaker poles during its switching operations. By analyzing these signals, it is possible to evaluate, non-intrusively, the equipment electric and mechanical status, providing important information to maintenance crews regarding the need for interventions. By performing laboratory tests, it was confirmed that the developed bioinspired PMA has adequate gain values, radiation pattern and frequency range to circuit breaker monitoring applications. Moreover, field tests on a 230 kV SF6 circuit breaker were carried out, from which the proposed technique applicability was confirmed. The proposed monitoring technique can be considered a continuous and non-invasive solution, since the antennas can be placed at a safe distance from the equipment under analysis, without compromising the insulation. In the substation, the technique has the potential to detect problems of electrical and mechanical nature, since important operational parameters can be detected, such as opening time and pole synchronicity. [ABSTRACT FROM AUTHOR]

The article discusses on the 32nd International Conference on Plasma Science (ICOPS) held in Monterey, California. This Special Issue focuses on Plenary and Invited Papers from ICOPS. There are invited talks included in the issue which subjects ranged from the traditional interests in basic plasma processes, microwave generation and charged particle beams, and other plasma-related topics.

This paper proposes a transformer integrated filtering system (TIFS) for harmonic suppression in the industrial dc supply system. Designed for the electric environment with large current and severe harmonic contamination and the installation space with restricted planning area, the proposed TIFS has the merits of lower transformer loss, stronger ability in harmonic elimination, and higher integration of the electric equipment in the high-power industrial applications. The winding arrangement of the inductive filtering transformer with integrated reactor is introduced. Considering the influence of the residual weak coupling, the electromagnetic decoupling model of TIFS is established. Then, the interaction between the zero-impedance designed filtering winding and the decoupled winding is analyzed to determine the restricted range of the design parameter. The control strategy together with the transformer design method is further illuminated. At last, the prototype of TIFS is established in the laboratory. The experimental results verify the feasibility and effectiveness of the proposed filtering method. [ABSTRACT FROM AUTHOR]

This paper proposes a multidisciplinary procedure to correctly design a microgrid of all-electric nearly zero energy buildings (nZEBs) from both electrical and thermal points of view. The procedure is suitable for new buildings supplied by local renewables, without the use of fossil fuel and with zero emissions. First, the thermal demand of each single nZEB is assessed, as a function of the installation site, building layout and physics, and material composing the envelope. Thanks to heat pumps, the thermal demand is transformed in electric load. Thus, the total electric consumption profiles, which include user's appliances and heating/cooling, are studied and compared with photovoltaic (PV) generation supported by electrochemical storages. Both PV and batteries are simulated, thanks to appropriate models. Regarding the PV production assessment, this work proposes an improvement with respect to the use of traditional models, and it is based on experimental results on PV generators of recent production. The design methodology is applied to a real case of “energy community” composed of three nZEB units that will be built in the campus of Politecnico di Torino, available to students and staff. The three units share PV production and storage capacity to reach the complete grid independence. [ABSTRACT FROM AUTHOR]

The open-phase fault in vector-controlled drives is known as one of the most prevalent failures that require immediate detection. It is still challenging to develop a trustable fault diagnosis scheme at light load, transients, and low-speed regions. This paper presents a novel open-phase fault diagnosis strategy for three-phase induction motor drives over the entire speed range and for different load conditions. By taking advantage of the second-order rotational park transformation (SORP), new fault indices are proposed to identify the open-phase location without using any additional sensors or electric equipment. Comparing with root-mean-square (RMS) calculation-based methods, the proposed method detects the fault at least twice faster, with minimal system resources. The presented scheme may be implemented simply and is robust against the operating point changes. Proof of the proposed fault detection and localization method has been shown through experimental tests on a 250-W three-phase induction machine which is controlled by TI-DSP F28335. [ABSTRACT FROM AUTHOR]

Modern power systems produce nonstationary harmonics which bring harm to the electric equipment. Real-time and accurate parameter estimation is the key step of the harmonic elimination. This paper proposes a novel technique of the parameter estimation for fundamental and harmonic using nonergodic $S$ -transform (NEST), which can effectively eliminates the estimated parameter error caused by nonsynchronous sampling. First, the signal is decomposed into the fundamental and harmonics NEST vectors (NESTVs) by NEST, and the amplitudes are detected accurately by extracting the magnitude of NESTVs, which are optimized by the Gaussian window width coefficient of the NEST kernel function. Second, the overlapping and abandoning method is used to remove the end effect of NESTVs so as to obtain the effective and complete data for the parameter estimation. Then, the estimated instantaneous frequency and phase are obtained using the linear phase characteristic of NESTVs. Finally, simulations and experiments prove that the proposed method can not only estimate the stationary signal parameters accurately but also trace the nonstationary signal parameters in the real time under the spectrum leakage condition. [ABSTRACT FROM AUTHOR]

This paper presents a modeling approach for capturing closed-loop load behavior in distribution networks using bottom-up time-variant load models and incorporating load-flow feedback for thermal loads. Traditional load models are useful for providing insights into instantaneous changes in power, however, they do not capture the time-variant response to changes in voltage due to the effects of appliances with closed-control loops such as those which are thermostatically controlled. This paper proposes a modeling and co-simulation platform to simulate closed-loop load-modeling using state-of-the-art bottom-up load modeling techniques for the residential sector with a feedback model for time series steady-state load-flow. It incorporates time-variant load models and discrete state-space representation of thermostatically controlled appliances. The developed methodology is used in a conservation voltage reduction case study on an urban distribution network, allowing detailed assessment of the voltage response and analysis of changes in active and reactive power and network losses. [ABSTRACT FROM AUTHOR]

This paper highlights the importance of chronology on voltage protection and control apparatuses in studies of voltage security in active distribution networks with high generation capacity. This paper presents simulation results of a real-life example of a long rural distribution feeder having three voltage regulators in cascade, and a customer whose demand accounts for a large percentage of the total feeder load. The customer is also an independent power producer and its location at the far end of the feeder yields an intricate voltage protection coordination when the customer ramps up and down its own generation at the peak-demand period. [ABSTRACT FROM AUTHOR]

In spite of the contemporary interest in renewable power plants, thermal power plants are still inevitable. Various electric equipment and apparatus are grounded via a large-scale grounding system in thermal power plants. In this paper, the three-dimensional finite-difference time-domain method has been employed to study the performance of such a large-scale grounding system against a lightning strike to a nearby transmission tower. The study has emphasized how a nearby sea, which is utilized for cooling purposes in thermal power plants, influences the ground potential rise on the large-scale grounding system considering soil ionization. The results show that the distribution of the ground potential rise on the large-scale grounding system is quite dependent on the alignment of sea with the large-scale grounding system. In addition, the extent that soil ionization affects the ground potential rise is dependent on the distance between the struck tower and the large-scale grounding system. [ABSTRACT FROM AUTHOR]

The socioeconomic development of a nation depends, among other factors, on the ability of electrical power sector growth in order to satisfy an increasing demand. The suitable level of hydropower installations system reliability requires reliable power generation and transmission systems. This paper presents a comparison between the Weibull and $q$ -Weibull reliability models, through a practical example, and the main reliability parameters of some Brazilian hydropower equipment. The application of the models to a practical example is done with parameters estimation by using probability plotting method. $R^{2}$ , Akaike information criterion, and mean squared error were calculated to verify the suitability of the model for the sample data and to compare the distributions adjustments. The maximum likelihood method was applied to determine the parameters of the $q$ -Weibull distribution and the results were compared with those of the probability plotting method. An analysis using 3-D contour plots for the likelihood function was performed for four types of equipment. The results were analyzed by reliability and failure rate plots. The failure rate plots were grouped according to their shapes. The modeling of the failure phenomenon done by $q$ -Weibull is closer to reality and allows better planning of maintenance and replacement policies. Hydropower data bank $q$ -Weibull parameters have not been introduced in the literature. [ABSTRACT FROM AUTHOR]

Objective: This paper presents an asyn-chronous electrooculography (EOG)-based human–machine interface (HMI) for smart home environmental control with the purpose of providing daily assistance for severe spinal cord injury (SCI) patients. Methods: The proposed HMI allows users to interact with a smart home environment through eye blinking. Specifically, several buttons, each corresponding to a control command, randomly flash on a graphical user interface. Each flash of the buttons functions as a visual cue for the user to blink. To issue a control command, the user can blink synchronously with the flashes of the corresponding button. Through detecting blinks based on the recorded EOG signal, the target button and its corresponding control command are determined. Seven SCI patients participated in an online experiment, during which the patients were required to control a smart home environment including household electrical appliances, an intelligent wheelchair, as well as a nursing bed via the proposed HMI. Results: The average false operation ratio in the control state was 4.1%, whereas during the idle state, no false operations occurred. Conclusion: All SCI patients were able to control the smart home environment using the proposed EOG-based HMI with satisfactory performance in terms of the false operation ratio in both the control and the idle states. Significance: The proposed HMI offers a simple and effective approach for patients with severe SCIs to control a smart home environment. Therefore, it is promising to assist severe SCI patients in their daily lives. [ABSTRACT FROM AUTHOR]

A novel scheme is proposed to monitor the operation of capacitors scattered in MV distribution systems. It first codes each capacitor with a distinctive switching character by setting a unique combination of a three-phase switching order and time interval. As a result, the transient of the three-phase reactive power during capacitor switching will appear in a unique way. Then, the reactive power disturbances monitored in the substation are decoded to identify which capacitor is being switchedonandoff. A detailed decoding method is developed to realize this identification without being impacted by the switching interference of loads and other reactive power compensation devices. Moreover, the implementation of the proposed scheme in the field is elaborated, and the resultant three-phase voltage unbalance is analyzed in this paper. Compared with existing methods, this scheme only requires one power quality monitor located at the substation to monitor the operations (energizing or de-energizing) of downstream distribution capacitors without extra communication devices. The operation information is valuable for tackling power quality problems caused by capacitor switching and optimizing the distribution grid operation. [ABSTRACT FROM AUTHOR]

Efficiency and power loss are the necessary metrics for evaluating the performance of electrical drives. These two metrics are calculated based on the measured input and output power of the drive. Input power is calculated from the measured terminal voltages and currents, whereas output power is calculated by multiplying the measured motor speed with the measured shaft torque. Torque transducers are normally used to measure the windup shaft torque. This method is effective for steady-state speed operation. This paper proposes an observer structure that uses standard dynamometer sensors that are capable of estimating the shaft torque during both steady-state and transient speed operations. This enables the motor losses to be measured during transient speed operations (acceleration/deceleration), which is generally not feasible using standard torque sensors. [ABSTRACT FROM AUTHOR]

This paper presents a 2-D hybrid analytical modeling method for the analysis of the magnetostatic field distribution with the capability of including nonlinear materials. The model combines Fourier modeling, which is accurate and fast, with meshed magnetic equivalent circuits that have unique permeability in mesh elements and, therefore, can model local saturation. To present the diverse applicability of the proposed method, it is applied to a linear machine with permanent magnet excitation and a rotary machine with current excitation. Magnetic field calculations are compared with finite-element analysis (FEA) with good agreement. [ABSTRACT FROM AUTHOR]

This paper at first proposes a method to calculate a trigger strategy before launching in order to control the muzzle velocity of railguns. Five triggering points are set equidistantly and six pulsed forming unit (PFU) groups are triggered in total. First, given a desired muzzle velocity, the expected uniformly accelerated rectilinear motion of the armature is calculated. Second, the module number of each PFU group is obtained according to the principle of minimizing the absolute relative error between the actual and the expected velocity at each triggering point. The results show that, when the desired muzzle velocity is within [1500, 2000] m/s, the absolute muzzle velocity relative error $\delta $ is less than 0.5%. In order to achieve a better control performance, the places of the five triggering points are then optimized by a genetic algorithm (GA). The objective function is the sum of absolute $\delta $ , when the desired muzzle velocities are 1500, 1600, $\ldots $ , 2000 m/s. After the optimization, $\delta $ is reduced to less than 0.05%. At last, based on this velocity control method, the railgun system is optimized to pursue the highest system efficiency $\eta $ by GA. The independent variables are the armature mass, the precharged voltage, and the places of the five triggering points. The constraints are that the desired muzzle velocity is 1800 m/s and the absolute $\delta $ is within 1%. The results show that $\eta $ increases from 6.57% to 25.37%. [ABSTRACT FROM AUTHOR]

High-voltage, nanosecond, high-repetitive-frequency, and portable pulse generators are always required in many fields. Avalanche transistor-based Marx circuits have been widely studied to generate pulses satisfying the above requirements. However, the basic topology of an avalanche transistor-based circuit, configuration of circuit parameters, and optimal working performance (including output impedance matching) were still scarcely discussed. In this paper, the detailed process of analyzing and designing a compact Marx generator using avalanche transistors was described. Based on the conventional principles of avalanche transistors and Marx circuit, a list of useful and interesting conclusions was discovered by experiment. An example with specific parameter requirements was utilized for the clearness of illustration. The 12~cm\times 4 cm Marx circuit could finally generate pulses with a 2.5-kV amplitude, 6.0-ns width, 10-kHz repetitive frequency, lower than a 100-ps jitter and $\sim 125$ -kW maximum peak output power on a matched 50- $\Omega $ resistive load. The pulse amplitude could be adjusted from 1.5 to 2.5 kV and the pulse width could also be broadened. This paper may help to provide a reference to similar methods of producing high-voltage, nanosecond, and high-repetitive-frequency pulses. [ABSTRACT FROM PUBLISHER]

This paper evaluates the relationship between hazardous-rated electrical equipment, which is suitable for installation in Class I, Division 1 (Zone 1), or Division 2 (Zone 2) locations, and an arc-rated switchgear, which is designed to withstand the effects of an internal arcing fault. Using UL 1203 (Explosion-Proof and Dust-Ignition-Proof Electrical Equipment for Use in Hazardous (Classified) Locations), IEEE C37.20.7 (IEEE Guide for Testing Metal-Enclosed Switchgear Rated Up to 38 kV for Internal Arcing Faults), and the paper titled “Pressure Developed by Arcs,” this paper will explore the applicability of hazardous-rated equipment in the protection of personnel from an arc-flash hazard. [ABSTRACT FROM PUBLISHER]

Armature-reaction-compensated permanent-magnet synchronous generators are a particular type of hybrid excitation synchronous generators, where the main flux is created by the permanent magnets and the field winding is needed only to compensate the armature reaction. This paper studies the feasibility of an armature-reaction-compensated permanent magnet synchronous generator in island operation by comparison with a conventional electrically excited synchronous generator and permanent magnet synchronous generator. The aim of this paper is to demonstrate the performance of an armature-reaction-compensated permanent magnet synchronous generator and its operation principle in island operation. As part of the study, a 55 kW prototype was built and tested. The experimental results of the prototype are presented. [ABSTRACT FROM PUBLISHER]

Batteries are the most commonly used electrical energy storage devices. The cost and performance of an electric vehicle (EV) are strongly affected by the proper selection of technology, number, and arrangement of the battery cells used. This paper formulates the problem of optimal sizing of the battery unit (BU) for a plug-in EV (PEV), given the specifications of the vehicle, battery cell data, and drive cycle. This paper employs a metaheuristic optimization algorithm to find the optimal size of the BU with the objective of minimizing the overall cost. Feasibility of the optimization results in terms of respecting the constraints is verified via simulation. The developed optimization platform is highly flexible and allows use of different vehicle designs, component data, and drive cycles. [ABSTRACT FROM PUBLISHER]

Heating and current drive (H&CD) systems are being investigated for a demonstration fusion power plant DEMO to deliver net electricity for the grid around 2050. Compared to ITER, which has to show the generation of 500-MW thermal power, the target of DEMO is the successful production of 300 to 500 MW electrical power to the grid and to aim for a self-sufficient tritium fuel cycle. Three H&CD systems are under development for DEMO in Europe, the electron cyclotron (EC) system, the neutral beam injection (NBI) system, and the ion cyclotron system. Based on present studies for plasma ramp-up, ramp-down, and flat top phases, to be further validated in more detailed simulations, the assumed total launched power needed from the H&CD system in DEMO is in the range of 50–100 MW, to be provided for plasma heating and control. This paper describes the design and Research and Development status of selected H&CD systems, considered for their deployment in the EU DEMO. It was always considered that different H&CD configurations and design variants will have an impact on the performances for the whole fusion plant. It shall be noted that the basis for the H&CD integrated design and system development is the actual version of the European fusion electricity roadmap. The project also elaborates on H&CD efficiency improvements which will reduce the recirculating power fraction in the future fusion power plants. Different studies under investigation will be discussed such as for NBI the photoneutralization and for EC novel concepts for gyrotron multistage-depressed collector. [ABSTRACT FROM AUTHOR]

The ground return current of a high voltage direct current system will intrude the transformers adjacent to the grounding electrode in the case of monopole operation, leading to the half-cycle saturation of transformers. To mitigate the adverse effect, placing dc blocking devices (BDs) in transformer neutrals is popularly advocated. The conventional switching method of BDs may redirect the dc flow from one transformer with a BD to neighboring transformers without BDs. In this case, the dc currents through the neutrals of those transformers may possibly exceed the threshold undesirably. This problem is due to the lack of guidance for dc current distribution from the global view by means of finite BDs. Thus, this paper presents an optimization approach for the switching of BDs based on the gravitational search algorithm. A mathematical model for investigating the dc global distribution is established with the equivalent resistive network of an ac system, the location distribution of substations and grounding electrodes. Then, an optimal switching scheme to minimize the adverse impact of dc bias is presented, and the principle and the concrete implementation process are detailed. The feasibility and the advantage of the proposed scheme are demonstrated by numerous comparative case studies. [ABSTRACT FROM AUTHOR]

In this paper, the investigation is focused on the iron loss prediction for electrical machines fed by low switching frequency inverter. An improved iron loss model is developed after reviewing various existing iron loss models considering pulse-width modulation (PWM) influence. In order to validate the improved iron loss model, iron loss tests are carried out on an electrical machine. The predicted iron loss results match well with the measured results, which shows that the improved iron loss model is able to predict iron loss in electrical machine fed by an inverter. The comparison between the predicted iron losses with and without considering the PWM influence shows that the iron loss can be significantly increased due to the influence of PWM, especially when the switching frequency is low. [ABSTRACT FROM AUTHOR]

This paper shows the generation of a local oscillator (LO) signal for cellular transceivers by means of a phase-locked loop and a phase interpolator (PI) digital-to-time converter (DTC). The PI-DTC allows arbitrary frequency shifts over a wide range. We derive a closed-form description of the spurs in the spectrum of the LO signal caused by quantization and nonlinear effects for the PI-DTC. Furthermore, we show the existence of a new class of spurs generated due to noise processes in the PI. Measurement and simulation results are in good agreement with our closed-form solution. [ABSTRACT FROM PUBLISHER]

In the islanded microgrid, distributed generators are controlled with virtual synchronous generator (VSG) strategy to simulate rotor inertia and droop characteristics of synchronous generators, in order to enhance the voltage and frequency support capabilities. Since the capacity and location distribution of each VSG is random, the VSG output impedance, line impedance and its capacity are mismatched, resulting in inaccurate sharing of reactive power. Based on the study of reactive power sharing schemes without communication and system parameters detection, and aiming at the contradiction between reactive power sharing error and voltage control accuracy of existing schemes, a reactive power sharing strategy based on virtual capacitor is proposed. The strategy simulates characteristics of paralleling capacitor at the VSG output terminal, and compensates the output voltage according to adaptive control of VSG output reactive power, thus to reduce reactive power sharing error, and improve the voltage control accuracy meanwhile. The design of virtual capacitor parameters and a two VSG parallel system stability with proposed strategy are analyzed in this paper. The correctness and effectiveness of the proposed strategy is verified by experiments. [ABSTRACT FROM PUBLISHER]

The significant benefits of preemptive arc-flash protection and the online condition monitoring of electrical equipment are quite well known. Our continuing research focuses on the development of new advanced sensor technologies that are cost-effective, reliable, and efficient for the early detection of faults in order to predict impending arc-flash occurrences in mediumvoltage and low-voltage switchgear and controlgear. More extensive and detailed measurements regarding significant defects that lead to an arc-flash event have been completed since the original work in Part I was completed. A more detailed analysis of the results of this additional testing is presented in this paper. It has been documented that the two major noncontact causes that lead to an arc-flash event in switchgear are insulation degradation and thermal stresses. This paper covers the detailed measurement results under both of these conditions. New sensor technologies for both the partial discharge measurement and the thermal detection are introduced and evaluated. An effective signal processing technique, which is needed for extracting the essential indication of a developing fault, is also presented. Finally, this paper outlines how a preemptive arc detection system can be connected to protection, the programmable logic controller, or the supervisory control and data acquisition. [ABSTRACT FROM PUBLISHER]

The rapidly quenched soft magnetic materials have found many practical applications in power electronics, electric engineering, telecommunications, and other industrial sectors. The aim of this paper was to present the results of a research on fabrication technology of the amorphous and nanocrystalline cores intended for: 1) soft magnetic cores for the stators of the high-speed permanent magnet brushless direct current (PMBLDC) motors; 2) nanocrystalline soft magnetic cores for application in high-frequency power conversion; and 3) three-limb amorphous cores for the three-phase distribution transformers. The cores intended for the stator of the high-speed PMBLDC motor were made from the Metglas 2605 SA1 ribbon and then subjected to the performance tests in a model of an electric motor. The research on soft magnetic materials for high-frequency high-power conversion was concentrated on the Finemet rectangular cores with a gap and the composite ones with distributed gap, and the comodified Finemet cores with the induced transverse magnetic anisotropy. The three-limb cores for 400 kVA three-phase distribution transformer were made from the Metglas 2605 SA1 ribbon and subjected to the performance tests in electricity distribution network. It was found that all the amorphous and nanocrystalline cores fabricated under this paper enable considerable reduction in power losses. [ABSTRACT FROM PUBLISHER]

Coreless transformers are used in several applications, operating in a large range of frequencies. Their equivalent circuit model is very important to allow the proper design of any electronic circuit or load that may be electrically coupled to them. Especially, in cases where the coils of these devices are modeled with a relatively large wire gauge (when compared with the skin depth), the losses due to eddy currents must be included, otherwise their circuit simulation will be incorrect. This paper proposes a method that allows modeling the lumped parameters of coreless transformers, including the eddy currents. The method uses an optimization algorithm search through a genetic algorithm solver. Although the scope of this paper lies within coreless transformers, the whole method was designed in a generic way to model different types of electric equipment. [ABSTRACT FROM AUTHOR]

Epoxy Resin is widely used for insulation in electric devices, in spite of its weak ability of thermal conduction. One approach to obtain a higher thermal conductivity is to introduce inorganic fillers which have high thermal conductivity. The purpose of this paper is to study the effect of boron nitride (BN) particles on thermal breakdown tracking process. In this paper, epoxy samples with BN particles were prepared with different weight ratios. In order to investigate the relationship between thermal accumulation and tracking failure process, tracking failure process under different frequency of pulse discharge was investigated by an infrared thermal imager from the front and back side. Obtained results showed that with increasing the concentration of BN particles, the time to tracking failure increased. The added BN fillers have a very significant inhibitory effect on thermal accumulation. The improvement of thermal conduction plays an important role in the results of tracking failure. High frequency discharges are more likely to cause the thermal accumulation, which is unfavorable to the reliability of materials. It is concluded that the tracking failure performance could be improved by reducing the thermal accumulation. [ABSTRACT FROM PUBLISHER]

This paper presents a modulation strategy for the modular multilevel converter (MMC) which provides the voltage balancing of the capacitors of different submodules comprising the converter. Not only is this modulation applicable to MMCs constructed with classic two level (2L) submodules, but it is also effective for arrangements with different submodule concepts, for instance, topologies like neutral point clamped (NPC), flying capacitors (FCs), neutral point piloted (NPP), etc. Therefore, firstly, the general modulation philosophy is explained applied to the two level (2L) submodule concept, and secondly, the extension to 3L-NPC and 3L-FC submodule topologies is analyzed. After that, the validation of the studied modulation strategy is carried out by means of successful simulation results, at different switching frequencies and number of submodules. The corresponding experimental results are shown in Part II of this paper after having implemented the aforementioned modulation strategy in a real test bench. In addition to this, a comparison based on thermal analysis and sizing of elements among the four studied submodule topologies is also included. [ABSTRACT FROM PUBLISHER]

This paper deals with a new family of high boost voltage inverters that improve upon the conventional trans-Z-source and trans-quasi-Z-source inverters. The improved trans-Z-source inverter provides continuous input current and a higher boost voltage inversion capability. In addition, the improved inverter can suppress resonant current at startup, which might destroy the device. In comparison to the conventional trans-Z-source/-trans-quasi-Z-source inverters, for the same transformer turn ratio and input and output voltages, the improved inverter has a higher modulation index with reduced voltage stress on the dc link, lower current stress flow on the transformer windings and diode, and lower input current ripple. In order to produce the same input and output voltage with the same modulation index, the improved inverter uses a lower transformer turn ratio compared to the conventional inverters. Thus, the size and weight of the transformer in the improved inverter can be reduced. This paper presents the operating principles, analysis and simulation results, and compares them with those of the conventional trans-Z-source/-quasi-Z-source inverters. To verify the performance of the improved converter, a laboratory prototype was constructed based on a TMS320F2812 digital signal processor with 100 V dc input and 115 Vrms output voltage. [ABSTRACT FROM AUTHOR]

Air-core pulsed alternators greatly enhance the power density capabilities of pulsed power supply for electromagnetic launchers. Compared with iron-core electric machines, they require very high-excitation currents. Usually, the self-excitation mode is adopted in these systems. However, the self-excitation mode is a positive feedback process that should be precisely controlled to avoid the system being destroyed. The excitation losses are very large during the process of establishing the large field current. To solve these problems, a new excitation mode, the pulse-excitation mode, is presented in this paper. The main idea is that a pulsed current charges the field coil so that the field coil and the armature coil conduct only for a short time around the main discharge pulse. This will avoid the machine being overheated and the risk of positive feedback process. Compared with the self-excitation mode, the pulsed alternator can be operated in a higher discharge frequency and the circuit schematic of the system is simpler. A larger field capacitor is used that charges the field coil to the desired current just by a pulse. As the energy density of pulse capacitor is enhanced rapidly, the volume and mass of the field capacitor are acceptable. The pulse-excitation mode is a combination of pulsed alternator and pulsed capacitor. In this paper, the characteristics of self-excitation and pulse-excitation are analyzed, respectively. The performances of both systems are simulated, and the main waveforms are presented. Finally, there is a practical comparison between them. [ABSTRACT FROM PUBLISHER]

The smart substation, revolutionarily changing every aspect of the modern substation, is developing fast in the world and being massively deployed in China quickly. A smart substation is typically implemented with a sophisticated combination of smart primary high-voltage equipment and hierarchically networked secondary devices. Based on the IEC61850 communication protocol, the functionalities, such as the information sharing and interoperability among smart electric equipment, are realized in smart substations. It is regarded as the basis for the development of smart grid and represents the future development trend of substation technologies. This paper reviews the fundamental vision of the smart substation. The state of the art and the challenges encountered in the practice of engineering implementation are presented. Future developments to solve the present challenges and promote the development of smart substations are also described. [ABSTRACT FROM PUBLISHER]

With the development of modern power systems, the overvoltage protection and high current fast bypass of important electric equipment or parts in EHV grids put forward a great demand for high reliable fast bypass techniques. The triggered spark gaps now used in H.V. grids are still confronted with many difficulties. This paper proposes a conceptual design of a new multi-gap spark switch connected with a frequency-dependent network. The device is composed of series gaps and a chain RC network for producing frequency-dependent voltage distribution along the gaps. An even voltage distribution under power frequency operating voltage while an extremely uneven voltage distribution under trigger impulse can be achieved by proper parameter setting. The even voltage distribution enables the multi-gap spark switch to withstand much higher voltage than that in operation, thus avoiding false firing. On the contrary, extremely uneven voltage distribution could initiate cascade discharge at low amplitude impulse, insuring reliable triggering. The working principle of the new multi-gap spark switch differs considerably from that of the current spark gaps in H.V. and pulsed power systems. It has high reliability and no dead zone of trigger control, which can be sufficiently used as a high speed bypass switch for overvoltage protection applications in EHV grids. The conceptual design of the multi-spark gap switch, simulation of the frequencydependent voltage distribution, cascade discharge of the spark gaps as well as the experimental performance verification on the prototype are presented in this paper. [ABSTRACT FROM PUBLISHER]

Various techniques of fault diagnostics in oil-filled electrical equipment have been used in many years and are well documented in literature. The common techniques include; IEEE key gas, IEC 60599 gas ratios, Rodgers ratios, Doernenburg ratios and the Duval triangle. Among all the available techniques, Duval triangle remains the most accurate to date. This paper presents a new fault diagnostic method which combines fuzzy trapezoidal membership functions derived empirically after analyzing faults documented in literature and the evidential reasoning techniques. Like in Duval triangle, three gases; methane, acetylene and ethylene are used. First these gases are normalized against their sum. The normalized values are transformed into fuzzy trapezoidal membership functions whose outcome are synthesized into a particular fault type by the evidential reasoning technique. One hundred and seventeen fault cases visually inspected by experts and documented in IEC TC 10 databases are used for verification. This new technique is easy to understand, uses simple standard mathematical expressions and can easily identify simultaneous faults. Unlike Duval triangle where two or more faults lying at the same spot are not easily recognizable, the new technique identifies faults based on numerical values hence it does not have this drawback. [ABSTRACT FROM AUTHOR]

In high-speed aircraft, an altitude adjustment system is an important auxiliary part that needs rapid power support. In this paper, an ultrahigh-speed generator is described. However, the ultrahigh-speed generator's safe operation and smooth power supply to the load can be threatened by mismatch between the open-loop generator and fickle load conditions. In this study, a power converter with a paralleled energy-matching link was developed, which can broaden the safe operation zone and ensure the generator's safe operation as well as the load's smooth power supply under relatively light-load conditions. This power converter can also ensure the power supply voltage under relatively heavy-load conditions. The validity of the proposed power converter was verified by experiments. [ABSTRACT FROM AUTHOR]

Magnetic shape memory (MSM) alloys are relatively new smart alloys, which have enormous potential to be used in actuators, sensors, and other electrical devices. Their large strain and considerable stress output can be controlled by magnetic fields or mechanical stresses. Maximum magnetic field-induced strain varies from 6% to 12% of the MSM element’s length depending on its microstructure. However, very low operational temperature limit is one of the main drawbacks of conventional MSM alloys. This makes their application in high-performance actuators challenging due to considerable power losses. This paper discusses different MSM actuator designs, optimized particularly for large force output for pneumatic electromagnetic valve applications. The thermal problem is addressed through analyzing the heat transfer conditions of each particular design and the effects of different cooling systems. An energy-efficient operating cycle for varying actuator loads that takes advantage of the shape memory effect is also proposed. This allows the minimization of energy losses, resulting in an acceptable increase in the temperature ensuring stable continuous actuation. [ABSTRACT FROM AUTHOR]

A novel apparatus based on variable inductors to control the insertion compensating voltage of the transmission line is proposed in this paper. The apparatus can change the alternative voltage into the desired alternative voltage directly by using the control strategy proposed in this paper and insert the voltage into the line. Since the amplitude and the phase angle of the voltage supplied by the apparatus can be adjusted continuously and independently, the apparatus can control the real- and reactive- power flow independently and realize the direct voltage regulation (DVR) and the phase angle regulation (PAR) of the transmission line. The control methods suited for the proposed apparatus about the independent control of real and reactive power flow in the transmission line and the DVR and the PAR are also proposed. The control strategy and methods are verified with experimental results and simulation results. [ABSTRACT FROM PUBLISHER]

This paper presents the models of three new-generation high-performance samples of ITER full-size Nb3Sn Cable-in-Conduit conductors (CICCs). These samples were recently tested in SULTAN, at CRPP (Switzerland), and demonstrated the technical feasibility of CICCs that satisfy the ITER specifications. The improvements of these samples regard not only the cable strand and the cabling parameters, but also the manufacturing details of their SULTAN samples. A set of changes have been adopted on the SULTAN sample termination and joint, to try to achieve a more uniform current distribution among the strands and a more accurate measurement of the strand longitudinal voltages. This paper presents a comparative numerical analysis of the effects that these different joint technologies have on the DC current distribution among the strands of the SULTAN samples cable. A correlation between the current distribution in the sample and the resistance distribution at the joint is also shown and discussed. [ABSTRACT FROM AUTHOR]

This paper presents investigations of voltage-sharing stabilization with the use of passive RLC circuit in switch-mode flying capacitor dc-dc converters. Practical and simulation results and also a mathematical analysis of the balancing process in boost and buck-boost converters are presented. Analyzed converters use additional capacitors (flying capacitors), charged to proper value, for decreasing the voltage on switches and increasing the inductor-current frequency. Such advantages are achieved under proper voltage sharing on the flying capacitors. The voltages are stabilized in a natural way by the load current and with the use of external RLC circuit to force the current that flows through the converters' capacitors under unbalance state. This paper focuses on the analysis of the balancing phenomenon with the use of the external RLC circuit in these topologies. The balancing booster improves the balancing process in these converters, making it independent of the load. It can also reduce oscillations that arise in the converters in transient states. [ABSTRACT FROM AUTHOR]

This paper presents the technology for fast code synchronization or reprogramming method during the testing and debugging phases in the development of consumer devices. The increasing number of features in cellular phones, car navigation systems, and other consumer devices has made it difficult to release bug-free devices. Software for these types of consumer devices has to be developed and tested using a cross-platform simulator. However, many cases have to be considered while using the target devices during testing, making several debugging phases and software update releases inevitable. These processes have to be performed iteratively. Therefore, the time required for the binary code to download to the target devices should be small. In this paper, we propose a fast synchronization or reprogramming algorithm for these types of consumer devices. [ABSTRACT FROM AUTHOR]