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This paper analyzed the flux characteristics of a single-phase tubular switched reluctance linear motor (TSRLM) based on magnetic equivalent circuit (MEC) method. The single-phase TSRLM is divided into five different parts, which are the teeth of the stator, the yoke of the stator, air gap, the teeth of the mover, and the yoke of the mover. The reluctance of every part is expressed in analytical formulas at five special mover positions. The flux linkages at five special mover positions are calculated by magnet tube method and Gauss–Seidel iteration method which takes the saturation into consideration. A high-order Fourier series method is used to map the nonlinear relationship between flux linkage, current, and mover position with the flux linkage data calculated by the MEC method. The calculated flux linkage is consistent with 3-D finite-element method and experimental results. The dynamic and static performance of the simulation utilized with MEC method is consistent with those in experiments, which verifies the accuracy of the MEC method proposed in this paper. [ABSTRACT FROM AUTHOR]

Pulsed alternator (PA) is a kind of high-power pulsed supplies widely applied in the field of electromagnetic (EM) launch. Over the past decades, the self-excited air-core PA is widely studied, but it has the disadvantages of poor heat transfer and high electric field loss. The hybrid excitation PA combined with the advantages of electric excitation and permanent magnet excitation PA, and the output voltage of armature winding can be adjusted by the electric field current. This paper presents double-electric-excitation hybrid excitation compensated PA (DEE-HECPA). In order to improve the adjustable performance for the output voltage of HECPA, the rotor structure is changed and double excitation coils are used in PA. In this paper, the equivalent magnetic circuit model for hybrid excitation region is established and the air-gap flux density is calculated. The dimensional parameters are calculated by the special EM design method for PA, the characteristics of electric excitation are verified by finite-element analysis, and the characteristics of output current for DEE-HECPA are analyzed. The research results demonstrate that DEE-HECPA is a feasible topology for PA. [ABSTRACT FROM AUTHOR]

DC arc evolution is a complicated and rapid time-dependent process. To better demonstrate the mechanism of the dc arc without external interference factors, a test circuit was built for the entire process of arc generation, maintenance, and extinction. Two different adjustment models were adopted. The macroscopic performance and characteristics of the arc were analyzed. The discharging and extinguishing conditions were measured and compared to the results of a burning candle located under a rod–rod air gap. This paper shows that the dc arc’s color changes from blue to purple and then yellow, finally forming a flame as the current increases. The macroscopic performance can be divided into eight periods in the first adjustment model, while only three periods are included in the second model. The arc discharging condition only depends on the applied high voltage, but the extinguishing condition may depend on either the limiting current or the drop-down voltage. Dynamic volt–ampere characteristics appear only if adjusted by the first model. The arc-root voltage is constant to 0.32 kV. The degradation of the ground electrode is far worse than that of the high-voltage electrode. This paper can be regarded as the first-step research for further studies on large-current dc arcs in arcing horns used in dc transmission grounding lines. [ABSTRACT FROM AUTHOR]

Homopolar inductor alternator (HIA) with rectifier and capacitive loads is a promising choice for pulsed power supply. The solid-iron rotor of HIA can rotate at a very high speed, but this causes serious eddy-current loss in the rotor and results in local overheating on rotor face. In this paper, the analytical method was used to calculate the rotor eddy-current loss for HIA with rectifier and capacitive loads, and the effect of eddy-current shielding on the rotor eddy-current loss was also discussed. The analytical results are coincided with the results simulated by a simplified 2-D field-circuit coupled simulation. This paper shows that in order to reduce the rotor eddy-current loss, the air-gap length and the pole number should be as large as possible and the windings should be distributed and short-pitch. Meanwhile, an important conclusion is that the eddy-current shielding cannot decrease the eddy-current loss for HIA with rectifier and capacitive loads; on the contrary, it increases the eddy-current loss, compared to the case with the rectifier and resistive load. [ABSTRACT FROM AUTHOR]

The pulsed high-power supplies in this paper employs a homopolar inductor alternator (HIA) as the motor/generator integrated energy storage pulsed alternator. Lumped parameter design equations are developed, which is used to establish the mathematical model of the HIA, and the analytic calculation method of inductance matrix is derived. Prototype flywheel energy storage was built, and the basic structure of HIA is analyzed by using finite-element method (FEM). This paper proposes a simplified equivalent 2-D salient-pole synchronous generator model to simplify the 3-D FEM of HIA and investigates the motor control method of HIA based on the simplified 2-D equivalent model. The experiments were conducted for speed up to 8000 rpm and the six-step inverter drive strategy presented in this paper achieves the motor/generator integrated control on inductor energy storage pulsed alternator (IESPA). Most experimental results were in line with designed value. [ABSTRACT FROM PUBLISHER]

In previous studies, the field winding of the brushless pulsed alternator (BPA) is embedded in the stator slots, which is supplied by dc power or variable frequency power. The advantage is that the field current can be independently adjusted. It means that the BPA system needs a standalone excitation system, which will increase the volume and cost of the system. If we substitute electric excitation for permanent magnet excitation, not only the volume and cost of the BPA system can be decreased but the efficiency and flexibility can be enhanced. In this paper, the design schemes for electric excitation and permanent magnet excitation BPA are presented. For comparison, the stator and rotor dimensions of the two kinds of BPA are both the same. The characteristics of electric excitation and permanent magnet excitation BPA are analyzed by the finite-element method and field-circuit coupling method. Finally, the BPA systems with a resistive load are established, the performances of both the two excitation modes are compared. According to the simulation results, we conclude their advantages and disadvantages. [ABSTRACT FROM AUTHOR]

Linear permanent-magnet brushless dc motor (LPMBLDCM) has the advantages of high flux density, high energy efficiency, simple structure, and other characteristics, which are suitable for high speed and high thrust applications. It is also used as an electromagnetic catapult to be applied to small- and medium-sized aircraft launches. This paper focuses on the influence of magnetic structure on electromagnetic and dynamic performance of a moving magnet type LPMBLDCM. Three magnetic structure candidates are presented, including the serial magnetic structure, parallel magnetic structure, and the Halbach magnetic structure. The dynamic process of LPMBLDCM is analyzed by a Maxwell-2-D transient solver for each magnetic structure. The influences of magnetic structure on the air-gap flux density, on the back electromotive force, and on the mover velocity and thrust output are analyzed. The electromagnetic characteristics and dynamic performance for three magnetic structure LPMBLDCMs are contrasted. This paper follows previous works in which some relevant experiments were also executed. Simulated and measured results can provide useful references to optimized design and prototype matching for an electromagnetic catapult. [ABSTRACT FROM PUBLISHER]

To understand the flashover of roof insulators in high-speed airflows, the breakdown characteristics and mechanisms of a short needle–plate air gap are investigated. An interesting and important phenomenon is found based on an artificial wind tunnel: the breakdown voltage first increases and then decreases. An experiential formula is established to describe the relationship among the airflow velocity, gap distance, and breakdown voltage. A good consistency with the experimental results is obtained. Furthermore, the breakdown mechanisms of the air gap in high-speed airflows are proposed, and the phenomenon is explained and verified according to the theories of gas discharge and fluid dynamics. The airflow blowing effect, which includes the deflection effect and blown away effect, and the airflow density effect are proposed as two dominant factors that affect the breakdown process of the air gap in high-speed airflows. The variation trend of the breakdown voltage with the airflow velocity is predicted. Two extreme points are expected during the variation process; i.e., the breakdown voltage has a maximum and a minimum, to which more attention should be paid. This paper is helpful for the safety operation of roof insulators on the high-speed train. [ABSTRACT FROM PUBLISHER]

Pulsed alternators have the merits of high energy and power densities, which are applied to a wide range of applications, such as the electromagnetic launch, the pulsed laser, and the pulsed high magnetic field. A new type of high-speed and high-frequency pulsed alternator integrating an alternator and a motor, is proposed in this paper. A solid rotor which is made of high-strength alloy steel with high yield strength is used in the pulsed alternator, so it can work at a high tip speed. This machine consists of two alternators and a motor which share one rotor and one field winding. According to different voltage levels and operation frequencies, the motor and the alternators with different stack lengths and pole-pairs are designed, respectively. Therefore, it has the abilities of being driven by low-frequency current and discharging high-frequency pulses. In this paper, the basic structure and fundamental of the pulsed alternator are introduced, the specific parameters of the prototype are given, and the performances are verified by the simulation. The results show that the machine proposed in this paper is suitable for the applications that require high-frequency pulsed discharge. [ABSTRACT FROM PUBLISHER]

Due to the ironless structure of the toroidal winding in the tubular linear voice coil motor (TLVCM), the winding thickness is one of the critical parameters that have an impact on air-gap flux density, and hence affects the copper loss at rated thrust. This paper investigates and determines the thickness of the ironless toroidal winding of the TLVCM for the purpose of a minimum copper loss. Magnetic equivalent circuit (MEC) method is used to analyze the air-gap flux density with respect to winding thickness, and the corresponding copper loss at the rated thrust is assessed by considering the slot fill factor. The optimal solution is obtained according to the U-shaped curve of the copper loss. Moreover, the finite-element analysis is combined to validate the results of MEC method, and a good agreement is reached. Two prototypes of TLVCMs having similar slot fill factor are made, one of which is with the optimal winding thickness. The expected current at the rated thrust is obtained by a test platform of static thrust, so as to obtain the corresponding copper loss for each prototype. The experimental results show that the TLVCM with optimal winding thickness features a lower copper loss. Hence, the attempt to minimize the copper loss by designing the thickness of the ironless winding is highly effective. [ABSTRACT FROM AUTHOR]

In this paper, the direct-axis ( $d$ -axis) and quadrature-axis ( $q$ -axis) synchronous reactances of homopolar inductor alternator (HIA) are calculated. First, an approximate 2-D model of HIA is developed and its relative air-gap permeance function is described. Then, the analytical expressions for the synchronous reactances in the $d$ -axis and $q$ -axis are derived from magnetomotive force-relative air-gap permeance function theory, including armature reaction reactance and armature leakage reactance. Finally, theoretical results are compared with the simulation and experimental results. [ABSTRACT FROM PUBLISHER]

The armature is usually partly in contact with rails, and in the noncontact portion, narrow air gap exists. It is difficult to simulate such narrow air gaps in the calculation of electromagnetic fields by the ordinary finite-element method (FEM), due to the difficulty of mesh generation inside and around the gap. A novel approach is presented to simulate the gap in this paper, in which the domain of air gap is not built and the conductors (the armature and rail) are made in contact geometrically but not electrically, so that the mesh generation difficulty can be avoided. The noncontact electrically means that with the A – $V$ algorithm of electromagnetic field, the electric potential variable $V$ on both sides of the interface between the conductors is made unrelated or discontinuous to achieve the effect that the current cannot go through the interface, while the magnetic vector potential variable $A$ is continuous on the interface, so that the magnetic field is normal or can go through the interface normally. By this novel approach, the air-gap effect can be reflected in the absence of the gap geometrical model, which can offset the defect of the ordinary FEM in the simulation of narrow air gaps. The presented approach is actually an improved FEM with A –V algorithm. [ABSTRACT FROM PUBLISHER]

This paper discusses the modeling of a peaking switch to study the reduction in rise time for the subnanosecond duration pulses. The effect of the various shapes of input pulse, inductance, and interelectrode distance on the output voltage and wave shape is discussed in this paper. The modeling has been carried out using the electromagnetic and microwave modeling software of Computer Simulation Technology. [ABSTRACT FROM PUBLISHER]

This paper describes a tubular linear motor with special permanent magnet. Then, two kinds of permanent magnet magnetization directions for this motor are proposed, and the air-gap magnetic field is calculated and researched based on a finite-element method. Moreover, the magnetic field of the slotless tubular linear motor is contrasted with that of the traditional interior axially magnetized permanent magnet tubular linear motors. Finally, the advantages of the motor are analyzed and pointed out. [ABSTRACT FROM AUTHOR]

In this paper, complex Poynting theorem is used to calculate the power transmitted from primary to other areas of single-sided linear induction motor. By the help of Poynting theorem and boundary conditions, the longitudinal end effect is completely included into the analysis. Having comprehensive information about power flow and using the coenergy method, it is possible to calculate traction and normal forces due to each existing wave. So, it is shown that each of the traction and normal forces consists of five components. Then, the effect of some important design parameters on the calculated components of forces is analyzed. Results by the proposed model have been compared with those evaluated by finite-element method and with experimental measurements. [ABSTRACT FROM PUBLISHER]

The compensated pulsed alternators (CPAs) have good applications in high-energy lasers, electromagnetic rail guns, and other electromagnetic launch devices. Among various electrical machine topologies, homopolar inductor alternators (HIAs) have attracted interest as CPAs due to their merits of simple and reliable structure, brushless excitation, and high-speed operation. However, the length of the conventional HIA is difficult to expand because it is limited by the rotor diameter, and the rotor diameter is restricted by the maximum speed of rotor tip, which results in low-energy storage capacity of a single machine. Besides, HIA suffers from the relatively low-power density due to its unipolar air-gap flux density (UAFD). To solve these problems, two novel HIAs with multistage stator cores (HIA-MSCs) are proposed in this paper. One is HIA with UAFD (HIA-UAFD) and the other is HIA with unipolar and bipolar air-gap flux density (HIA-UBAFD). First, the structure and operation principle of HIA-MSCs are illustrated. Then, the key parameters of HIA-MSCs are derived, and the corresponding models are built. Finally, the electromagnetic performances of HIA-MSCs are investigated by 3-D finite-element analysis method. Compared with HIA-UAFD, HIA-UBAFD has relatively higher discharge current and output power, which indicates that HIA-UBAFD is a better candidate for the pulsed alternator. [ABSTRACT FROM AUTHOR]

In this paper, the effect of the corona space charge on the leader initiation is experimentally and theoretically investigated. The critical corona charge for the stem–leader transition is reviewed and a more proper charge criterion is recommended based on the experimental measurements and theoretical analysis. It is shown that the chocking effect of the corona space charge for the second corona inception should not be ignored, which decreases the electric field strength of the stem tip and hinders the initiation of the leader. A simple physical model is proposed to calculate the leader initiation time, which can consider the thermodynamic mechanism for stem–leader transition and the chocking effect of the corona space charge, and a good agreement with the experimental results was obtained. [ABSTRACT FROM PUBLISHER]

In this paper, the variation of the development of positive first corona space charge in long air gaps is investigated. A 1-m rod-plane air gap under different rising rates dU/dt of impulse voltages is reported. The current signals and still photographs are recorded during the first corona development. The relationship between the first corona charge Qi and the inception voltage Ui is presented. The physical mechanism of the influence of the first corona is provided. With the experiments and the single branch propagation model, a semi-empirical calcultion method for positive first corona charge under impulse in long air gaps is obtained through the calculation of the number of branches Nb. Using this method, the variations between Qi and Ui for different dU/dt and electric field distributions are calculated and compared with the reported experimental results. Reasonable agreement between the calculated and experimental results is obtained. It shows that this calculation method is suitable for predicting the positive first corona charge Qi and the discharge current at a given dU/dt and Ui. [ABSTRACT FROM PUBLISHER]

In this paper, a stair-step-shaped magnetic pole structure is proposed to use in a permanent-magnet linear synchronous motor (PMLSM) for its application in an electromagnetic launch system. The aim of this configuration is to shape the air-gap flux density distribution produced by poles to be as close to a sine waveform as possible for the reduction of thrust ripple and the increase of motor controllability. An analytical model is derived for the PMLSMs by solving Maxwell equations and applying the superposition theorem for calculating the magnetic field, electromotive force, and thrust/torque of the motor. Magnet dimensions are then optimized using the analytical method and genetic algorithm, where the reduction of air-gap flux density harmonics is considered as the optimization target. Finally, the effectiveness of the proposed technique to enhance the motor performance is investigated by a time-stepping transient finite-element method. The results show an improvement in the optimal motor performance. [ABSTRACT FROM PUBLISHER]

Homopolar inductor alternator (HIA) has been widely used as a high-speed pulsed alternator in the electromagnetic launch field due to its merits of high-speed operation, power density, and reliability. To achieve the above-mentioned merits, a high-strength and high-stiffness solid rotor is usually adopted in the HIA. However, the solid rotor would be subject to high eddy current loss. Some works have been done to analyze the rotor eddy current of the HIA, while the research on analytic calculation and reduction of rotor eddy current loss is relatively few. In this paper, an analytic calculation method is established to calculate no-load rotor eddy current loss for HIA, which is validated by the finite-element analysis and corresponding experiments. Besides, to minimize the rotor eddy current loss, a simple method, by slitting the rotor tooth, is proposed. Moreover, the influence of circumferential and axial slits on the rotor eddy current loss and air friction loss is comparatively studied. Finally, the influence of the width, depth, and number of slits on the eddy current loss is investigated. It is shown that the circumferential slits have better performance than that of axial slits to reduce the eddy current loss. [ABSTRACT FROM PUBLISHER]

This paper investigates a homopolar inductor machine (HIM) for flywheel energy storage in electromagnetic launch applications. An equivalent 2-D finite-element model is presented to predict the machine behavior, and the effectiveness of the equivalence is validated by the comparison of 2-D and 3-D results. Based on the 2-D model, the rotor tooth shape is then optimized to achieve high fundamental value of the air-gap flux density for a given rotor diameter. It is shown that the proposed 3-D to 2-D equivalence can predict the performance of the HIM in an accurate and fast way, which is quite valuable in the design stage of a HIM. [ABSTRACT FROM PUBLISHER]

The length of the air gap in a negative corona discharge, which affects many corresponding parameters in the discharge process, is of vital importance for the physical investigations. A hydrodynamic drift–diffusion approximation model considering photoionization utilizing the finite-element method has been used in needle-to-plane air gaps. Trichel pulses, pulse frequency, electron, and electric field distribution, and surface current density distribution on the anode plate were presented to study the effect of the gap length. An approximate exponential relationship was found to exist between the corona current and the gap length, and also a linear function was found between the pulse frequency and the gap length. The analysis shows that the characteristics of the Trichel pulse are strongly dominated by the length of the air gap. [ABSTRACT FROM AUTHOR]

Different types of lightning protection systems (LPSs) have been developed for wind turbines to protect the blades from lightning strikes. However, severe damages caused by lightning strikes still happen frequently, which creates huge costs. Experiments using a 5-m blade specimen with tip receptors from 1.5-MW wind turbine blades under 3-m air gap were conducted to investigate the lightning attachment manner to the wind turbine blade with LPS in different situations. Factors including the polarity of the lightning strikes, the orientation of the blade, and the lateral distances (LDs) between the wind turbine blade and the lightning downward leader were taken into account. It was found that the types of discharge paths under positive and negative lightning strikes are quite different, and the positive discharges are much more dangerous to wind turbine blade than the negative ones. The LD between the downward leader and the wind turbine blade is a key factor that influences the interception efficiency. Three types of receptor interception failures were discovered. Multiple upward leaders may incept from the blade body as to intercept the downward leader. However, the protection range of the tip receptor is quite limited, and the connection of the tip receptor and the blade body is the most vulnerable position hit by the lightning strikes. The results present the useful reference to the optimal design of the wind turbine blade LPS. [ABSTRACT FROM AUTHOR]

The permanent-magnet (PM) synchronous motor (PMSM) takes advantages of small capacity, high efficiency, and high power density and have become commonplace in electric-vehicle driving systems. However, the excitation of PMSM cannot be adjusted, which restrains the PMSM from widening the speed range above its base speed. A PMSM with a variable magnetic reluctance field adjustment is presented in this paper. A new structure of the rotor is introduced, and flux-weakening (FW) principle is formulated. Analysis is discussed, including the force on the main PM, the movement process of the PM in the PM slot, the characteristics of the movement of the PM, and the FW performance of the new PMSM used for electric vehicles. The emulation analysis coincides with the test result, which verifies the availability and feasibility of the FW method for this kind of PMSM used for electric vehicles. [ABSTRACT FROM PUBLISHER]

The asynchronous induction linear motor (AILM) is the key part in the asynchronous induction coil launcher, and a multisegment primary block feeding AILM is investigated in this paper. The phase unbalance characteristics of a traditional linear motor could be ignored when the poles are six or more; however, due to the existence of long unexcited primary between the entry and exit end of AILM with multisegment primary, the static longitudinal end effect is significantly different compared with a traditional linear motor. Through many experiments, a phenomenon has been found that the AILM had unbalanced mutual inductances, where Lac = Lbc = kLab, and the scale of k is from 1.57 to 6.25, which depends on the length of the unexcited primary. Under balanced terminal voltage conditions, the phase current shows serious unbalance in the prototype machine. It may bring much difficulty to the control system. Based on the unbalanced phenomenon and discipline of mutual inductances, the unbalance mechanism is analyzed by electromagnetic field theory and Ansoft software. The influence of the thrust, yoke field, and parameters because of this kind of unbalance is presented. The experimental results show a good agreement with the theory analysis. It provides a new way for the design and implementation of this kind of machine in the future. [ABSTRACT FROM AUTHOR]

New geometrical counterparts to the conventional Einzel lens, cubic, and the continuous body electrostatic (CBE) lenses are introduced and their performances are investigated in terms of different aberrations and input beam properties. Design curves for the continuous body electrostatic lens are presented. Relative sensitivity is proposed as a figure of merit, based on which the focusing characteristics of the two new lenses are compared with that of a conventional Einzel, and a quadrupole lenses of the same size, as well. Moreover, performance and characteristics of the lenses are compared in terms of their corresponding sensitivities to the applied voltage and the incidence beam nonidealities. Electric field distributions of the lenses are studied, and different aberrations are discussed. It is shown that considering chromatic nonparaxial beams, the CBE lens outperforms the conventional Einzel lens in terms of the sensitivity and the absolute value of the lens demagnification. [ABSTRACT FROM AUTHOR]

The simulation of typical air-gap discharge process is of great significance to the long air-gap discharge mechanism and UHV transmission project design. A positive fractal dynamic streamer discharge model of a rod-plane air gap was established. On the basis of the original fractal streamer model, this new model proposed an electric field calculation method based on a dynamic boundary condition, as well as a new calculation method of the time parameters based on the charge accumulation process. In the model, the electric field and the development time of the discharge step were obtained by solving the electric field distribution and charge accumulation equations. The processes of streamer starting, streamer development, charge accumulation, and discharge extinguishing were all contained in the model. Discharge process of various voltage amplitudes (235 and 595 kV), the waves of which were lighting impulses (2/50 \mu \texts ), was simulated by this model in the 1-m rod-plane air gap. As shown in the results, for a gap under 235 kV, the length of the streamer is 200 mm, the streamer development time is 5.02~\mu \texts , the velocity is $3.98 \times 10^{{\mathrm {4}}} m/s, and the total charge accumulation in the streamer channel is 23.2 \mu \textC , while for a gap under 595 kV, the gap is broken down, and the streamer development time is 9.92~\mu \texts , its velocity is $1.01 \times 10^{{\mathrm {4}}}$ m/s, increasing to $1.60 \times 10^{{\mathrm {5}}}$ m/s before discharge, and the total charge accumulation is 258.3~\mu \text{C} . The model matched the test results well in the dynamic processes of the length of discharge channels, the electric field waveform, and charge accumulation. This model is meaningful to research into long air-gap streamer discharge mechanisms and leader discharge processes. [ABSTRACT FROM AUTHOR]

A $\pi $ model of equivalent circuit has been proposed for single-sided linear induction motors, whose parameters have been obtained using the 1-D field analysis method and the complex Poynting theorem. The longitudinal end effect (LEE), transverse edge effect, saturation effect in secondary back iron, and half-filled primary slots are included in the suggested method. The LEE is considered, completely, with the help of the Poynting theorem and new boundary conditions. The well-known iterative method is modified to improve the calculation accuracy of saturation factor, K_{s} , the permeability of back iron, and the equivalent secondary resistance. The effect of half-filled primary slots is also included by the modification of the effective motor length and the primary equivalent current sheet. The simulation results are evaluated by the finite-element method and experimental measurements. [ABSTRACT FROM PUBLISHER]

Research on the attachment processes in competition tests can provide insights into the influencing factors involved in the selection process that determines the lightning strike point. In this paper, a series of competition tests with a rod–rod gap configuration are designed and carried out. The test results indicate that the strike mechanism is decided by two discharge processes, namely the free development of the downward-propagating discharge and the interception process of the upward and downward discharges. If the first process prevails, the strike probabilities for different grounded rods will tend to be equal. For the second process, the strike probabilities reflect the different performances of the grounded rods for intercepting downward discharges. As the scale of the discharge gap increases, the development of the downward leader becomes more and more dominant in selecting the strike point. In natural lightning strikes, the scale of the downward leader is normally more than 90% of the discharge gap, hence the protective effect of lightning rods with different tips will not be significant for low rod heights and small lightning currents. To reflect the effect of the downward leader development on the choice of the strike point, a minimum discharge air gap of 10 m is suggested. [ABSTRACT FROM PUBLISHER]

Magnetic flux distributions of the permanent magnet (PM) section and the homopolar induction (HI) section in a hybrid excitation synchronous generator (HESG) are calculated by using the finite element method (FEM). The influences of the axial-length ratio of the two sections on the back EMF, inductance, and terminal characteristics of the PM section, the HI section, and the HESG are analyzed. The prototype experiments have verified the validity of the calculation and analysis processes. The studies on the HI section have shown the following: 1) The operating air-gap flux distribution along the axial direction is uneven; 2) there is an approximate linear relationship between the radial component average of the operating air-gap flux density and the axial length; 3) a quadratic relationship between the back EMF and the axial length exists; and 4) it is necessary to compute and optimize the axial-length ratio of the PM section and HI section to increase the output voltage and improve the terminal characteristics of the HESG. [ABSTRACT FROM AUTHOR]

Icicles on the ice-covered insulator string will shorten the air gap between the adjacent sheds of the insulator and make the discharge propagate along the air gap easier. The processes and the leakage current waveforms of the discharge propagation along the air gap are recorded and investigated under two different experimental conditions. The common and different discharge phenomena are shown and compared. [ABSTRACT FROM AUTHOR]

The prebreakdown phases of a barrier discharge in a short gap in atmospheric-pressure air are investigated by numerical modeling. A highly nonhomogeneous electric field caused by residual charges deposited on the dielectric surfaces is taken into account. The simulation results of barrier discharge radiation are compared with experimental data. [ABSTRACT FROM AUTHOR]