To address the issue of the current distribution network's difficulty in accurately and quickly detecting single-phase high-impedance grounding fault (HIF) in lines, a method for detecting HIF in Resonant Grounding Systems based on the polarity difference of transient zero-sequence currents is proposed. By representing the nonlinear arcing high impedance through a segmented linear equivalent of the voltage-current characteristic curve during HIF, an analysis of the fault characteristics is conducted. Based on this, it is determined that the transient components of the faulty feeder and the healthy feeder have opposite polarities during a HIF. Subsequently, each feeder's zero-sequence current is subjected to low-pass filtering within the characteristic frequency band. The first extremum point is assigned a value, and an extremum point matrix is established. Finally, HIF detection is achieved through polarity characteristics.

In order to improve the processing ability of single-phase grounding faults in distribution network cable lines, a method of defining cable and overhead line faults using the size of transition resistance is proposed based on the characteristic of low resistance faults in cable lines. The calculation expression of transition resistance used in conjunction with phase-controlled pre-coordinated arc suppression coil is derived. The transition resistance measurement method is verified by digital simulation, and the relationship between damping rate, out-of-resonance, capacitance current and capacitor current observation error and transition resistance measurement error is analyzed in detail. Finally, the transition resistance measurement method was validated through real type experiments, and the results showed that this method can effectively distinguish between high resistance faults and low resistance faults, that is, cable faults and overhead line faults.

The paper addresses the mathematical description problem of nonlinearity and characteristic differentiation in the breakdown of high-impedance fault (HIF) media. It proposes an improved Mayr arc model. Firstly, the physical process of the arc at the fault point and the nonlinear characteristic changes of the arc under high-resistance fault were studied. By analyzing the main characteristic dimensions of the nonlinear resistance, the transferability of model parameters, controllability of nonlinear characteristics, and simulation accuracy were improved. Finally, by comparing the existing high-resistance fault models, the controllability and accuracy of the proposed model were verified. In practice, due to significant differences in fault current waveforms under different grounding media in HIF, traditional detection algorithms often lack adaptability. The improved arc model can accurately depict the arc current waveforms under various working conditions, greatly expanding the applicability of subsequent detection algorithms. This lays a foundation for the accurate detection of HIF.

The penetration of microporous layers (MPL) into gas diffusion layers (GDL) is a common phenomenon in proton exchange membrane (PEM) fuel cells. However, research on this phenomenon is few and its influence law and mechanism need to be further investigated. In this study, a three-dimensional, multiphase and non-isothermal fuel cell model is established to investigate the effects of penetration ratio, total thickness of GDL and transition region (TR) and operating pressure on fuel cells' mass transport and performance. The results show that, under high output voltage, performance increases as the increase of penetration ratio. Under low output voltage, 15% penetration ratio achieves the best fuel cell performance. In addition, 15% penetration ratio attains the lowest average membrane electrode assembly ohmic resistance, GDL and TR thicknesses and operating pressures. The existence of TR changes the liquid distribution; saturation decreases from the GDL side to the MPL side. Moreover, the penetration affects the membrane water content, and its distribution becomes more non-uniform as penetration ratio increases.

Fuel cell is one of the main powers of new energy vehicles. In the fuel cell, bipolar plate is an important component for its normal operation, which plays a variety of roles, such as distributing reaction gas, collecting current, draining water, conducting heat and supporting machinery. Its flow field structure determines the proportion of reaction area, the uniformity of reaction gas distribution, etc., and significantly affects many important parameters such as fuel cell power, current density distribution in the range of electrode plates, voltage consistency between electrode plates, etc., thus determining the working performance index and service life of fuel cell, which is an important content of fuel cell structure design. at present, the hydrogen fuel cell technology is in the initial stage, and there are some problems, such as uneven distribution of reaction gas in the whole system, low conversion rate of hydrogen and electricity, and high production cost, especially the low reaction effect of bipolar plate flow field and the utilization rate of membrane electrode, which seriously affect the popularization of fuel cells.

Corona discharge characteristics are measured in a corona cage. The difference is found between the q–u curves under double exponential and damped oscillation surges. The behavior of the minor loops is revealed for the q–u curves under positive and negative damped oscillation surges. An extended improvement is made on the traditional approach for modeling of the q–u curves under damped oscillation surges. The extended approach has the capability of describing the complicated trajectory feature of the minor loops. On the basis of the extended approach, an efficient method is proposed for performing lightning surge analysis of overhead lines considering the corona effect. In the proposed method, an overhead line with corona is divided into a certain number of line segments. Each segment is converted into a circuit unit consisting of a non-linear branch and a linear circuit. With these circuit units connected in sequence, a complete equivalent circuit is constructed for the overhead line with corona. The transient responses can be obtained from the solution to the equivalent circuit. Then, the calculated results are compared with the field test results on a test overhead line.

An algorithm is proposed in this paper for calculating the impulse earthing resistances of vertical earthing electrodes. The proposed algorithm employs the average potential method to derive the formula of the low current earthing resistance. Unlike the previous algorithm, the soil ionization effect under high impulse current is taken into account by introducing a nonlinear characteristic to represent the relationship between the electric field and current density in the ionization zone around the earthing electrode. On the basis of the nonlinear characteristic, the effective radius is evaluated for the equivalent earthing electrode. Then, the impulse earthing resistance can be calculated by substituting the effective radius into the formula of the low current earthing resistance. A comparison is also made between calculated and measured results to confirm the validity of the proposed algorithm. Keywords: Earthing Resistance; Vertical Earthing Electrode; Average Potential Integral; Soil Ionization; Current Density;

接地电阻是表征风电机组接地装置性能的一个重要指标.笔者建议了一种计算风电机组接地电阻的有效计算方法,即模拟电流算法.该算法将机组接地装置中各接地体分段离散化,分别在各接地体和不均匀土壤分界面两侧设置模拟电流,从恒定电场的边界条件入手,建立模拟电流所满足的方程组,求取模拟电流,再由模拟电流来确定接地电阻.将按该算法得到的接地电阻值分别与实测值和专业软件CDEGS计算值进行了对比,以校验该算法的可行性.

An effective method is proposed in this paper for calculating the transient magnetic field and induced voltage in the photovoltaic bracket system under lightning stroke. Considering the need for the lightning current responses on various branches of the photovoltaic bracket system, a brief outline is given to the equivalent circuit model of the photovoltaic bracket system. The analytic formulas of the transient magnetic field are derived from the vector potential for the tilted, vertical and horizontal branches in the photovoltaic bracket system. With a time–space discretization scheme put forward for theses formulas, the magnetic field distribution in an assigned spatial domain is determined on the basis of the lightning current responses. The magnetic linkage passing through a conductor loop is evaluated by the surface integral of the magnetic flux density and the induced voltage is obtained from the time derivative of the magnetic linkage. In order to check the validity of the proposed method, an experiment is made on a reduced-scale photovoltaic bracket system. Then, the proposed method is applied to an actual photovoltaic bracket system. The calculations are performed for the magnetic field distributions and induced voltages under positive and negative lightning strokes.

The corona characteristics of the single and bundle conductors are investigated experimentally under negative damped oscillation impulses. The experimental setup consisting of a modified impulse generator, corona cage and digital measurement system is built for measuring the charge–voltage (q‐u) curves. An exploratory experiment is described with special attention to the effect of the number of bundle conductors on the feature of q‐u curves. The behavior of the minor loops on the q‐u curves is examined from a single‐conductor to four‐conductor bundle. In terms of the measured corona inception voltage, the corona inception field strength is evaluated at a critical distance from the inner electrode. The capacitance increase coefficient and energy dissipated by corona are extracted from the measured q‐u curves. Then, a discussion is also presented on these characteristic indices according to the gas discharge mechanism. © 2019 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.

Compared with the pure electromagnetic suspension system, the hybrid suspension system has the characteristics of lower energy consumption, can indirectly increase the safety of the system, and reduce the construction difficulty and engineering cost. In this paper, an electromagnetic-permanent-magnet hybrid levitation model of a maglev train is a control object, and a constrained model predictive computer controller is utilized for the levitation control. The simulation results show that the constrained predictive controller can satisfy the multiple constraints, and real-time and anti-disturbance requirements in the suspension process for this kind of hybrid suspension system.

The effective removal and transport of water in flow channels play an important role in the water management of proton exchange membrane fuel cells (PEMFCs). In this paper, a novel design of anode serpentine flow channel with the wettability gradient wall is discussed and numerically investigated by utilizing the volume-of-fluid (VOF) method. The effects of the contact angle and the wettability gradient of channel walls, as well as hydrogen flow velocity and water droplet size, on the droplet dynamic behavior are studied. The results indicate that compared with the conventional flow channel, the water droplet can be more effectively removed from the turning part in the wettability gradient flow channel. And the water removal ability in the turning part is improved with the increase of the wettability gradient. Moreover, the wettability gradient flow channel can also improve the water removal performance for the cases with different hydrogen flow velocities and water droplet sizes. This study provides ideas for guiding the design of flow channel to effectively enhance anode water management.

A calculating method is proposed for lightning transient analysis in photovoltaic bracket systems. The circuit parameters are evaluated for the conducting branches and grounding electrodes. On the ground of the circuit parameters, the equivalent circuit model is set up for photovoltaic bracket systems. The transient calculation is made by the circuit model and the potential and current responses are obtained in photovoltaic bracket systems. The laboratory-experiment is performed on a reduced-scale photovoltaic bracket system. The results obtained from the measurement are compared with those from the transient calculation to confirm the validity of the circuit model. Then, the probability density function of lightning current is further introduced into the statistical analysis of lightning transients. By means of the transient calculations made in a large interval of lightning current amplitudes, the statistical values of the nodal potential and branch current amplitudes are calculated by probability weights. A numerical example is also given for examining the difference between the statistical and non-statistical values. The proposed method can take account of the actual randomness of lightning discharge and afford a sound basis for lightning protection design of photovoltaic bracket systems.

In view of the actual random behavior of lightning strikes, an efficient algorithm is proposed in this paper for statistical analysis of the lightning transients on wind turbines. The equivalent circuits are established for blades, moving contact site, tower and grounding arrangement. A set of formulas is provided for evaluating their respective circuit parameters. With the equivalent circuits connected in sequence, a complete circuit model of wind turbines (WTs) is constructed for calculating lightning transients. The lightning transient responses can be obtained at different locations on a wind turbine by using the circuit model to perform the transient calculation. For checking the validity of the circuit model, the experiment measurement is also made on a laboratory-scale WT. An approximate match appears between the measured and calculated results. On the basis of the circuit model, the transient calculation is performed sequentially for each discrete amplitude in a large interval of lightning current. The random distribution of lightning current is taken into account by a cumulative probability function of exponential type. The corresponding probability density function is derived to weight the peak values of the lightning transient responses. The statistical values of the lightning transient responses can be determined by totalizing the weighted peak values in the interval of lightning current. Then, a case study is carried out to contrast the statistical values with the non-statistical ones calculated from the standard lightning current amplitudes, and a significant difference is discovered between them.

Photovoltaic (PV) system is easy getting stroke for its outdoor characteristics and defendless protective measures. To provide the quantify basis for PV lightning protection formulation, a lightning transient modeling method is presented. With the PV lightning transient model, the lightning transient response that includes the currents on the branches and the potentials at the nodes of PV frame structure could be calculated. The simulated results reveal that the positions of the striking node and the structure of frame system have pronounced influence to the transient responses. The flowing currents on the frame branches closing to the striking node are significantly higher than distant ones. Meanwhile, the transient potential distribution on supporting frame work has an initial distortion and then tends to approximate equalization.

The lightning transient calculation is carried out in this paper for photovoltaic (PV) bracket systems. The electrical parameters of the conducting branches and earthing electrodes are represented by resistances, capacitances, and inductances. A set of formulas are derived to evaluate the electrical parameters, which are appropriate for the complicated spatial locations of the conducting branches. On the basis of the electrical parameters, the equivalent circuits are constructed for the segmented branches and electrode units in a PV bracket system. By integrating all the equivalent circuits, a complete circuit model is built for the PV bracket system. The lightning transient responses can be obtained from the circuit model. In order to confirm the validity of the circuit model, experimental measurement is made with a reduced-scale PV bracket system and the measured results are compared with the calculated ones. Then, an actual PV bracket system is used as the numerical example. The lightning transient responses are calculated for typical locations of attachment points. The distribution characteristic of lightning transient responses is also explored in the PV bracket system.

在光伏发电系统直流侧通常是通过在电池板出线端、汇流箱、配电柜及逆变器端等重要部位设置电涌保护器来限制雷电电涌过电压.基于光伏发电系统直流侧的电涌保护器的设计需要,本文对复合型电涌保护器进行了仿真研究.首先对由压敏电阻和气体放电管串联构成的保护支路进行PSCAD软件暂态仿真,并进行实测加以校验.然后仿真考察了3种常用结构的电涌保护器在全模下的雷电暂态响应及保护特性.通过对比分析,发现在可实现保护功能的若干种保护器结构中,Δ型结构为最优选择.本文提出的仿真研究结果可为光伏发电系统直流侧电涌保护器的设计提供定量化的参考依据.

Offshore wind turbines are often struck by lightning due to their tall structures and the harsh marine environment. The high transient potential from lightning strike can cause serious damage for the devices of offshore turbines. For analysing the effect of transient potential, a complete transient circuit model is established and an efficient algorithm is also presented to evaluate the circuit parameters of blade, tower, and jacket foundation. On the basis of the circuit model, the transient potential at the different locations of the offshore wind turbine can be carried out during direct lightning strike by PSCAD. Finally, the circuit model is used by a numerical example of an actual Chinese-built offshore wind turbine.

The growth of electric energy demand has resulted in a dramatic increase in the fault currents. To limit the fault currents, a viable approach is proposed in this article. In the approach, a resonance‐type fault current limiter (FCL) is employed. The FCL has a parallel circuit structure composed of a reactor and a capacitor. The key feature of the FCL is based on using a discharge gap to control the inductive reactance of the reactor. During a short‐circuit fault, the breakdown of the discharge gap makes the inductive reactance of the reactor approximately equal to the capacitive one of the capacitor and the resultant parallel resonance produces a high impedance in the fault circuit to limit the fault currents. The experimental model of the FCL is built to measure the limited fault current waveforms. The case study is also carried out by PSCAD (Power Systems Computer Aided Design) simulation, in which the FCL is applied to an actual 500 kV electric network. A desired current‐limiting effect is exhibited in both the experimental measurement and case study. © 2018 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.

An efficient method is proposed for predicting the attenuation and distortion of the damped oscillation surges traveling on single-phase overhead lines under the influence of corona and frequency dependence of line parameters. The finite-difference time-domain algorithm is employed in the transient computation. The Suliciu's corona model is extended to simulate the charge-voltage curves with minor loops under the damped oscillation surges. The corona effect is considered by adding a corona current term in the telegraphers' equations. The frequency-dependence effect is also taken into account by using the vector fitting and recursive convolution in the time domain. The computed voltage waveforms are compared with the measured ones to examine the validity of the proposed method. The computed results show that the minor loops have a greater effect on the attenuation and distortion for the damped oscillation surges under negative polarity.