Calculation of Eddy Current Loss and Short-circuit Force in SSZ11-50000/110 Power Transformer

The ?method is used in this paper to calculate the leakage magnetic field of SSZ11-50000/110 Power transformer, and by which the structures’ influences to the main leakage flux are analyzed. Through the combination of the product and TEAM Problem 21B, the surface impedance method shows its great advantage in the calculation of eddy current loss.

Fe-Cr-Ni合金碱性SCC的电化学研究

采用控制电位下恒变形C形环试样试验研究了Fe -Cr-Ni合金 (80 0M )在含硫代硫酸钠杂质的热浓碱溶液中的应力腐蚀破裂 (SCC)行为 ,测量了C形环试样恒电位极化时的稳定溶解电流密度ist(稳定溶解速率 ) .用电化学方法研究了腐蚀形貌与电位和 ist的相互关系 ,发现ist随电位的变化呈单调增加趋势 ,ist为 0 6 8mA/cm2 ～ 1 6 2mA/cm2 ,对应电位ESCE=- 30mV～ 4 0mV ,C形环试样发生碱性SCC ;当电位和ist为其它值时 ,发生全面腐蚀 (含晶间腐蚀 ) .

Placement optimization of Multi-Type fault current limiters based on genetic algorithm

The fault current limiter(FCL)is an effective measure for improving system stability and suppressing short-circuit fault current.Because of space and economic costs,the optimum placement of FCLs is vital in industrial applications.In this study,two objectives with the same dimensional measurement unit,namely,the total capital investment cost of FCLs and circuit breaker loss related to short-circuit currents,are considered.The circuit breaker loss model is developed based on the attenuation rule of the circuit breaker service life.The circuit breaker loss is used to quantify the current-limiting effect to avoid the problem of weight selection in a multi-objective problem.The IEEE 10-generator 39-bus system in New England is used to evaluate the performance of the proposed genetic algorithm(GA)method.Comparative and sensitivity analyses are performed.The results of the optimized plan are validated through simulations,indicating the significant potential of the GA for such optimization.

Research on Numerical Simulation of 3D Leakage Magnetic Field and Short-circuit Impedance of Axial Dual-low-voltage Split-winding Transformer

It is difficult to accurately calculate the short-circuit impedance, due to the complexity of axial dual-low-voltage split-winding transformer winding structure. In this paper, firstly, the leakage magnetic field and short-circuit impedance model of axial dual-low-voltage split-winding transformer is established, and then the 2D and 3D leakage magnetic field are analyzed. Secondly, the short-circuit impedance and split parallel branch current distribution in different working conditions are calculated, which is based on field-circuit coupled method. At last, effectiveness and feasibility of the proposed model is verified by comparison between experiment, analysis and simulation. The results showed that the 3D analysis method is a better approach to calculate the short-circuit impedance, since its analytical value is more closer to the experimental value compared with the 2D analysis results, the finite element method calculation error is less than 2%, while the leakage flux method maximum error is 7.2%.

Single-phase earth fault current distribution between optical fiber composite overhead ground wire and ordinary ground wire in transmission system

It is important for the safety of transmission system to accurately calculate single-phase earth fault current distribution.Features of double sided elimination method were illustrated.Quantitative calculation of single-phase earth fault current distribution and case verification were accomplished by using the loop method.Influences of some factors,such as single-phase earth fault location and ground resistance of poles,on short-circuit current distribution were discussed.Results show that:1) results of the loop method conform to those of double sided elimination method;2) the fault location hardly influences macro-distribution of short-circuit current.However,current near fault location is evidently influenced;and 3) the short-circuit current distribution is not so sensitive to the ground resistance of poles.

Active Current Sharing of LCLC Resonant Converter with Switch-Controlled-Capacitor Technology

In this paper,an interleaved LCLC converter with enhancement-mode(E-mode)GaN devices is introduced to achieve the accurate current sharing performance for data center applications. Any tolerance in the resonant tank elements can lead to large load imbalance between any two different phases. Due to the steep gain curves of LCLC converters,conventional current sharing methods are not effective. In the proposed converter,the impedances of the resonant networks are matched by switching a capacitor,i.e.,switch controlled capacitor(SCC),in series with the resonant capacitor in one or some of the phases,which results in accurate load current sharing among the phases with an accuracy around 0.025%. The load share of a phase is sensed through the resonant current on it,and the control logic applied to such current sharing can be achieved. By this method,accurate current sharing is achieved for a wide input voltage range required for the hold-up time in data center applications. Interleaving is applied in the proposed multiphase LCLC converter,resulting in low current stress on the output capacitor and allowing ceramic capacitor implementation. Moreover,phase shedding accomplishes high light load efficiency. The performance of the proposed interleaved LCLC converter is verified by a two-phase 1 k W prototype with an input voltage ranging from 250 V to 400 V and a fixed 12 V output voltage.

Characteristics of Bi-2223 HTS Tapes Under Short-Circuit Current Impacts in Hybrid Energy Transmission Pipelines

A hybrid energy transmission pipeline is proposed with the aim of long-distance cooperative transmission of electricity and chemical fuels, which is composed of an inner high-temperature superconducting (HTS) power cable and outer liquefied natural gas (LNG) pipeline. The flowing LNG could maintain the operating temperature of the inner HTS power cable within the range of 85 K-90 K, thus the Bi-2223 superconductors in the HTS power cable produce little Joule loss with the transmission current below the critical current. Owing to the advantages of high power density, low transmission losses and economical manufacturing costs, the hybrid energy transmission pipeline is expected to be widely utilized in the near future. In order to ensure the safety of the HTS power cable and explosive LNG in case of short-circuit faults, this paper tests and analyzes the characteristics of Bi-2223 HTS tapes of the Type HT-CA, Type HT-SS and Type H models under short-circuit current impacts at the LNG cooling temperature (85 K-90 K). An experimental platform is designed and established for the ampacity tests of HTS tapes above LN2 cooling temperature (77 K). The AC over-current impact tests at 85 K-90 K are carried out on each sample of Bi-2223 tapes respectively, and the experimental results are analyzed and compared to evaluate their performances under different operating conditions. The results indicate that the Type HT-CA tape can withstand 50 Hz short-circuit current impact with the amplitude of 1108 A (10 times of critical current Ic ) for 100 ms at 90 K, and its resistance is the smallest of the three tested samples under similar current impacts. Therefore, the Type HT-CA Bi-2223 tape is the optimal superconductor of the HTS power cable in the hybrid energy transmission pipeline.

统一潮流控制器近端母线的短路电流计算方法

针对目前实际投运的统一潮流控制器(UPFC)及其采用的故障控制策略,基于电网络理论推导了UPFC近端母线短路电流的计算方法。使用UPFC串联线路对故障母线的转移导纳描述了UPFC的近端母线,由于UPFC串联侧在近端母线故障时立即被旁路保护,导致故障母线的戴维南等值电势发生突变,进而对短路电流的计算结果产生影响,计算结果的相对变化与UPFC故障前运行电压和电流分布系数有关。在IEEE 9节点系统中,研究了运行条件变化以及UPFC参数变化对短路电流的影响,并使用PSCAD对计算结果进行了仿真验证;在IEEE 118节点系统中,分析了UPFC对大规模电网短路电流的影响。结果表明,UPFC对其两侧母线短路电流的影响相反,且对近端母线短路电流的影响随着电气距离增大而减小。

含串补电容的超高压输电线路暂态保护判据

串补电容能提高超高压系统输电能力,但会引起超高压输电线路传统继电保护的不正确动作。运用波过程和频域响应理论,分析了含串补电容超高压线路上暂态电流在不同故障点的频域特征。小波变换提取其高频与次高频分量,通过比较高频与次高频之间的能量积分比与能量比的差异,将高频与次高频的能量积分比作为超高压输电线路暂态保护判据。测试结果表明,该判据在不同故障情形和系统运行方式下均能可靠动作,提高了保护的可靠性和灵敏度。

埋地油气管道腐蚀研究

关于埋地油气管道腐蚀研究一直都是油气储运及集输工程的一个重要课题。阐述埋地油气输送管道腐蚀的主要形式及机理。在输油管道的内腐蚀、杂散电流干扰、应力腐蚀开裂、涂层失效等方面进行了分析,探讨高强度管道钢腐蚀中最突出的问题。

基于限流可行方案边界集的最优支路投切

针对在最优支路投切中难以处理非凸非线形的短路电流约束问题,基于限流全方案的性质,定义了一种可通过少量方案判断所有投切方案短路电流状况的可行方案边界集,将其代替节点自阻抗约束,建立了考虑短路电流约束的最优支路投切模型并提出了求解方法。将原问题分解为最优支路投切主问题和短路电流约束子问题;子问题利用可行方案边界集对主问题求解结果进行检验,当短路电流约束不满足时向主问题添加割平面约束;主问题迭代求解直至满足限流要求。实际电网算例表明,限流可行方案边界集在线路投切方案中占比很小,不会造成计算机的存储负担,其与最优支路投切的结合可提升系统运行经济性并兼顾短路电流安全。

计及机组启停与线路投切显式短路电流约束的电力系统日前优化调度

随着电网的不断发展和新能源的接入,电力系统短路电流超标问题愈发显著,相对于其他限流方式,线路投切方式拥有更好的灵活性和经济性。针对线路投切限流方式中线路切断过多导致电网安全性降低的问题,提出一种考虑机组启停和线路投切的短路电流抑制方法。根据节点导纳矩阵和节点阻抗矩阵的物理关系以及节点自阻抗的物理意义,推导出投切线路和启停机组与短路电流之间的关系,避免导纳矩阵求逆环节中的非线性项近似误差,得到更为准确的短路电流显式表达方法;进而以综合考虑发电成本、机组启停和线路投切成本为目标,提出计及显式短路电流约束的电力系统日前优化调度混合整数线性规划模型。最后,使用IEEE30节点和118节点系统验证所提模型的有效性和通用性,而后与导纳矩阵求逆法对比证明短路电流显式表达模型的精确性,并给出考虑机组启停和线路投切的日前调度运行方案。

考虑感应电动机负荷电磁暂态特性的系统短路电流计算方法

首先分析了BPA程序所采用的二阶静态负荷模型对系统短路电流计算之前的潮流计算中迭代算法所涉及的问题,然后深入研究分析了感应电动机负荷特性及其对系统短路电流计算的影响。建立了在现有以恒定阻抗作为系统各节点负荷的短路电流计算方法中考虑适应感应电动机电磁暂态过程的系统短路电流的修正计算方法,提出了相应的系统短路电流计算程序编制的具体实施思路。初步验证了本文所提出的方法的可行性。

Numerical study on short-circuit current of single layer organic solar cells with Schottkey contacts

The influence of the cathode work function,carriers mobilities and temperature on the short-circuit current of single layer organic solar cells with Schottkey contacts was numerically studied,and the quantitative dependences of the short-circuit current on these quantities were obtained.The results provide the theoretical foundation for experimental study of single layer organic solar cells with Schottkey contacts.

Regulating effect of Tong Xie-Yao Fang on colonic epithelial secretion via Cl- and HCO3- channel

AIM To investigate the pharmacological effect of Tong XieYao Fang(TXYF) formula, a Chinese herbal formula, on Diarrhea-predominant irritable bowel syndrome(D-IBS) rats.METHODS In a neonatal maternal separation plus restraint stress(NMS + RS) model of D-IBS, male Sprague Dawley rats were randomly divided into two groups(NMS + RS group and TXYF-formula group) with no handlings were used as controls(NH group). Starting from postnatalday 60, rats in TXYF-formula group were administered TXYF-formula(4.92 g/100 g bodyweight) orally twice a day for 14 consecutive days while NH group and NMS + RS group were given distilled water. Using short-circuit current technology, we observed 5-HT-induced changes of current across ion channels, such as cystic fibrosis transmembrane conductance regulator(CFTR) Clchannel, epithelial Na+ channel(ENaC), Ca2+-dependent Cl- channel(CACC), Na+-K+-2Cl- co-transporter(NKCC), and Na+-HCO-3 co-transporter(NBC), in the colonic epithelium of three groups after exposure to drugs and specific blockers with a Power Lab System(AD Instruments International).RESULTS Under basal conditions, the changes of short-circuit current(?Isc, μA/cm2) induced by 5-HT were similar in NH group and TXYF-formula group, and both higher than NMS + RS group(70.86 μA/cm2 ± 12.32 μA/cm2, 67.67 μA/cm2 ± 11.68 μA/cm2 vs 38.8 μA/cm2 ± 7.25 μA/cm2, P < 0.01, respectively). When CACC was blocked by 4,4′-diisothiocyanato-stilbene-2,2′-disulfonic acid, 5-HT-induced ?Isc was smaller in NMS + RS group than in NH group and TXYF-formula group, respectively(48.41 μA/cm2 ± 13.15 μA/cm2 vs 74.62 μA/cm2 ± 10.73 μA/cm2, 69.22 μA/cm2 ± 11.7 μA/cm2, P < 0.05, respectively). The similar result could be obtained when ENaC was blocked by Amiloride(44.69 μA/cm2 ± 12.58 μA/cm2 vs 62.05 μA/cm2 ± 11.26 μA/cm2, 62.11 μA/cm2 ± 12.01 μA/cm2, P < 0.05, respectively). However, when CFTR Cl- channel was blocked by 1,1-dimethyl piperidinium chloride(DPC), 5-HT-induced ?Isc did not significantly differ in three groups(42.28 μA/cm2 ± 10.61 μA/cm2 vs 51.48 μA/cm2 ± 6.56 μA/cm2 vs 47.75 μA/cm2 ± 7.99 μA/cm2, P > 0.05, respectively). The similar results could also be obtained in three groups when NBC and NKCC were respectively blocked by their blockers.CONCLUSION TXYF-formula can regulate the Cl- and HCO-3 secretion of colonic mucosa via CFTR Cl- channel, Cl-/HCO-3 exchanger, NBC and NKCC co-transporters.

Simulation and experimental study of a novel bifacial structure of silicon heterojunction solar cell for high efficiency and low cost

A novel structure of Ag gridlSiN_(x)/n+-c-Si/n-c-Si/i-a-Si:H/p^(+)-a-Si:HlTCO/Ag grid was designed to increase the ef-ficiency of bifacial amorphous/crystalline silicon-based solar cells and reduce the rear material consumption and production cost.The simulation results show that the new structure obtains higher efficiency compared with the typical bifa-cial amorphous/crystalline silicon-based solar cell because of an increase in the short-circuit current(J_(sc)),while retaining the advantages of a high open-circuit voltage,low temperature coefficient,and good weak-light performance.Moreover,real cells composed of the novel structure with dimensions of 75 mm×75 mm were fabricated by a special fabrication recipe based on industrial processes.Without parameter optimization,the cell efficiency reached 21.1%with the J_(sc)of 41.7 mA/cm^(2).In addition,the novel structure attained 28.55%potential conversion efficiency under an illumination of AM 1.5 G,100 mW/cm^(2).We conclude that the configuration of the Ag grid/SiN_(x)/n^(+)-c-Si/n-c-Si/i-a-Si:H/p^(+)-a-Si:H/TCO/Ag grid is a promising structure for high efficiency and low cost.

Application of thyristor controlled phase shifting transformer excitation impedance switching control to suppress short-circuit fault current level

Short-circuit fault current suppression is a very important issue in modern large-interconnected power networks. Conventional short-circuit current limiters, such as superconducting fault current limiters, have to increase additional equipment investments. Fast power electronics controlled flexible AC transmission system(FACTS)devices have opened a new way for suppressing the fault current levels, while maintaining their normal functionalities for steady-state and transient power system operation and control. Thyristor controlled phase shifting transformer(TCPST) is a beneficial FACTS device in modern power systems, which is capable of regulating regional powerflow. The mathematical model for TCPST under different operation modes is firstly investigated in this study. Intuitively, the phase shifting angle control can adjust the equivalent impedance of TCPST, but the effect has been demonstrated to be weak. Therefore, a novel transformer excitation impedance switching(EIS) control method, is proposed for fault current suppressing, according to the impedance characteristics of TCPST. Simulation results on IEEE 14-bus system have shown considerable current limiting characteristic of the EIS control under various fault types. Also, analysis of the timing requirement during fault interruption, overvoltage phenomenon, and ancillary mechanical support issues during EIS control is discussed,so as to implement the proposed EIS control properly for fast fault current suppression.

Electro-Discharge Fine Truing of Metal-Bonded Fine-Grain Diamond Wheel Based on Real-Time Monitoring

A data acquisition system based on LabVIEW is designed and implemented, and electro-discharge(ED) fine truing of metal-bonded fine-grain diamond wheel based on real-time monitoring is researched. Real-time monitoring not only makes efficient impulse specification of ED truing easily obtained, but also is good for timely identifying no-load, avoiding short circuit and arc discharge phenomena and then for obtaining normal machining state. ED fine truing of the fine-grain wheel includes two steps: rough truing for high efficiency and fine truing for high precision. Final ED truing precision and efficiency not only depend on electric process specification, but also is concerned with electrode shape, insulated performance of operating fluid and vertical feed quantity value and frequency. Experiments indicate that ED fine truing based on real-time monitoring can improve the truing precision and efficiency. Average machining efficiency of W10 wheel is about 0.95 μm/min; the final run-out by ED truing is less than 2 μm.

一种新型多路独立调光LED驱动器

多路电流不均衡是影响LED照明系统寿命的主要原因,但现有无源均流和有源均流方案均有其各自的局限性,给LED驱动器的设计带来新的挑战。同时,在实践中完成不同亮度的独立控制亦为重要。基于此,论文提出一种新型电路拓扑;在上、下半桥谐振网络中,开关电容(Switched-Capacitor Control,SCC)单元替代固态电容,从而定频下调节SCC模块完成LED独立调光的目的,EMI电路简单;同时,SCC单元复用作均流模块,均流精度高。最后,本文通过仿真和样机实验证明了所提电路的正确性和可行性。

Research on Influence of Motor Parameters on the Negative-Salient Permanent Magnet Synchronous Motor

The d-axis inductance(Ld)of the negative-salient permanent magnet synchronous motor(NSPMSM)is larger than the q-axis inductance(Lq).Compared with the traditional motor,the NSPMSM has the characteristics of a high overload capacity,wide speed range,and preventing permanent magnet demagnetization.Positive d-axis current(id)is applied to control positive reluctance torque when running at base speed.When the motor is running at high speed,a relatively small id can achieve speed expansion and effectively expand the motor flux-weakening range.The use of a magnetic bridge to increase the Ld and a W-type permanent magnet to reduce the Lq is proposed in this article as a novel NSPMSM rotor structure.Firstly,the working principle of the NSPMSM was determined according to the equivalent magnetic circuit.Secondly,using the finite element method,the influence of motor structure on torque and speed performance of NSPMSM was analyzed,and the motor structure was optimized.Thirdly,the effect of the internal power factor angle on the performance of the two motors is analyzed.Finally,the short circuit simulation and analysis verified that the NSPMSM has a stronger short circuit current suppression ability without sacrificing overload ability.