Short-circuit Characteristics Research Articles

Research on Single-phase Power Supply in Short-circuit Test of Transformer on Magnetic-force Coupling Field

The short-circuit test is a test of the comprehensive technical ability of transformer manufacturing. The three-phase power supply is usually used for short-circuit test of transformer. To investigate the feasibility of using a single-phase power supply in the short-circuit test of transformer, in this paper, we modeled a 200 kVA power transformer in three dimensions, using the finite element method to calculate the short-circuit current and short-circuit electromagnetic force of the windings under different excitation modes when the three-phase short-circuit occurs in the low-voltage windings. Analyze and compare the short-circuit current and short-circuit electromagnetic force distribution characteristics of windings under different working conditions. The results show that when the three-phase short-circuit condition occurred in the low-voltage windings, regardless of the three-phase excitation or single-phase excitation exerted on the high-voltage windings, the short-circuit current and the short-circuit electromagnetic force of the voltage zero-crossing closing phase is basically the same. This proves that a single-phase power supply can be used instead of a three-phase power supply for short-circuit tests. the analysis result has certain reference significance for improving the short-circuit test of transformer.

Analysis and calculation method for multiple faults in low-resistance grounded systems with inverter-interfaced distributed generators based on a PQ control strategy

The short-circuit characteristics of low-resistance grounded systems (LRGSs) under multiple faults have fundamentally changed because of the high penetration level of inverter-interfaced distributed generators (IIDGs). However, an analysis and calculation method for multiple faults (ACMMF) with IIDGs that is a standard basis for fault features, relay protection, safe evaluation and design of LRGSs is currently lacking. A novel systematic ACMMF is analytically proposed in this paper based on ideal transformer and multiport network theory. Based on the proposed ACMMF, composite networks under various fault conditions are established, which provides a straightforward presentation of fault current paths and equivalent impedance and simplifies the modelling procedure for fault analysis and calculation. Furthermore, to overcome the strong nonlinear inter-IIDG couplings, an iterative correction algorithm is proposed for accurate IIDG fault current calculations. Finally, the accuracy of the proposed method is verified by PSCAD/EMTDC simulation. The results show that the proposed methods have good adaptivity to different system structures, operation modes, fault types and flexible access of IIDGs.

Photovoltaic Device Application of a Hydroquinone-Modified Conductive Polymer and Dual-Functional Molecular Si Surface Passivation Technology.

In the last decades, the conductive polymer PEDOT:PSS has been introduced in Si-based hybrid solar cells, gaining noticeable research interest and being considered a promising candidate for next generation solar cells which can achieve both of low manufacturing cost and high power conversion efficiency. This study succeeded in improving the electrical conductivity of PEDOT:PSS to 937 S/cm through a simple process of adding hydroquinone (HQ) to the pristine PEDOT:PSS solution. The results also showed that the addition of HQ to PEDOT:PSS(HQ-PEDOT:PSS) could not only dramatically improve the conductivity but also well-sustain the work function characteristics of PEDOT:PSS by promoting the formation of more continuous conductive-PEDOT channels without removing the insulating PSS. In this report, we reveal that the application of the HQ-PEDOT:PSS to the Si/PEDOT:PSS HSC could significantly improve the short-circuit current and open-circuit voltage characteristics to increase the power conversion efficiency of the HSCs compared to the conventional approaches. Moreover, we also treated the Si surface with the organic monomer, benzoquinone (BQ) to (1) passivate the excess Si surface defect states and (2) to improve the properties of the Si/PEDOT:PSS interface. We show that BQ treatment is able to dramatically increase the minority carrier lifetime induced by effective chemical and field-effect passivation in addition to enhancing the wettability of the Si surface with the PEDOT:PSS solution. As a result, the power conversion efficiency was increased by 10.6% by introducing HQ and BQ into the fabrication process of the Si/PEDOT:PSS HSC.

Design and Photoelectric Performance of Perfect Solar Absorber Based on GaAs Grating

In recent years, solar energy has received extensive attention as a clean and renewable energy. We present a perfect broadband solar absorber based on tungsten and semiconductor GaAs in this paper. The structure of GaAs grating-GaAs film-W substrate has been proposed. And the finite time domain difference method (FDTD) has been used for the numerical simulation of the model. Broadband absorption has been realized in the 500–1,850 nm, by adjusting the parameters of geometry to excite high-efficiency surface plasmon resonance. The absorption spectrum of the structure can be changed by adjusting the geometric parameters to meet different needs. The proposed absorber has incidence insensitive (0–60°) and high short-circuit current characteristics. The structure is simple and easy to manufacture, and has superior photoelectric properties to be application in photothermal conversion, collection and utilization of solar energy.

Short circuit fire risk assessment in investigating and examining fires caused by emergency modes in overhead transmission lines

Emergency modes (short circuits) in electric power system and equipment are the main technical cause of fires. However, it is not always possible to prove the involvement of a particular operating mode in a fire. The fire hazard can be due to three components: a fuel load, an oxidizer and an ignition source. Since overhead transmission lines are used in an open space, they are oxidized. The presence of a fuel load is confirmed by a fire. The source of ignition should be identified. The aim of the study is to develop an algorithm for assessing the fire hazard for short circuits in overhead transmission lines with 1000 V. The study was conducted using scientific analysis, physical experiment and simulation. The ignition source is due to the appearance of an energy source with parameters sufficient to ignite a fuel load. The probability of ignition in overhead line wires depends on the probability of occurrence of the short circuit itself ( Qi (v1) ) , the probability of failure of protection devices ( Qi (v2) ), and the probability that the electric current value in the event of a fault is in the range of fire hazard values (Qi(z)). The values of the first two components are determined on the basis of statistical data, taking into account the theory of reliability. The third component is based on the experiment results. The experimental studies made it possible to establish the ranges of fire hazard values for uninsulated aluminum wires of various cross-sections, thereby providing the possibility of calculating ( Qi (z). Using the data obtained and information about the nature of changes in short-circuit currents and performance characteristics of protection devices, depending on the line length, an algorithm for assessing the fire hazard for a short circuit was developed. The results make it possible to assess the fire hazard for short circuits in various sections of the electrical network, made by overhead transmission lines, and to establish the involvement of sparks generated by short circuits in a fire

The Effect of Deep JFET and P-Well Implant of 1.2kV 4H-SiC MOSFETs

1.2kV 4H-SiC MOSFETs with different junction depths of JFET and P-well regions were fabricated. For each JFET/P-well depth combination, channel lengths and JFET widths were also varied to compare specific on-resistance, breakdown voltage, and short-circuit withstand time. It was discovered that deep JFET structure provides low specific on-resistance (12% lower) with high breakdown voltage. On the other hand, MOSFETs with deep P-well result in high breakdown voltage with low leakage current even in shorter channel length (0.4 lm). Moreover, trade-off relationship between Ron,sp and short-circuit withstand time is discussed for MOSFETs with different JFET widths and channel lengths; the deep JFET implant provides better trade-off relationship due to the feasibility of narrow JFET width. For the further improvement of trade-off relationship, MOSFETs with deep JFET and P-well implant are proposed. Lastly, the importance of high channel mobility for not only static characteristics but also short-circuit characteristics was investigated. The in-depth understanding of measured electrical characteristics was supported by 2D-device simulations.

An improved desaturation short-circuit protection method for SiC power modules

Silicon Carbide (SiC) MOSFET devices have smaller chip size and higher current density than Si counterparts, which results in the limited short-circuit capability of SiC power modules. The presently used protection circuit is actually conventional desaturation protection method, which is very suitable for IGBT modules. But this conventional protection circuit has relatively slow response, and cannot be directly used in SiC modules due to its higher di/dt and weaker ruggedness compared to IGBT modules. So we propose an improved desaturation protection method. We first analyse the short-circuit process to obtain the short circuit characteristics of SiC MOSFET. Then, we give the principle of the improved desaturation protection method, and present the comparison between the conventional protection circuit and the improved one. At last, short-circuit protection tests under HSF and FUL faults have been conducted to verify the improved desaturation protection circuit. The experimental results show that the improved desaturation protection circuit has a faster response than the traditional one, and can make SiC modules work reliably.

Design of Grating Type GaAs Solar Absorber and Investigation of Its Photoelectric Characteristics

In recent years, as a renewable clean energy with many excellent characteristics, solar energy has been widely concerned. In this paper, we propose an ultra-broadband solar absorber based on metal tungsten and semiconductor GaAs structure. A multilayer metal semiconductor composite structure composed of W-Ti-GaAs three-layer films and GaAs gratings is proposed. The finite difference time domain method is used to simulate the performance of the proposed model. High efficiency surface plasmon resonance is excited by adjusting the geometric parameters, and the broadband absorption of up to 2,350 nm in 500–2850 nm is realized. The spectrum of the structure can be changed by adjusting the geometric parameters to meet different needs. The proposed absorber has good oblique incidence characteristics (0–60°) and high short-circuit current characteristics. The geometry of the absorber is clear, easy to manufacture, and has good photoelectric performance. It can realize solar energy collection, light heat conversion, high sensitive sensing and other functions.

운용환경요인을 고려한 리튬이온전지의 외부단락 특성 연구

최근 몇 년간 국내외에서 전기자동차(electric vehicle, EV)와 에너지저장장치(energy storage system, ESS)에 적용되는 중대형 이차전지의 수요가 급격하게 늘어나고 있고, 이에 따라 시장 규모도 기하급수적으로 증가하고 있다. 하지만, 최근 발생하고 있는 EV와 ESS용 이차전지의 화재는 시장에 부정적인 영향을 주고 있다. 특히, 2017년 8월부터 발생한 국내 ESS 화재는 2021년 5월 현재까지 총 31건으로 보고되고 있어, 중대형 이차전지의 안전성 검증을 강화하기 위한 체계적인 연구의 필요성이 대두되고 있다. 따라서, 본 논문에서는 국내 중대형 이차전지에 사용되는 배터리 셀 중 범용으로 활용되는 NMC계열 각형 및 파우치형 전지를 대상으로 대표적인 안전성 시험 중 하나인 외부단락 시험을 수행하기 위한 사고모의 장치를 구현한다. 여기서, 외부단락시험용 사고모의장치는 단락저항, 계측장치부, 제어장치부 등으로 구성되며, 다양한 운용환경 시험조건에 따른 외부단락 특성을 분석할 수 있도록 구현한다. 이를 바탕으로 리튬이온전지의 형태, 단락저항 및 SOC에 따른 외부단락 시험을 수행하여, 단락저항과 SOC에 따른 전류 및 온도 특성을 제시한다. 또한, 전처리 온도와 전지 모듈 내 보호소자별 외부단락을 수행한 결과, 보호소자에 따른 전류 및 차단시간, 전처리 온도에 따른 외부단락 특성을 확인할 수 있어, 본 논문의 유효성을 확인하였다.

Effect of high- and low-side blocking on short-circuit characteristics of SiC MOSFET

Silicon carbide (SiC) metal oxide semiconductor field-effect transistors (MOSFETs) are susceptible to unexpected short-circuit (SC) impacts in high-voltage inverters operating in complex applications. This paper presents a research on the effect of high-side blocking and classical low-side blocking on short circuit characteristics. Simulation of the steady-state electric field, which equivalent to the states after LSB and HSB, was performed. The obvious electric field concentration appears in the source-drain pn junction of the DUT after the LSB, and is much larger in value than that appearing in the DUT after the HSB. DUTs, which failed, were decapsulated from the side of the drain to allow for an emission microscope (EMMI) investigation. In response to the results of the EMMI investigation, it was discussed that the occurrence of source leakage was caused by electric field concentration after the DUT is blocked. The hazards of this failure and the expected further research are mentioned simply.

Comparative Investigations of Inverter Short-Circuit Fault and Winding Terminal Short-Circuit Fault in Open-End Winding Five-Phase PM Machine System

The open-end winding multi-phase permanent-magnet (PM) machine driven by full-bridge inverter is a potential choice for safety-critical application fields. Based on the open-end winding multi-phase PM machine system, comparative investigations of the inverter short-circuit (ISC) fault and winding terminal short-circuit (WSC) fault are carried out to indicate the special characteristics of the ISC in aspects of short-circuit (SC) current characteristics and post-fault performances. The analytical prediction of the SC current under ISC fault is investigated based on the results of WSC conditions. The maximum SC current estimation, SC current rms value variation, and torque harmonic component distribution under the two fault conditions are further investigated. The results can be used for ISC fault diagnosis, PM demagnetization evaluation, and post-fault performance prediction of ISC fault. The post-fault hardware reconfiguration method is further provided to alleviate the effect of ISC fault and reduce the difficulty of compensation.

Impact of Inverter Based Resources on System Protection

Inverter-based resources (IBRs) exhibit different short-circuit characteristics compared to traditional synchronous generators (SGs). Hence, increased uptake of IBRs in the power system is expected to impact the performance of traditional protective relay schemes—set under the assumption of a SG-dominated power system. Protection engineers need to study these challenges and develop remedial solutions ensuring the effectiveness of system protection under higher levels of IBRs. To address this need, this paper studies the impact of IBRs on a variety of protective relay schemes including line distance protection, memory-polarized zero sequence directional protective relay element, negative sequence quantities-based protection, line current differential protection, phase comparison protection, rate-of-change-of-frequency, and power swing detection. For each protection function, potential misoperation scenarios are identified, and recommendations are provided to address the misoperation issue. The objective is to provide an improved understanding of the way IBRs may negatively impact the performance of traditional protection schemes as a first step towards developing future remedial solutions ensuring effective protection under high share of IBRs.

Short-Circuit Characteristics of Superconducting Permanent Magnet Generators for 10 MW Wind Turbines

Superconducting permanent magnet generators (SCPMGs) are a potential candidate for 10 MW direct-drive wind turbine applications. This paper presents two 10 MW SCPMG designs using MgB <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> cables for the armature winding and investigates the short-circuit characteristics of the designed SCPMGs. The first part of the results shows that the SCPMGs can double the shear stress of a conventional low-speed permanent magnet (PM) generator (from 65 kPa to 130 kPa) whilst avoiding demagnetization of the PMs in rated-load operation. However, the power factor has to drop to a range of 0.7-0.8. The second part of the results shows that during a sudden three-phase short circuit, the superconducting armature winding is prone to quench and the PMs are likely to be demagnetized in both proposed designs.

A Coordinated Voltage–Frequency Support Scheme for Storage Systems Connected to Distribution Grids

Power electronics converters are utilized for interconnecting distributed energy storage systems into the grid. These converters can support the stability of the power system under abnormal grid conditions. In this article, a new coordinated voltage-frequency support strategy is proposed for energy storage systems considering the reactance-to-resistance ratio of the grid impedance. Unlike conventional support schemes for transmission grids, where voltage and frequency support is decoupled, the proposed strategy considers the coupling between voltage and frequency due to the resistive characteristics of the grid impedance in low-voltage distribution grids. An advanced frequency support scheme is also developed considering both droop-based frequency support and virtual inertia control for improving frequency stability. The proposed strategy ensures a fair compensation between voltage and frequency support by utilizing an adaptive gain that is calculated online according to the short-circuit fault characteristics. Simulations and experimental tests are carried out using a laboratory setup to validate the proposed strategy.

Determination of failure degree of 1.2 kV SiC MOSFETs after short-circuit test using an improved test setup

Abstract Analysis of the short-circuit characteristics of SiC metal-oxide-semiconductor field-effect transistors (MOSFETs) is very important for their practical application. This paper studies the SiC MOSFET short-circuit characteristics with an improved test setup under different conditions. A high-current Si insulated gate bipolar transistor is used as a circuit breaker in the test circuit rather than the usual short-circuit test conducted without a circuit breaker. The test platform with a circuit breaker does not influence the calculation results regarding the short-circuit withstand time and energy, but the SiC MOSFET will switch off after failure in a very short time. In addition, the degree of failure will be limited and confined to a small area, such that the damage to the chip will be clearly observable, which is significant for short-circuit failure analysis.

Mechanism of second harmonic generation of photovoltaic grid-connected system faults and its impact on transformer protection

The short-circuit transient characteristics of photovoltaic(PV) power system are different from traditional power sources. When the grid voltage drops, the output current of PV will contain a high proportion of second harmonics which cannot be ignored. This paper takes a single-phase turn-to-turn short-circuit fault inside the PV grid-connected transformer as an example. First, it analyzes the mechanism of single-frequency input and double-frequency output of a three-phase grid-connected inverter based on a phase-locked loop (PLL), and secondly, considering the comprehensive grid-connected control strategy, the principle of current second harmonic in the minor faults is analyzed and the analytical expression of second harmonics is derived. It is pointed out that the transient dc component will produce second harmonic component in the grid-connected current through control system of the inverter. This current induces a second harmonic voltage in the impedance, and as a disturbance term it generates a new harmonic current through the control link. Superimposed second harmonic currents in two scenarios may threaten the reliability of transformer differential protection. Finally, the correctness of the theoretical analysis is verified by simulation based on MATLAB/Simulink.

Faulty Synchronization of Salient Pole Synchronous Hydro Generator

This article presents the simulation results of hydro generator faulty synchronization during connection to the grid for various voltage phase shift changes in a full range (−180°; 180°). A field-circuit model of salient pole synchronous hydro generator was used to perform the calculation results. It was verified using the measured no-load and three-phase short-circuit characteristics. This model allowed observing the physical phenomena existing in the investigated machine, especially in the rotor which was hardly accessible for measurement. The presented analysis shows the influence of faulty synchronization on the power system stability and the construction components which are the most vulnerable to damage. From a mechanical point of view, the most dangerous case was for the voltage phase shift equal to −120°, and this case was analyzed in detail. Great emphasis was placed on the following physical quantities: electromagnetic torque, stator current, stator voltage, rotor current, current in rotor bars, and active and reactive power. The physical quantities existing during faulty synchronization were compared with a three-phase sudden short-circuit state. From this comparison, we selected the values of physical quantities that should be taken into account during design of new hydro generators to withstand the greatest possible threats during long-term work.

Нелінійна Simulink-модель синхронного генератора як об’єкта регулювання напруги

Представлена нелінійна математична модель синхронного генератора як об'єкта регулювання напруги. Модель побудована на основі рівнянь Парка-Горєва для ідеалізованого синхронного генератора при припущенні, що перехідні процеси в колах якоря і демпферної обмотки протікають значно швидше, ніж в колі обмотки збудження. У моделі враховується вплив ступеня насичення магнітної системи на індуктивності синхронної машини, що дозволяє досліджувати роботу генератора в контурі регулювання напруги при значних змінах струму збудження і навантаження. Вихідними даними для отримання залежностей індуктивностей від струму збудження є експериментальні характеристики холостого ходу і короткого замикання. Модель синхронного генератора побудована в середовищі імітаційного моделювання MatLab/Simulink. В процесі моделювання порівнювалися моделі синхронного генератора без урахування насичення магнітної системи, з урахуванням впливу насичення тільки на індуктивність обмотки збудження і з повним урахуванням насичення. Отримані результати моделювання показують важливість урахування впливу струму збудження на індуктивності генератора при дослідженні процесів регулювання напруги. Запропонована модель може бути корисна при аналізі роботи системи автоматичного регулювання напруги синхронного генератора для отримання кривих перехідних процесів, наближених до реальних експериментальних даних.

Detection Technology for Battery Safety in Electric Vehicles: A Review

The safety of electric vehicles (EVs) has aroused widespread concern and attention. As the core component of an EV, the power battery directly affects the performance and safety. In order to improve the safety of power batteries, the internal failure mechanism and behavior characteristics of internal short circuit (ISC) and thermal runaway (TR) in extreme cases need to be tested and studied. The safety of lithium ion batteries (LIBs) has become a research hotspot for many scholars. With unreasonable misuse or abuse of lithium ion batteries, it is easy to cause internal short circuits, resulting in thermal runaway, which poses a great threat to the safety of the whole vehicle. This comprehensive review aims to describe the research progress of safety testing methods and technologies of lithium ion batteries under conditions of mechanical, electrical, and thermal abuse, and presents existing problems and future research directions.

Research on dynamic simulation technology and fault characteristics of Pumped Storage Power Station

The fault equivalent circuit model of the pumped storage unit is established, the key electrical parameters of the generator motor of the pumped storage power station are analyzed, and the short-circuit fault characteristics of the generator motor of the pumped storage power station are studied. Based on the typical connection mode of pumped storage power station, a dynamic model test platform including dynamic model pumped storage unit, excitation system, frequency conversion starting device and its control system is established. The dynamic model tests of metal or transition resistance short circuit fault, stator ground fault and stator turn to turn short circuit are carried out.