Short-circuit Characteristics Research Articles

Methods for Determining Losses and Parameters of Cylindrical-Rotor Medium-Power Synchronous Generators

This paper presents the analytical and numerical application of a method to determine the parameters and power losses in the core of two medium-power synchronous generators. These generators are used as emergency power sources powered by diesel engines, gas engines, and gas turbines. They cover peak electricity demand but can also be used in traction drives. This article presents a new numerical method for determining losses in the generator core based on the use of a time-stepping solution using the FEM method and calculating these losses using analytical formulas. In calculating the losses for the FEM method, approximations of the loss characteristics of the sheet were used with a wide range of induction values and frequencies. This method is specific to the solution used and was adapted from the authors’ previous work on losses in induction machines. A one-phase winding with alternating voltage was supplied to determine the basic parameters in the form of synchronous reactance. Also, an important novelty is the introduction of a new method of determining the saturation state of the magnetic circuit, which significantly affects the machine parameters. The obtained results were used in analytical calculations and implemented in a computer program that allows for the calculation of electromagnetic parameters, operating characteristics, and core losses, taking into account additional losses, total losses, and efficiency, as well as machine parameters in unsteady operating states and the current characteristics of a three-phase symmetrical short circuit at the machine terminals. The calculations obtained were verified experimentally by measurements of real machines.

Investigating the impact of magnetic air gap variations on short circuit characteristics of partially high temperature superconducting generator

Partially high-temperature superconducting generators (PHTSGs) feature large magnetic air gaps imposed by using cryostats for HTS field windings. This increased air gap significantly affects end winding inductance and can lead to elevated fault torque levels. This study investigates the influence of magnetic air gap variation on generator design and end winding inductance and its implications for short-circuit faults in PHTSGs. Through a combination of numerical simulations and analytical analysis, the study explores how changes in the magnetic air gap affect end winding inductance and subsequently influence short-circuit fault behavior. The results reveal a direct correlation between magnetic air gap length, end winding inductance, and key short-circuit parameters such as stator current, field currents, and electromagnetic torque. Notably, an increase in the magnetic air gap is observed to elevate stator and field currents and electromagnetic torque during short-circuit events. These insights underscore the importance of considering magnetic air gap variation and its impact on end winding inductance and its relationship with short circuit characteristics in the design and operation of PHTSGs, providing valuable insights for enhancing the resilience and performance of high-temperature superconductor-based generator systems.

Study on the Design of Valve Base Insulation and Power Supply Transformer for High-Voltage DC Circuit Breaker

Abstract High-voltage DC circuit breaker is a key piece of equipment to building DC power grids. DC circuit breakers need to support and isolate from high voltage to ground through valve-based equipment and use valve-based power supply transformer to continuously supply energy to high potential components, the electrical performance of these two equipment determines whether DC circuit breakers and DC networks can be operated safely and reliably. For this reason, this paper carries out the research on the insulation capability of the valve base and the performance of the power supply transformer, such as the design and simulation of electric and thermal fields, as well as the test program. Firstly, the insulation design and simulation study of the valve base as a whole is carried out, and the design optimization of the equipotential scheme of the top homogeneous tubular bus, diagonal pull insulator and hydroelectric pole is completed. Secondly, the design and simulation verification of the thermal field distribution of the energy-supply transformer, the overvoltage between the ends of the output windings and the optimization scheme, and the short-circuit impedance were carried out. Finally, the insulation performance of the valve base, the temperature rise of the energy supply transformer, the overvoltage simulation of the output winding and the short-circuit characteristics were tested. The results show that: after optimization, the maximum field strength of the homogenizer is 2.3kV/mm, and the overall maximum field strength of the valve base is 2.61 kV/mm on the diagonal insulator, and there is no pressure difference between the water circuit and the fittings using the three-pin vertically distributed hydropower electrode scheme; the temperature rise of the supply transformer in the simulation and the actual measurement is 27K and less than 30K; by means of the parallel connection of the MOV, the overvoltage of the output winding of the power supply transformer under voltage impulse is effectively reduced to -1.8kV; the measured short-circuit impedance of the power supply transformer is 69.5%. The optimized design of DC circuit breaker valve base and power supply transformer can operate safely, and effectively support the construction of DC circuit breaker and DC power network.

An investigation into the short-circuit characteristics of Sic MOSFET power devices

Silicon carbide (SiC) metal-oxide-semiconductor field-effect transistor (MOSFET) devices exhibit substantial prospects for application under extreme operational conditions, including elevated temperatures, high voltages, and high frequencies. Nevertheless, owing to their distinctive material and structural attributes, SiC MOSFET devices are not devoid of challenges, with the short-circuit phenomenon constituting a pivotal avenue of inquiry. The short-circuit effect pertains to the abrupt escalation of leakage current that these devices might undergo under elevated voltage conditions, thereby exerting a perturbing influence on their stability and reliability. Investigations into the short-circuit effect predominantly revolve around two dimensions: one involves comprehending its underlying physical mechanisms, while the other centers on identifying commensurate remedial approaches.With respect to the underlying physical mechanisms, researchers have discerned that the elevated breakdown field strength and augmented carrier mobility intrinsic to SiC materials engender an augmentation in leakage current, consequently giving rise to the short-circuit effect. Furthermore, factors such as oxide layer anomalies and surface states are also conceivable catalysts for the surge in leakage current. To rectify this predicament, scholars have proffered a panoply of stratagems, encompassing the optimization of material synthesis processes, enhancement of oxide layer quality, refinement of device structural designs, and incorporation of protective circuitry, among others. In summation, the investigation of the short-circuit effect in silicon carbide MOSFET devices is fundamentally aimed at attaining an in-depth comprehension of its causative mechanisms. Moreover, it endeavors to proffer efficacious resolutions conducive to augmenting the reliability and steadfastness of these devices within high-temperature and high-voltage environments, thereby facilitating their widespread integration within the ambit of high-performance power electronics.

The advantages and short circuit characteristics of SiC MOSFETs

SiC MOSFETs have exhibited considerable benefits in high-frequency, high-voltage, and high-temperature power electronics applications with outstanding material attributes as a result of the rapid advancement of power electronics technology. SiC MOSFETs slower short-circuit tolerance and faster switching rates provide new issues for the short-circuit prevention technology. In the opening section of the study, Si and SiC MOSFETs are compared and evaluated using various models and parametric factors. It has been demonstrated that SiC MOSFETs outperform Si MOSFETs in a variety of conditions and applications. The many SiC MOSFET short-circuit failure types as well as their underlying theories are initially explained in the papers main body. In addition, it examines the fundamentals of short-circuit test procedures and SiC MOSFET test circuits. The issues and limitations of the currently available SiC MOSFET short-circuit protection technology are then explored, along with factors impacting the short-circuit of SiC MOSFETs that are thoroughly examined. Lastly, the SiC MOSFET short-circuit protection technology development trend is forecasted, and potential future areas for improvement and innovation are considered. SiC MOSFET short-circuit protection technology will be enhanced and optimized to satisfy the needs of efficient and dependable power electronic systems as technology advances and application requirements expand.

Comparative analysis of the characteristics of outlet short circuit and winding insulation fault of distribution transformer and its preventive measures

AbstractOutlet short circuit on the low‐voltage (LV) side and winding inter‐turn short circuit faults are hazardous to transformer operation. To investigate the formation mechanism of winding insulation faults of distribution transformer, ANSYS Maxwell was used to build a coupled magnetic field‐circuit model with the same structural dimension as the actual distribution transformer. An outlet short circuit and winding inter‐turn insulation faults were set by using the voltage‐controlled switch in the external circuit of the model. Subsequently, the differences in the electromagnetic characteristics and the electrodynamic force distributions of the windings under three operating conditions, namely, nominal load, three‐phase outlet short circuit on the LV side and inter‐turn insulation failure were studied, respectively. The results show that compared with the rated load, in the cases of outlet short circuit and inter‐turn insulation faults, the amplitude of winding current increases by 20 and 50 times, the magnetic field strength grows by 20 and 17 times, and the electrodynamic force rises by 400 and 230 times, respectively. Outlet short circuit fault is more likely to cause the winding instability and deformation, and inter‐turn short circuit fault can easily burn out winding insulation. Therefore, corresponding preventive measures were proposed.

Analysis and research on short-circuit current characteristics and grid access faults of wind farms with multi-type fans

As the grid-connected capacity of a large number of wind farms continues to increase, their short-circuit current will have a great impact on protection. Therefore, accurate short-circuit current calculation is beneficial for correct protection action evaluation. Considering the issues related to the diversity of wind turbine types in wind farms and the inability to accurately simulate the failure transient process in previous studies, this research focuses on investigating the impact of control strategies during faults on the transient process of wind turbines. In this paper, the single-machine equivalent model of doubly-fed induction generators (DFIG) and permanent magnet synchronous machine (PMSM) is established by considering the types of wind turbines, and the calculation method of short-circuit current of hybrid wind farms is further proposed by using the classification aggregation equivalent effect method. The accuracy of short-circuit current calculation proposed in this article was verified on RTDS, and a power grid fault analysis method suitable for wind farm connection was proposed based on the characteristics of equivalent circuits of DFIG and PMSM during fault steady-state.

A Broadband Magnetic Probe with Multi-Components Measurement Characteristics

In this study, a broadband magnetic probe with multi-components measurement characteristics is presented. Two orthogonal detection loops with short-circuit characteristics are introduced into the bottom of the probe to simultaneously sense two orthogonal magnetic-field components. Multiple via fences are used to restrain unwanted electromagnetic modes. Two different vias are used to form these detection loops: a connected via is used as a part of the vertical loop, and a shorted via is used for shorting these detection loops. Due to the existence of these orthogonal loops, the proposed probe is capable of simultaneously measuring two orthogonal magnetic-field components. The working frequency band is from 1 MHz to 18 GHz. The simulated and measured results are shown, compared, and analyzed to demonstrate the design rationality.

Calculation method of external fault short-circuit current for variable-speed pumped storage units based on time-domain dynamic circuit

The calculation method of the external fault short-circuit current of large units with clear mechanisms and practicality is of great value in engineering practice. Due to the special AC excitation structure and control mode, the external fault short-circuit characteristics of variable-speed pumped storage units (VSPSUs) are very different from those of conventional units. Therefore, this paper proposes a calculation method for external fault short-circuit current based on a time-domain dynamic circuit. According to the excitation and control characteristics of VSPSUs under external fault, the VSPSU under external fault is divided into two cases: continuous excitation and jumper action. Based on space vector analysis, the time-domain dynamic circuit models are established, respectively. On this basis, the analytical formula of the external fault short-circuit current of VSPSUs is derived by combining the transition boundary conditions of the two cases and the dynamic characteristics of the stator flux linkage. Finally, the comparison with PSCAD/EMTDC simulation results shows that the proposed VSPSUs’ external fault short-circuit current calculation method has high accuracy and practical value, which can meet the needs of primary equipment selection and relay protection of variable-speed pumped storage power plants.

Protection for AC transmission line between DFIG wind farm and MMC station

The characteristics of power electronic controlled sources are reflected at both ends of the AC line applied to the integration of long-distance wind farms into the MMC-HVDC converter station, and the fault characteristics of the system have undergone fundamental changes. For the doubly-fed wind power AC transmission line with a modular multilevel converter, the short-circuit current characteristics provided by the power supply at both ends of the line lead to the inadaptability of longitudinal differential protection. In view of the significant difference in the complexity of the short-circuit current component provided by the doubly-fed wind power and the converter at both ends of the AC transmission line, a line pilot protection idea based on the complexity of the current component is proposed. The complexity of the current component is characterized by singular entropy theory, and then the singular entropy algorithm and its scheme for pilot protection are constructed. A refined electromagnetic transient model of MMC-HVDC for doubly-fed wind farms is built in PSCAD for simulation verification. The simulation results show that the proposed method can quickly and reliably identify various types of internal and external faults, and solve the problem of incorrect action of traditional protection in this scenario. In addition, the scheme is not affected by fault type, location, or transition resistance.

Analysis of short-circuit behavior and failure modes in SiC power devices

This essay presents the advantages of SiC power devices, while the short-circuit characteristics limit their development. The device short-circuit will seriously affect the efficiency of the use of the period. When a load short circuit occurs, both ends of the power MOSFET device will be directly connected to the high bus voltage; therefore, the short circuit process poses a great challenge to the device's ability to withstand high voltage, high current, and high junction temperature simultaneously. In this thesis, the short-circuit process of SiC power devices is investigated by designing a detection circuit, and two failure mechanisms of SiC MOSFET power devices are explained through the understanding of the failure mechanism.

Investigation of Impulse Aging of Energy-Absorption Elements for Hybrid DC Circuit Breakers

The state of the energy-absorption branch MOV in the hybrid DC circuit breaker (DCCB) has a very important impact on the short fault breaking operation of the circuit breaker. Therefore, it is necessary to evaluate the state of the MOV, which is also called the “sleep component”. Due to DCCB being placed indoors, the aging is mainly caused by short-circuit impulse current. Therefore, this paper mainly focuses on the study of the short-circuit impulse aging characteristics of the energy-absorption branch MOV. The dynamic simulation system of a hybrid DCCB was built to investigate the impulse of short-circuit current on the MOV of the energy-absorption branch during the circuit breaking process. Then, an accelerated impulse aging test platform was built and the accelerated impulse aging tests of the MOV were conducted. The aging characteristics of the MOV were analyzed in detail and detailed analysis was conducted of the macroscopic parameters and microstructure changes. The results indicate that the nonlinear coefficient α could be emphasized as a basis for judging the “sleeping” component states and aging degree of the hybrid DC circuit breaker, and can be expected to be applicable to MOV condition monitoring of BCCB in the future.

Investigate the performance characteristics of three phase synchronous machine

The paper presents a step by step procedure to identify the parameter values of synchronous machines and determine the equivalent circuit. Furthermore the study expands to exam the performance characteristics of the machines. In other wards study the three phase synchronous machines behaviour in steady-state or dynamic behaviour. The results are exposed that the advantage of three phase synchronous machines and why three phase synchronous machines have been used for widely range in electrical system applications and network grid. Usual standards recommend different tests on a platform in order to determine these parameters. This report include the result of tests at open circuit characteristic (OCC) and short circuit characteristic (SCC) of the machine, open loop voltage/frequency (V/F) control mode of the drive system, operating with high frequency PWM (pulse width modulation), exhibits the impact of load changes on the synchronous motor with a fixed field excitation by plotting the phasor diagram and impact of varying field excitation on the synchronous motor with fixed load in terms of V-curves. Furthermore the correlation between current, excitation and torque is investigated. The purpose of this experiment is to obtain the machines parameters experimentally and comparing with manufacture data sheet. Eventually, discussing the obtained results for all milestones individually.

The Investigation of 1200V SiC MOSFET Short-Circuit Ruggedness and Turn-Off Current Tail

Short circuit characteristics of 4H-SiC MOSFETs with different channel lengths are studied in this work. The peak drain-source current during the short-circuit period is measured. These results show that short channel devices has lower capability to sustain short-circuit condition. This work found an evident current tail after the gate turning off. Through the investigation with different device design, circuit condition and numeric simulation. The cause of the current tail is found to be due to the increased ionization of electron-hole pair as the junction temperature is elevated at long short-circuit condition.

Comparison of Gamma Irradiation Effects on Short Circuit Characteristics of SiC MOSFET Power Devices between Planar and Trench Structures

The short circuit withstand energy (SCWE) variations, and short circuit withstand time (SCWT) variations, of planar and trench silicon carbide (SiC) metal-oxide-semiconductor field-effect transistor (MOSFET) power devices are studied after exposure to a total ionizing dose (TID). The results for ON bias are explored. The SCWE and SCWT are studied for planar and trench SiC MOSFET power devices tested for TID with gamma irradiation. A higher degradation phenomenon for the SCWE and SCWT are observed for the planar SiC MOSFET. The physical mechanisms for these variations are analyzed and confirmed by technology computer-aided design (TCAD) simulation.

Effect of Various Radiant Heat Fluxes on the Types and Characteristics of Short Circuit on Residential Electrical Cables

Effect of Various Radiant Heat Fluxes on the Types and Characteristics of Short Circuit on Residential Electrical Cables

Analysis of Short-Circuit Fault Current Characteristics on AC Side of Wind-PV-Storage Integrated Grid Connected System

The penetration rate of Wind-Soloar-Storage integrated grid-connected systems in the power grid is getting higher and higher. However, the mechanism of its influence on the short-circuit current is still not deeply understood. This paper analyzes the low-voltage ride-through and reactive power compensation strategies of a Wind-PV-Storage integrated grid-connected system; the short-circuit process of the AC side is studied, and the voltage sag degree and limiting link affect the steady amplitude and phase of the current. Through establishing the Wind-PV-Storage integrated grid connected system model in PSCAD/EMTDC, theoretical analysis and verification are carried out on the influence of factors such as the collection line inside the station and different capacity distribution proportions of the station on the short-circuit current.

Waveform differential based pilot protection for transmission line connected to renewable energy sources

Affected by the control objectives of the inverter, the short-circuit characteristics of renewable energy sources are quite different from those of traditional synchronous generators. As a result, the performance of traditional protection is degraded, and may lead to mis-operation and rejection, posing hazards for the safety of the power grid. In this research, the fault characteristics of renewable energy sources and traditional synchronous generators are analyzed and compared. Then, according to the difference between the fault transient current waveforms of two power sources, a pilot protection principle based on Canberra distance is proposed. Considering the phase angle error and amplitude error during normal operation, the protection constant is theoretically set to 0.35. Simulations and field experiments show that the protection principle reliably distinguishes the faults inside and outside the zone in different scenarios. The protection is less affected by short-circuit current amplitude and abnormal data, because the numerator of Canberra distance signifies the difference between the transient current waveforms and denominator normalizes the difference. In addition, the Canberra distance is 1 when the output of renewable energy sources is 0, so the proposed protection is also applicable to the scenario where the renewable energy sources output is 0.

Research on Pilot Protection for Tie Line of Renewable Energy Sources

With the continuous increase in the proportion, renewable energy sources have brought great challenges to the traditional protection based on fundamental frequency, due to their complex short-circuit current characteristics which are different from synchronous generators. As the main protection of the tie line (outgoing line) of the renewable energy station, the differential protection will also be seriously affected in terms of its operation performance, and even the operation failure or maloperation may occur in some cases. This paper proposes a new principle of pilot protection based on cosine similarity comparison by analyzing the fault characteristics of renewable energy sources. With the full current as the main criterion and the current fault component as the auxiliary criterion, this principle comprehensively utilizes the time domain information of the current on both sides of the line to improve the protection sensitivity. At the same time, a method of capacitive current compensation for the sampling value is proposed according to the algorithm characteristics of similarity comparison, to prevent the protection maloperation in the case of external faults. The simulation results show that, compared with the existing pilot protection based on similarity comparison, the new protection principle proposed in this paper has good engineering application value by identifying internal and external faults in a more reliable and sensitive manner.

Model Evaluation and Analysis for Multi-topology Lithium Battery Pack External Short Circuit Characteristics

Model Evaluation and Analysis for Multi-topology Lithium Battery Pack External Short Circuit Characteristics