Short-circuit Tests Research Articles

Type tests on MMC-based HVDC valve section with synthetic test circuits

Summary Electrical type tests are a key step to verify the design of voltage source converter valves for a specific modular multilevel converter (MMC) high-voltage direct current (HVDC) project. For a high-power handling capability of modern insulated gate bipolar transistor (IGBT), it is very difficult to balance between type test quality and test rig investment. In compliance with IEC 62501 and CIGRE 447 requirement, this paper presents a kind of synthetic test circuits (STCs), consisting of a steady-state test circuit, an IGBT overcurrent turn-off test circuit, and a short-circuit current test circuit, used for operational tests on MMC-based IGBT valve sections. Using the STCs, the current stress, the voltage stress, the junction temperature, di/dt, the performance of the valve's electronic circuits, and the protection capability of the parallel thyristor can be validated. Further, the parameters of the test circuits can be adjusted with the number of submodules of the MMC test valve. Thus, the STCs are an economical alternative for testing a representative part of an MMC valve. The paper describes and discusses the type tests, completely performed with the three test circuits, on MMC valves for a Xiamen MMC HVDC scheme, which is rated at 1000 MW/±320 kV. Copyright © 2016 John Wiley & Sons, Ltd.

Verification of Short Circuit Test Results of Salient Poles Synchronous Generator

Verification of Short Circuit Test Results of Salient Poles Synchronous Generator

Fault Transient Analysis and Protection Performance Evaluation within a Large-scale PV Power Plant

In this paper, a short-circuit test within a large-scale PV power plant with a total capacity of 850MWp is discussed. The fault currents supplied by the PV generation units are presented and analysed. According to the fault behaviour, the existing protection coordination principles with the plant are considered and their performances are evaluated. Moreover, these protections are examined in simulation platform under different operating situations. A simple measure with communication system is proposed to deal with the foreseeable problem about the current protection scheme in the PV power plant.

Modelling of aircraft harness tests via Petri network

In aircraft factories, automated cable test equipments are used at the final stage of harness manufacturing before hooking up process. They try to find whether there is a broken wire or a leakage on cable. This paper examines the continuity (open-circuit) and insulation (short circuit) test operations of an aircraft cable by using Petri net model and also explains operation principle of test equipment theoretically. The proposed model basically identifies aircraft wiring test operations that are applied by automated test equipments and presents all real test conditions in a realistic way. Different from other literature studies, a general model of automated test equipment is tried to model for detecting both open circuit and short circuit faults. Furthermore, this work shows that basic training test equipment can be constructed easily combining adjustable voltage sources, analog to digital converter (ADC), switches and so on.

Modelling of aircraft harness tests via Petri network

In aircraft factories, automated cable test equipments are used at the final stage of harness manufacturing before hooking up process. They try to find whether there is a broken wire or a leakage on cable. This paper examines the continuity (open-circuit) and insulation (short circuit) test operations of an aircraft cable by using Petri net model and also explains operation principle of test equipment theoretically. The proposed model basically identifies aircraft wiring test operations that are applied by automated test equipments and presents all real test conditions in a realistic way. Different from other literature studies, a general model of automated test equipment is tried to model for detecting both open circuit and short circuit faults. Furthermore, this work shows that basic training test equipment can be constructed easily combining adjustable voltage sources, analog to digital converter (ADC), switches and so on.

Analysis of Series-Connected IGBTs Protection Method under Short Circuit II

The difference between single and series-connected insulated gate bipolar transistor (IGBTs) during short circuit II (SC II) is analyzed contrastively, and requirements for an improved protection have been advanced to solve the SC II problem of series-connected IGBTs. A new principle of short circuit protection based on the logic of SC II fault processing used by the main control unit was proposed, using an active voltage clamping circuit to balance the dynamic voltage during breakdown, using an RC circuit to balance the voltage during tail current stage, and a formula to estimate the absorption capacitance and the selection principle of static voltage balancing resistance was proposed. The parameters under the actual test condition was given, the short circuit test system of series-connected IGBTs established, and the experimental verification carried out under the actual conditions. The result shows that under a Vbus of 1400V (2.65kV maximum peak voltage for each IGBT), the new protection method can provide synchronization of protect operation and voltage balancing during turning-off process, and the unbalance of steady stage voltage is under 5%.

続流遮断型アークホーンの遮断部溶発を考慮した数値流体解析手法の開発

This paper has presented a computational fluid dynamics simulation technique for Fault Current Interrupting Arcing Horns (FCIAH) to obtain the pressure and wear mass by an arc in the interruption core. The physical quantities have been calculated spatially and temporally by applying heat source inside the interruption core corresponding to arc power and solving conservation laws step by step taking into account the physical property and ablation. The validity of the simulation technique has been verified by comparing the pressure and wear mass obtained from short-circuit test results.

A Structural Based Thermal Model Description for Vertical SiC Power MOSFETs under Fault Conditions

The accurate prediction of the SiC MOSFET withstanding time for single fault events greatly influences the requirements for device protection circuits for these devices in power converter applications, like voltage source inverters or power electronic transformers. For this reason, a thermal model, based on the structural design and the physical dimensions of the chip as well as material properties of 4H-SiC, is proposed. This article gives a general description of the thermal behaviour of vertical SiC MOSFET under various driving and boundary conditions in case of a short-circuit event. The thermal model substitutes destructive tests of a device for an individual set of boundary conditions of an occurring fault event. The validity of the analytically parametrised thermal model is verified by experimental short-circuit tests of state-of-the-art vertical SiC MOSFETs for a set of various boundary conditions. The investigated thermal model can furthermore be used to standardise different gate-oxide degradation values from the literature for means of lifetime prediction of the gate oxide for an individual application under repetitive occurring fault or overload conditions. These manufacturer specific reported values measured with no standardised testing procedures can be translated into a maximum junction temperature, which is repeatedly reached. The thermal model therefore provides a unifying parameter for the gate-oxide lifetime calculation for an individual chip and application.

A feasibility study of full-bridge type superconducting fault current controller on electric machine power stability

Recently, because of the advent of Smart Grid and integration of distributed generations, electrical power grids are facing uncountable challenges. Increase of fault current is one of such serious challenges and there are some fault current limiters (FCLs) that can limit the fault current. Existing grid protection FCLs, however, simply limit the fault current passively and can allow the existing protection coordination schemes to fail. This phenomenon leads to catastrophic failure in the complex system and may cause unpredictable power grid operation. Unlike a FCL, a superconducting fault current controller (SFCC) employs a full-bridge thyristor rectifier, a high temperature superconducting (HTS) DC reactor, and an embedded control unit to maintain the fault current level at a proper value by adjusting the phase angle of thyristors. This paper contains experimental and numerical analysis to design and fabricate a SFCC system for protection and stability improvement in power grids. At first, fundamental characteristics of a SFCC system were introduced. System circuit diagram and operational principles were proposed. Secondly, the developed small-scale SFCC system was introduced and verified. A 40 Vrms/30 Arms class prototype SFCC employing HTS DC reactor was fabricated and short circuit tests that simulate various fault conditions were implemented to verify the control performance of the fault current. Finally, the practical feasibility of application of the SFCC system to the power system was studied. The problems caused by three-phase faults from the power grid were surveyed and transient stability analysis of the power system was conducted by simulations. From the experimental and simulation results, we can verify the feasibility of the SFCC in power system.

Extended Aging of Ag/W Circuit Breaker Contacts: Influence on Surface Structure, Electrical Properties, and UL Testing Performance

Samples of 120 V, 30 A commercial circuit breakers were subjected to various aging treatments and the resulting microstructures at the surfaces of the Ag/W contacts were studied using a combination of x-ray diffraction, scanning electron microscopy, and energy-dispersive x-ray spectroscopy techniques. Breakers aged naturally in a hot, humid climate were compared to those subjected to accelerated aging in dry and humid environments. The most extensive oxidation was observed for contacts from breakers subjected to accelerated humid aging; these contacts exhibited thick surface layers consisting of Ag2O, Ag2WO4, Cu(OH)2∙H2O, and WO3 phases. Far less surface degradation was observed for dry-aged contacts. Naturally aged contacts showed variations in degradation with more oxidation at the surface regions outside the physical contact area on the contact face. A correlation was found between the contact resistances measured from these samples following ASTM standard B 667-97 and the observed surface microstructures. To evaluate the effects of the surface oxides on breaker performance, humid-aged breakers were subjected to standardized UL overload/temperature-rise, endurance, and short-circuit testing following UL489. The contacts in these breakers exhibit similar microstructural and property changes to those observed previously for as-manufactured contacts after UL testing. These data illustrate the robust performance of this contact technology even after being subjected to aggressive artificial aging.

A New Method for Determining the Leakage Inductances of a Nine-Phase Synchronous Machine From No-Load and Short-Circuit Tests

The accurate determination of stator leakage inductances is presently an open issue in the analysis and testing of multiphase electric machines. Calculation methods are available, which involve complicated and often poorly precise three-dimensional (3-D) analyses. Experimental determination techniques, using measurements on the wound stator with the rotor removed, are also possible, but quite impractical, as they need to be performed during machine manufacturing or require rotor withdrawal. In this paper, a new approach is proposed to determine all the stator self- and mutual leakage inductances of a nine-phase synchronous machine based on a minimal set (a couple) of magnetostatic finite-element (FE) simulations, and on the measurements taken during no-load and short-circuit routine tests. The procedure is applied to a wound-field salient pole nine-phase synchronous generator for validation, showing good accordance with the results obtained from measurements on the machine with the rotor removed. A discussion is also proposed on the possibility to extend the presented procedure to other multiphase topologies.

Design of Transformer With High-Permeability Ferromagnetic Core and Strengthened Windings for Short-Circuit Condition

This paper provides the design of 1 MVA three-phase oil-immersed distribution transformers considering short-circuit testing (SCT) and its impact on the windings. To maintain the transformer function after the SCT, only an impedance variation within 5% is allowed. Therefore, in conjunction with the particle swarm optimization (PSO), a simulation-based optimal approach is developed for the design of the distribution transformers. Finite-element analysis is used to work with the PSO for the calculation of flux densities, costs, core losses, and magnetostriction variations for the transformers under a prescribed noise level. Three transformer prototypes are then built using two types of amorphous cores and a conventional silicon steel core, respectively. The performance after the SCT is evaluated for the prototypes constructed. From the test results, it is found that the amorphous core is suitable for transformers in terms of lower noise level, core loss, and magnetostriction variation.

Maximum Efficiency per Torque Direct Flux Vector Control of Induction Motor Drives

In this paper, a loss-minimizing strategy is proposed for induction motor drives to ensure maximum efficiency operation for a given torque demand. The proposed strategy directly regulates the machine stator flux, according to the desired torque, using an optimal stator flux reference. Therefore, the proposed strategy is suitable for motor control schemes that are based on direct flux regulation, such as direct torque control or direct flux vector control. The maximum efficiency per torque (MEPT) stator flux map is computed offline using the traditional no-load and short-circuit test data. An iron loss model based on the stator flux and frequency is also proposed for the calibration of the machine loss model and also for online monitoring of the iron losses during motor operation. The proposed MEPT strategy has been validated on a 2.2-kW induction machine, and the motor efficiency has been measured for different speed values and variable load conditions. The experimental results confirm the effectiveness of the proposed solution.

Test of an Original Superconducting Synchronous Machine Based on Magnetic Shielding

We present a new concept for a two-pole superconducting synchronous machine. This electrical motor is composed of a classical stator yoke, and an original superconducting inductor. The inductor is composed of two coaxial circular superconducting coils separated by superconducting bulks. Both solenoids are fed by a direct current and each of them produces a magnetic field in the same direction. An inclined superconducting bulk is placed between the two solenoids. It is used as superconducting magnetic barrier. The diamagnetic behavior of a superconducting bulk cooled under zero-field is used to obtain a variation of the magnetic flux density in the air-gap. The inductor is made of low-temperature superconducting wires for the coils, NbTi, and a high-temperature superconducting YBCO bulk, cooled down to 4.2K using liquid helium for the flux barrier. The armature is wound with copper wires as a classical one. We present design and tests of this superconducting motor. We made no load, short-circuit and full load tests.

Teaching Calculation of Transformer Equivalent Circuit Parameters using MATLAB/Simulink for Undergraduate Electric Machinery Courses

Background/Objectives: Computer-based educations have become popular thanks to their useful and flexible structures in classroom environment. Methods/Statistical analysis: This paper presents MATLAB/Simulink implementation of transformer tests, namely dc, open-circuit, and short-circuit tests performed to identify equivalent circuit parameters and effective education of transformer modeling at electric machinery courses and reinforcement of the theoretical concepts given at these courses. Results: The proposed method has been successfully integrated into electric machinery courses at Author University with very encouraging results. The results show that relative errors are negligible, and the proposed simulation models accurately predict equivalent circuit parameters. Conclusion/Application: This method will be very helpful for students when they carry out hardware laboratory experiments in electric machinery courses.

Surface Degradation of Ag/W Circuit Breaker Contacts During Standardized UL Testing

The near-surface microstructure of Ag/W contacts from 120 V, 30 A commercial circuit breakers in the as-manufactured condition and after standardized UL overload/temperature-rise, endurance, and short-circuit testing have been investigated using a combination of x-ray diffraction, scanning electron microscopy, energy-dispersive x-ray spectroscopy, focused ion beam milling, and transmission electron microscopy. The as-manufactured contacts comprised three constituents: sintered Ag/W composite particles with fine-grained Ag and coarse-grained W, coarse-grained pockets of Ag infiltrate, and a nano-crystalline surface Ag layer. There are also WO3 and Ag2O phases at the surface. After UL overload/temperature-rise testing, there is Ag loss giving a porous W-rich layer at the contact surface. In addition to binary oxides, we observe the formation of Ag2WO4. After UL endurance testing, material is swept across the surface by the breaker action giving a W-rich eroded porous surface on one side and a build-up of mixed oxides on the other. After UL short-circuit testing, a W crust forms due to melting and re-solidification of W and vaporization of Ag, and mid-plane cracks form due to the severe thermal gradients. There is a strong correlation between the observed microstructural features and the contact resistance measurements obtained from these samples.

In-depth investigation of metallization aging in power MOSFETs

The long-term reliability of modern power MOSFETs is assessed through accelerated electro-thermal aging tests. Previous studies have shown that the source metallization (top metal and wires) is a failure-prone location of the component. To study how the top aluminum metallization microstructure ages, we have performed ion and electron microscopy and mapped the grain structure before and after avalanche and short-circuit aging tests. The situation under the bond wires is significantly different as the bonding process induces plastic deformation prior to aging. Ion microscopy seems to show two inverse tendencies: grain growth under the wires and grain refinement elsewhere in the metallization. Transmission electron microscopy shows that the situation is more complex. Rearrangement of the initial defect and grain structure happen below and away from the wire. The most harmful fatigue cracks propagate parallel to the wire/metal bonding interface.

ROZWÓJ WYŁADOWANIA ŁUKOWEGO W OSIOWYM POLU MAGNETYCZNYM

The test results of the contacts generating the axial magnetic field made in Electrotechnical Institute are presented. Short-circuit test were made in dismountable vacuum chamber on two contacts. The diffusion arc of the interrupted short circuit currents recorded by means of a high speed camera are shown. At the first part of this paper the tests circuit and the equipment used were described. At the second part of this paper oscillograms and diffusion arc of the interrupted short circuit currents recorded by means high speed camera are attached. Conclusions contained the results of these investigations.

Preliminary Results of 1.5 kJ Mather-Type Plasma Focus with Stainless Steel Anode

A new low energy (1.5 kJ) Mather-type dense plasma focus, called Sahand University of Technology Dense Plasma Focus (SUT-DPF) device has been designed, constructed and operated. The paper reports on the preliminary results with argon as filling gas. A Rogowski coil has been used to measure the experimental discharge current. The current signal contains a set of data from physical processes in the device as well as discharge current characteristics. The device circuit parameters were calculated using the short-circuit test. In a typical discharge experiment, these values were obtained: the discharge period was 15.4 ± 0.1 μs, the discharge current 100.8 ± 0.7 kA, the total inductance of the device 197 ± 3 nH and electrical resistance of circuit 11.3 ± 1 mΩ. The Rogowski coil sensitivity was obtained 49.65 ± 0.3 kA/V. A resistive voltage divider was also used to measure the transient voltage across the plasma. The experimental results showed that the pinch time at a constant pressure of the argon gas, decreased by increasing the charging voltage. The optimum pressure for 5, 6.5 and 7.5 kV obtained 0.75, 1 and 1.5 mbar, respectively.

Experimental Results of 275-kV 3-kA REBCO HTS Power Cable

A 30-m-long 275-kV 3-kA high-temperature superconducting (HTS) cable had been developed in a national project of the Materials and Power Applications of Coated Conductors project in Japan. The design of the cable was based on the design values obtained from ac loss properties, thermal behavior under short-circuit tests, and electrical properties, such as partial discharge properties, impulse withstand properties, and dielectric properties. Through the development, the material of the cable insulation was determined and designed on the basis of its design stresses and test conditions based on the IEC, JEC (Japan electrical standards), and other HTS demonstrations. This cable was also designed to withstand a short-circuit test of 63 kA for 0.6 s and to have low losses of 0.8 W/m at 3 kA, 275 kV, including ac loss and dielectric loss. Based on these designs, a 50-m cable was manufactured and tested. The short samples obtained from 50 m were confirmed to have the designed characteristics. Furukawa Electric constructed a demonstration system of a 30-m cable with two terminations and a cable joint. The demonstration had started since November 2012 at Shenyang in China. In this demonstration, a 30-day long-term test was conducted and monitored at a current of 3 kA and at a test voltage selected to verify a 30-year operational lifetime. Removal tests revealed the superior reliability of the 275-kV HTS cable system.