Short-circuit Conditions Research Articles

RESEARCH ON SHORT-CIRCUIT IMPEDANCES OF NEW CONVERTER TRANSFORMER

The short-circuit impedance of converter transformers is one of the most important specifications in HVDC system. Compared with the traditional converter transformers, the new converter transformer has unique windings connection diagrams. Based on the topological structure of the new converter transformer, this paper proposes a new method to establish the mathematical relationship of short-circuit impedances and filters impedances under considering the valve side and grid side shortcircuit conditions. The analysis on short circuit at valve side and grid side shows that short-circuit impedances values are almost the same in both two conditions, so that the impedance of the new converter transformer is symmetrical. Finally, simulation and experimental results verify the correctness of the theoretical analysis.

The anion exchanger PAT-1 (Slc26a6) does not participate in oxalate or chloride transport by mouse large intestine.

The membrane-bound transport proteins responsible for oxalate secretion across the large intestine remain unidentified. The apical chloride/bicarbonate (Cl-/HCO3-) exchanger encoded by Slc26a6, known as PAT-1 (putative anion transporter 1), is a potential candidate. In the small intestine, PAT-1 makes a major contribution to oxalate secretion but whether this role extends into the large intestine has not been directly tested. Using the PAT-1 knockout (KO) mouse, we compared the unidirectional absorptive ([Formula: see text]) and secretory ([Formula: see text]) flux of oxalate and Cl- across cecum, proximal colon, and distal colon from wild-type (WT) and KO mice in vitro. We also utilized the non-specific inhibitor DIDS (4,4'-diisothiocyano-2,2'-stilbenedisulfonic acid) to confirm a role for PAT-1 in WT large intestine and (in KO tissues) highlight any other apical anion exchangers involved. Under symmetrical, short-circuit conditions the cecum and proximal colon did not transport oxalate on a net basis, whereas the distal colon supported net secretion. We found no evidence for the participation of PAT-1, or indeed any other DIDS-sensitive transport mechanism, in oxalate or Cl- by the large intestine. Most unexpectedly, mucosal DIDS concurrently stimulated [Formula: see text] and [Formula: see text] by 25-68% across each segment without impacting net transport. For the colon, these changes were directly proportional to increased transepithelial conductance suggesting this response was the result of bidirectional paracellular flux. In conclusion, PAT-1 does not contribute to oxalate or Cl- transport by the large intestine, and we urge caution when using DIDS with mouse colonic epithelium.

Dynamic Simulation of Unbalanced Magnetic Force in Doubly-Fed Induction Machine with Inter-turn Short-Circuited Stator

In the presented work, a dynamic model is provided for the wound-rotor induction machines with short-circuited stator winding. Both inter-turn phase-to-ground and inter-turn phase-to-phase short circuit faults are considered in the provided model. The self- and mutual-inductances of the windings of the faulty machine are the parameters of the provided state-space equations. As well as the machine electromagnetic torque and its stator and rotor currents, the waveform of the unbalanced magnetic force (UMF) in the faulty induction machine is predicted in the provided model. The UMF of the faulty machine is expressed by a static function of the machine currents. The parameters of the UMF function are obtained by using the Maxwell definition. The machine inductances and the air gap flux density distribution are obtained by means of winding function method. Since the exact waveforms of the machine turn functions are considered in computation of the air gap flux density, the special harmonics are taken into account inherently in the provided model. Finally, the developed model is verified by means of the time-stepping finite element model.

Annealing temperature dependence of the performance of bulk heterojunction polymer: Fullerene solar cells under short and open circuit conditions

The current density-voltage(J-V) characteristics and cole-cole impedance plots (-Im(Z) vs Re(Z)) of ITO/PEDOT:PSS/AnE-PVab:PCBM/Ca/Ag solar cells were measured under thermal annealing range 25–125 °C using AM 1.5 G (80 mW/cm2) solar simulator (white light). The fill factors (FF), the short-circuit current density (JSC) and the open-circuit voltage (VOC) initially increased up to 110 °C and then decayed considerably for higher annealing temperatures. Under short circuit conditions at 0 V DC, The Cole-Cole plots demonstrate an increase in the semicircle radius for devices annealed at 25 °C and 100 °C. Then, the semicircle radii decrease with increasing annealing temperatures from 105 °C and above. However, at VOC conditions, we observe that the semicircle radii increase with increasing the thermal annealing. To reproduce theoretically the observed cole-cole impedance plots at 0 V DC and VOC conditions for different annealing temperatures, we used an equivalent circuit in the framework of the transmission line model, incorporating the chemical capacitance (Cµ), the recombination resistance (Rrec), the transport resistance (Rt) and the contact electrical resistance (Rco). We determined the diffusion time (τdif), the recombination time (τrec), the diffusion length (Ln) at 0 V DC and VOC voltages. At VOC voltage, average mobility of global carriers for the device is around 4 10−3 cm2V−1s−1 , which is in good agreement with that derived using PCBM electron-only devices.

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.

Quantitative diagnosis of internal short circuit for cylindrical li-ion batteries based on multiclass relevance vector machine

Battery internal short circuit (ISC) state should always be supervised. To facilitate the use of battery thermal behaviors, this work develops a lumped thermal evolution model (TEM) based on the equivalent circuit model (ECM). Then, multiple dispersedly-configured TEM/ECM sub-models are synthesized using the extreme learning machine to approximate the distribution nature of real batteries. To acquire ISC dataset, three kinds of active-destruction experiments are carried out on the battery. Thereafter, from thermal and electrical residuals, four ISC features are extracted whereby the multiclass relevance vector machine is utilized to discriminate ISC state. Specially, according to the posterior probability outputs, ISC degree can also be quantified. Experimental results on cylindrical li-ion batteries verify the reliability of the model structure and suggest the proposed diagnosis scheme can recognize ISC faults effectively with a grade misjudgment rate of 14.59% and a state misjudgment rate as low as 3.13%.

Electro-photoluminescence study in InGaAs/AlGaAs multi-quantum-wells

Photoluminescence (PL) plays an important role in the study of luminescence characteristics of multi-quantum-well (MQW) structures. In this work, we study electro-photoluminescence spectra of InGaAs/AlGaAs MQWs under open-circuit, short-circuit, and forward-voltage conditions. The dependences of photocurrent and photovoltage on excitation power are discussed in this paper, which allows us to explore the carrier behavior in InGaAs/AlGaAs MQW LEDs deeply. We propose that the photovoltaic effect in open-circuit (OC) conditions should be properly considered for PL characterization and calculation of the internal quantum efficiency (IQE) as well as non-radiative recombination (NRA) efficiency in InGaAs/AlGaAs MQW LEDs.

Safety Issues Referred to Induced Sheath Voltages in High-Voltage Power Cables—Case Study

Load currents and short-circuit currents in high-voltage power cable lines are sources of the induced voltages in the power cables’ concentric metallic sheaths. When power cables operate with single-point bonding, which is the simplest bonding arrangement, these induced voltages may introduce an electric shock hazard or may lead to damage of the cables’ outer non-metallic sheaths at the unearthed end of the power cable line. To avoid these aforementioned hazards, both-ends bonding of metallic sheaths is implemented but, unfortunately, it leads to increased power losses in the power cable line, due to the currents circulating through the sheaths. A remedy for the circulating currents is cross bonding—the most advanced bonding solution. Each solution has advantages and disadvantages. In practice, the decision referred to its selection should be preceded by a wide analysis. This paper presents a case study of the induced sheath voltages in a specific 110 kV power cable line. This power cable line is a specific one, due to the relatively low level of transferred power, much lower than the one resulting from the current-carrying capacity of the cables. In such a line, the induced voltages in normal operating conditions are on a very low level. Thus, no electric shock hazard exists and for this reason, the simplest arrangement—single-point bonding—was initially recommended at the project stage. However, a more advanced computer-based investigation has shown that in the case of the short-circuit conditions, induced voltages for this arrangement are at an unacceptably high level and risk of the outer non-metallic sheaths damage occurs. Moreover, the induced voltages during short circuits are unacceptable in some sections of the cable line even for both-ends bonding and cross bonding. The computer simulations enable to propose a simple practical solution for limiting these voltages. Recommended configurations of this power cable line—from the point of view of the induced sheath voltages and power losses—are indicated.

Electrothermal Phenomena in Ferroelectrics

Physical properties of lead-zirconate-titanate (PZT) ceramics change according to the initial electric poling process and electrical boundary conditions. This paper reports the electrothermal, piezothermal, and piezoelectric coupling phenomena in ferroelectrics from thermodynamics viewpoints, in particular, thermal property differences between unpoled and poled PZT’s in the poling direction for open circuit and short circuit conditions. We propose a new terminology, “secondary electrothermal” coupling factor kλ, which is analogous to the electromechanical coupling factor k, relating the elastic compliances under short- and open-circuit conditions, in order to explain the fact that the short-circuit condition exhibited the larger thermal diffusivity than the open-circuit condition. On the other hand, the unpoled specimen exhibits the lowest thermal diffusivity. This tutorial paper was authored for providing comprehensive knowledge on equilibrium and time-dependent thermodynamics in ferroelectrics.

A Comprehensive Investigation on Short-Circuit Oscillation of p-GaN HEMTs

This article presents a study on the short-circuit (SC) instability of p-doped gate gallium nitride (p-GaN) high-electron-mobility transistors (HEMTs). Under SC condition, self-sustained oscillation occurs when a package stray inductance is introduced in a common source. The SC oscillation features some unique characteristics. With higher dc-bus voltage, the SC oscillation tends to be more unstable. The SC oscillation of p-GaN HEMTs is, thereby, a real threat to the converter operation. When the common-source inductance is eliminated or a larger gate resistor is utilized, the SC oscillation can be dampened. Due to the SPICE simulation, the self-sustained SC oscillation is reproduced. The analyses on the simulated waveforms reveal a positive feedback mechanism that excites the SC oscillation. An analytical model is, thereby, derived to analyze the instability of the positive feedback system. The analyses reveal that the SC oscillation becomes more unstable when the power loop or gate loop has smaller stray inductances, which makes some conventional oscillation suppression methods invalid. To avoid SC oscillation, some effective guidelines are proposed at the end of the article.

Simultaneous Wireless Data and Power Transfer for a 1-Gb/s GaAs VCSEL and Photovoltaic Link

We study the trade-off between energy harvesting and data communication for a two-meter wireless gallium-arsenide vertical-cavity surface-emitting laser and photovoltaic link. The use of orthogonal frequency-division multiplexing with adaptive bit and power loading results in a peak data rate of 1041 Mb/s at a bit-error ratio (BER) of $2.2\times 10^{-3}$ under short-circuit conditions. The receiver is shown to provide power harvesting with an efficiency of 41.7% under the irradiance of 0.3 W/cm2 and simultaneous data communication with a rate of 784 Mb/s at a BER of $2.8\times 10^{-3}$ . The experimental system is envisioned to become a paradigm for next-generation wireless backhaul communications and Internet-of-Things applications.

Eradication of non-capacitive effects with potassium incorporation in perovskite solar cells

The presence of redox reactions due to slow-moving ions at perovskite/contact interfaces is a major concern for the long-term stability of perovskite solar cells. In this work, we have evidently demonstrated the contribution of K+ ions on the removal of these non-capacitive effects that primarily accelerate the degradation mechanism in the devices. The intermittent current–voltage characteristics at the short-circuit conditions elucidate the role of K+ ions on reducing the rapid degradation at the interfaces due to the chemical reactivity of the accumulated ions by eliminating the burn-in decay in the photocurrent. Dark current–voltage measurements, time-resolved staircase voltammetry, and electrochemical impedance spectroscopy verified that both capacitive and non-capacitive currents, consequence of slow ion migration, are reduced by the incorporation of K+. Thus, this work signifies how K+ incorporation diminishes the internal degradation and enhances intrinsic stability of perovskite solar cells.

Fault Ride-Through Capability with Mutual Inductance in Low-Voltage Single-Phase Microgrid

Improving the microgrid fault ride-through capability and enhancing the transient performance of microgrid operation due to voltage sags is of great importance. This paper investigates the ride-through capability and feasibility of integrating a mutual inductance between the main grid and the microgrid under short circuit condition. The fault ride-through capability of the microgrid DGs is examined by placing the mutual inductance at PCC to suppress the fault current and to maintain the microgrid grid connected. This inductance requires no control to operate in which the sudden current increase is the key point of its operation. The microgrid DGs can operate successfully in grid-connected mode without reactive power support during the voltage sag duration. The effectiveness of the inserted mutual inductance has been validated considering two case scenarios of the microgrid power flow condition. The proposed methodology shows promising results, in which it confirms the applicability of the mutual inductance in riding through the fault current and maintaining the microgrid DG operation in the grid-connected mode. SimPowerSystems and PLECS toolboxes of Matlab/Simulink software are utilized to implement the proposed work.

Performance of Air-Stable Cs<sub>2</sub>SnI<sub>6</sub> Perovskite as Electron Transport Layer in Inverted Bulk Heterojunction Solar Cell

In recent years, perovskite material has been extensively studied due to its unique physical properties and promising application in the third generation of solar cells. In particular, Sn-based perovskite has been considered to replace Pb-based perovskite because of the toxic effects and it can lead to other serious problems related to the environment. Cs2SnI6 perovskite has been known to be synthesized in a simple chemical process and it can be produced on a large scale. Moreover, this material is also oxygen and moisture stable due to the high oxidation state of tin. In this study, we synthesize air-stable Cs2SnI6 perovskite by the use of the wet chemical process at room temperature. Next, we attempt to fabricate the inverted bulk heterojunction solar cells incorporated Cs2SnI6 as electron transport layer in the configuration of ITO/ZnO/Cs2SnI6/P3HT:PCBM/PEDOT:PSS/Ag to improve device performance. The Cs2SnI6 perovskite shows an Fm-3m space group with a cubic lattice parameter of 11.62Å confirmed by X-Ray Diffraction (XRD) measurement, while UV-Vis measurement indicates this type of perovskite has direct band gap ~3.1 eV. The fabricated solar cell device reveals the enhancement in current density at short circuit condition (Jsc) from 64.69 mA/cm2 to 77.02 mA/cm2 with the addition of 2.25 mg/ml Cs2SnI6 along with the enhancement of power conversion efficiency (PCE) from 7.05% to 9.75% as characterized by J-V measurement. In our case, the voltage at open circuit condition (Voc) of the device does not perform significant improvement. Besides, it is found that the solar cell devices are quite stable even after exposure in the air for six weeks after fabrication, as indicated by PCE performance.

Photovoltaic Characterization of Hybrid Bulk Heterojunction Solar Cell Incorporated Gold Nanoparticles Embedded in Active Layer

We attempt to study the effect of gold nanoparticles embedded into the active polymer of regioreguler poly (3-hexylthiophene) (P3HT) and phenyl-C61-butyric acid methyl ester (PCBM) on the charge kinetic to enhance the performance of bulk-heterojunction solar cell. It has been known that the generation of localized surface plasmon resonance (LSPR) would both increase the photon absorption and improve the efficiency of charge separation. Synthesis of gold nanoparticles stabilized by oleylamine (AuOA) was carried out by reduction method and resulted in the spherical shape of nanoparticles with a diameter size of ~12 nm. The absorbance spectra show the typical of surface plasmon peak of AuOA in solution at ~527 nm. Fabrication of inverted bulk-heterojunction solar cell device was done in the configuration of ITO/ZnO/P3HT:PCBM:AuOA/PEDOT:PSS/Ag. Incorporation of AuOA in polymer solution is clearly detected from the enhanced absorbance peak resulted from UV-Vis measurement and the mix solution of P3HT:PCBM:AuOA is quite stable in the concentration of AuOA less than 10 wt%. In our experiment, fabricated solar cell reveals the enhancement in current density at short circuit condition (Jsc) from 44.57 mA/cm2 to 56.14 mA/cm2 with the addition of 3.9 wt% AuOA in polymer solution along with the enhancement of power conversion efficiency (PCE) from 4.07% to 6.23% as characterized by J-V measurement. In our case, the voltage at open circuit condition (Voc) of the device does not show significant improvement.

Accelerated Testing of SiC Power Devices under High-Field Operating Conditions

Power metal-oxide-semiconductor field-effect transistors (MOSFETs) experience conditions of high field during normal operation. During switching conditions, unexpected transient events may occur which force devices into avalanche or short circuit conditions. Moreover, silicon carbide devices typically experience higher fields in the gate oxide and drift regions than comparable Si devices due to channel and drift property differences. A summary of SiC MOSFET reliability and ruggedness test results are reported here. Reliability tests under high field conditions: positive-bias and negative-bias temperature instability (PBTI, NBTI) to examine threshold stability; time-dependent dielectric breakdown (TDDB) for gate oxide lifetime extrapolation; high-temperature reverse bias (HTRB); and HTRB testing under high neutron flux to determine terrestrial neutron single-event burnout (SEB) rates. High-power ruggedness evaluation is presented for SiC MOSFETs under forced avalanche conditions (unclamped inductive switching (UIS)) and under short-circuit operation to bound device safe operating areas. Overall results demonstrate the intrinsic reliability of SiC MOSFETs.

Short Circuit Ruggedness of 600 V SiC Trench JFETs

Silicon Carbide JFETs with low on-state resistance are suitable for a number of high power applications. The static, dynamic and short circuit characterization of 600 V SiC Trench JFETs are reported in this paper. Typical JFETs fabricated with a 1.2 μm cell pitch had an on-resistance value around 40 mΩ and blocking voltages of ~600 V across the wafer. JFETs were successfully switched with a dc link voltage of 300 V, a current of 15 A and operating temperature of 125 °C. These JFETs were subjected to a short circuit condition with duration ranging from 10 μs to 45 μs at a dc link voltage of ~300 V, and operating temperatures of 25 °C and 125 °C. The device could withstand subsequent short circuit successfully without any failure at both 25 °C and 125 °C. The short circuit current showed consistent dependency on the applied gate voltage, when it was varied from 0 V to 15 V.

Electromechanical behaviors of soft and hard PZTs under different compressive stress pulses

In the present study, soft and hard PZTs discharge experiments under extrusion/impact were carried out to analyze the electromechanical behaviors under open and short circuit conditions. The results show that when subjected to extrusion, the soft PZT is more sensitive to stress, the hard PZT has higher discharge capacity under high-impedance (regard as open-circuit) condition, and the force-electric relationship of the two PZTs satisfy the traditional piezoelectric equation. Under impact, the open-circuit elastic compliance coefficient of two PZTs increases with the increase of stress, the maximum value is about 50 times of the quasi-static value, and the piezoelectric voltage coefficient is about 20% of the quasi-static value. The short-circuit elastic compliance coefficient of soft PZT is 10 times of the quasi-static coefficient, and the dynamic piezoelectric strain coefficient is 250% of the quasi-static coefficient. However, the dynamic stress-strain of hard PZT is nonlinear and the dynamic piezoelectric strain coefficient is 500 × 10−12 m/V, which is about double of the quasi-static constant.

A New Diagnostic Technique for Reliable Decision-Making on Transformer FRA Data in Interturn Short-Circuit Condition

Interpreting results of a transformer frequency response analysis (FRA) is quite challenging. One of the common methods to summarize FRA data is to employ statistical indicators (SIs) over FRA spectra. However, SI-specific boundary conditions for various operational modes of transformers are left unexplored. The lack of such boundary conditions renders interpretation of SIs difficult and subjective. In this article, in an attempt to find data-driven boundary conditions, first the conventional measurement setup of FRA technique is modified to emulate interturn winding short-circuit. Then, the boundary conditions of various SIs for normal, suspicious, and critical operational modes of transformers under fault are obtained. Nevertheless, the price of moving subjective boundaries to their objective data-driven counterparts is paid in an intrinsic uncertainty introduced by the process of data collection per se. In order to capture and quantify this uncertainty, a novel solution inspired by bolstered error estimation used in pattern recognition is proposed. In particular, the proposed method allows reporting the level of confidence that an observed magnitude of SI belongs to a specific operational mode. Having this confidence level is also warranted from an operational perspective because it enables utility operators to enhance the decision-making process and estimate the severity of transformer faulty conditions.

10-kV Transmission Line Experimental Platform for HEMP Immunity Test of Electrical Equipment in Operation

To investigate the high-altitude electromagnetic pulse (HEMP) immunity of electrical equipment in operation, a 10-kV transmission line (TL) experimental platform is built in this paper. The conducted transient electromagnetic disturbance (TED) could be injected to the electrical equipment of 10-kV TL with power on or power off. The TED is produced by the pulsed current injection (PCI) generator, whose rise time is less than 20 ns and full width at half maximum is in the range of 500 ~ 550 ns on short-circuit state with 60 Ω resistor. On the other hand, the 10-kV TL is equivalently designed in cross section to make its characteristic impedance being 330 Ω to conform to the value of practical case. The voltages and currents applied on the tested equipment can be measured at nano-second level simultaneously, which are of great use to learn the effect mechanisms and compare the results under different working conditions. Some 10-kV pin-type porcelain insulators are tested under different conditions, which shows the capacity of the proposed platform to test immunity of 10-kV electrical equipment.