Excess Current Research Articles

60Co gamma radiation effects on NPN transistor at cryogenic temperature.

The 60Co gamma radiation effects on the DC electrical characteristics of silicon NPN transistor were studied in the dose range of 100krad to 6Mrad at room temperature (300K) and cryogenic temperature (77K). The measurements were carried out at both 300 and 77K temperature. The electrical characteristics such as Gummel characteristics, excess base current (ΔIB), current gain (hFE), transconductance (gm) and output characteristics were studied in situ as a function of total dose. The results show that there is a considerable degradation in the electrical parameters of the device irradiated both at 300 and 77K as a consequence of increase in excess base current (ΔIB) because of the formation of generation and recombination centers in the emitter-base spacer oxide (SiO2). At cryogenic temperature irradiation, the degradation in electrical characteristics is less because of the physical phenomena such as carrier freezeout effect, decreased recombination rate, reduced charge yield, decreased electron mobility, etc.

Self-power, multiwavelength photodetector based on a Sn-doped Ge quantum dots/hexagonal silicon nanowire heterostructure.

Tin-doped germanium quantum dots (Sn-doped Ge QDs)-decorated hexagonal silicon nanowires (h-Si NWs) were adopted to overcome the low infrared response of silicon and the excess dark current of germanium. High-quality Sn-doped Ge QDs with a narrow bandgap can be achieved through Ge-Sn co-sputtering on silicon nanowires by reducing the contact area between heterojunction materials and Sn-induced germanium crystallization. The absorption limit of the heterostructure is extended to 2.2 µm, and it is sensitive to 375-1550 nm light at 0 V, which has optimality at 1342 nm, with a photo-to-dark current ratio of over 815, a responsivity of 0.154 A/W, and a response time of 0.93 ms. The superior performance of the Sn-doped Ge QDs/h-Si NW photodetector in multiwavelength is attractive for multi-scenario applications.

An investigation on tensile shear strength of CMT spot weld-brazing of 5052 aluminium alloy and SS 400 galvanized steel

The main purpose of the research is to investigate the effects of spot weld-brazing variables, such as cold metal transfer (CMT) modes and current, on the tensile shear strength of 5052 aluminium alloy for dissimilar joining to SS400 galvanized steel.The method employed in the study was a 3k full factorial design with three replications. Analysis of variance (ANOVA) techniques were employed to identify the variables that influenced the responses of interest. The response optimiser method displayed which factors affected the variables and their impact on strength. In addition, the response optimiser method was employed to find which factors produced the best value for the response variable. A mathematical model was developed to predict the strength of the joints. An optical microscope (OM) and scanning electron microscope (SEM) were also employed to confirm the microstructure. Energy dispersive spectroscopy (EDS) was used to determine the chemical composition of the microstructure.The strength of the weld-brazing joints was affected by the modes and currents used in the joining process. The weld-brazing mode selection was found to have an impact on strength. The synergic mode was shown to have a strength greater than the CMT pulse and pulse synergic modes. The excess or little weld-brazing current was shown to be unsuitable for the joint. The maximum tensile shear strength value was obtained in the synergic mode with a current of 110 A. The resulting prediction model was evaluated with the newly collected experimental data, and the average per cent error was estimated to be 2.07%. In addition, the reaction layer at the aluminium alloy and steel interface was composed of a Fe(Al, Si)3 phase. The optimal conditions for the spot weld-brazing activities resulted in a larger fracture area, a small contact angle, and excellent weld bead geometry.The prediction accuracy of the model appeared satisfactory. However, the altered chemical composition of the filler metals and substrate materials could impact the findings. It is recommended that the electrical signal waveform be studied during spot weld-brazing, as well as the characteristics of other material joints with various other parameters.The weld-brazing mode and current had no significant effect on the type of interface layer of the joints.It is highly possible that the CMT spot weld-brazing technique could be applied to join other dissimilar materials in order to reduce the joining time, but the filler metal chosen must be appropriate.

Heat Dissipation Mechanisms in Hybrid Superconductor-Semiconductor Devices Revealed by Joule Spectroscopy.

Understanding heating and cooling mechanisms in mesoscopic superconductor-semiconductor devices is crucial for their application in quantum technologies. Owing to their poor thermal conductivity, heating effects can drive superconducting-to-normal transitions even at low bias, observed as sharp conductance dips through the loss of Andreev excess currents. Tracking such dips across magnetic field, cryostat temperature, and applied microwave power allows us to uncover cooling bottlenecks in different parts of a device. By applying this "Joule spectroscopy" technique, we analyze heat dissipation in devices based on InAs-Al nanowires and reveal that cooling of superconducting islands is limited by the rather inefficient electron-phonon coupling, as opposed to grounded superconductors that primarily cool by quasiparticle diffusion. We show that powers as low as 50-150 pW are able to suppress superconductivity on the islands. Applied microwaves lead to similar heating effects but are affected by the interplay of the microwave frequency and the effective electron-phonon relaxation time.

Universal Input Single-Stage High-Power-Factor LED Driver with Active Low-Frequency Current Ripple Suppressed

In this paper, a light-emitting diode (LED) driver with a high power factor (PF) and low-frequency current ripple suppression over a wide input range is presented, and a flyback converter is designed to operate in the discontinuous conduction mode (DCM), with a digital controller used to keep the duty cycle constant for half of the utility cycle under a fixed load and input voltage. This method ensures that the input current is in phase with the universal input voltage, thus achieving a high power factor without utilizing feedforward control. Furthermore, on the secondary side, the time of the zero point of the utility voltage can be attained so that the duty cycle can be updated at this time. In addition, a simple auxiliary circuit is connected parallel to the output side to absorb the excess output current of the flyback converter or to release the current to the load to make up for the shortage of the output current of the flyback converter so that the low-frequency ripple of the output current can be inhibited. There are only two current-detecting resistors used in this study: one is the output current-sensing resistor of the flyback converter, and the other is the output current-sensing resistor of the auxiliary circuit.

InSb ФОТОДІОДИ (ОГЛЯД. ЧАСТИНА VI)

In this review, a brief overview of epitaxial methods of growing single-crystal InSb films and their application for the manufacture of infrared photodiodes is provided. The results of growing InSb epitaxial films on Si and GaAs substrates are described. The main attention in the review is paid to InSb/CdTe heterostructures, which is explained by the almost perfect matching of their lattices and coefficients of thermal expansion. The properties of heterovalent InSb/CdTe interfaces as promising objects for spintronics and topological insulators are described. The results of experimental studies of InSb photodiodes for the mid-wavelength region of 3-5 μm, passivated with polycrystalline CdTe films by the hot wall epitaxy method are given. To investigate the electrical properties of polycrystalline fims, the direct conductivity was measured as a function of bias voltage and temperature. For this purpose, polycrystalline fims with a thickness of 200 to 1800 nm were grown on p-InSb substrates. The type of conductivity and resistivity of polycrystalline films were determined. Conclusions were made regarding the possibility of using this technique for effective and stable passivation. Photodiodes were characterized by measuring the dark current and the lifetime of minor carriers. Properties of heterovalent CdTe/InSb and isovalent CdTe/HgCdTe interfaces are compared. It is shown that they have different effects on the transport and photoelectric characteristics of photodiodes. It was established that when the passivation layer is deposited on the chemically etched surface of the mesa, an excess current of tunneling nature occurs in the photodiodes. The best results were obtained when surface treatment of the mesa includes the use of CP4A and HCl etchants, sulfidization in a non-aqueous Na 2 S solution, and deposition of a CdTe protective layer. Passivation of HgCdTe photodiodes using polycrystalline CdTe films does not affect the lifetime of charge carriers, but it needs improvement to achieve better stability of their characteristics.

Analisis Arus Gangguan Hubung Singkat Pada Feeder Tampinna Gardu Induk Tegangan Ekstra Tinggi Wotu

An electric power system is a complex system consisting of a powerplant, transmission system and distribution system that operates simultaneously in distributing electric power. In the distribution of electric power can not be separated from the occurrence of abnormal conditions of the system or disruption so that it needs a protection system to overcome the occurrence of interference. Disruption that often occurs in the electrical power system is a short circuit disruption so that a short circuit analysis is carried out as a first step in determining the right protection system. Short circuit disorder is a type of disruption that occurs in an electric power system due to an increase in excess current due to a decrease in the strength of isolation from the channel both between phases and between phases and earth. Tampinna feeder is one of the feeders in Wotu Extra High Voltage Substation. In this study will be calculated how much the current of short circuit interference in the feeder and the working time of the protection relay, namely OCR and GFR. From the calculation obtained a maximum short circuit disruption in three phases amounting to 771.86 A, two phases amounting to 668.45 A and one phase to the ground amounting to 370, 6 A.

Application and Comparison of a Modified Protection Scheme Utilizing a Proportional–Integral Controller with a Conventional Design to Enhance Doubly Fed Induction Generator Wind Farm Operations during a Balanced Voltage Dip

The doubly fed induction generator (DFIG) is vulnerable to grid faults due to its direct stator connection, causing issues like excess stator current during voltage dips. Consequently, sensitive inverters suffer from increased currents, and the DC-link capacitor undergoes overcharging. This document examines two protection strategies employing a proportional–integral (PI) controller to manage the transient rotor current and mitigate DC-link overcharging, thereby optimizing DFIG behavior during network faults. One option combines a classic crowbar circuit with a DC-chopper, while the other is a modified protection scheme (MPS) that includes an impedance with passive elements and a crowbar. The impedance forms a resistance Rp parallel with an inductance Lp. Both configurations, situated between the rotor coils and the rotor-side converter (RSC), augment the capacity for low-voltage ride-through (LVRT). MATLAB/SIMULINK simulations of the two schemes demonstrate successful rotor current reduction at 2.9 kA and 3.4 kA, and DC-link tension reduction below and at 1.4 KV. In addition, the conventional crowbar and MPS configurations efficiently restrict the RSC current to levels below 0.21 kA and 2.94 kA, while absorbing up to 2.52 kA and 1.52 kA, respectively. The key difference lies in the fact that fine-tuning the parameters in the MPS design prevents rotor disconnection when faced with a balanced fault. This enhancement enhances machine performance and enables full stator power control via the RSC.

Theoretical analysis of conduction-cooled current lead for superconducting magnet

CCCL is a typical CL type to energise SC magnets from room to cryogenic temperatures (<100 K) for its simplicity and reliability, but causes a relatively large heat leak (∼50 W kA−1 from 300 K) compared to the heat leak (∼1.0 W kA−1 from 300 K to liquid helium) of VCCLs, which necessitates a comprehensive understanding of designers and users. However, systematic studies on CCCLs are still lacking up to now. This study starts from the differential equation governing heat conduction and generation in CCCLs and firstly derives a completely exact theoretical solution by adopting the WFL law for thermal conductivity and electrical resistivity with temperature dependence. The solution facilitates the CCCL design optimisation to achieve the minimum heat leak, which is determined only by the temperature range but independent of both materials and geometrical parameters. Practical optimum designs are concerned with material properties and approached by calculating a shape factor to determine the conductor length and cross-sectional area, which is detailed and illustrated in this paper. Furthermore, the practical behaviours at low and excess currents can also be mathematically deduced, and the corresponding heat leaks are found to rely on materials but not on geometrical parameters. This paper also describes the agreements between the theoretical analysis and the numerical simulation and comparison with material properties of the non-WFL law.

Damage Separation in Proton-Irradiated Bipolar Junction Transistors as a Function of Energy

Damage separation analysis was performed for two types of bipolar junction transistors following proton irradiation over the energy range of 1.6 to 650 MeV. The functional dependence of excess base current on fluence for each device type is consistent with base polarity as it relates to the effect of oxide-trapped charge on surface recombination. For a given fluence, the excess base current decreases with proton energy due to reductions in NIEL and stopping power. Relative damage coefficients, computed from normalized Δ <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">I</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">B</sub> vs fluence curves, imply a mix of ionization and displacement damage. The relative amounts of ionization damage and displacement damage as a function of proton energy are consistent with charge yield, stopping power and NIEL. A simple model for the energy dependence of damage contributions, based on charge yield and the relative amounts of deposited ionizing and non-ionizing energy, is described. The model calculations as a function of proton energy are in good agreement with the relative damage contributions estimated from the damage separation analysis.

Current-voltage characteristics of 100-pixel 200-μm-square superconducting tunnel junction X-ray detector array

The superconducting tunnel junction (STJ) X-ray detector is an important tool for materials analysis because of its high energy resolution and high counting rate. In this work, the current-voltage (I-V) characteristics were investigated for a 100-pixel STJ array with a pixel size of 200 μm having a layer structure of Nb-Al/AlO x /Al-Nb and working at 0.3 K. The fabrication yield of the 200-μm STJ reached approximately 90%. A series of I-V curves for a single pixel in different cooling runs showed a discrete excess current, possibly due to the trapping of single fluxoids. With a reduction of the ambient magnetic field during cooling, larger STJ pixels can be used.

Calculation of the Total Current Generated in a Tunnel Diode Under the Action of Microwave and Magnetic Fields

In this paper, a formula was derived for calculating the total current generated in a tunnel diode under the action of a microwave field and a magnetic field. In addition, the dependence of the total current of the tunnel diode on the total power induced by the microwave field is theoretically presented and compared with experimental data. For the total current in the tunnel diode, without taking into account the excess current, volt-ampere characteristics was obtained for cases with and without the influence of a microwave field.

Reliability studies on bipolar transistors under different particles radiation

The reliability of silicon bipolar junction transistors (Si BJTs) and silicon germanium heterojunction bipolar transistors (SiGe HBTs) were studied under 80 MeV nitrogen (N6+) ions and 60Co gamma radiation in a total dose from 1 to 100Mrad at 300 K. Different DC electrical parameters namely Gummel Characteristics (IB, IC–VBE), excess base current (ΔIB), current gain (hFE), and output characteristics (IC–VCE) were studied before as well as after being subjected to radiations. Both radiations caused substantial degradation in parameters such as an increase in IB, a decrease in the hFE, and a decrease in ICsat. The parametric degradation is more in Si BJT (99% degradation in hFE after ion irradiation) when compared to SiGe HBT (45% degradation in hFE). The SRIM/TRIM simulations were employed to analyze the energy loss phenomenon and ion range in device structures. Annealing studies were also conducted to study the recovery behavior of irradiated devices. The influence of linear energy transfer (LET) of radiations on damage mechanism is also discussed based on irradiation and annealing results. The results show that SiGe HBTs are more radiation hardened than Si BJTs.

The dependence of proton energy on the parametric degradation in silicon bipolar junction transistors

The effects of high total dose proton irradiation on the reliability of silicon NPN rf power bipolar junction transistor (BJT) were examined by subjecting to 1, 3, and 5 MeV protons in the dose range from 100 Krad to 100 Mrad. The electrical characteristics such as Gummel characteristics (IB, IC-VBE), excess base current (ΔIB = IBpost – IBpre), current gain (hFE), and output characteristics (IC-VCE), built-in potential (Vbi) and the effective doping concentration (Nd) were studied before and after irradiation. SRIM simulation was conducted to understand the range and energy loss of protons in the BJT structure. SRIM and experimental results infer that the proton irradiation at lower energy (1 MeV) was found to degrade the current–voltage(I-V) and capacitance–voltage (C-V) characteristics more severely than higher-energy (3 and 5 MeV) proton irradiation. Thermal annealing on irradiated devices was also conducted to study the parametric recovery of irradiated devices.

Superconducting source and sensor of single bubbles to study nucleate boiling of liquid helium

Joule heat generated by resistive elements of cryogenic micro- and nanodevices often originates boiling of the cooling cryogenic liquids (helium, nitrogen). The article proposes an experimental method to explore the dynamics of the formation and development of a single vapor bubble in cryogenic liquid by sensing the temperature change of a superconducting thin-film microbridge being in the resistive state with single phase slip center or line. It serves both the source of heat for generating single bubbles and the surface temperature sensor due to its temperature-dependent excess current. The average bubble detachment rate and the average single bubble volume were experimentally determined for nucleate helium boiling. The obtained values are in good agreement with the data of other authors found in literature.

On the Suitability of Proton Pump Experiments to Evaluate New Hydrogen Evolution Electrodes for PEM Electrolysis Cells

The increased interest in green hydrogen has fostered an increased interest in electrolysis technology and in particular PEM-electrolysis as it allows currently best to absorb intermittent occurring renewable excess current. The challenge is the high expenditure of scarce PGM materials in PEM electrolysis cells. While this is most relevant for the iridium used as anodic oxygen evolution catalyst still also a reduction of the platinum expenditure at the cathode would at least serve to the Capex for PEMEL facilities. The group of Prof. U. Apfel at Ruhr University Bochum and Fraunhofer UMSICHT in Oberhausen is investigating pentlandite based hydrogen evolution catalyst for this purpose1 . Within the Fraunhofer internal project CINES, Fraunhofer ICT had the task to develop hydrogen evolution electrode from this catalyst. Now, as the hydrogen evolution and hydrogen oxidation in an acidic environment are both very fast reactions2 the difficulty is to monitor this reaction in a full electrolysis cell versus a oxygen evolution electrode with much more sluggish reaction. The idea was therefore to employ proton pumping as experiment wherein the electrode which is tested is used as cathode and a standard Pt/C electrode at a reasonable platinum loading as anode. In that way the performance of the new hydrogen evolution electrode should be much easier to evaluate.In a first step a commercial fuel cell CCM bought at Quintech, Germany was compared to a homemade CCM with platin layers on both sides both operated as proton pump. The results show that the performance differ in detail. So, the initial voltage loss due to charge transfer resistance is smaller for the commercial CCM likely due to the use of a more performant catalyst. The homemade CCM perform better however in the ohmic region. For both type of CCM the voltage at 800 mA cm-2 did not exceed -0.12 V (cf. Fig 1).In comparison first test with the Pentlandite based HER catalyst showed a strong over potential increase at low current densities and a hysteresis between the forward and the backward scan. The strength of the hysteresis did depend on the type of pentlandite (cf. Fig 2). After discussion with Prof Apfel’s group the effect of hot pressing was evaluated. It was found that hot pressing helped to reduce the over potential and in particular strongly reduce the hysteresis of the polarization curves (cf. Fig 3).If the results from the proton pumping are now compared to results obtained in a PEM electrolyser cell (cf. Fig. 4) it becomes obvious that many features observed in the proton pump experiments can be found here to. This is in particular true for the strong potential increase at low current densities.In total it can be said that proton pump experiments can be used to evaluate hydrogen evolution catalyst for PEM electrolysis at least in an initial stage. More experiments and details will be discussed in the presentation. B. Konkena, K. junge Puring, I. Sinev, S. Piontek, O. Khavryuchenko, J. P. Dürholt, R. Schmid, H. Tüysüz, M. Muhler, W. Schuhmann and U.-P. Apfel, Nat Commun, 7(1), 12269 (2016).J. Durst, C. Simon, A. Siebel, P. J. Rheinländer, T. Schuler, M. Hanzlik, J. Herranz, F. Hasché and H. A. Gasteiger, ECS Transactions, 64(3), 1069–1080 (2014). Figure 1

Experimental evaluation of the influence of excessive electric current on the fire hazard of lithium-ion power cell

Panasonic NCR18650B (LiNi0.8Co0.15Al0.05O2) lithium-ion power cell (LIPC) and its performance after exposure to excess direct current are considered in this paper. The basic fire hazard indicators (element ignition temperature, flame temperature, element heating time, etc.) were experimentally established and mathematically confirmed for the examined LIPC. According to the results of experimental studies, the time of occurrence of an irreversible thermochemical reaction in a lithium-ion power cell was determined depending on the different DC current strengths. Additionally, the critical temperature of the onset of an irreversible thermochemical reaction and the total combustion temperature of the element have been established. The application of the Joule-Lenz and Fourier laws allowed for a mathematical notation of the dependence (influence) of DC strength over time and the heating of the element to a critical temperature. The heating time of Panasonic NCR18650B LIPC (LiNi0.8Co0.15Al0.05O2) to a critical temperature of 100–150 °C under the influence of excess current was experimentally established and mathematically confirmed. The determined critical indicators of the element (temperature, time, etc.) make it possible to further devise a number of necessary regulatory documents that will allow them to be certified, tested, and, in general, to better understand the dangers that they may pose. A mathematical model was built, which, taking into account the geometrical parameters of the element, makes it possible to calculate the onset of the critical temperature of such elements with excellent geometric parameters without conducting experimental studies

Tracking the Meissner Hole and Relaxation of Magnetization in (Ba,Rb)Fe2As2

We investigated the unstable interface between vortices and anti-vortices in single crystals of iron-based superconductors (Ba0.67Rb0.33)Fe2As2 (Tc ∼ 37.6 K). These interfaces, also known as the Meissner hole, were captured with magneto-optical imaging in both pristine crystal and one with artificial point defects. Local excess current were observed flowing along the interface. In addition, we confirmed that the creep mode of such an interface follows the prediction of the critical state model, accompanied with a finite relaxation rate of magnetization.

Analyzing and tuning the time scale characteristics of the short circuit current of the synchronous condenser in the UHVDC inverter station of the heavy load center

The synchronous condenser with fast control has been installed in UHVDC inverter station recently to remain voltage and avoid continuous commutation failures (CCFs) during short circuit faults. However, the synchronous condenser can produce excess short circuit current (SCC) which may cause relay protection failure if the total SSC exceeds the interrupting capacity. It seems that there is a contradiction between the ability to avoid CCFs and the effect of the excess SSC for the synchronous condenser in the heavy load center with high level SCC. In order to solve the contradiction, the time scale characteristics of the synchronous condensers SCC are analyzed and tuned in this paper. Firstly, the synchronous condensers SCC is formulated in different time scales related to CCFs and relay protection. Then the relationship between the SCC and manufacture parameters, initial conditions together with excitation control of the synchronous condenser is investigated. Thus the time scale characteristics of the synchronous condensers SCC are discovered. And then a tuning strategy of the time scale characteristics of the SCC is proposed to ensure the ability to avoid CCFs as well as reduce the adverse effect on relay protection. Finally, simulation study is performed to validate the work.

Analysis of local burnout in a sub-scale test coil for the 32 T magnet after spontaneous quenches during fast ramping

Industrial production of REBa2Cu3O7-δ (REBCO) coated conductors has made it possible to construct the 32 T magnet, the first successful all-superconducting user magnet to exceed 30 T, which now serves users as SCM4 (superconducting magnet) at the NHMFL. Here, we present an analysis of the damage that occurred in late-stage proof testing of the 32 T prototype coil after many essential facets of the design had been proven through more than 100 intentionally triggered quenches at fields up to 24 T. This prototype coil was then subjected to accelerated charge–discharge cycles at a rate 44 times faster than its design ramp rate in an attempt to address its fatigue tolerance. The extra hysteresis loss of the fast ramps led to heating of the end pancakes, which was induced after 55 fatigue cycles, three spontaneous quenches at progressively lower currents. Recognizing that the coil was damaged, the pancakes were then unwound and their REBCO tapes run through our continuous in-field transport I c and remnant-field magnetization monitoring device, YateStar, which revealed three highly localized zones of low I c in the end pancake that induced quench. Careful examination of these zones, especially the most intensely damaged one, revealed that the worst hot spot reached at least 779 °C during the quenches. Magneto-optical imaging showed that this damaged zone was about 5 mm in diameter and indeed the perpendicular damage length induced in neighboring turns by this localized quench heating was almost as great. Although there is much present concern about fatigue crack propagation from edge defects, we actually attribute this damage not to fatigue but to fluctuations in vortex pinning density due to imperfect BaZrO3 (BZO) nanorod growth that locally reduced the critical current I c. These localized low-I c regions then had to shed their excess current into the copper stabilizer, producing intense heating. We provide transmission and scanning electron microscopy evidence for local fluctuations of the BZO pinning structure and relate it to recent work that shows significant variations of 4 K, high field I c values due to apparent production fluctuations of the growth conditions of the Zr-doped metal-organic chemical vapor deposition REBCO used for this test magnet.