Papers by Keyword: Leakage Current

Abstract: Nitride-based light emitting diodes (LEDs) is an attractive material due to its high temperature tolerance and suitable to be used in extreme environment. The irradiation process of Gallium Nitride (GaN) diode was carried out by electron irradiation with 1000 kGy and 1500 kGy doses with a conveyor speed of 50 kGy per pass. Capacitance-voltage (C-V) and current-voltage (I-V) characterization for both pre and post irradiation samples was done. Both current and capacitance show decreasing while reverse leakage current increased after irradiation. The reverse leakage current revealed that the current were start leakage at 1.0 x10 ^-7 A and 1.0 x10^-9 A for 1000 kGy and 1500 kGy irradiations respectively. The current-voltage graph indicated that the effect of electron irradiation on diode produced weak spots as defect cause leakage current. The traps and bulk defect is believed to contributed to the leakage current increased.

Abstract: As the pumped storage stations played an important role in peak and frequency modulation, the reversible pump turbines were often subjected to rapid temperature transitions. In this research, considering the complexity operation condition of these kinds of motors, a novel thermal cycle aging platform was designed and the thermal cycling aging test was conducted on epoxy/mica insulation stator bars. Dielectric loss angle tangent (tanδ), capacitor (C), leakage current (I) and other electrical properties of stator bars were investigated at different aging time. The results showed that, tanδ and C of the stator bars increased with increasing aging time, while I (current) did not change significantly.

Abstract: As one of the most important parts of the generator, Epoxy/mica insulation system has the direct effect on the reliability of generator operation. The accelerated aging of insulation system was taking place under the complex operation condition, and resulting in the insulation system breakdown. It had always been the target for the researchers to find an efficient way to evaluate the state of generator insulation system. According to the real operation situation, the multi-factor aging test sequence with electric field, temperature field, mechanical vibration and thermal cycling was developed, and the test platform with multi-factor aging was built in this research. The partial discharge test was conducted at the end of each cycle. The result showed that, with the insulation aging time prolonged, the maximum partial discharge quantity decreased first then increased while skewness and kurtosis varied the opposite way. And the phase range of partial discharge began to expand. This research provided a new way to evaluate the state of generator insulation system.

Abstract: Short-circuit (SC) robustness of 1200 V-rated SiC npn Junction Transistors (SJTs) and commercial power DMOSFETs is investigated. Due to low (2x) overdrive base currents and low short-circuit currents, SJTs demonstrate superior SC capability including: (a) minimum short-circuit withstand time (t_SC) of 14 µs, even at V_DS=1000 V (b) Perfectly stable output and blocking characteristics after 10,000, 10 µs long SC pulses at 800 V, (c) t_SC ≥ 18 µs at 800 V up to (at-least) 175°C base-plate temperatures. In contrast, commercial (Gen-II) 1200 V/80 mΩ SiC MOSFETs exhibit catastrophic failure beyond t_SC = 7 µs at 500 V, and t_SC = 3 µs at 800 V, due to excessive SC currents of > 200 A resulting in junction temperatures in excess of 650°C. The MOSFET’s drain leakage current increases by a factor of 120, and the V_TH reduces by 20%, after 7 µs-long SC pulses at 500 V.

Abstract: An ultrafast I-V measurement technique has been developed to measure simultaneously C-V and leakage parameters of SiC power devices. After considering the coupled contribution of both static (leakage current) and dynamic (capacitive current) aspects with respect to high dV/dt voltage ramps, a time-based characterization is detailed and validated on SiC Junction Barrier Schottky (JBS) power diodes.

Abstract: The leakage currents of high nominal voltage conductive polymer tantalum (Ta) electrolytic capacitors are the difficulties in the research and development processing. The optimized and improved forming technical of increasing current density with the voltage rising was used in the present paper, and silane coupling agent has been used to the dielectric surface of the electrode body before polymerization, and conductive slurry was used to forming the cathode electrolyte of capacitors. Low leakage currents and high breakdown voltage have been tested; otherwise, the endurance capabilities of reverse voltage have prodigious enhanced.

Abstract: This article investigates the characteristics of cap and pin glass insulator and its enhancement due to contamination particles or elements by means of laboratory experiments. The insulator surface is simulated for dry conditions as well as its changes under wet conditions. To find the influence of the contamination layers on the leakage current and voltage distribution, various levels of the ESDD of the insulators were applied in the study. Additionally, experimental results show that the higher contamination level of insulator may have lower breakdown voltage especially in wet condition.

Abstract: Leakage current is known to be directly related to the degree of degradation of arrester. Leakage current is commonly flow across arrester under non-conducting condition. In this work, a two-dimensional (2D) axial-symmetrical 11kV surge arrester model was developed and used to simulate the leakage current under normal condition. The influence of insulator shed widths, housing materials and sizes of ZnO in an 11kV ZnO surge arrester design on its leakage current was studied using finite element method (FEM) software, which is COMSOL Multiphysics. The simulation results show that leakage current is mostly affected by the sizes of the ZnO and material of the housing. From this work, an understanding on the leakage current behaviors in a ZnO surge arrester can be enhanced. This study may also help in improving the design of surge arresters in reducing leakage current.

Abstract: This paper presents the development of on-line monitoring for condenser type bushing of power transformer in order to detect a degradation of bushing and to provide the alarm before bushing failure. For the bushing degradation analysis, the capacitance and power factor of bushing internal insulation are on-line monitored and measured by installing the sensing device at the test tap of bushing. The changing of internal insulation capacitance leads to the change of voltage across tap capacitor and the change of leakage current through bushing insulation at the test tab. Such changes result in the change of power factor or phase angle of leakage current. Thus, the leakage current is additionally detected by installing the Hall Effect sensing device to observe the trend of bushing failure. A total of eight cases of both normal and degraded insulation are investigated. The internal insulation capacitance as well as the magnitude and phase angle of three phase leakage current were measured and compared with the commissioning value or observed the increasing trend to set the alarm level. In case of degraded bushing, the leakage currents changed and caused the summation of leakage current value to be greater than the standard value. Then the alarm is activated. This knowledge was used to develop the detection and decision making algorithms in LabVIEW program to determine the condition of transformer bushing.

Abstract: Single-crystalline BaTi₂O₅ nanowires were synthesized by a simple molten salt method, using BaC₂O₄•H₂O and TiO₂ powders as precursors. Electrical characterization was conducted with the as-synthesized BaTi₂O₅ nanowires. The current-time data of the nanowires obeyed the Curie-von Schweidler law. Steady-state I-V curve was obtained at room temperature from current-time data and it revealed that the leakage current of BaTi₂O₅ nanowires obeyed the ohmic law under low voltage, and obeyed the space-charge limited current (SCLC) law under higher voltage. The conductivity value of the BaTi₂O₅ nanowires is 2*10^-6 S/cm.