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An alternative high voltage isolator for electric propulsion and ground-based ion source applications has been designed and tested. This design employs a transverse magnetic field that increases the breakdown voltage. The design can greatly enhance the operating range of laboratory isolators used for high voltage applications.
Layered aluminum polymer capacitors (APC) may be viable replacements to current chip tantalum capacitors due to their lower ESR, weight, and smaller size. So far, there is a lack of information regarding the reliability of these parts. Available technical literature is mostly related to the effect on humidity. Although APCs have a limited moisture resistance, it may be contained to the level sufficient for space applications. In this work, seven types of commercial APCs manufactured by four vendors and rated to voltages from 6.3 to 35 V were used to evaluate reliability of the parts under environmental stresses and highly accelerated life tests. Characteristics of the parts, including breakdown voltages, the level of anomalous charging currents (ACC), capacitance, DF, ESR and leakage currents were measured in the process of storage at high-temperatures (from 100 to 150 °C) and high humidity at 85 °C. Monitored highly accelerated life tests have been carried out at temperatures of 85 °C and 125 °C and voltages varying from 1.2 to 1.9 times the rated voltage. Degradation processes and reliability of APCs have been analyzed and compared to polymer tantalum capacitors.
A pulsed electrothermal (PET) thruster with 1000:1 ratio nozzle is tested in a repetitive mode on water propellant. The thruster is driven by a 60J pulse forming network at repetition rates up to 10 Hz (600W). The pulse forming network has a .31 ohm impedance, well matched to the capillary discharge resistance of .40 ohm, and is directly coupled to the thruster electrodes without a switch. The discharge is initiated by high voltage breakdown, typically at 2500V, through the water vapor in the interelectrode gap. Water is injected as a jet through a .37 mm orifice on the thruster axis. Thruster voltage, current and impulse bit are recorded for several seconds at various power supply currents. Thruster to power ratio is typically T/P = .07 N/kW. Tank background pressure precludes direct measurement of exhaust velocity which is inferred from calculated pressure and temperature in the discharge to be about 14 km/sec. Efficiency, based on this velocity and measured T/P is .54 + or - .07. Thruster ablation is zero at the throat and becomes measurable further upstream, indicating that radiative ablation is occurring late in the pulse.
Protective gate device consisting of alternating heavily doped n(+) and p(+) diffusions eliminates breakdown voltages in silicon oxide on sapphire arrays caused by electrostatic discharge from person or equipment. Diffusions are easily produced during normal double epitaxial processing. Devices with nine layers had 27-volt breakdown.
The purpose of this study is to use both theoretical and experimental evidence to determine the impact of doping imbalance and symmetry on the physical and electrical characteristics of doped multiple quantum well avalanche photodiodes (APD). Theoretical models have been developed to calculate the electric field valence and conduction bands, capacitance-voltage (CV), and carrier concentration versus depletion depth profiles. The models showed a strong correlation between the p- and n-doping balance inside the GaAs wells and the number of depleted stages and breakdown voltage of the APD. A periodic doping imbalance in the wells has been shown to result in a gradual increase (or decrease) in the electric field profile throughout the device which gave rise to partially depleted devices at low bias. The MQW APD structures that we modeled consisted of a 1 micron top p(+)-doped (3 x 10(exp 18) cm(exp -3)) GaAs layer followed by a 1 micron region of alternating layers of GaAs (500 A) and Al(0.42)Ga(0.58)As (500 A), and a 1 micron n(+) back layer (3 x 10(exp 18) cm(exp -3)). The GaAs wells were doped with p-i-n layers placed at the center of each well. The simulation results showed that in an APD with nine doped wells, and where the 50 A p-doped layer is off by 10% (p = 1.65 x 10(exp 18) cm(exp -3), n = 1.5 x 10(exp 18) cm(exp -3)), almost half of the MQW stages were shown to be undepleted at low bias which was a result of a reduction in the electric field near the p(+) cap layer by over 50% from its value in the balanced structure. Experimental CV and IV data on similar MBE grown MQW structures have shown very similar depletion and breakdown characteristics. The models have enabled us to better interpret our experimental data and to determine both the extent of the doping imbalances in the devices as well as the overall p- or n-type doping characteristics of the structures.
The newly patented micro-multilayer multifunctional electrical insulation (MMEI) system was developed for future electric aircraft applications which critically require lightweight but high voltage (HV), high temperature, and corona or partial discharge (PD) resistant insulation. During the initial development stages, the concept and practicability of the MMEI system were successfully validated with its exceptionally high dielectric breakdown voltages. The multilayer structures were optimized in terms of material type, individual layer thickness, and overall layer configuration along with potential mechanisms identified for its superior performance. Subsequently, scalability, manufacturability, and commercial applicability of the MMEI system were demonstrated with the 1 meter long, 3-phase HV, high power (HP) bus bar prototypes. Two prototypes, one with the conventional SOA insulation system including Mica sheet and the other with an optimized MMEI, were designed, fabricated, and tested successfully. Both prototypes passed both HiPot and PD tests up to the highest test voltage available, 15 kVAC, although the latter showed a slight increase in PD activities at 12.5 kV. However, the prototype with MMEI was 15% lighter or 12% thinner than the other one. Current efforts to significantly enhance the PD resistance of the MMEI system by employing semiconductive shielding layers, which can be also multifunctional, e.g., electromagnetic interference shielding, moisture blocking, heat dissipation, for various HV applications are also discussed in this paper.
The newly patented micro-multilayer multifunctional electrical insulation (MMEI) system was developed for future electric aircraft applications which critically require lightweight but high voltage (HV), high temperature, and corona or partial discharge (PD) resistant insulation. During the initial development stages, the concept and practicability of the MMEI system were successfully validated with its exceptionally high dielectric breakdown voltages. The multilayer structures were optimized in terms of material type, individual layer thickness, and overall layer configuration along with potential mechanisms identified for its superior performance. Subsequently, scalability, manufacturability, and commercial applicability of the MMEI system were demonstrated with the 1 meter long, 3-phase HV, high power (HP) bus bar prototypes. Two prototypes, one with the conventional SOA insulation system including Mica sheet and the other with an optimized MMEI, were designed, fabricated, and tested successfully. Both prototypes passed both HiPot and PD tests up to the highest test voltage available, 15 kVAC, although the latter showed a slight increase in PD activities at 12.5 kV. However, the prototype with MMEI was 15% lighter or 12% thinner than the other one. Current efforts to significantly enhance the PD resistance of the MMEI system by employing semiconductive shielding layers, which can be also multifunctional, e.g., electromagnetic interference shielding, moisture blocking, heat dissipation, for various HV applications are also discussed in this paper.
Characterization results of a MOS controlled thyristor (MCTA60P60) are presented. This device is rated for 60A and for an anode to cathode voltage of -600 V. As discussed in the last report, the MCT failed during 500 V leakage tests at 200 C. In contrast to the BJT (bipolar junction transistor), MOSFET, and IGBT (insulated gate bipolar transistor) devices tested, the breakdown voltage of the MCT decreases significantly with increasing temperature.
Development of the novel patented high voltage insulation system, namely micro-multilayer multifunctional electrical insulation (MMEI) was continued particularly for the future hybrid or all electric aircraft applications. Initially, the concept and feasibility of the MMEI system were successfully demonstrated with its exceptionally high dielectric breakdown voltage via optimizing the multilayer structures of the Kapton® PI films and binder layers such as PFA in terms of individual film thickness and layer configuration. Overall, MMEI structures outperformed most of the state-of-the-art (SOA) polymer insulation materials or structures. Since then, further optimizations and improvement of the system were pursued with specific emphasis on multifunctionalities such as moisture blocking, partial discharge (PD) resistance, durability, etc. Efforts have been also continued to identify the controlling mechanisms for the major improvement in dielectric strength of the MMEI structures via 3-dimensional dielectric failure mode analysis. At the same time, significant progress has been made in scaling up the MMEI structures and assessing their commercial applicability and manufacturability by developing full-scale prototypes of electrical components, such as power cable and bus bar. Overall progresses on the MMEI development to date will be presented in this paper.
Polymer aluminum capacitors from several manufacturers with various combinations of capacitance, rated voltage, and ESR values were physically examined and electrically characterized. The physical construction analysis of the capacitors revealed three different capacitor structures, i.e., traditional wound, stacked, and laminated. Electrical characterization results of polymer aluminum capacitors are reported for frequency-domain dielectric response at various temperatures, surge breakdown voltage, and other dielectric properties. The structure-property relations in polymer aluminum capacitors are discussed.
Polymer aluminum capacitors from several manufacturers with various combinations of capacitance, rated voltage, and ESR values were physically examined and electrically characterized. The physical construction analysis of the capacitors revealed three different capacitor structures, i.e., traditional wound, stacked, and laminated. Electrical characterization results of polymer aluminum capacitors are reported for frequency-domain dielectric response at various temperatures, surge breakdown voltage, and other dielectric properties. The structure-property relations in polymer aluminum capacitors are discussed.
Significant reduction in carbon dioxide emission for future air transportation system will require adoption of electric propulsion system and more electric architectures. Various options for aircraft electric propulsion include hybrid electric, turboelectric, and full electric system. Realization of electric propulsion system for commercial aircraft applications will require significant increases in power density of electric motors and energy density of energy storage system, such as the batteries and fuel cells. In addition, transmission of MW of power in the aircraft will require high voltage power transmission system to reduce the weight of the power transmission system. Finally, there will be significant thermal management challenges. Significant advances in material technologies will be required to meet these challenges. Technologies of interest include materials with higher electrical conductivity than Cu, high thermal conductivity materials, and lightweight electrically insulating materials with high breakdown voltage, high temperature magnets, advanced battery and fuel cell materials, and multifunctional materials. The presentation will include various challenges for commercial electric aircraft and provide an overview of material improvements that will be required to meet these challenges.
Reliability of base metal electrode (BME) multilayer ceramic capacitors (MLCCs) that until recently were used mostly in commercial applications, have been improved substantially by using new materials and processes. Currently, the inception of intrinsic wear-out failures in high quality capacitors became much greater than the mission duration in most high-reliability applications. However, in capacitors with defects degradation processes might accelerate substantially and cause infant mortality failures. In this work, a physical model that relates the presence of defects to reduction of breakdown voltages and decreasing times to failure has been suggested. The effect of the defect size has been analyzed using a thermal runaway model of failures. Adequacy of highly accelerated life testing (HALT) to predict reliability at normal operating conditions and limitations of voltage acceleration are considered. The applicability of the model to BME capacitors with cracks is discussed and validated experimentally.
Gridded ion engines represent a class of electric thrusters characterized by high propulsive efficiency and high total impulse capabilities. These engines operate by applying high voltage to multi-aperture electrodes, thereby electrostatically accelerating plasma to generate thrust. Within the course of normal operations, periodic occurrences of high voltage breakdowns manifest within the thruster. These breakdowns constitute an inherent aspect of operation, with observations indicating a diminishing frequency and total count over the thruster's operational lifespan. To safeguard the propulsion system during such occurrences, the power processing unit (PPU) employs an automated arc extinction sequence, termed "recycle," which is triggered upon detection of an over-current condition. The initial phase of this sequence involves momentarily deactivating the high voltage and reducing the discharge current to a predetermined level, minimizing plasma impingement as the ion beam is defocused. The high voltage is subsequently reapplied, and the discharge current is returned to its nominal value. The entire sequence typically spans approximately 800 milliseconds. Throughout a recycle event, the propulsion system experiences various current and voltage transients as the arc current traverses the system and different power supplies are toggled on and off.
Polybenzimidazole, a linear thermoplastic polymer with excellent thermal stability and strength retention over a wide range of temperatures, was evaluated for its potential use as the main dielectric in high temperature capacitors. The film was characterized in terms of its dielectric properties in a frequency range of 50 Hz to 100 kilo-Hz. These properties, which include the dielectric constant and dielectric loss, were also obtained in a temperature range from 20 C to 300 C with an electrical stress of 60 Hz, 50 V/mil present. The alternating and direct current breakdown voltages of silicone oil impregnated films as a function of temperature were also determined. The results obtained indicate that while the film remained relatively stable up to 200 C, it exhibited an increase in its dielectric properties as the temperature was raised to 300 C. It was also found that conditioning of the film by heat treatment at 60 C for six hours tended to improve its dielectric and breakdown properties. The results are discussed and conclusions made concerning the suitability of the film as a high temperature capacitor dielectric.
A power converter now undergoing development is required to operate at a DC input potential ranging between 5.5 and 10 kV and a DC output potential of 400 V at a current up to 25 A. This power converter is also required to be sufficiently compact and reliable to fit and operate within the confines of a high-pressure case to be lowered to several miles (approx.5 km) below the surface of the ocean. The architecture chosen to satisfy these requirements calls for a series/ parallel arrangement of 48 high-frequency, pulse-width-modulation (PWM), transformer-isolation DC-to-DC power converter blocks. The input sides of the converter blocks would be connected in series so that the input potential would be divided among them, each of them being exposed to an input potential of no more than 10 kV/48 . 210 V. The series connection of inputs would also enforce a requirement that all the converter blocks operate at the same input current. The outputs of the converter blocks would be connected in a matrix comprising 6 parallel legs, each leg being a cascade of eight outputs wired in series (see figure). All the converter blocks would be identical within the tolerances of the values of their components. A single voltage feedback loop would regulate the output potential. All the converter blocks would be driven by the same PWM waveform generated by this feedback loop. The power transformer of each converter block would have a unity turns ratio and would be capable of withstanding as much as 10 kVDC between its primary and secondary windings. (Although, in general, the turns ratio could be different from unity, the simplest construction for minimizing leakage and maximizing breakdown voltage is attained at a turns ratio of unity.)
A new class of silicon devices operating without p-n junctions has been studied for radiation hardness. The electric field in these devices is uniform over most of the device, thus causing high-voltage breakdown to increase with electrode spacing. Deep acceptor levels are created in the silicon by diffusing gold atoms into the lattice, or by electron radiation. These acceptor levels, near the center of the band gap, trap out electrons so that the low resistivity of the n-type doped wafer can be raised to intrinsic resistivity. Switching between a high-resistivity state at low currents and a low-resistivity state at high currents occurs at a definite threshold voltage, exhibiting characteristics similar to silicon-controlled rectifiers. Compensating 0.1 ohm-meter (10 ohm-cm) silicon wafers requires electron fluxes of 10 to the 23rd electrons per square meter (10 to the 19th electrons per square centimeter). Experiments demonstrating gamma tolerance to 1 Gigarad(Si) are described. Calculations for maximum tolerable neutron fluence are shown, and a phenomenological explanation for these results is presented.
Experiments were carried out to evaluate four candidate materials for high temperature capacitor dielectric applications. The materials investigated were polybenzimidazole polymer and three aramid papers: Voltex 450, Nomex 410, and Nomex M 418, an aramid paper containing 50 percent mica. The samples were heat treated for six hours at 60 C and the direct current and 60 Hz alternating current breakdown voltages of both dry and impregnated samples were obtained in a temperature range of 20 to 250 C. The samples were also characterized in terms of their dielectric constant, dielectric loss, and conductivity over this temperature range with an electrical stress of 60 Hz, 50 V/mil present. Additional measurements are underway to determine the volume resistivity, thermal shrinkage, and weight loss of the materials. Preliminary data indicate that the heat treatment of the films slightly improves the dielectric properties with no influence on their breakdown behavior. Impregnation of the samples leads to significant increases in both alternating and direct current breakdown strength. The results are discussed and conclusions made concerning their suitability as high temperature capacitor dielectrics.