Ahmad N. Hammoud

High temperature dielectric properties of Apical, Kapton, PEEK, Teflon AF, and Upilex polymers

Apical, Upilex, Kapton, Teflon AF, and PEEK polymers are characterized for AC and DC dielectric breakdown in air and in silicone oil at temperatures up to 250 degrees C. The materials are also tested in terms of their dielectric constant and dissipation factor at high temperatures with an electrical stress of 60 Hz, 200 V/mil present. The effects of thermal aging on the properties of the films are determined after 15 h of exposure at 200 and 250 degrees C. The preliminary data indicate that most of the tested films remain relatively stable when exposed to temperature as high as 250 degrees C. The PEEK film however tends to display some wrinkling and exhibit discoloration when exposed to temperatures of about 200 degrees C and higher. All other films displayed good dielectric and physical properties even up to 250 degrees C.<<ETX>>

Low temperature characterization of ceramic and film power capacitors

Among the key requirements for advanced electronic systems is the ability to withstand harsh environments while maintaining reliable and efficient operation. Efforts were taken to design and develop power capacitors capable of wide temperature operation. Ceramic and film power capacitors were developed and characterized as a function of temperature from 20/spl deg/C to -185/spl deg/C in terms of their dielectric properties. These properties included capacitance stability and dielectric loss in the frequency range of 50 Hz to 100 kHz. DC leakage current measurements were also performed on the capacitors. The paper presents the results that indicate good operational characteristic behavior and stability of the components tested at low temperatures.

Evaluation of high temperature capacitor dielectrics

Four candidate materials were evaluated for use as high-temperature capacitor dielectrics. The materials investigated were polybenzimidazole polymer and three aramid papers. The samples were characterized with and without heat treatment in terms of their dielectric constant and loss. These properties of the heat-treated samples were also evaluated in a temperature range of 20 to 250 degrees C in the presence of electrical stress of 60 Hz, 50 V/mil. The AC and DC breakdown strengths of both dry and impregnated samples were determined at ambient conditions. The preliminary data indicate that heat treatment of the materials tested improves their dielectric properties and breakdown voltages. The AC and DC dielectric strengths are further improved upon impregnation with a suitable liquid.<<ETX>>

Electrical properties of Teflon and ceramic capacitors at high temperatures

Experiments were carried out to evaluate Teflon and ceramic capacitors for potential use in high-temperature applications. The capacitors were characterized in terms of their capacitance and dielectric loss as a function of temperature, up to 200 degrees C. At a given temperature, these properties were obtained in a frequency range of 50 Hz to 100 kHz, DC leakage current measurements were also performed in a temperature range from 25 to 200 degrees C. The experimental procedures and results are discussed.<<ETX>>

Effects of combined stressing on the electrical properties of film and ceramic capacitors

Advanced power systems which generate, control and distribute electrical power to many large loads are a requirement for future space exploration missions. The development of high temperature insulating materials and power components constitute a key element in systems which are lightweight, efficient, and are capable of surviving the hostile space environment. In previous work, experiments were carried out to evaluate film and ceramic capacitors for potential use in high temperature applications. The effects of thermal stressing, in air and without electrical bias, on the electrical properties of the capacitors as a function of thermal aging up to 12 weeks were determined. In this work, the combined effects of thermal aging and electrical stresses on the properties of teflon film and ceramic power capacitors were examined. The ceramic capacitors were thermally aged for 35 weeks and the teflon capacitors for 15 weeks at 200/spl deg/C under full electrical bias and were characterized, on a weekly basis, in terms of their capacitance stability and electrical loss in the frequency range of 50 Hz to 100 kHz. DC leakage current measurements were also obtained. The results obtained represent the influence that short-term thermal aging and electrical bias, have on the electrical properties of the power capacitors characterized.<<ETX>>

Electrical Characterization Of Glass, Teflon, And Tantalum Capacitors At High Temperatures

Dielectric materials and electrical components and devices employed in radiation fields and space environment are often exposed to elevated temperatures among other things. These systems must, therefore, withstand the high temperature exposure while still providing good electrical and other functional properties. In this work, experiments were carried out to evaluate glass, teflon, and tantalum capacitors for potential use in high temperature applications. The capacitors were characterized in terms of their capacitance and dielectric loss as a function of temperature up to 200/spl deg/C. At a given temperature, these properties were obtained in a frequency range of 50 Hz to 100 kHz. DC leakage current measurements were also performed in a temperature range from 20 to 200 /spl deg/C. The results obtained are discussed and conclusions are made concerning the suitability of the capacitors investigated for high temperature applications.

Evaluation of pyrolysis and arc tracking on candidate wire insulation designs for space applications

Polyimide wire insulation has been found to be vulnerable to pyrolization and arc tracking due to momentary short-circuit arcing events. This report compares arc tracking susceptibility of candidate insulation configurations for space wiring applications. The insulation types studied in this report were gauge 20 hybrid wiring constructions using polyimide, tetrafluoroethylene (TFE), Cross-linked Ethylene Tetrafluoroethylene (XL-ETFE) and/or polytetrafluoroethylene (PTFE) insulations. These constructions were manufactured according to military wiring standards for aerospace applications. Arc track testing was conducted under DC bias and vacuum (10/sup -6/ torr). The tests were conducted to compare the various insulation constructions in terms of their resistance to arc tracking restrike. The results will be presented and discussed in this paper.<<ETX>>

Statistical analysis of multistress aging studies of polyetherimide

Multistress accelerated aging experiments on polyetherimide (PEI) film were conducted by applying a combination of accelerated thermal and electrical (400 Hz) stresses in a full factorial experiment. Weibull and lognormal distributions are used along with general goodness-of-fit measures, the Shapiro-Wilk, W test, and the Shapiro-Brain, Wtest, to assess the statistical distribution of the lifetimes for all stress combinations. To detect significant interaction between the individual stresses and quantify the effect of each stress on the life of the film, an analysis of variance is conducted. The obtained mean life data are then fitted to various existing empirical multistress aging models to suggest the most statistically significant among the tested models. It is shown that either the Weibull or the lognormal distribution can estimate statistical mean within a range of acceptable linearity. The goodness of fit measures, W test and W test, also consistently support the hypothesis and provide no evidence of rejecting either as an adequate statistical distribution.<<ETX>>

Effects of thermal and electrical stressing on the breakdown behavior of space wiring

Several failures in the electrical wiring systems of many aircraft and space vehicles have been attributed to arc tracking and damaged insulation. In some instances, these failures proved to be very costly as they have led to the loss of many aircraft and imperilment of space missions. Efforts are currently underway to develop lightweight, reliable, and arc track resistant wiring for aerospace applications. In this work, six wiring constructions were evaluated in terms of their breakdown behavior as a function of temperature. These hybrid constructions employed insulation consisting of Kapton, Teflon, and cross-linked Tefzel. The properties investigated included the 400 Hz AC dielectric strength at ambient and 200/spl deg/C, and the lifetime at high temperature with an applied bias of 40, 60, and 80% of breakdown voltage level. The results obtained are discussed, and conclusions are made concerning the suitability of the wiring constructions investigated for aerospace applications.

Operational characteristics of a 200/spl deg/C LC parallel resonant circuit

Research efforts are currently underway at the NASA Lewis Research Center to design and demonstrate an inverter capable of operating with a baseplate temperature of 200/spl deg/C. In support of this project, various electrical components including capacitors, inductors, transformers, cables, and semiconductor switches are being developed or evaluated for integration into the inverter. In this work, a parallel LC resonant circuit was constructed and evaluated under simultaneous electrical and thermal stressing. The tests were performed in the temperature range of 25/spl deg/C to 200/spl deg/C with an applied voltage of up to 90 V, 20 kHz. The individual components were comprised of high temperature film capacitors and powder core inductors developed in-house. The circuit was characterized in terms of the component currents and case temperatures as well as frequency of resonance as a function of applied bias and temperature. The results obtained, which have indicated good functional stability up to 200/spl deg/C, are presented and discussed.