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On May 11-12, 1989, the first Symposium for Reliability of Multilayer Ceramic Capacitors was held on the University Park Campus of The Pennsylvania State University. Reliability has been definedl.2 as "the probability that a product or device will perform a specified function, under a set of external conditions for a specified period of time." We may also think of reliability as the timebased concept of quality. The subject can involve complicated discussions of probability and statistics, which are crucial to its complete understanding and utilization, but that was not the main intent of the symposium. Indeed, we sought, rightly or wrongly, to emphasize the more practical aspects of reliability in place of its mathematical foundations. For a treatment of these important fundamentals the reader is referred to several recent texts and articles.3-14As all devices-from computers to automobiles-become more complex, manufacturers are demanding ever higher reliability from conventional electronic components. Just as quality requirements are exceeding the ability of producers to supply direct statistics,15 reliabilities are being requested that specify times which may exceed any ability for direct test. Defining, measuring, and guaranteeing reliability requires improved testing methods that properly simulate use stresses in reasonable time frames. Meeting ever more stringent demands requires improved understanding of the relationship between materials processing and the performance of the product under use conditions. Absolute improvements in reliability can only come from a detailed understanding of the physical and chemical processes that contribute to degradation and failure.We sought to stress these topics during the symposium. Most of the papers were by invitation of the technical committee. It is the nature of reliability to be a sensitive topic among industrial participants. This can be seen in the controversy over the applicability of many military specifications and also in the justification and methods for accelerated testing. It is unfortunate that several potential presenters could not participate in the symposium because their data could not be cleared in time by company or military reviewers. We hope that the 1989 symposium will stimulate further advances in the field and encourage everyone to participate in the next meeting. standards of ACerS. The speakers whose busy schedules did not permit the extensive work required to convert their presentations into scientific papers are encouraged to publish them as soon as possible. Attendees were all asked for their comments on this conference and their responses were such that we could not discount a single paper.Many authors and attendees have asked when the next symposium will be held. This is a question we began to discuss even before the first one took place. Certainly, the excellent attendance and the great encouragement from both industry and academic participants would favor another symposium in the near future. Recently, however, it was decided that a me...
The NASA's Evolutionary Xenon Thruster (NEXT) project is developing an advanced ion propulsion system for future NASA missions for solar system exploration. A critical element of the propulsion system is the Power Processing Unit (PPU) which supplies regulated power to the key components of the thruster. The PPU contains six different power supplies including the beam, discharge, discharge heater, neutralizer, neutralizer heater, and accelerator supplies. The beam supply is the largest and processes up to 93+% of the power. The NEXT PPU had been operated for approximately 200+ hr and has experienced a series of three capacitor failures in the beam supply. The capacitors are in the same, nominally noncritical location-the input filter capacitor to a full wave switching inverter. The three failures occurred after about 20, 30, and 135 hr of operation. This paper provides background on the NEXT PPU and the capacitor failures. It discusses the failure investigation approach, the beam supply power switching topology and its operating modes, capacitor characteristics and circuit testing. Finally, it identifies root cause of the failures to be the unusual confluence of circuit switching frequency, the physical layout of the power circuits, and the characteristics of the capacitor. Nomenclature I. IntroductionThe NASA's Evolutionary Xenon Thruster (NEXT) project is developing an advanced ion propulsion system for future NASA missions for solar system exploration. A critical element of the propulsion system is the power processing unit (PPU) which supplies regulated power to the key components of the thruster. The PPU contains six different power supplies: beam, discharge, discharge heater, neutralizer, neutralizer heater, and accelerator supplies. The beam supply is the largest and processes up to 93+% of the power. After the first 200+ hr of operation, the NEXT PPU experienced a series of three capacitor failures in the beam supply. The capacitors are in the same, nominally non-critical location-the input bypass capacitor to a switching inverter. This paper provides a description of the PPU, including the beam module and its electrical design, discusses the failure including insight into the capacitor design and its characteristics, identifies the approach for determining the root cause including the capacitor testing, and finally describes the initial and long term fixes for the problem. II. Description of the PPUAn engineering model (EM) PPU for the NEXT project was designed and fabricated under contract with NASA Glenn Research Center (GRC). This modular PPU is capable of processing from 0.5 to 7.0 kW of output power for the NEXT ion thruster. Its design includes many significant improvements for better performance over the state-of-the-art NASA's Solar Electric Propulsion Technology Application Readiness (NSTAR) PPU. The most significant difference is the beam supply which is comprised of six modules and capable of very efficient operation through a wide voltage range because of innovative features like du...
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