F.W. MacDougall

High energy density pulsed power capacitors

Pulsed power in mobile systems requires high energy density capacitors as energy storage and power compression devices. Applications range from medical defibrillators to naval artillery, with a wide envelope of operating conditions requiring several technology approaches. The ongoing, multifaceted development effort on high energy density pulsed power capacitors at General Atomics Energy Products has yielded capacitors with significantly higher energy densities (> 5 J/cc) than were available a few years ago. Substantially higher energy densities are also being achieved in capacitors designed for microsecond discharge applications. This paper describes this progress and the state of the art in pulsed power capacitors.

Self-healing pulse capacitors for the National Ignition Facility (NIF)

Approximately 4000 capacitors, each storing 83.5 kJ of energy, will be required for the United States Department of Energy National Ignition Facility (NIF), being built at Lawrence Livermore National Laboratory (LLNL). To achieve the required system reliability lifetime, and cost goals, the capacitors were specified to be of the self-healing, metallized electrode type of construction. Maxwell Energy Products has previously delivered a number of banks of self-healing capacitors, including the 52 MJ bank at the US Army ARDEC facility at Picatinny Arsenal, NJ. Development of capacitors specifically for NIF began several years ago and continues today at Maxwell, with the primary goal of reducing the manufacturing cost. In support of this effort, LLNL has procured prototypes and life tested a number of our designs over the past three years. This paper reviews the development of NIF capacitors at Maxwell, focussing on the lifetime performance of different designs during the development. This work has resulted in Maxwell Type CM capacitor designs, whose demonstrated lifetime capability has far exceeded the 20000 shot NIF requirement, having energy densities as high as 0.84 J/cc.

High energy density capacitors for pulsed power applications

The improvement in the performance of high energy density capacitors used in pulsed power has accelerated over the past few years. This has resulted from increased research sponsored by the US Army Research Laboratory, in support of the US Militarys needs. The capacitor development effort will be discussed as well as the results of both short term and long term testing of a new generation of high energy density capacitors.

High energy density capacitors

Metallized film capacitors with energy densities as high as 3 J/cc and stored energy as high as 260 kJ per unit are now commercially available. These capacitors can be custom-designed for specific applications so as to minimize the size and weight of the capacitance for the lifetime and duty required. Applications requiring pulsed energy discharge times of 10 microseconds to 10 milliseconds are typical, but DC filtering and other types of duty can also be addressed. Packaging options include industry-standard drawn steel cans, proprietary molded plastic cases, and large welded steel cases. The performance of these capacitors as a function of voltage and size will be described.

Large High Energy Density Pulse Discharge Capacitor Characterization

The energy density of film capacitors continues to increase. This paper discusses the performance issues of limited life pulsed discharge capacitors operating at better than 2 J/cc (2 MJ/m3) in the 5 kV to 20 kV range. Self-healing metallized electrodes have been utilized in these designs to provide graceful aging at electric fields greater than 500 MV/m. A variety of polymer films have been evaluated for use in these capacitors. The pulse rise times where the capacitors find application are in the range of microseconds to milliseconds. Life tests have been performed with the goal of achieving at least 1000 charge/discharge cycles at maximum energy density. Failure modes in normal charge/discharge pulse service, and short- circuit fault conditions have been evaluated. Design modifications to increase life and energy density were made based on those analyses. Capacitors delivering greater than 100 kJ above 2 J/cc have been built, tested, and shipped.

Progress in the reduction of inductance in the standard 100 kV energy storage capacitor

The basic metal case low profile bushing energy storage capacitor design has changed little from the 1.85 /spl mu/F, 60 kV capacitor developed for the LANL SCYLLAC program in the late 1960s. Their enduring use testifies to a robust design. Today energy storage capacitors having a lower equivalent series inductance (ESL) will contribute to increasing the power capability of new or revised pulsed power machines. Lower ESL coupled with an improved terminal configuration for better integration with the system design, will produce faster discharge times and lower driver impedance, making higher power systems more sensible and energy efficient. A lower ESL capacitor that is compatible with existing proven hardware will also make upgrading more cost effective. This paper discusses the establishment of standardized test methods for determining the inductance of different SCYLLAC style energy storage capacitors; for example Maxwell Type C capacitors, which are now manufactured by General Atomics Energy Products, a part of Sorrento Electronics, and units from Aerovox. The effects leading to imprecision in inductance measurements will be noted. The inductance of existing designs will be compared with new hardware compatible prototype configurations with a goal of reducing the inductance up to 50%.

High voltage capacitors designed to avoid catastrophic failure modes

A major concern in the operation of high voltage capacitors is the failure mode at end of life. While progress has been made in this area at lower voltages, little has changed for high current capacitors operating above 30 kV in steady state and pulsed power applications. Based on a new development at Maxwell Energy Products, Inc., it is now possible to build capacitors that can operate with a high degree of safety at high voltages. The capacitors reach the normal end of life, while avoiding the catastrophic failures, collateral damage, and unscheduled maintenance, associated with the normal failure mode of todays high voltage capacitors. This paper discusses the problem, capacitor failure modes, capacitor designs and describes a solution to the problem of catastrophic high voltage capacitor failures.

Pulsed Power Capacitors

The U.S. Army Research Laboratory has sponsored a capacitor development program for film-dielectric capacitors. The program has evaluated dielectric materials for high energy density capacitors from industrial and academic research programs. High-performance capacitors have been developed that meet the needs of todays military applications. The performance of recently developed capacitors will be discussed.

High-Specific-Power Capacitors

Energy density is not the only metric for capacitors. In high pulse repetition rate modulators and other types of power conditioning systems, the reactive power (kVAR) is often the factor driving the physical size of capacitors. The specific power (kVAR/cm3) capability of a capacitor depends on many factors, including frequency, voltage, waveform, duty cycle, ambient temperature, and available cooling. The design of capacitors for high specific power requirements will be described. Designs using high-temperature polymer films as dielectrics and metallized electrodes will be compared to designs using common dielectrics such as polypropylene and both metallized and discrete foil electrodes.

Preliminary Design of a 200 MJ Pulsed Power System for a Naval Railgun Proof of Concept Facility

The Navys decision for implementation of an Integrated Power System into the next generation of surface combatants (DDX Warship) provides the opportunity for introduction of high powered electric weapons systems. An electromagnetic railgun is a candidate that provides enhanced capabilities for indirect fire support with increased ranges and velocities. Additionally, improvements of logistics for ammunition handling and storage make the railgun an attractive solution for the next generation Naval Electric Warship Armament. The notional naval railgun at full scale will fire a 20 kg launch package at a velocity of 2500 m/s providing 63 MJ of muzzle energy. It is estimated that a 200 MJ pulse forming energy storage system (PFN) will be required to achieve the desired muzzle velocity and energy. A land based Proof-of- Concept (PoC) Facility can validate the notional railgun performance and pulsed power requirements. Components for the barrel, launch package, sabot and projectile designs will also be validated. Terminal effects can also be studied at the facility. This paper describes preliminary design assessments associated with the 200 MJ Naval PoC Facility. Included are the facility requirements, PFN modeling and component technical assessment. Additionally the facility layout, capacitor bank modules and bussing requirements are illustrated.