Laser Induced Pulse Pressure for Advanced Dielectric Research for Pulsed Power and Electric Propulsion
Abstract
To understand the origins of electrical breakdown and particularly the prebreakdown processesthat lead up to breakdown, which include charge injection, carrier transport, defects creation,charging of defects, novel experimental tools are needed to go beyond the reaches of bestimaging and spectroscopic characterization tools available today. Charge profiling technique forpin-pointing charge injection, transport and more importantly defects creation and charge trappingat atomic and nanoscale regions will be developed to extract various energetic modes oftransport for indicative signatures of the onset of instability as a result of charging and the triggeringof discharge at various time and spatial scales (Fig.1). It is anticipated and highly preferredto have computational studies such as Density Functional Theory and Molecular Dynamicschampion these experimental investigations. In turn, experimental study will not only providecritical validations for predictive models but also generate input parameters (e.g., trap depth fortransport) for computational tool development. Ultimately, new dielectric materials with highresistance to electrical breakdown, electrical discharge, space-charge accumulation yet with highheat transfer capability will be developed through nanostructure-engineering by suppressing correspondingenergetic modes for operation under pulsed discharge, fast rise time, DC polarity reversal,as well as convoluted electrical-thermo-mechanical multi-stresses. The anticipated impactsof this new experimental capability will include a broad spectrum of basic dielectricresearches for pulsed power and all the major critical components of NGIPS for marine electricalpower and propulsion systems (Fig.1).2.2 Science Based Approach1) Prebreakdown Conduction MeasurementFundamental understanding of carrier mobility-centric pre-breakdown phenomena in dielectricsprovides insights into high field transport phenomena as well as the associated agingand onset of charge injection instability. A system for measuring resistive current through a planardielectric film during a linear ramp voltage to breakdown has been developed to address thelimits of conventional steady-state approaches in which the sample typically fails at ~60% of thebreakdown field.With dynamic feedback to cancel the capacitive current from the ramp, resistive and absorptioncurrents from polymer thin films can be measured up to breakdown. The superimpositionof a small sinusoidal modulation signal on the ramp voltage provides the basis for active cancellation.The dynamic range and linearity of the feedback loop were carefully designed to facilitatecancelation of capacitive current during substantial changes in sample dielectric constant as afunction of field, as can occur in highly nonlinear materials. For the first time, direct measurementof the prebreakdown conduction and charging currents was obtained for commercial capacitorfilms with this unique tool [7], as shown in Figure 2. In general, these direct prebreakdownconduction data correlate to the dielectric breakdown strength of these capacitor grade films.Furthermore, Charge-Limited Conduction (SCLC) model will yield a straight line with a slope of3. All the plots in the insert of Fig.2 have slopes of greater than 3, indicating the presence oftraps and the resulting trap modulated SCLC conductions for capacitor grade films at fields higherthan 400kV/mm. Further understanding of the trap modulated conduction requires advanceprofiling technique with high spatial and temporal resolutions for prebreakdown charge injectionand transport study.Charge Injection and Transport Profiling TechniqueA pulsed electroacoustic apparatus (PEA) has been developed with DOE funding for theprofiling of charge injection and transport for HVDC Cabling [8-10]. As shown in Figure 3, thedynamic behavior of space charges in cross-linked polyethylene thick film of 170 micron under100 kV/mm is visualized in a 3-D plot, showing clearly ~packets~ of
Document Details
- Document Type
- DoD Grant Award
- Publication Date
- Sep 30, 2016
- Source ID
- N000141612885
Entities
People
- Yang Cao
Organizations
- Office of Naval Research
- United States Navy
- University of Connecticut