ONR Electric Ship
Electromagnetic Materials for Machinery Development and Characteristics
I. Overview and Goals
This materials program emphasizes development and characterization to support the ONR Electric Power Systems Division and the Electric Ship R&D Consortium (ESRDC). Concurrently, CEM design and prototype programs benefit. This program involves active materials: electrical insulation, magnetic materials, and coils.
The materials program goal is reduced power losses and improved endurance and reliability, which are directly interrelated in the operating regimes we seek. These operating regimes are higher frequency, higher temperature, and higher rotation speeds for power-dense rotating machines of all types and sizes. A fundamental thesis is that the materials operating conditions must be addressed during initial design efforts and accurate characterization is required. The materials program can provide state-of-art quality assurance guidelines during prototype and builds. We seek to perform focused research projects to address questions regarding materials behavior, processing variables, and diagnostic techniques. The next three sections give a synopsis of our current project plans for insulation, magnetic materials, and coils, respectively.
Materials Behavior: Current issues with electrical insulation behavior for power-dense machines are in two categories: (i.) the formation of localized high fields (especially with fillers); and (ii.) aging (whereby organic materials degrade with time under applied thermal, mechanical, and electrical stresses). These issues are being studied by examining dielectric parameters (such as permittivity and loss tangent) and partial discharge behaviors. These studies are an extension of our growing experience working with commercial, high performance polymers.
We are operating an extremely sensitive ac partial discharge (PD) prototype diagnostic tool developed by NIST and researchers in the Air Force Research Laboratory, Propulsion Directorate, Power Division specifically to characterize such materials behavior. This tool allows us to study the effects of PD in well-controlled experiments. Our focus is serial high voltage insulation studies of: (i.) electrode surface finish and interface conditioning behavior; (ii.) frequency and pwm stress characterization; (iii.) filler effects and space charge development with nano-particulate; (iv.) combined thermal and electrical stresses. Improved and alternative insulation materials will be characterized and referred to these baseline studies. Some of the findings of these studies have direct application to power electronics development.
Charge injection with pulsed power under extremely high current and relatively low voltage conditions is also of programmatic interest at CEM (e.g., for EM Gun bore wear control).
Diagnostic Tool: Extending the use of the ac partial discharge diagnostic tool to operating machines and other high voltage equipment is under investigation. The simplicity, economics, and compactness of this tool (potentially consisting of a preamp of less than 300 cubic centimeters connected to a computer) may lend itself to real-time condition-based monitoring of rotating machines. We are interested in collaboration with WPAFL in the development of a second generation tool of this type.
III. Magnetic Materials Projects
Materials Behavior: We seek fatigue resistant, low loss, high induction efficiency, soft magnetic materials of extremely high elastic moduli and yield strength. Under current investigation are the effect of biaxial mechanical stress on power reduction and the minimization of magneto-mechanical effects. In pursuing characterization studies in this area, evidence has been found of alternating magnetic field degradation of the mechanical properties of certain precipitate-hardened laminate steels. This study is continuing.
Diagnostic Tools: A multipurpose hysteresisgraph system is operating at CEM. The system is capable of characterizing both soft and hard (permanent) magnetic materials. Sample temperature capability ranges from -50˚ to ~200˚C and frequency is variable up to 50 KHz for soft materials. Higher temperatures is a feasible upgrade. The system is used for quality assurance measurements such as remanance, coercivity, and core loss as the processing of laminate materials is varied.
The design and prototype of a second diagnostic tool has been proposed. This tool is a revolutionary magnetostriction parameterization instrument. The instrument would apply a cryogenic to ~400˚C temperature range, biaxial mechanical stress state, and ac magnetic field to seek windows of zero magnetostriction under machine operating conditions. Such “windows” are theoretically design optimization targets to reduce power loss and increase reliability, as well as reduce acoustic noise. Researchers at CEM also have access to a squib magnetometer and a magnetic force microscopy (MFM)- capable scanning probe microscope lab
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IV. CoilProjects
Materials Behavior: Low impedance metals exhibit ductile behavior and also can produce large quantities of heat in certain pulsed-power applications. Insulation systems that permit proximity of active cooling and concurrently provide a stiffening sheath are sought.
Diagnostic Technique: A diagnostic technique is being developed to quantify impedance mismatch at coil joints. Impedance mismatch can lead to electrical noise (potentially damaging to insulation), power losses, and heat generation. The technique of choice is a non-contacting eddy current coil and ideal reference sample for comparison. The equipment will allow measurements with applied mechanical stress and at elevated temperatures to simulate operating conditions. The technique is conducive to examining the effect of joint corrosion/oxidation and brazing/welding processes.
For more information about this, please contact
Aleta Wilder
See Also Related Topics on ONR Electric Ship:
Approaches to Shipboard Power Management by Kent Davey
Power System Modeling and Simulation by Hamid Ouroua |
