Frequency dependence of partial discharge initiation voltages with embedded electrodes

Partial discharge initiation voltages of a dielectric insulation material exposed to ac voltages show little dependence on frequency in the power frequency range. This results after significant voltage conditioning at the measured frequencies with samples configured for embedded electrodes. Comparison to previously published results is made.Center for Electromechanic

Factors Contributing to Streamer Morphology

Recent work shows that the range of morphology of anode streamers in liquid dielectric breakdown is predicted when it is represented as stochastic growth of a branching fractal tree. This model may be analogous to the critical volume model of breakdown used in gases. Assuming there is a relationship, leads to a concept of how affecting the electron production and recombination rates in a fluid can affect streamer behavior. These concepts were tested by measuring the effect on streamer behavior due to adding a commercial antistatic additive to toluene. The results were consistent with the concepts of the model but insufficient to define the limits of the model's applicability.Center for Electromechanic

Electrical Insulation Challenges for Rotating Machines Used on Future Electric Ships

The electrification of ships coupled with a demand for very high power and energy density raises challenges for insulation system designers for this market. The physical reason the design is challenging is that the electrical, mechanical, and thermal environment on a ship is sufficiently far from the land-based environment that key parts of the data and experience base needed for insulation system design do not exist.Center for Electromechanic

Electric ship power system - research at The University of Texas at Austin

Recognizing the importance of electric ships and the myriad of technical challenges they present, the University of Texas at Austin, with seed funding from the Office of Naval Research, established a virtual electrical ship research and development center. The reason for the virtual center is that the complex challenges of the future require multidisciplinary solutions. The virtual center contains staff members from Electrical Engineering, Mechanical Engineering and two research centers who work collaboratively with a number of other universities and with industry. This program has two anticipated significant outcomes. At the system level, the first anticipated outcome is to develop a comprehensive set of modeling approaches that guide the evolution of electric ship power systems. The second outcome is an approach to the replacement of the hydraulic system on current ships with electrical actuators on future ships.Center for Electromechanic

Pulsed power electromechanics - permanent magnets versus copper coils

A number of emerging military systems operate using short, repetitive, high-power pulses. Rotating electromechanical machines incorporating inertial storage are natural candidates for supplying these high power pulses. The short duty cycle characteristic of these devices introduces an interesting physics trade off in the choice of field excitation. A quantitative comparison of permanent magnet machines to copper coil systems is performed on an equal weigh basis. The results indicate that copper coil based systems using exciters are superior to permanent magnet counterparts in pulsed applications of 20 s and less. The recommended use of copper coils becomes stronger when the issues of magnet life due to vibration, thermal cycling, and slot harmonic heating are considered.Center for Electromechanic

A new strategy for representation and control of self-contained power systems

Power systems on naval vessels and airplanes are good examples of self-contained power systems. State of the art LEM modules and voltage sensors provide real time current and voltage data. This paper shows how that information can be used to construct dynamic equivalent impedance representations of the system discretized into key trunk lines. Error analysis indicates that the algorithm performing this representation can be updated in one fifth of a cycle if the signal to noise data ratio is 5% or less. The magnitude of the equivalent impedance is sufficient to determine when fault control on either end of the trunk line is required. These same equivalent impedances can be used to determine the best switch configuration to maximize load power while minimizing transmission loss subject to line load capability. The accuracy of the equivalent impedance approach is assessed for transients with active and passive loads.Center for Electromechanic

Inconsistencies in Electric Motor Certification Requirements

The Final Rule on certification requirements for induction motors issued by the Department of Energy contains different assumptions for the compliance and the enforcement procedures. These differences may yield unexpected results under certain conditions. For example, at times, the enforcement procedure can support a higher nameplate rating for a motor lot than would be possible by an appropriate application of the compliance procedure and vice versa. This paper examines, in detail, the nature of the problem and gives several examples where the enforcement plan fails to achieve its intended purpose.Center for Electromechanic

Development of a Multicore Power System Simulator for Ship Systems

An important impediment to using widely available software to simulate the behavior of advanced power systems for electric ships is that the simulation time is too long to be practical. Consequently, the Center for Electromechanics at the University of Texas at Austin (UT-CEM) is developing a multicore power system solver to simulate large shipboard power systems. In its first year of development, the focus is on testing CEM’s solver (CEMS) for accuracy. This paper presents an overview of the major traits of CEMS, and compares its simulation results to the well-known commercial power system simulator SimPowerSystems. Preliminary results show that accuracy is maintained and improved in specific test cases.Center for Electromechanic

A fundamental look at energy storage focusing primarily on flywheels and superconducting energy storage

This paper compares energy storage efficiency of Superconducting Energy Storage devices (SMES) with high speed flywheels employing magnetic bearings. Both solid cylinder and shell cylinder flywheels are examined from fundamental physics. Solid cylinder flywheels have a fixed energy density by weight and volume dependent only on the constitutive properties of the flywheel. For a target energy storage, the flywheel’s radius, length, and rotation speed are determined given the governing limitation on hoop stress and the requirement that operation will occur below the first bending mode. No design parameters are open for engineering judgment except the margin of safety. Thus the volume necessary to reach a target energy storage is well defined. The shell cylinder has only the thickness of the shell as an open design variable. The constraint for a SMES system is that the magnetic field density remain below the quench value for the superconductor. This constraint involves the current density, the magnetic field density, and the temperature. A theoretical upper limit can be reached by considering a volume with a B field just under the quench value. In this theoretical upper limit, given the materials available today, the flywheel stores the same energy in a volume 7.4 times smaller than the SMES system even when assuming a 20 T field for the SMES system. Both systems allow for energy to be added and removed rapidly by comparison to battery and capacitive storage, but the flywheel is by far the more efficient choice when examined on a per volume basis.Center for Electromechanic

Reconfiguration of shipboard power systems

The electrical system on a ship is well contained. Among the challenges proffered by naval systems is real time monitoring for the purpose of fault analysis and reconfiguration. The power system can be considered as a grid of interconnected trunk lines each with its own equivalent parallel load impedance and series transmission impedance. These equivalent impedances provide a natural means of reducing a rather large, complex system to a small compact system. The reduced system can be optimized to maximize power flow through the equivalent parallel impedances and minimize the loss in the series components. Binary integer optimization techniques offer the most promise in solving these problems quickly.Center for Electromechanic