J.D. Herbst

A DC Arc Model for Series Faults in Low Voltage Microgrids

This paper presents a dc arc model to simplify the study of a critical issue in dc microgrids: series faults. The model is derived from a hyperbolic approximation of observed arc voltage and current patterns, which permit analyzing the arc in terms of its resistance, power, energy, and quenching condition. Recent faults staged by the authors on a dc microgrid yielded enough data to develop an arc model for three fault types: constant-gap speed, fixed-gap distance, and accelerated gap. The results in this paper compare experimental and simulation results for the three fault types. It is concluded that because the instantaneous voltage, current, power, and energy waveforms produced by the model agree well with experimental results, the model is suitable for transient simulations.

A 2 MW flywheel for hybrid locomotive power

The University of Texas at Austin Center for Electromechanics (UT-CEM) is currently developing an Advanced Locomotive Propulsion System (ALPS) as part of the Next Generation High-Speed Rail program sponsored by the Federal Railroad Administration (FRA). The ALPS consists of a gas turbine and synchronous alternator, combined with an induction motor coupled flywheel energy storage system (FESS). The prime power and FESS are coupled through a DC power link, as is the conventional AC traction drive system. The energy system includes auxiliary support systems to provide thermal management, bearing systems, controls, and power conversions. The energy exchange capacity of the flywheel is 360 MJ (100 kW-hr). This paper presents the requirements, considerations, and design of the integrated turbine and flywheel power system. Significant development efforts have gone into the high-speed synchronous alternator, the flywheel power converter, and the highspeed induction machine for the flywheel, the flywheel itself and its magnetic bearings. The fabrication status of these components and testing progress is also reported.

A field based, self-excited compulsator power supply for a 9 MJ railgun demonstrator

Fabrication efforts have begun on a field-based compulsator for firing 9 MJ projectiles from a railgun launcher. The machine is designed to store 200 MJ kinetic energy and fire a salvo of nine rounds in three minutes at velocities between 2.5 and 4.0 km/s. Prime power required to meet this firing schedule is 1.865 kW, and will be supplied by a gas turbine engine. It is also possible to fire a burst of two shots in rapid succession, if desired. Operating speed of the machine is 8250 r/min and it has design ratings of 3.2 MA peak current and 20 GW peak power into a 9 MJ railgun load. A two-pole configuration is used for pulse-length considerations, and selectivity passive compensation is used to produced a relatively flat pulse and limit peak projectile acceleration to about 980000 m/s/sup 2/. Other distinguishing features include an air core magnetic circuit, separate rotor armature windings for self-excitation and railgun firing, ambient temperature field coils, and excitation field magnetic energy recovery capability. A detailed description of the machine as designed, and its auxiliary and control systems, is provided. Fabrication and assembly methods are reviewed, and the current status of the project is discussed. >

Design of a self-excited, air-core compulsator for a skid-mounted repetitive fire 9 MJ railgun system

The design of a lightweight, compulsator-driven 9-MJ electromagnetic (EM) launcher has been completed and is in the fabrication phase. Scheduled for initial field testing in early 1989, the system will be capable of firing a salvo of nine rounds in three minutes at muzzle velocities between 2.5 and 4.0 km/s. Prime power for the compulsator is supplied by a 5000-hp gas turbine engine through a gearbox and clutch arrangement, and auxiliary power is provided by a small 750-hp turbine. Electrical power generation and pulse conditioning for the launcher are performed by the compulsator, which features a self-excited, air-core magnetic circuit and selectively passive armature compensation designed to minimize peak projectile acceleration. Peak power from the machine is 27 GW, and a total of 30 MJ is extracted from the rotor during each firing of the gun. System mass, including gun, compulsator, prime power, and auxiliary systems, is less than 22 tons and will be mounted on a 36-ton concrete slab which simulates the mass of an armored vehicle on which the system will eventually be integrated. >

Advanced Induction Motor Endring Design Features for High Speed Applications

This paper presents advancements in induction motor endring design to overcome mechanical limitations and extend the operating speed range and joint reliability of induction machines. A novel endring design met the challenging mechanical requirements of this high speed, high temperature, power dense application, without compromising electrical performance. Analysis is presented of the advanced endring design features including a non uniform cross section, hoop stress relief cuts, and an integrated joint boss, which reduced critical stress concentrations, allowing operation under a broad speed and temperature design range. A generalized treatment of this design approach is presented comparing the concept results to conventional design techniques. Additionally, a low temperature joining process of the bar/end ring connection is discussed that provides the required joint strength without compromising the mechanical strength of the age hardened parent metals. A description of a prototype 2 MW, 15,000 rpm flywheel motor generator embodying this technology is presented

Dynamic Load and Storage Integration

Modern technology combined with the desire to minimize the size and weight of a ships power system are leading to renewed interest in more electric or all-electric ships. An important characteristic of the emerging ship power system is an increasing level of load variability, with some future pulsed loads requiring peak power in excess of the available steady-state power. This inevitably leads to the need for some additional energy storage beyond that inherent in the fuel. With the current and evolving technology, it appears that storage will be in the form of batteries, rotating machines, and capacitors. All of these are in use on ships today and all have enjoyed significant technological improvements over the last decade. Moreover, all are expected to be further enhanced by todays materials research. A key benefit of storage is that, when it can be justified for a given load, it can have additional beneficial uses such as ride-through capability to restart a gas turbine if there is an unanticipated power loss; alternatively, storage can be used to stabilize the power grid when switching large loads. Knowing when to stage gas turbine utilization versus energy storage is a key subject in this article. The clear need for storage has raised the opportunity to design a comprehensive storage system, sometimes called an energy magazine, that can combine intermittent generation as well as any or all of the other storage technologies to provide a smaller, lighter and better performing system than would individual storage solutions for each potential application.

Flexible test bed for MVDC and HFAC electric ship power system architectures for Navy ships

Several power architectures have been considered for Navy ships and significant effort has been focused on simulation of the various power system topologies. The University of Texas at Austin Center for Electromechanics (UT-CEM) has taken a step forward by assembling a microgrid capable of operating at MW power levels to experimentally validate key elements of these system models. The present system is an MVDC architecture but can easily be reconfigured as an HFAC network. This paper describes the UT-CEM microgrid and plans to demonstrate critical technical issues in naval power systems and enable model validation. The intent is for the microgrid to be a flexible test bed for investigation of naval power systems and to become a useful bridge from theoretical and computer studies to a realistic experimental platform.

Status of the 9 MJ Range Gun system

The 9 MJ Range Gun system under construction at the Center for Electromechanics at The University of Texas at Austin is designed as a self-contained, field portable electromagnetic launch system to accelerate a salvo of three projectiles to a muzzle energy of 9 MJ at velocities ranging from 2.5 to 4.0 km/s. The Range Gun system will consist of a self-excited air-core compulsator, a 90 mm bore railgun launcher, prime power and auxiliary systems, solid state switches for field rectification and gun discharge, and the controls and data acquisition required to operate the system. The compulsator is designed to deliver 3.2 MA current pulses to the railgun launcher at a peak power rating of 10 GW. This paper describes some of the innovations incorporated into the design of the 9 MJ Range Gun system compulsator and presents the status of the fabrication and testing efforts. Initial performance of the 90 mm railgun during testing at the Electric Armaments Research Center will also be presented. >

Design, Fabrication, and Testing of 10 MJ Composite Flywheel Energy Storage Rotors

Flywheel energy storage systems employing high speed composite flywheels and advanced electric motor/generators are being evaluated by the Department of Defense (DoD), NASA [1], and firms [2,3] to replace electrochemical battery banks in satellites and manned space applications. Flywheel energy storage systems can provide extended operating life and significant reduction in weight and volume compared to conventional electrochemical systems. In addition, flywheels can provide momentum or reaction wheel functions for attitude control. This paper describes the design, fabrication, and spin testing of two 10 MJ composite flywheel energy storage rotors. To achieve the demonstrated energy density of greater than 310 kJ/kg in a volume of less than 0.05 m3, the rotors utilize flexible composite arbors to connect a composite rim to a metallic shaft, resulting in compact, lightweight, high energy density structures. The paper also describes the finite element stress and rotordynamics analyses, along with a description of the fabrication and assembly techniques used in the construction of the rotor. A description of the experimental setup and a discussion of spin testing of the rotors up to 45,000 rpm (965 m/s tip speed) are also presented. Accurate measurements of rotor centrifugal growth made with laser triangulation sensors confirmed predicted strains of greater than 1.2% in the composite rim. Due to the weight penalty associated with flywheel designs requiring containment structures, there is a strong need to develop flywheel systems which operate safely in space, preferably without dedicated containment structures. A future paper will describe results of a 28,600 rpm composite rotor burst test performed in a containment structure as a step towards understanding composite rotor failure modes. INTRODUCTION Power systems subject to cyclic variations in prime power availability or needing to satisfy intermittent demands for high power may benefit from the addition of an energy storage element to reduce prime power requirements. The Center for Electromechanics (CEM) at The University of Texas at Austin has been developing high performance composite energy storage flywheels for 15 years as part of the Electromagnetic Gun Weapons System Program for the U.S. Army and, more recently, for the Defense Advanced Research Projects Agency (DARPA) Electric Vehicle Program. CEM is currently under contract to the Department of Transportation Federal Railroad Administration (FRA) to develop an advanced locomotive propulsion system (ALPS) including a composite energy storage flywheel for use in a high speed passenger locomotive application.[4] ALPS consists of a 600 MJ flywheel energy storage system coupled to a 3 MW motor/generator and a second 3 MW high speed alternator direct coupled to a gas turbine prime mover. Figure 1 shows the power flow diagram for the locomotive propulsion system application. Design, Fabrication, and Testing of 10 MJ Composite Flywheel Energy Storage Rotors J.D. Herbst, S.M. Manifold, B.T. Murphy, J.H. Price, R.C. Thompson, and W.A. Walls Center for Electromechanics, The University of Texas at Austin A. Alexander and K. Twigg

Advanced Locomotive Propulsion System (ALPS) Project Status 2003

The University of Texas at Austin Center for Electromechanics (UT-CEM) is currently engaged in the development of an Advanced Locomotive Propulsion System (ALPS) for high speed passenger rail locomotives. The project is sponsored by the Federal Railroad Administration as part of the Next Generation High Speed Rail program. The goal of the ALPS project is to demonstrate the feasibility of an advanced locomotive propulsion system with the following features: • Operation up to 150 mph on existing infrastructure • Acceleration comparable to electric locomotives • Elimination of