W.A. Walls

Application of electromagnetic guns to future naval platforms

Designs for future naval vessels are strongly considering electric drive systems. Already employed in commercial cruise ships, electric drive offers the advantages of increased ship design flexibility, improved efficiency, reduced maintenance and allows ship prime power to be easily diverted to other electrical loads as needed. The ability to use ship prime power generation, which ranges between 40 and 150 MW depending on vessel class, for other electric loads provides the opportunity to electrify many existing functions as well as add new performance enhancing systems. The recent and ongoing emergence of electric gun and guided projectile technologies now allows very long range naval fire support functions to be evaluated for viability. In this paper, conceptual system designs for surface fire support of forces in littoral campaigns are considered. Key advantages of an EM fire support weapon over conventional technologies include reduced logistics burden and cost per round, greater lethality, shorter time of flight, improved survivability and the ability to stow more rounds. Notional mission requirements, projectile, power supply issues and ship integration issues are discussed. Also, other shipboard uses for the pulse power system required for these notional electric gun systems are also reviewed.

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. >

Compact homopolar generator developed at CEM-UT

For electromagnetic launchers (EMLs) to become practical devices, they must evolve from laboratory test beds to field-portable systems. Such systems require the development of compact, lightweight, high-energy, high-current power supplies. Investigation of the candidate systems -- flux compressors, capacitors, inductors, batteries, and rotating machines -- showed the homopolar generator (HPG) to be a device with immediate potential for development. HPGs were selected because of their demonstrated ability to produce the high-energy, high-current electrical pulse required of an EML power supply from a relatively compact light-weight machine. By taking state-of-the-art HPG technology and integrating it with a machine designed specifically for high energy density, a field-portable HPG-powered EML system can be realized.

Status of the Advanced Locomotive Propulsion System (ALPS) Project

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

Improved energy density homopolar generator

3-5M per mile electrification costs • Fuel efficient operation with low noise and exhaust emissions The propulsion system consists of two major elements: a gas turbine prime mover driving a high speed generator and an energy storage flywheel with its associated motor/generator and power conversion equipment. The 2.5 MW high speed generator is a three phase, eight pole synchronous machine designed to directly couple to a 15,000 rpm gas turbine. Power from the turbine/alternator system feeds the locomotive dc bus through a conventional full bridge rectifier. The energy storage flywheel features a graphite/epoxy composite rotor operating on active magnetic bearings and is designed to store 480 MJ at 15,000 rpm. An induction motor/generator and variable frequency motor drive provide the link to the dc bus and are used to control power flow into and out of the flywheel. In addition to design and fabrication of the propulsion system components, the project is also developing a distributed control system with power management algorithms to optimize the hybrid propulsion system. Fabrication of the major components of the propulsion system is nearing completion and some preliminary testing of the flywheel and high speed generator has been completed. After completion of the laboratory testing, the propulsion system will be integrated onto a locomotive platform for rolling demonstrations at the Transportation Technology Center test track in Pueblo, Colorado. The paper presents an overview of the propulsion system operation and control strategies, gives detailed descriptions of the major components, and presents component test results.

A study of operating modes for compulsator based EM launcher systems

The preliminary design of a self excited, air-core (SEAC) homopolar generator (HPG) which stores about 250 MJ inertially and is4 capable of delivering 3.2 MA current pulses is presented. In aiming for maximum energy density in an HPG and inductor power supply for electromagnetic (EM) accelerators, the improved energy density (IED) machine uses its self-excited field coils as energy storage inductors and a lightweight graphite reinforced flywheel for inertial energy storage. Weighing approximately 5,000 kg, the design represents a twenty-fold increase in mass energy density over the state of the art and addresses the problem of trapping flux in the rotor during discharge by separating the voltage generating and energy storage functions. Voltage is generated across a squirrel-cage rotor armature by an opposed pair of five-turn cryogenically cooled field Coils/inductors. Inertial energy is stored in a graphite-reinforced epoxy flywheel which will operate at a maximum tip speed of 1,100 m/s. Current collection is accomplished at the smaller radius of the squirrel-cage armature which implies brush slip speeds of no more than 300 m/s at the design speed. The machine is expected to develop about 500 V at half speed while charging the coils to 130 MJ at 3.2 MA. Peak output voltage during discharge of coils will be roughly 10 kV.

A systems tester for compact HPG component development

The compensated pulsed alternator (compulsator) is a versatile power supply capable of interfacing with the electromagnetic launcher in various ways. The method that has been explored at length with several systems is the single phase option. Several variants of this option, some using advanced pulse shaping techniques, have been discussed in prior publications. Besides this basic single pulse method of operating there are several other methods each with its pros and cons. The multiphase option is discussed in this paper. Within the broad class of multi-phase systems there are further sub-classes, namely alternating current drive and unidirectional current drives. Thus the branching of these operating modes gives rise to a variety of operating modes. Each one of these operating modes is described and simulation results are presented.

Operating modes for compulsator based electromagnetic launcher systems

To facilitate the development of more compact homopolar generators (HPGs), the compact HPG systems tester was designed and built to develop the system and component technology necessary to design HPGs having energy densities of up to 60 MJ/m3. The systems tester is one-half of a full-scale counter-rotating HPG storing 2.5 MJ at 6,900 rpm and generating 20 V. Incorporated in the tester are two new types of components, face brushes and a stationary-shaft hydrostatic bearing, which will lead to HPG designs that will rotate a larger fraction of the magnetic circuit while eliminating much of the stationary support structure. The systems tester is designed to provide a facility for future bearing research and development of the higher-current-density brushgear required for drawing larger currents from the smaller slip ring areas of more compact machines.

Rotating Machine Development At Tire University Of Texas

The compensated pulsed alternator (compulsator) is a versatile power supply capable of interfacing with the electromagnetic launcher in various ways. The method that has been explored at length with several systems is the single phase option. Several variants of this option, some using advanced pulse shaping techniques, have been discussed in prior publications. Besides this basic single pulse method of operating there are several other methods each with its pros and cons. The multi-phase option is discussed in this paper. Within the broad class of multi-phase systems there are further sub-classes, namely alternating current drive and unidirectional current drives. Thus the branching of these operating modes gives rise to a variety of operating modes. Each one of these operating modes is described and simulation results are presented.