Browsing by Subject "FTP"

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Application of Electromagnetic Guns to Future Naval Platforms
(IEEE, 1999-01) Walls, W.A.; Weldon, W.F.; Pratap, S.B.; Palmer, M.; Adams, D.
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
Brush/Slip Ring Current Collector Performance and Anomalies During Compulsator Commissioning
(IEEE, 2001-01) Hahne, J.J.; Kitzmiller, J.R.; Penney, C.E.
During recent tests associated with a model scale compulsator development program at The University of Texas at Austin Center for Electromechanics (UT-CEM), the performance of severe duty trailing arm brush current collectors was evaluated. The original material of choice for the brush slip ring design was 70075-T6 aluminum to minimize machine mass and simplify slip ring assembly on the rotor shaft. The slip rings have a nominal diameter of 5.5 in. The combination of CM1S copper, trailing arm brushes, and aluminum slip rings performed well up to about 80% full speed, although the design did not appear to be very damage tolerant. As testing continued at higher speeds, one of the slip rings began to exhibit small shallow arc pits in the brush track on the slip ring outer diameter. This was observed on only one slip ring and had no apparent affect on machine performance. Left unchecked, this shallow arc damage can cause a high speed brush to “bounce” excessively during a run and cause more severe damage, as well as increase the circuit impedance from the arcing. This paper presents a general description of the observed brush performance during normal and fault conditions. It also includes a description of mechanical analysis and field strength measurements done around the brushes in an effort to explain the “one brush” bouncing. Brush and slip ring design upgrades (including a reinforced brush actuator for increased brush down-force and a newly implemented two-layer aluminum and steel slip ring design) are discussed
Characterization of Triggered Vacuum Switches for High Current Operation
(IEEE, 1999-01) Pappas, J.A.; Pish, S.P.; Salinas, M.J.
Triggered vacuum switches show promise for use in high-power, high-current and high-frequency conversion and switching circuits. Their specific power and power density ratings are well above silicon devices. TVS are robust devices that can survive faults that would destroy other types of switching devices. In addition, TVS are capable of fast recovery. However, there is not much performance data at high current and frequency and TVS are unable to recover reliably under reversing current and voltage conditions after passing a peak current greater than 20 kA. This paper describes the results of tests performed to obtain a wide variety of characteristics, including V/I characteristic, ability to share current, and ability to recover when a reverse voltage is applied
Compensation in Pulsed Alternators
(IEEE, 1999-01) Pratap, S.B.; Driga, M.D.
This paper presents a generic discussion on compensation in pulsed alternators. It COVerS all aspects Of compensation i.e., types of compensation, alternative methods for the physical realization of the various compensation schemes, the pros and cons of compensation or the rationale for compensation The intent of this paper is to form a guiding reference on the issues of compensation in pulsed machinery
Compulsator Rotor Assembly Methods
(0000-00-00) Kitzmiller, J.R.; Werst, M.D.; Manifold, S.M.; Hahne, J.J.; Walls, W.A.
High energy density requirements for fieldable electric gun applications have led to the development of air-core compulsators which utilize hybrid metal/composite rotor designs. In addition to supporting the required generator windings, these rotors also must store large amounts of kinetic energy. To satisfy energy density requirements, the tip speeds of the electric gun class compulsator rotor are appreciable with typical values exceeding 500 m/s for near term designs. High performance composites are utilized in the rotor structures and large amounts of radial pre-load is required to hold the rotor structure and electrical windings together at the tip speeds required.
Continued Testing of the Cannon Caliber Electromagnetic Gun System (CCEMG)
(IEEE, 1999-01) Werst, M.D.; Penney, C.E.; Hotz, T.J.; Kitzmiller, J.R.
The cannon caliber electromagnetic gun system is based upon a compulsator driven 30 mm rapid fire railgun system. The objective of the program was to develop a compact, lightweight test bed capable of launching three, five round salvoes of 185 g integrated launch packages to 1.85 km/s at a firing rate of 5 Hz. Per contractual requirements, the pulse power system is also size compatible with the amphibious assault vehicle. The pulse power system was developed around a fourth generation air-core, 4-pole rotating armature, self-excited, compulsator design. Although the contract for this effort has expired, the system continues to be used in part to demonstrate compulsator driven railgun technology. This system has performed seven single shots using identical control settings for each shot, which is the first such experience using a compulsator driven railgun system. This paper describes the experimental set-up for the demonstrations and compares the generator, converter, gun switch, and launcher performances for each shot
Convective, Diffusive Effects on Magnetic Fields and Eddy Current in Compulsators
(0000-00-00) Thiagarajan, V.; Ozdemir, M.; Min Chan, W.
Compulsators are being designed at ever increasing energies and energy densities and are required to deliver energy to the load in less than 10 ms. These require high speeds of operation and dense spacing of conductors. Diffusion of magnetic fields into the conductors and the formation of nonuniform, time-dependent distribution of eddy currents become dominant design considerations due to their major mechanical, thermal, and thermodynamic impact. A semi-analytical method has been developed for the two-dimensional analysis of field diffusion and eddy currents in high speed rotary machines to aid design decisions. Analytical results for fields are utilized and computations are restricted to the conductor domains alone. The semi-analytical method has been tested with two conductors (one in the stator and one in the rotor rotating at high speed). The resulting distributions of fields and eddy currents are presented.
Design and Implementation of Explosive Opening Switches in Inductive Circuits
(IEEE, 2001-01) Penney, C.E.; Hotz, T.J.; Kitzmiller, J.R.; Thelen, R.F.; Zowarka, R.C.
Self-excitation in pulsed duty alternators is utilized to meet energy and power density system requirements. In the eventually fielded system, a small energy source will be pulsed into the field coil to start the excitation process. At this point, power electronics on the ac output of the generator will control the charging of the field coil and invert the field energy safely back into the rotor inertia at the end of the discharge sequence (or in the event of a fault). A static rectifier was used in the selfexcitation process in the laboratory testing of a subscale prototype compulsator. Without control of this bridge, a simple cost effective method was devised to terminate the excitation process safely at the end of a generator discharge sequence or in the event of a fault. To safely dissipate the field energy an explosive opening switch in parallel with a resistive element was placed in series with the bridge output and field coil. On command, the opening switch would commutate current into the resistive element properly sized to terminate the excitation process and with sufficient thermal mass to dissipate the field coil energy. The test program for the compulsator was designed to increment the self-excitation current in small steps in the commissioning of the system. Near the end of the test program, it was observed that the opening switch was having difficulty commutating the current into the inductance of the dissipation resistor. A shunt capacitor was sized to limit the commutation voltage and allow the opening switch plasma time to extinguish before large voltage developed across the resistive element. This paper presents information on the sizing of the resistor and capacitor and test data on its performance in the compulsator self-excitation circuit. This work is important because future systems under the control of active power converters will still require a fail-safe element to dissipate field energy in the event of a control system fault.
Electromagnetic and Structural Analyses of an Integrated Launch Package
(IEEE, 1999-01) Liu, H-P.; Ting, Y.L.; Zowarka, R.C.; Alexander, A.
In this paper, detailed three-dimensional (3D) transient electromagnetic (EM) analyses with temperature-dependent material properties were performed using a state-of-the-art analysis tool to calculate current densities, body force densities, and temperature distribution in launch package and rail conductors. The body force densities, temperature distribution, and package accelerations generated by the EM model were then provided to a 3D multiple-step nonlinear static structural model for detailed mechanical analyses. The combined 3D EM and structural analyses can be used to accurately predict the EM launching performance and launch package structural integrity. Furthermore, armature optimization and package survivability enhancement can also be achieved with the help of these analyses
Field Excitation and Discharge Switching for Air-Core Compulsators
(IEEE, 1995-07) Thelen, R.F.
The Center for Electromechanics at The University of Texas (CEM-UT) has designed and built three generations of air-core compulsators for railgun application. These systems rely on compact power electronics to provide rapid self-excitation of the field windings and control of the main current discharge. All three systems built so far have been single-phase armature machines. The parameters for these systems range from 20 to 42 kA field excitation at 125 to 400 Hz rectification and 2.5 to 12 kV. The main discharge peak current ranges from 0.3 to 3 MA. The design and performance of past switching systems is reviewed and the prospects for further mass and volume reductions is presented.
High Strain Insulation Systems for Compulsator Rotors
(IEEE, 1999-01) Hahne, J.J.; Graf, C.; Kitzmiller, J.R.; Walls, W.A.; Brinkman, W.G.; Alexander, A.; Russo, D.
As the power density requirement for new compulsator (CPA) designs increases, designers are driven to use more composites to reduce mass, spin the rotors faster to store more energy, and operate the machine at higher voltages to increase machine power output. In any particular compulsator design, the rotor windings are subjected to high strain levels as the rotor is spun and experiences radial growth. A critical component in the rotor winding design is the high voltage insulation. As the rotor is spun, the induced strains are applied to the insulation system on the coil conductors. This implies that over the operating life of a compulsator, the coil structure and the high voltage insulation must remain structurally intact, while undergoing repeated cyclic loading. This paper presents the design and testing of a compulsator rotor winding that has been recently fabricated at the Center for Electromechanics at The University of Texas at Austin. The paper focuses on the testing done both at room and elevated temperature to evaluate the winding structure and high voltage insulation system under both tensile and transverse strain conditions. Data presented suggests a factor of safety of at least five for strain to failure values and high voltage insulation good for at least twice line voltage after testing to strain failure
A Moving Boundary Diffusion Model for PIN Diodes
(IEEE, 2001-01) Zhang, H.; Pappas, J.A.
A large number of diode models exist that simulate the reverse recovery process. Many models assume an abrupt change of current during reverse recovery. Some models were verified by calculating the diode's response after the application of a step forcing voltage. Only a few models described in the literature compare simulation results with experimental data. The abrupt change in current calculated by most diode models will ensure large di/dt, which in turn will result in the calculation of an excessive voltage spike. The diode model described in this paper is aimed at the application of high power rectification where the exciting voltage is more likely to be sinusoidal rather than a step change. The formulation is particularly useful in modeling very high power systems such as electromagnetic launch systems where calculation speed and accuracy of results are held at a premium. The model is formulated based on a p+in+ type diode. In addition, by considering the fact that the width of the intrinsic bulk region reduces significantly during the reverse biased condition, the model will more accurately calculate reverse recovery current and voltage. Finally, the model is verified by comparing simulation results to experimental data
Operating Modes for Compulsator Based Electromagnetic Launcher Systems
(IEEE, 1995-07) Pratap, S.B.; Kajs, J.P; Walls, W.A; Weldon, W.F; Kitzmiller, J.R; Murthy, S.K.
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 [I-3]. 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.
Power Converters for Railguns
(IEEE, 2001-01) Pappas, J.A.; Piccone, D.E.
The University of Texas at Austin Center for Electromechanics (UT-CEM) has been developing power converters for use with DC railguns. Special design rules have been established and demonstrated in the construction of laboratory hardware. Power converter requirements for electric guns are dependent on the characteristics of the power supply, load, circuit topology, and switching devices used. This paper discusses some of the design requirements particular to these converters and shows why simple figures of merit (FOMs) developed in the early design of a converter are not valid. An alternate FOM that can be used to compare converters and judge development progress is offered. Use of this FOM requires that an adequate amount of design work be completed on a converter before it is applied. The FOM is applied to previously demonstrated converters. Possibilities for near term development of devices and converters are examined and the potential results of that development are compared to past work by using the new FOM
Predicted versus Actual Performance of a Model Scale Compulsator System
(IEEE, 2001-01) Kitzmiller, J.R.; Cook, K.G.; Hahne, J.J.; Hotz, T.J.; Manifold, S.M.; Pappas, J.A.; Penney, C.E.; Pratap, S.B.; Rech, B.; Thelen, R.F.; Walls, W.A.; Werst, M.D.; Zowarka, R.C.
Performance testing of the model-scale CPA was completed at the University of Texas Center for Electromechanics. A major part of the project was the development of design and simulation codes that would accurately represent the performance of pulsed alternators. This paper discusses the components of the system and its operational sequence. Details of the performance simulation model are presented along with test data. The test result is compared to the predicted data
Railgun Solid Armature Scale Modeling
(IEEE, 1997-01) Zowarka, R.C.; Yun, H.D.; Alexander, A.
This paper describes a methodology for using two finite element (FE) codes, MAGTRPL and DYNA, to perform electromechanic, thermal, and structural modeling of railgun solid armatures. We analyze subscale armature experiments and present results that begin to identify the important engineering limits for materials used in armature fabrication
Rotordynamics Design and Test Results for a Model Scale Compulsator Rotor
(IEEE, 2001-01) Murphy, B.T.; Kitzmiller, J.R.; Zowarka, R.C.; Hahne, J.J.; Walls, W.A.
The model scale compulsator is a high speed (12000 rpm), high energy rotating machine. The rotor is a highly optimized pulsed power electrical machine consisting of electrical windings, slip rings, and highly pre-stressed composite bandings. This paper describes the design of this machine from the standpoint of rotordynamics. The rotor is supported on oil-lubricated hybrid ceramic duplex ball bearings, which in turn are supported on compliant squeeze film dampers. Test results are presented for both mechanical checkout runs and full energy discharge experiments. Also described is experience gained from low speed balancing on a commercial balancing machine, followed by high speed in situ balancing
Single and Multiphase Compulsator System Architectures: A Practical Comparison
(IEEE, 2001-01) Kitzmiller, J.R.; Pappas, J.A.; Pratap, S.B.; Driga, M.D.
The Center for Electromechanics at the University of Texas at Austin (UT-CEM) has designed, built, and tested three generations of iron-core and air-core compensated pulsed alternators (CPA). These include the iron core, small caliber, cannon caliber, and model scale compulsators. Early CPA were single-phase machines that were optimized for a specific load and desired performance. The most recent machine, the model-scale CPA, is a multiphase alternator coupled to the load through a rectifier. This paper includes a discussion of the requirements and capabilities of both single-phase and multiphase systems, a point design for each system type, and a comparison of system performance in driving a cannon caliber launcher
Single Shot Switch Performance on the Cannon Caliber Electromagnetic Gun Program
(IEEE, 1999-01) Hotz, T.J.; Penney, C.E.; Kitzmiller, J.R.; Werst, M.D.
Analyzer (DMA) tests. Also documented in this paper will be the results from specialized viscoelasticity tests performed on representative composite windings to determine preload loss versus time, temperature, and stress. Also, in collaboration with the Army Research Laboratory, a nested cylinder code is being developed to predict viscoelasticity induced preload losses.
A Study of Operating Modes for Compulsator Based EM Launcher Systems
(IEEE, 1997-01) Pratap, S.B.; Kajs, J.P.; Walls, W.A.; Weldon, W.F.; Kitzmiller, J.R.
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