V.V. Vadher

Design, construction and testing of explosive-driven helical generators

This paper describes the development of a very efficient computer model for the design and performance prediction of explosive-driven helical generators. The model is based on simple theoretical considerations. Validation of the model is achieved by comparing the theoretical and measured performances of existing both high- and low-energy generators. It is shown that, although the basic model predicts accurately the load current history of high-energy generators, a somewhat more elaborate model is needed for low-energy devices. The model has been used in the design of a simple 1 MJ generator with an eight-section stator coil, intended for use as a current source in an investigation of high-current conditioning systems. A description is given of the construction and testing of this device. Experimental results are in accordance with predictions from the design code and establish that, when primed with 40 kJ at 50 kA from a capacitor bank and using 15 kg of high explosive, the generator is capable of delivering an output of 1 MJ at 7 MA to a coaxial load.

Generalized model of brushless DC generator

A generalized model is described for a brushless DC machine consisting of a multiphase synchronous machine with a full-wave bridge rectifier connected to its output terminals. The state-variable equations for the machine are suitable for numerical integration on a digital computer, and are assembled in a form which permits investigations to be made on the effects of different numbers of armature phase windings and different winding connections. The model has been used in both steady-state and transient studies on a number of generating units, with the detailed information which is provided being beneficial to design engineers. Comparisons presented between predicted and measured results illustrate the validity of the model and the mathematical techniques adopted, and confirm that accurate information on the performance of a brushless generator may be obtained prior to manufacture. >

Simulation of Permanent Magnet Generator/Rectifier Combination

Permanent magnet generators are often used as the pilot exciters of three-stage generating units to provide an efficient and reliable source of electrical power. No external power supply is then necessary, and the problems associated with brushwear and with arcing at the rubbing contacts are eliminated. A technique is presented here by which the performance of a permanent magnet generator, when combined with a rectifier-fed d.c. load at its output terminals, may be accurately and efficiently computed. The machine model takes into account the magnetization characteristic of the permanent magnet rotor and involves only parameters which can be determined from terminal measurements on the machine at standstill. Both computed and measured characteristics for an experimental machine are presented, and a comparison of these characteristics shows that the model can predict accurately all the major characteristics of the machine, as well as its detailed internal performance, when supplying a typical resistiveinductive load.

A fast electro-optic high-voltage sensor

This communication describes the construction and testing of a fast electro-optic high-voltage sensor, intended for use in a variety of pulsed-power applications. A 150 kV coaxial high-voltage cable is adapted to form an adjustable voltage divider, with the voltage across the lower section of the divider being measured with the aid of a Pockels cell. As developed, the sensor has been employed to measure 15 kV pulses with a rise time of less than 3 ns, and work is in hand to extend the pulse voltage measurement into the megavolt region.

Fuse conditioning of the output of a capacitor bank to drive a PEOS

The paper details power capacitor bank experiments performed to assess the performance of a pulsed power plasma erosion opening switch (PEOS). A description is given of the PEOS, which was of an inexpensive and expendable design, and was intended for use as the final stage of a flux compressor output conditioning circuit. Techniques using automatically operating exploding foils, as both opening and closing switches, condition the 9 /spl mu/s quarter-wave output pulse from the capacitor bank to a 400 ns pulse to the PEOS. An outline is given of the computer modelling and the experimental procedures used to establish the optimum operating conditions, and results are presented which illustrate the behaviour of the PEOS.

Experimental validation of a capacitor discharge induction launcher model

This paper describes the early stages of the experimental validation of a mathematical model of a capacitor discharge co-axial induction launching system. The model forms part of a family of computer programs produced to aid the design of launchers, so that either the maximum possible armature velocity on exit from the launcher or a specific performance requirement such as a controlled armature acceleration is achieved. The programs range in complexity from relatively simple models, used for initial capability studies, to detailed representations used in the design and development of launcher structures and their control systems. The model described is one of the more complex under development, being based on filamentary representations of both the stator and armature conducting regions. The single-stage experimental launcher described in the paper has been constructed purely for model validation purposes. To this end its geometry is constrained to a straightforward co-axial form, with the armature being a simple 80 gm aluminium ring of 100 mm diameter. The launcher operates vertically, accelerating the armature in free flight in order to avoid difficulties caused by barrel friction. Current and position data are obtained using digital sampling techniques, with post-processing allowing a direct comparison to be made with simulated results. >

Performance of a segmented rotor tubular linear induction motor

Results are presented of an investigation into the performance of a segmented rotor tubular linear induction motor (SRTLIM) and measurements of equivalent circuit parameters, together with theoretical analysis of the SRTLIM to obtain a verified model suitable for design purposes. It is shown that the classical equivalent circuit of an induction motor, suitably modified to take account of the change in topology of the motor stator and rotor is suitable for design of SRTLIMs for low speed applications. >

Mathematical Modeling of a VSCF Aircraft Generating System

DC-link converters having a variable input frequency but a constant output frequency now provide a viable alternative to the constant-speed mechanical drive as a means of providing a constant frequency power supply from an aircraft generator. The ease of replacement and repair, the reduction in servicing needs, and the ability to locate the components of the electrical system throughout the aircraft all combine to bring about a considerable reduction in the maintenance time which is required. A computationally efficient technique for the mathematical modeling of a typical electrical system, in which the overall power network is torn initially into a set of convenient subnetworks, is described. Connection matrices are employed to combine the equations computed for the various subnetworks with the equations for the overall network. Typical results are presented for the overall system. The performance detail enables many important design considerations to be investigated prior to manufacture.

SHARPENING A FLUX COMPRESSOR OUTPUT USING EXPLODING FOIL & PLASMA SWITCHING TECHNIQUES

The paper describes an on-going research programme into compact explosively-driven energy sources, together with the techniques and conditioning circuits used to produce sharp high-voltage output pulses. Both flux compressor (FC) and magnetohydrodynamic (MHD) sources are considered. An outline is given of FC designs and firing arrangements, and the potential and use of explosively-driven MHD sources with meatgrinder techniques for initial priming are mentioned. A description is given of output conditioning experiments, both in the laboratory and on the firing range, in which exploding and explosively-formed foil and plasma switching techniques are all used.

Microprocessor-based DC motor drive with spillover field weakening

A microprocessor-based speed control scheme for a separately excited DC motor fed from a DC source, which incorporates both armature-voltage control and spillover field weakening to provide smooth and precise control from standstill to speeds well above the base value, is described. Armature-current limitation during transient operation is achieved using an interventionist system external to the microprocessor controller, thereby simplifying considerably the overall system design. Experimental results obtained from a prototype 5 kW drive are presented to illustrate the excellent dynamic behavior of the scheme. >