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The aim of this work is to investigate the possibility of detecting faults in a 3 phase Induction motor by monitoring and analysing the transient line current waveform during the starting period. This is a particularly onerous time for the machine and the inter-relationships between parameters such as current, torque, speed and time are very complex. As a result two parallel paths of investigation have been followed, by methods of experimentation and computer simulation. Transient line current signals have been obtained from purpose built test rigs and these signals have been analysed in both the time and frequency domains. In order to assist with the comprehension of this data a sophisticated computer simulation of the induction motor during the starting period has also been developed. Computer simulation of the induction motor has been developed initially using the two and then three phase induction motor voltage equations which are solved by numerical integration. Using these techniques it has been possible to detect small degrees of fault level for both wound and cage rotor machines by analysing the line current waveform during the starting period. Good agreement has been found between the real and simulated data. A range of Digital Signal Processing techniques have been utilised to extract the components indicative of rotor faults. These techniques were at first wideband and highly numerically intensive, some originating from Speech Processing. The final processing techniques were far simpler and selected by analysis of the results from experimental data, both real and simulated.

No description available.

No description available.

No description available.

No description available.

The plasma opening switch (POS) is used in pulsed power systems where a fast opening and very high current switch is required. Plasma is injected into the switch, which carries a large conduction current before it opens in a process that lasts for a few nanoseconds and transfers the current to a parallel-connected load The conduction and opening times of the switch are dependent on the plasma parameters such as distribution, speed, temperature and species, which are all determined by the plasma source. This thesis begins with a description of the POS, with its conduction and opening mechanisms and the techniques of plasma generation all being considered, before it concentrates on the simple and inexpensive carbon gun. Plasma is normally produced by a pulsed discharge that evolves plasma from the evaporation and ionisation of a carbon based insulator. The first prototype carbon gun discussed in the thesis uses a classical coaxial arrangement that successfully produces dense, fast and hot plasma, although this is only capable of filling a small region with plasma. A number of plasma diagnostic techniques are described, before details are provided of the electrical probes that were used to characterise the plasma In a large POS a well-distributed plasma is obtained by combining a large number of guns in a complex and large system. This restncts the compactness of the POS resulting in a problem for any future commercial applications. A succession of developments to the prototype gun has led to a novel ring-shaped version that produces a much improved distribution of plasma, without the need for additional guns. In this, a pulsed discharge is initiated at a single point and the self-generated magnetic field forces the discharge to spread and to travel around the gun, whilst continuously ejecting plasma into the POS. The ideas and theories that explain how a discharge can be forced to move are described, together with details of the prototype designs. Results are given to confirm the operation of the gun, using high speed photography and electrical probes.

The thesis is concerned with microprocessor-based control of a d.c. drive system using armature voltage control technique with a separately-excited, chopper-fed d.c. motor. The chopper circuit has a full-bridge configuration employing gate-turn-off (GTO) thyristors, and. is capable of four-quadrant operation, making the drive both reversible and regenerative. The control of motor speed is achieved by a completely digital technique, which does not require any analog-to-digital or digital-to-analog converters. A microcomputer, specially designed and built, generates the triggering signals for the GTO's by using the unipolar switching strategy, which is accomplished totally by software using look-up tables.

Brushless dc motor drives have become increasingly popular, following recent developments in rare-earth permanent-magnet materials and the semiconductor devices used to control the stator input power and to sense the rotor position. They are now frequently used in applications such as flight control systems and robot actuators, and for drives which require high reliability, long life, little maintenance and a high torque-to-weight ratio. In many motor drives the presence of torque and speed ripples, especially at low speed, is extremely undesirable. The mathematical model developed in this thesis was used to investigate their occurrence in a typical brushless dc drive system, with the objective of establishing factors which effect their magnitude and ways by which they may be reduced. The model is based on the numerical solution of the differential equations for the system, with those for the motor being formulated in the phase reference frame. Tensor methods are used to account for both the varying topology and the discontinuous operation of the motor arising from changes in the conduction pattern of the inverter supply switches. The thesis describes the design, construction and testing of an experimental voltage source PWM inverter, using MOSFET switching devices, to drive a 1.3 kW 3-phase brushless dc motor. A practical circuit is described which implements current profiling to minimize torque ripple, and the optimum phase current waveforms are established. The effect of changes in the firing angle of the inverter switches on the torque ripple are also examined. Throughout the thesis, theoretical predictions are verified by comparison with experimental results.