Wesley Doorsamy

Investigation of thermal instability testing on synchronous generator rotors using an experimental direct mapping method

Utilities employ Thermal instability testing (TIT) for final acceptance testing alter the construction and refurbishment of turbogenerator rotors. This type of testing is performed through two methodologies namely current injection and friction/windage in order to assess the thermal sensitivity of the machines rotor. Although there are distinct differences between the two methods, no apparent preference is shown by service providers/OEMS globally. There is also no definitive evidence or standards that offer a comparison of the two methods and suitability assessment thereof. The presented research investigates these two methods of TIT for a synchronous generator rotor. An experimental setup with infrared thermography is employed to investigate the thermal behaviour of the machines rotor for each of the test methods. Experimental results show that the thermal behavior of the generator rotor is significantly different for each methodology. It is also shown in this paper that contemporary TIT practice requires an augmented test methodology.

Investigation into effects of a novel rotor cut-off design for synchronous reluctance machines

This paper presents an investigation into the effects of a novel rotor cut-off design on the performance of a synchronous reluctance machine. The rotor design consists of a sinusoidal lamination shape in the axial direction thereby varying the magnetic flux in the g-axis direction and reducing torque harmonics due to slotting effects. The presented study uses single-factor experimental design, with Analysis of Variance (ANOVA), and Finite Element Analysis (FEA) to quantitatively and qualitatively assess the effects of the rotor cut-off on the torque, torque ripple, saliency, power factor and efficiency of the machine. Results of the investigation indicate that although variation in the rotor cut-off design significantly reduces the torque ripple, the effects on the average output torque, saliency, power factor of the machine are relatively insignificant.

On-line monitoring of metal-oxide surge arresters using improved equivalent model with evolutionary optimisation algorithm

A resistive-current extraction algorithm to assist with on-line monitoring of surge arresters is proposed in this paper. The algorithm is based on the improved equivalent model for surge arresters and combines evolutionary optimisation with the base-frequency approximating method. A genetic algorithm is used to obtain the optimal capacitance such that the phase shift between the base-components of the branch voltage and current is minimised thereby yielding a good approximation of the resistive current. In this paper, the algorithm is implemented and tested using Matlab/Simulink. Results indicate that the proposed algorithm is able to efficiently and accurately obtain the resistive component of the leakage current, using the improved equivalent model, under both ideal and distorted supply conditions.

Optimal parameter inference method for effective design of synchronous reluctance machines

This paper presents a method for evaluating, both qualitatively and quantitatively, the effects of specific rotor design parameters on the performance of a Synchronous Reluctance Machine (SynRM). The method uses multi-factor experimental design, with Analysis of Variance (ANOVA), and Finite Element Analysis (FEA) to determine the optimal rotor design parameter according to a specific objective. Using this method, two factors — rotor flux barrier pitch angle and barrier width — are selected at simultaneously varied levels for assessment with the aim of analyzing the response variables, which are, the average torque and torque ripple. Results from the investigation show that the influence of the rotor flux barrier pitch angle on the torque ripple is more statistically significant than the influence of the barrier width. However, the effect of the barrier width on the average torque is more significant.