Subsynchronous Resonance (SSR) is a condition which occurs when turbogenerators are connected to series capacitively compensated transmission systems and it can cause large scale damage to the turbogenerators. The accuracy of predictions of this phenomenon are limited by the accuracy of the mathematical models used for the various system elements. The modal method of modelling a turbogenerator shaft, in which parameters are associated with each natural torsional mode of the shaft, is investigated in detail and the sensitivity of SSR predictions (both small signal and transient) to uncertainties in the mode parameters is evaluated. The modal model is then used to obtain reduced order shaft models and the accuracy of these reduced order modal models in SSR predictions is ascertained. The determination of mode parameters from generator transient response waveforms is investigated. A continuing problem in this field is the separation of damping values obtained from measurements on a synchronized generator, into their mechanical and electrical components. A method is proposed in this thesis which uses eigenvalue scanning techniques together with FFT analysis to achieve this separation. The SSR stability of, and the torsional interaction between two adjacent generators at a power station is studied. The analysis covers identical generators, nominally identical generators with small differences between their mode parameters and different generators with a coincident torsional mode. In addition, the torsional interaction between generators at different power stations which are remote from each other is investigated. This entire analysis is greatly assisted by modelling the turbogenerator shafts in modal form. Finally the damping of SSR oscillations in two non-identical adjacent turbogenerators with a single controlled shunt reactor, which uses the sum of the generator speed signals as an input to the controller, is investigated. / Thesis (Ph.D.)-University of Natal, Durban, 1987.

The main objective of this research was to study DC conductor corona loss (CL) and audible noise (AN) in the context of local climatic conditions, through corona cage measurements, and do a comparative analysis of the measured data with results available in literature and EPRI TLW software simulation results. The ultimate aim was to assess the applicability of the software to our local conditions and hence determine, if necessary, appropriate correction factors for application in HYDC transmission line designs. For this study, short term measurements of corona AN and currents were carried out in an indoor meshed cylindrical corona cage, under DC and AC voltages. The cage was later converted into a short test line and some of the measurements repeated. The DC supply was obtained from a two stage ±500 kV Walton-Cockroft generator. The AC voltages were obtained from a 2x 100 kV, 50 Hz, AC test transformer set. The tests were performed using single solid and stranded aluminum conductors with three different diameters (1.6 cm, 2.8 cm, and 3.5 cm). All the measurements were carried out at low altitude. A CoroCAM I camera was used to determine the corona inception gradients and to observe the corona activity at different surface gradients and under different voltages and polarities. AN measurements at different conductor surface gradients were done using the Rohde&Schwarz and the Bruel&Kjaer sound level meters. To obtain the frequency spectra, a Bruel&Kjaer octave-band filter set attached to the sound level meter was used. The measured data was corrected for both height and length effects, and then compared with simulations from the EPRI-TLW software through curve fitting. A digital micro-ammeter connected to the centre of the cage through a 560 .Q measuring resistor was used to measure the corona current. Current pulses were viewed using a digital storage oscilloscope. To verify the corona current results obtained from the cage measurements, current measurements were also done for a point-plane spark gap. The corona current data was, later on, used to evaluate the total corona power loss for DC. The results obtained from test line measurements were used to compare the CL and AN for different configurations. The effect of the space charge under DC voltages was assessed through current measurements. The measurements were done with the cage covered with an aluminum foil to trap the charge and then repeated with the cage uncovered. On the test line, the space charge effect was investigated using a high power fan blowing along the conductor, to simulate the wind factor. The results of this study have shown the characteristics of corona discharges under different system voltages. The results also give an understanding of how factors such as conductor surface conditions and size, polarity and system voltage affect CL and AN. Both CL and AN were found to increase with conductor size for the same conductor surface gradient and to be higher for stranded conductors. Positive polarity DC and AC noise levels were higher than the negative polarity levels. CL under positive polarity DC was lower than the negative polarity loss. The effects of space of space charge were noted to some extend. The comparison of test line results and cage results showed that CL depends more on the gap size and the shorter the gap the higher the loss. Hence CL results were not compared with the software simulations. The comparison between the corrected AN results and the software simulations showed a very good agreement. The comparison was done for the 3.5 cm and the 2.8 cm diameter conductors under both positive and negative polarities. The trends compared through curve fitting were quite similar and the trend line equations were of the same order of magnitude. The magnitudes of the corrected noise levels were higher than the CRIEPI and BPA predictions but closer to the EPRl prediction. Generally there is a very good and encouraging agreement between the available literature, simulation results and the results obtained from the laboratory measurements. It is proposed, as part of further studies, to extend this work to high altitude regions and use bundled conductors as well. Consideration of different and larger test configurations will provide an understanding of the effects of geometry on corona discharges. Space charge analysis will also assist in determining the effect of space charge on different configurations. / Thesis (M.Sc.Eng.)-University of KwaZulu-Natal, Durban, 2007.

Poorly damped oscillations that occur between the generators in large interconnected power systems often limit the amount of power that can be transmitted through a transmission corridor and are a threat to secure system operation. Coordinated insertion and removal of capacitors in series with a transmission line is one of the approaches that has been known for many years to be capable of enhancing the damping of power system oscillations. Unfortunately however, this approach historically relied on the operation of mechanical circuit breakers which were too slow and unreliable for the high-speed and repetitive operation that such an application demands. Recently-emerged, high-speed power-electronic-based switching devices are finding increasing use in modem power systems in the so-called Flexible AC Transmission Systems (F ACTS) concept. One particular FACTS impedance controller, namely the inverter-based series compensator, can rapidly alter the magnitude of capacitive compensating reactance in series with the line to make it practically feasible to enhance the damping of power system oscillations via dynamically-controlled series compensation. This thesis identifies, in the literature, an insightful approach to the design of an idealised controllable series compensator (CSC) damping scheme; such an approach has been considered in the analyses of the thesis. Three mathematical models of a single-machine infinite bus (SMIB) system are developed and are subsequently used in the initial design and analysis of a CSC damping controller carried out in the thesis. The simple SMIB system case study is used to identify and investigate the factors that have a significant impact on the performance of a CSC damping controller before studying the more complex issue of inter-area mode damping using a CSC. This thesis successfully confirms the results of a previous analytical study in which an idealised representation of the CSC was used, and extends the scope of that previous study by also considering a detailed representation of one particular type of CSC: the inverter-based series compensator. The two key findings of this extended investigation are that the inverter-based form of controllable series compensator can successfully be used to damp power oscillations and that, where the damping of oscillations is the particular focus of study, an idealised representation of the inverterbased CSC is suitable for the analyses. In the case of the inter-area mode damping problem, the selection of an appropriate input signal to the CSC damping controller is a key issue, since the oscillations that are to be damped involve a number of participating generators. This thesis examines the suitability of a few candidate input signals that have been proposed in the literature using the conceptually simpler SMIB system analytical models that have been developed. Finally, the thesis applies the understanding of CSC damping controller design gained from the SMIB study to the problem of inter-area mode damping on a four-generator study system. Time-domain simulation results are presented to demonstrate the impact of the controlled inverter-based series compensator on the damping of the inter-area mode of this system. / Thesis (M.Sc.Eng.)-University of Natal, Durban, 2000.

South African medium voltage underground electrical networks consist mainly of cables of paper insulated lead covered construction. This construction is still the standard used for most utilities in South Africa. While the in-service performance history of these cables has been excellent, global manufacture of this cable type is decreasing. Internationally, the use of polymeric cables is increasing, resulting in the security of the supply chain for paper cable becoming an increasingly important issue. The most widely used polymeric construction is cross-linked polyethylene. Modern distribution switchgear, which is increasingly used in South Africa, is designed for the newer polymeric technology as this enables more compact construction and reduced equipment footprint. The reduced clearances present installation and operational issues when using modern switchgear with paper insulated cables. Although a comprehensive literature review was conducted, not much academic work has been done on the process of migrating from one cable platform to another. Manufacturer data, academic reference sources, industry experts and software modelling tools are used to demonstrate that the use of polymeric technology is viable for South African utilities. This dissertation focuses on the difference between paper and polymeric technologies, and explores the advantages and disadvantages of each. Integration issues are examined along with the methods used to overcome the challenges of hybrid or mixed dielectric networks. Economic comparisons between paper and polymeric cables with respect to purchase and operating costs (including the cost of losses) as well as steady state, cyclic, distribution and emergency current ratings are made. The dissertation concludes that it makes economic and engineering sense for users of paper cable in South Africa to change to polymeric technology, taking the recommendations given into consideration in order to choose an optimised cable design and gain maximum benefit from the change. / Thesis (M.Sc.Eng.)-University of KwaZulu-Natal, Durban, 2011.

Power line function is to transfer electrical power. Power lines represent a major component in the transport process of electricity and they are subjected to various types of failures. Causes of failure include wind-induced oscillations or Aeolian vibrations. Wind causes transmission line conductors to undergo oscillatory motions which cause failure. To mitigate oscillations of line conductors, Stockbridge dampers are used. It has been observed that dampers are subjected to the same undesirable and destructive effects from vibrations as the conductors they are meant to protect. In the case of a damper, the cyclic bending as well as the friction between its wire cables are caused by vibrations leading to failure. The mathematical model describing the bending stress of the symmetrical Stockbridge damper’s messenger cable near the clamped end is analyzed. The reliability of the mathematical model is assessed using experimental data obtained from the forced response test conducted at the VRTC laboratory at the University of KwaZulu-Natal, Durban. Data from the experiment has been compared with the MatLab model established by the researcher. Due to friction between the wires of the messenger cable, variation of temperature is observed in the messenger cable during operation. Change of temperature of the messenger cable was investigated, as a function of time, at constant velocity and constant displacement. Experimental data were generated during dynamic characteristic tests on Stockbridge dampers and thereafter the prediction of the variation temperature was undertaken. There are various mechanical characteristics of a damper that can be affected with time. To reach the aim of this study, three types of vibration test were conducted on the Stockbridge damper: the fatigue test, the forced vibrations test and the free vibrations test. Tests were conducted on a shaker machine with new and used Stockbridge dampers to determine the remaining life of those dampers by looking at their different mechanical properties. The frequency domain and time spectrum were used to display the results. The fatigue test investigated one of the commonest types of Stockbridge damper failure, namely, loss of the small mass because of sustained high frequency resonance. Ultimately, data correlated well and two mathematical models were developed: one for predicting damage in the life of a Stockbridge damper (based on the highest resonance frequency of the damper), and one for predicting the temperature of the messenger cable. / Thesis (M.Sc.Eng.)-University of KwaZulu-Natal, Durban, 2012.

No description available.

Some of the challenges associated with the multi-objective optimization on a modern power system were addressed in this work. Optimization of reactive resources was performed in order to simultaneously optimize several criteria: transmission losses, distribution losses, voltage stability, etc. The optimization was performed simultaneously on the entire power system; transmission and distribution subsystems included. The inherent physical complexity of modeling together transmission and distribution systems was considered first. After considering all pros and cons for such a task, a model of the entire power system was successfully developed. The inherent mathematical complexity of high-dimensional optimization space was handled by introducing the decoupling principle. System is first decoupled in several independent models and optimizations were performed on each part of the system. An algorithm is developed that properly combines the independent solutions to reach the overall system optima. The principle of algorithm synthesis is used to reduce the size of the solution space. Deterministic algorithms are used to locate the local optima which are subsequently refined by probabilistic algorithm. The algorithm is applied on a "real-life" test system and it is shown that the obtained solutions outperform the solution obtained with the conventional algorithms.

Thesis (MAppSc in Project Management)--University of South Australia, 1995

Mémoire (M.Sc.A.)-- Université du Québec à Chicoutimi, 1992. / Bibliogr.: f. 108-109. Document électronique également accessible en format PDF. CaQCU

Mémoire (M.Eng.)--Université du Québec à Chicoutimi, 2000. / Document électronique également accessible en format PDF. CaQCU