Transient stability analysis is an important part of power planning and operation. For large power systems, such analysis is very time consuming and expensive. Therefore, an online transient stability assessment will be required as these large power systems are operated close to their maximum limits. In this thesis swallowtail catastrophe is used to determine the transient stability regions. The bifurcation set represents the transient stability region in terms of power system transient parameters bounded by the transient stability limits. The system modelling is generalized in such, that the analysis could handle either one or any number of critical machines. This generalized model is then tested on a three-machine as well as a seven-machine system. The results of the stability analysis done with the generalized method is compared with the time solution and the results were satisfactory. The transient stability regions determined are valid for any changes in loading conditions and fault location. This method is a good candidate for on-line assessment of transient stability of power systems. / Applied Science, Faculty of / Electrical and Computer Engineering, Department of / Graduate

This work demonstrates the use of digital simulation for analyzing protection system performance. For studies of complex, multi-relay protection systems, digital simulation provides utility engineers with an attractive alternative to relay testing techniques. The cost of digital simulation facilities can be lower than the cost of comparable testing facilities; relay hardware does not have to be made available for the test laboratory. Digital simulation would ordinarily be impractical for security and dependability studies, due to the thousands of individual simulations involved. The number of simulations needed can be greatly reduced by using a technique called "numerical logic replacement" for implementing the protection scheme logic. This unconventional technique makes near-misoperation visible from individual simulations. The likelihood of overlooking potential misoperation is thus much lower than with the usual direct (Boolean) implementations. / Applied Science, Faculty of / Electrical and Computer Engineering, Department of / Graduate

The output characteristics of five compression hearing aids in response to a transient signal were examined to determine if, the input-output function (i.e. output levels of the hearing aid as a function of input level) for a transient signal could be made to approximate that of a continuous signal, by activating the compression circuit with a second signal (activator). Input-output functions for three input compression and two output compression hearing aids were obtained in order to determine if: 1. the automatic gain control (AGC) was activated by the second signal and the transient signal output approximates that of a continuous tone, and 2. if the second tone was evident in the output of the hearing aid and thereby potentially being an interfering factor in aided auditory brainstem response (ABR) measurement.

This thesis discusses applications of phasor measurement units to power system monitoring and synchronous generator modeling. Adjustments to a previously developed PMU placement algorithm are described which observe generator and tie line flows explicitly and reduces the number of PMUs required for a system, still observing the major dynamic components of a system. This adjusted methodology leaves some buses unobserved. A method for estimating the state of the unobserved region is developed based on using constant admittance or constant current load models. These models are accurate for a small neighborhood around the operating point when they were calculated. To determine the maximum error expected for any given system estimate, an equation relating the maximum error in the voltages to the maximum change in load power is derived. Once the issue of power system monitoring has been presented, the application of PMUs to the synchronous generator modeling is explored. This thesis deals with the on-line identification of the generator transient model using a recursive version of the generalized least squares algorithm. Simulations have been performed to demonstrate the validity and difficulties with these methods. / Master of Science

M.S.

M.Ing. / Spoornet currently has a fleet of more than 1500 electric locomotives in service. The majority of electric locomotives are resistor controlled but there are many chopper as well as thyristor controlled locomotives which all incorporate direct current (dc) traction motors. In recent years Spoornet has also bought locomotives employing alternating current (ac) traction motors. Because locomotives are very expensive and the running costs are high it is important that these locomotives must be available and reliable. Most of the newer generation locomotives, which are the semiconductor controlled locomotives, must be in service for at least another 20 years. The availability and reliability are often influenced by delayed design problems as well as problems arising due to changes in the total system configuration. One way of solving these problems, or at least understanding them, is by employing computer simulations. The availability and reliability can also be improved by using new technologies which were not originally employed on the locomotives. By doing computer simulations the optimal solution can be obtained when introducing new technologies on the locomotive. A good example of this type of application within Spoornet is given in [6], where simulation models for high technology locomotives were developed which were suitable to be used in the assessment of electromagnetic compatibility between modern power electronic locomotives and the railway signaling system. However, these models are also suited to be used in other applications. These models make use of the ATP-EMTP simulation program.

Submitted in fulfillment of the requirements for the degree of Master in Technology, Durban University of Technology, Durban, South Africa, 2015. / The primary objective of this research was to investigate the failures occurring in the family of surge arresters used within EThekwini Electricity, making use of different diagnostic methods, such as leakage current testing (LC), infrared scanning (IR), and partial discharge (PD) measurements. The different diagnostic tests were used to assess the degradation process of the polymer housed surge arresters and their failure. The measurements were used for diagnosis of 120 kV/65 kA surge arresters of different brands. Tests were performed on surge arresters that were still in the system and these test results were compared with results from tests performed on failed units. Results obtained from the different tests were compared to the test results for different families or designs. An imperfect arrester will exhibit excessive heating when an electrical surge is discharged. The aforementioned tenets are the primary factors influencing degradation and causing failure of Metal Oxide Surge Arrester (MOSA) in a system. These factors can decrease creepage and flashover distance on insulation, which could result in a substantial increase in resistive leakage current, (which is a few microamperes in ideal condition), overheating, and PD formation on the zinc oxide varistor element. Therefore, it is extremely important to assess the status of the surge arresters whilst they are in service, firstly so that they can be removed from the system before they fail and, and secondly, to verify their condition, and their ability to effectively protect the substation apparatus. Using infrared inspection, valuable information of condition of surge arresters was obtained, heat inside the surge arresters was detected and this shows that IR analysis can therefore be considered as an additional method to assess the condition of polymer housed surge arresters. It was observed that partial discharge activity is an indication of degradation in arrester varistor. LC test, IR, and PD measurement were valuable in obtaining sufficient information for failure of surge arresters. In additional, during the visual internal inspection of arresters, evidence of punctures, treeing, tracking, and moisture masks were noted on ZnO blocks and seals. These results indicate that the moisture ingress through the sealing collar can cause unnecessary outages. / M

Typescript (photocopy). / Digitized by Kansas Correctional Industries / Department: Electrical and Computer Engineering.

A thesis submitted to the Faculty of Engineering at the University of the Witwatersrand, Johannesburg, in fulfilment of the requirements for the degree of Doctor of Philosophy. / Particularly at the higher system voltages, certain faults have been attributed to VFTs. This work presents a full frequency domain mathematical model of the effects likely to be introduced by the application of a thin ferromagnetic coating to the surfaces of the busbars as a means of attenuating these transients. Experimental verification shows the model to perform accurately as an analysis tool for a continuous coated co-axial system. While comparison between the model developed here (based on a planar conductor) and the very accurate Bessel function solution is presented, it must be remembered that it is not feasible to include the effects of coatings in the latter solution. Hence it is used merely as a bench-mark for improvements to the general model. Consideration is also given to the transient skin effect, and this is shown to result in an increased attenuation of VFTs. detectable during high voltage experimentation. The frequency domain model is extended to that of a full travelling wave model for VFTs in GIS. The Fourier technique is used to move between the frequency and time domains. Laboratory results obtained at high voltage.show that this technique will introduce both risetime increase and peak magnitude attenuation of VFTs. As the most frequent faults directly attributable to disconnector operation are known to be faults to earth at the switch, it is noted that the technique proposed in this work is uniquely suited for use in a design strategy that requires totally robust disconnectors at the expense of more severe VFTs in the GIS. The model is used to determine a range of physical characteristics of materials suitable for use in this application. While the characteristics of the most suitable materials have therefore been established, it is concluded that extensive metallurgical experimentation remains before this technique may be economically applied. / Andrew Chakane 2018

[Truncated abstract] The present thesis is devoted to the development of new methods for transient stability-constrained optimal power flow, probabilistic transient stability assessment and security-constrained ancillary services allocation. The key objective of the thesis is to develop novel dispatch and assessment methods for power systems operation in the new environment of electricity markets to ensure power systems security, particularly transient stability. A new method for economic dispatch together with nodal price calculations which includes transient stability constraints and, at the same time, optimises the reference inputs to the Flexible AC Transmission System (FACTS) devices for maintaining power systems transient stability and reducing nodal prices is developed. The method draws on the sensitivity analysis of time-domain transient stability simulation results to derive a set of linearised stability constraints expressed in terms of generator active powers and FACTS devices input references. '...' The low computing time requirement of the two-point estimate method allows online applications, and the use of detailed power systems dynamic model for time-domain simulation which offers high accuracy. The two-point estimate method is integrated in a straightforward manner with the existing transient stability analysis tools. The integrated software facility has potential applications in control rooms to assist the system operator in decision making process based on instability risks. The software system when implemented on a cluster of processors also makes it feasible to re-assess online transient stability for any change in system configuration arising from switching control. The method proposed has been tested on a representative power system and validated using the Monte Carlo simulation. In conjunction with the energy market, by which forecasted load demand is met by generator dispatch, ancillary services are required in relation to control for secure system operation and power quality. The final part of the thesis has a focus on the key aspect of allocating these ancillary services, subject to an important constraint that the dispatch of the ancillary services will not impair the system security achieved in the load dispatch. With this focus and requirement, the thesis develops a new dispatch formulation in which the network security constraints are represented in the optimal determination of generator active power schedule and allocation of ancillary services. Contingencies considered include power demand variations at individual load nodes from the values specified for the current dispatch calculation. The required changes in generator active powers to meet the new load demands are represented by additional control variables in the new dispatch formulation which augment those variables in the traditional OPF dispatch calculation. Based on the Lagrange function which includes the extended set of security constraints, the formulation derives the optimality condition to be satisfied by the dispatch solution, together with the marginal prices for individual ancillary service providers and LMPs. The effects of the security constraints are investigated and discussed. Case studies for representative power systems are presented to verify the new dispatch calculation procedure.