Thesis (Ph. D.)--University of Texas at Austin, 2008. / Vita. Includes bibliographical references.

Thesis (M.S. in electrical engineering)--Washington State University, May 2007. / Includes bibliographical references (p. 70-73).

The research work conducted and presented forward in this document is the evaluation of real time values obtained using three recording devices at two independent locations and implementing them as recorder devices in Eskom’s power system. The research work conducted was presented at an IEEE International Conference (ICIT2013) and Appendix A shows the accepted paper presented. A derived model within a simulation software package known as DIgSILENT PowerFactory is created and Electromagnetic Transient (EMT) studies are performed and then compared to the real time values obtained using the OMICRON CMC 356’s. Transformers are normally energised via a circuit breaker which is controlled by an auxiliary closing contact. By applying system voltage at a random instant in time on the transformer windings may result in a large transient magnetizing inrush current which causes high orders of 2nd harmonic currents to flow under no load conditions. A philosophy known to mitigate these currents is to energise the transformer by controlling each individual phase 120 degrees apart with the first pole closing at the peak on the voltage waveform. Transients produced due to 500MVA transformers been introduced into the power system at a certain space in time can cause nuisance tripping’s at the particular location where the respective transformer is energised. OMICRON EnerLyzer is the software tool used for the Comtrade recordings at both locations. Four independent case studies are generated within EnerLyzer software and the relevant Comtrade files are extracted for the four independent case studies relative to Transformer1 and Transformer2 switching’s. TOP software, which is a mathematical tool used to analyse Comtrade files, is then used to analyse and investigate the four case studies. Results from DIgSILENT PowerFactory are then generated according to the derived model. The results extracted depict three scenarios, indicating a power system that is weak, strong and specifically a power system that correlates to the actual tripping of a Static VAr Compensator (SVC). The results are all formulated and then evaluated in order to produce a conclusion and bring forward recommendations to Eskom in order to effectively ensure the Dedisa/Grassridge power system is reliable once again.

The object of this research is to develop a satisfactory method for locating high-impedance faults in underground cables. Most methods of locating faults require that the fault-impedance be reduced to a low value before the measurement can be made. After a careful investigation of the available literature, it was decided that the most desirable method would be one utilizing the traveling-wave. Of the traveling-wave methods, the fault-generated surge method appeared to have the greatest possibilities; yet, according to the author's knowledge, this method has not been applied to power cables. In this method, the cable itself may be considered as the network that generates the required surges. The cable is initially charged to a voltage sufficiently high to establish an arc at the fault. The sudden collapse of the high voltage at the fault generates a surge which travels along the cable to the monitoring end, where it Initiates a timing device and is reflected back along the cable toward the fault. The arc which is still conducting reflects the surge back to the station. The time interval between the first and second arrival of the fault-surge at the station is recorded by the timing device and is proportional to the distance to the fault. In mathematically analyzing the surge phenomena in cables, the La Place operational method of analysis is used. The calculations for the transient produced by the discharge of a distortionless cable are worked out in full detail. The wave-form calculated is plotted and substantiated with experimental results. The transient produced is a rectangular wave that is exponentially attenuated and whose period is 4δ, where δ is the one-way transmission time of the cable in seconds. It is this wave-form generated by the cable itself that is used to locate the fault. Basically, the fault-locator developed consists of, a high-voltage low-current power pack, a triggering unit, a timing-pip generator, two uniform delay lines, and a double-beam oscilloscope. The block diagram of the fault-locator and the circuit diagrams of the triggering unit and timing-pip generator are given. The operation of the circuits and the procedure for measuring cable faults are fully explained. The fault-locator was tested on coaxial cable only, since no power cables were available. The results obtained were very satisfactory. The oscilloscope traces obtained were photographed and the experimental results discussed. It is concluded that the fault-locator can be used without modification for locating low and medium-impedance faults, as well as high-impedance faults in power cables. If the timing-pip interval is increased, the fault-locator can also be used for locating faults on overhead transmission lines. / Applied Science, Faculty of / Electrical and Computer Engineering, Department of / Graduate

Techniques for modelling of synchronous generators in the simulation of electromagnetic transients are described. First of all, an adequate mathematical model of the generator is established. It uses the conventional set of generator data only, which are readily available, but it is flexible enough to accommodate additional data, if and when such become available. The resulting differential equations of the generator are then transformed into linear algebraic equations, with a time varying coefficient matrix, by using the numerically stable trapezoidal rule of integration. These equations can be interfaced with the equations of an electromagnetic transients program in one of two ways: (a) Solve the equations of the generator simultaneously with the equations of a three-phase Thevenin equivalent circuit of the transmission network seen from the generator terminals. (b) Replace the generator model with a modified Thevenin equivalent circuit and solve the network equations with the generator treated as known voltage sources e[sup red][sub ph] (t-Δt) behind constant resistances [R [sup red][sub ph]]. After the network solution at each time step, the stator quantities are known and used to solve the equations for the rotor windings. These two methods cover, in principle, all possible interfacing techniques. They are not tied to the trapezoidal rule of integration, but can be used with any other implicit integration technique. The results obtained with these two techniques are practically identical. Interfacing by method (b), however, is more general since it does not require a Thevenin equivalent circuit of the network seen from the generator terminals. The numerical examples used in this thesis contain comparisons with field test results in order to verify the adequacy of the generator model as well as the correctness of the numerical procedures. A short discussion of nonlinear saturation effects is also presented. A method of including these effects into the model of the generator is then proposed. Typical applications of the developed numerical procedures include dynamic overvoltages, torsional vibrations of the turbine-generator shaft system, resynchronization of the generator after pole slipping and detailed assessment of generator damping terms in transient stability simulations. / Applied Science, Faculty of / Electrical and Computer Engineering, Department of / Graduate

Thesis (Ph. D.)--Naval Postgraduate School, 2002. / Thesis advisor(s): Herschel H. Loomis, Jr., Alan A. Ross. Includes bibliographical references (p. 157-161). Also available online.

Thesis (M.S.)--Virginia Polytechnic Institute and State University, 1994. / Vita. Abstract. Includes bibliographical references (leaves 53-56). Also available via the Internet.

In this work, the accurate representation of transmission lines for the digital simulation of electromagnetic transients in power systems has been examined. A model has been developed that accounts for the frequency dependence and distributed nature of the line parameters over the entire frequency range. This model can easily be incorporated into a time-domain network solution of the complete power system. The model consists simply of a constant resistence in parallel with a current source evaluated at each time step of the solution. The equivalent resistance results from a finite-step-width discretization of the differential equations of a resistance-capacitance (R-C) network that simulates the line characteristic impedance. The equivalent current source accounts for the time delays and attenuations of the different frequency components of the travelling waves and for the discretization of the time-domain equations. Rational-function approximations are used to synthesize the R-C network and the line propagation ("weighting") function in the frequency domain. These rational approximations allow the corresponding time-domain functions to be obtained directly in a closed-form, thus circumventing the need for numerical inverse Fourier transformations. The numerical technique used to obtain the rational functions yields very accurate, high-order approximations. This technique is based on a direct, step-by-step allocation (and reallocation) of poles and zeros and avoids the instability problems which can be encountered with optimization techniques based on search methods. A series of analytical evaluations and simulation tests were performed in order to assess the validity of the model. The results of these tests show that the model is accurate, fast, and reliable. The model was incorporated into the code of the University of British Columbia's version of Dr. H.W. Dommel's Electromagnetic Transients Program (EMTP). i / Applied Science, Faculty of / Electrical and Computer Engineering, Department of / Graduate

published_or_final_version / Electrical Engineering / Master / Master of Science in Engineering

In this research, we are concerned with obtaining characteristics of a scattering object from transient input-output data. The input is a transient pulse with broad bandwidth. The output is the field scattered by the object. Specifically, we consider two classical structures: First a single lossless dielectric slab backed by a perfect conductor; second, a double-layer lossless dielectric slab backed by a perfect conductor. We begin with two generic solution forms: First, the ray-optic form, which emphasizes local object features; second, the singularity expansion method (SEM) form, which emphasizes object resonances. Using these two forms, we generate a variety of solutions for each structure. For the single slab, we obtain five solution forms for the transient response as follows: The ray-optic, the SEM, two hybrids, and one closed. We find that the input signal plays an important role in the results. We believe the specific hybrid solutions for the slab are new. For the double slab, we find four solution forms as follows: Two ray-optic and two quasi-hybrid. The quasi-hybrid solutions involve a ray-optic expansion in one slab and SEM in the other. We believe the quasi-hybrid forms are new and lead to some interesting comparisons with work by other researchers. As a result of critical study of the various solution types, we reach some conclusions concerning determination of parameters that classify an object (the parametric inverse problem). We find that a given SEM pole set does not always correspond to a unique object. In addition, we show that it is often not possible to relate SEM poles to object size or constitution. Because of these facts, it is necessary to add knowledge of the specific form factor of the object to permit classification. We include some conclusions concerning object identification and point out some areas for future research.