The ability to implement Wide Area Monitoring and Control in power systems is developing into a need in order to prevent wide scale cascading outages. Monitoring of events in the power system provides a great deal of insight into the behaviour of the system. The research work presented in this thesis focussed on two tools that aid in monitoring: State Estimation and Synchronised Phasors provided by Phasor Measurement Units (PMU). State Estimation is essentially an on-line data processing scheme used to estimate the best possible state (i.e. voltage phasors) from a monitored set of measurements (active and reactive powers/voltage phasor measurements). The ever growing complexity and developments in the state of art calls for robust state estimators that converge accurately and rapidly. Newton’s method forms the basis for most of the solution approaches. For real-time application in modern power systems, the existing Newton-based state estimation algorithms are too fragile numerically. It is known that Newton’s algorithm may fail to converge if the initial nominal point is far from the optimal point. Sometimes Newton’s algorithm can converge to a local minima. Also Newton’s step can fail to be a descent direction if the gain matrix is nearly singular or ill-conditioned. This thesis proposes a new and more robust method that is based on linear programming and trust region techniques. The proposed formulation is suitable for Upper Bound Linear Programming. The formulation is first introduced and its convergence characteristics with the use of Upper Bound Linear Programming is studied. In the subsequent part, the solution to the same formulation is obtained using trust region algorithms. Proposed algorithms have been tested and compared with well known methods. The trust region method-based state estimator is found to be more reliable. This enhanced reliability justifies the additional time and computational effort required for its execution. One of the key elements in the synchrophasor based wide area monitoring is the Phasor Measurement Unit. Synchronized, real time, voltage phasor angle, phasor measurements over a distributed power network presents an excellent opportunity for major improvements in power system control and protection. Two of the most significant applications include state estimation and instability prediction. In recent years, there has been a significant research activity on the problem of finding the suitable number of PMUs and their optimal locations. For State Estimation, such procedures, which basically ensure observability based on network topology, are sufficient. However for instability prediction, it is very essential that the PMUs are located such that important/vulnerable buses are also directly monitored. In this thesis a method for optimal placement of PMUs, considering the vulnerable buses is developed. This method serves two purposes viz., identifying optimal locations for PMU (planning stage), and identifying the set PMUs to be closely monitored for instability prediction. The major issue is to identify the key buses when the angular and voltage stability prediction is taken into account. Integer Linear Programming technique with equality and inequality constraints is used to find out the optimal placement set. Further, various aspects of including the Phasor Measurements in state estimation algorithms are addressed. Studies are carried out on various sample test systems, an IEEE 30-bus system and real life Indian southern grid equivalents of 24-bus system, 72-bus system and 205-bus system.

In this dissertation, the problem of multi-area load frequency control in large power systems is investigated. The load frequency control problem is concerned with the minimization of the deviations in the frequencies of the different areas and in the tie line power exchange between these areas, and is a problem of major importance in the satisfactory operation of large power systems. Some new techniques for designing load frequency control systems are presented through the use of concepts from singular perturbation and hierarchical system theory. To provide appropriate vehicles for the design of the new control systems, state variable models for power systems are developed. These models progress from a two-area interconnected power system model to large scale models comprising of N areas. Two centralized state feedback schemes are proposed for the load frequency control by utilizing the separation of the system models into two time scales. In the first scheme, composite controls and reduced order controls are developed to meet the required performance specifications by. The second scheme is obtained by using the theory of variable structure systems where the existence of a sliding regime leads to the design of a single discontinuous state feedback controller that meets the performance requirements. In order to further improve the performance of the closed loop system, a two level hierarchical control scheme is developed. This consists of a set of local controllers that are designed using either the singular perturbation approach or the variable structure system approach as before and a set of global control functions provided by a higher level controller that attempts to coordinate the local controllers. The interaction prediction principle is used as a tool in the design of the global controller. The performance of the presently developed control schemes is examined in detail for the illustrative cases of a two-area and a three-area power system. From this analysis, it is shown that these controllers provide an improved performance compared to the existing control schemes in reducing the frequency and tie line power deviations.

Thesis (MBA)--Stellenbosch University, 2015. / ENGLISH ABSTRACT: Power equipment suppliers that manufacture goods to customer requirements face various opposing forces, such as increasing customer expectations, increasing competition and escalating costs. To sustain margins, companies need to understand what constitutes customer satisfaction, thereby enabling them to differentiate their goods and services from those of competitors, and to charge appropriately for those goods and services. Although customer satisfaction is important to industrial goods suppliers such as power equipment suppliers, most studies have been conducted in the business-to-consumer (B2C) environment, focusing on consumer goods and services, with very few studies focusing on the business-to-business (B2B) environment. Compounding the difficulties with customer satisfaction for South African industrial suppliers is that most literature on the subject is applicable to markets outside of South Africa. This paper aims to give South African industrial goods suppliers some insight into those factors that improve customer satisfaction. The identification of critical success factors seen as important by customers was, therefore, the focus of this research assignment. First, customer satisfaction as a critical success factor is reviewed by comparing it to other success factors in an attempt to validate whether it influences organisational performance positively. Second, a list of appropriate items comprising customer satisfaction is identified from the literature review, and the differences between direct customers and indirect customers are identified and discussed. To reduce the number of constructs to be surveyed, the variables that make up customer satisfaction were ranked using prioritisation matrices against Porter’s Five Forces model (Porter, 2008) and the Blue Ocean Strategy model (Kim & Mauborgne, 2004). The shortened list comprised 39 items, which measured ten constructs of customer satisfaction. Questionnaires were sent to customer representatives who were critical decision-makers when deciding on purchases of industrial equipment. The responses were evaluated as a complete group and showed some statistical significance between the constructs. The responses were then evaluated according to organisational types, which showed no statistical significant differences or interaction effects.

published_or_final_version / Electrical and Electronic Engineering / Doctoral / Doctor of Philosophy

published_or_final_version / Electrical and Electronic Engineering / Master / Master of Philosophy

An Integrated Power System (IPS) with a DC Zonal Electrical Distribution System (DC ZEDS) is a strong candidate for the next generation submarine and surface ship. To study the implementation of an IPS with DC ZEDS, members of the Energy Sources Analysis Consortium (ESAC) are currently constructing a reduced-scale laboratory. One fundamental component of DC ZEDS is the Ships Service Converter Module (SSCM), commonly known as a buck DC-DC converter. This thesis documents the design, simulation, construction and testing of a 500V/400V, 8kW resonant soft-switched DC-DC converter. In theory, resonant converters will operate more efficiently and generate less Electromagnetic Interference (EMI) when compared to a standard hard-switched converter. In this thesis, the resonant converter is tested and compared to a hard-switched DC-DC converter that was designed for ESAC's reduced-scaled IPS. The results verify that the resonant DC-DC converter realizes significant efficiency and EMI generation improvements over the hard-switched converter at the cost of a more complex control system and power section. / US Navy (USN) author

Approved for public release; distribution is unlimited / This thesis formulates and solves a mixed-integer program to plan the recovery of an electrical power transmission grid that has been damaged by a natural disaster or terrorist attack. The damage can be extensive and recovery can take weeks or months. An efficient recovery plan that maximizes the utilization of repair resources can help ensure swift restoration of services. The network recovery-planning model is implemented in GAMS (General Algebraic Modeling System) and uses CPLEX as the solver. An electrical grid based on IEEE's 300-bus transmission network is used for testing. To simulate varying degrees of damage to the network, we choose up to 20% of the grid's lines, buses and transformers to be placed out of service. Based on the availability of repair resources, the repair-time horizon and penalties for unserved demand, the model produces a repair schedule that minimizes the cost of power shed. We demonstrate that for a network with up to 8% of its components damaged, the model can produce an optimal recovery plan within 20 minutes on a 2 GHz personal computer. For our largest test-case with 20% of network components damaged, the recovery plan is within 7% of optimal after 1 hour of solver time. / Outstanding Thesis

M.Ing. / With the increased use of nonlinear loads such as variable speed motor drives and rectifiers, the voltages and currents on the power system grid are no longer sinusoidal. These non-sinusoidal waveforms cannot be analyzed by conventional power theories and the usual recourse is to decompose the nonlinear waveform into a set of harmonics. Harmonic voltage and current components are detrimental to the power system and may cause additional losses, or premature failure of equipment, and as such they have a definite influence on the quality of supply. This thesis shows the limitations and potential pitfalls of harmonic decomposition and other power theories, and examines various methods used for identifying, quantifying and modelling nonlinear loads. The aim of the thesis is to evaluate methods for attaching a specific disturbance or non-linearity on the voltage waveform to a specific load connected at the point of common coupling. The power theories examined include the total complex power, the IEEE working group definitions of apparent power, true power factor and harmonic adjusted power factor. Some new techniques for estimating the degree to which a load is disturbing the voltage at the point of common coupling is introduced, including the calculation of correlation indices, and the the use of wavelets.

A research report submitted to the Faculty of Engineering and the Built Environment, University of the Witwatersrand, Johannesburg, in partial fulfilment of the requirements for the degree of Master of Science in Engineering, 2016 / The power system frequency must be kept as close as possible to the nominal value. This is due to the inherent design of electrical equipment to operate efficiently at the nominal frequency. Frequency regulation in an interconnected power system is the duty of all members of the interconnection. However, in the Eskom-ZESA interconnected power system Eskom engineers ignore the contribution of the ZESA system to primary frequency control. This is mainly due to the prevalent assumption that the ZESA control area is small relative to the Eskom control area and its contribution to primary frequency control of the interconnected power system is negligible. This document presents a project that examines the validity of this assumption via determination of the contribution of the ZESA system to the interconnected power system’s primary frequency control. The interconnected power systems background was studied to understand the theory behind the operation of two or more interconnected power systems. System frequency disturbances deemed to be a good representation of the Eskom-ZESA interconnected power system’s performance were selected and analysed to validate the current assumption. The results show that there is a significant support from ZESA during a system frequency disturbance. This proves that the existing assumption is not valid anymore. Furthermore; the generator model that mimics the Eskom-ZESA tie-line governing behaviour was developed. Two different types of governor models were employed; firstly the IEEEG1 governor was tuned to control generator output to match the tie-line performance and then the TGOV5 governor model was used. The IEEEG1 governor model is a simplified governor representation; as a result, it is not easy to tune the parameters to match tie-line response. However, the performance is acceptable and it can be used to represent the tieline governor response. The TGOV5 governor model is very complex as discussed in section 4.2. The model includes boiler dynamics, and this improves performance such that it is possible to tune the parameters to follow the tie-line performance as close as necessary. / GR2016

Bi, Suzhi. / Thesis (Ph.D.)--Chinese University of Hong Kong, 2013. / Includes bibliographical references (leaves 113-119). / Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Abstract also in Chinese.