Browsing by Author "Gaunt, Charles T"

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    Allocation of transmission losses to determine tariff
    (2018) Adebayo, Adeyinka Victor; Gaunt, Charles T
    The recent widespread restructuring and unbundling of the electricity industry has introduced some changes in the organization of the sector, thereby creating a more competitive environment in which each participant must bear its own cost and be responsible for its own contribution to losses in the system. The allocation of transmission losses has become an important issue as this determines how and what to charge each of the participants in the industry. This allocation is best assessed and based on their individual contributions to grid losses. Earlier methods used in loss allocation include: The Pro rata approach which arbitrarily allocates 50% each to the load and generator; the Marginal procedure allocation, which is either positive or negative; the Proportional sharing method which bases its allocation on the Kirchhoff’s current law and allocates no losses to the transmission line and the Equilateral bilateral exchange (EBE) method. Most of the other methods, such as the Game theory method, Circuit theory method, Graph theory method, and Optimization methods are either mathematically complex in operation or time-consuming. And till date, none of these methods could be used to allocate transmission losses with fairness and transparency. Currently, power loss measurements have been estimated based on ideal conditions in which there exist a balanced load and reactive power, while the inefficiency caused by distortion and the unbalanced load is not usually taken into consideration. This research introduces a novel and a fairer method of determining power losses by using the Thévenin impedance in calculating the line parameters used in the determination of power losses. Since losses associated with a transmission power line depend on the wire resistance and the line current (I2 R), the Thévenin equivalent of the system is calculated from the point of connecting each participant (generator or load), i.e. the point of common coupling, to determine the system losses without prior knowledge of the power system supply quantities. This thesis identifies the avoidable losses in the system, which participants pay for because of the inadequacy of current methods which use only reactive powers (inductive and capacitive) to determine the power losses in the allocation of losses and in the calculation of the power system tariff. This report elucidates how to estimate the losses that can be avoided by the participants. This loss is equal to the numerical power difference in the conventional power loss and the new power loss calculation method which utilizes the general power theory where two components that are orthogonal to each other, making non-active power (reactive power and distortion power) are used. This difference, which is an extra loss created by the participants, can be conserved to reduce power generation cost and tariffs. This method which was tested on a standard IEEE test system is transparent, fair and requires a comparatively short time to execute, making it suitable for decision making thus emphasizing the importance of the proposed solution.
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    Comparative review of the benefits and flexibility of small modular reactor designs
    (2020) Featherstone, Keith; Gaunt, Charles T
    Over the past few years, there has been a sustained interest in the development of small modular reactors (SMRs) evident by the number of global initiatives focused on SMR development. This desktop study was performed to review the viability of SMRs based on their benefits and flexibility, focusing predominantly on the light water NuScale and the gas cooled AHTR designs. In assessing the level of safety, the typical general design and safety criteria were reviewed to establish a basis to compare the NuScale and AHTR designs. The need for flexibility to support grid operators and the ability of a nuclear plant to load follow were reviewed to confirm their flexibility. The principal of cogeneration and the feasibility for cogeneration and energy storage with SMRs was explored to determine the potential industrial application. Finally, the technical readiness and uncertainties, the potential market and economic competitiveness of SMRs were reviewed. The review established that SMRs with safety performance levels exceeding those of current reactor designs are definitely viable. The ability to prevent fuel failure through passive cooling simplifies the design by eliminating the need for complex safety systems and reduces the constraints associated with siting, opening up energy markets where previously nuclear reactors would not have been viable. Their flexibility and the ability to add additional units over time enable them to integrate into any size electrical network and a variety of energy markets. As a clean energy source, SMRs are well suited to support strategies to reduce greenhouse gas emissions and replace fossil-based energy sources. SMRs operating at high temperatures have the added option of considering thermal storage as a means to provide additional flexibility. The biggest uncertainty in the deployment of SMRs is associated with the regulatory and licencing processes. However, there is a large potential market for SMRs and the lower capital cost per unit, the shorter period until a revenue stream is established and the ability to stagger the financial impact of additional units are expected to make SMRs easier to finance than large nuclear units. This preliminary review concluded that SMRs are definitely viable, but until a SMR design has been successfully licenced, constructed and operated, the uncertainty associated with the licencing of a new technology and the potential for long delays during construction are likely to prevent any large-scale deployment in the near future.
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    Measurements and finite element modelling of transformer flux with dc and power frequency current
    (2019) Chisepo, Hilary Kudzai; Gaunt, Charles T; Folly, Komla A
    Geomagnetically induced currents (GIC’s) caused by solar storms or other sources of dc excitation in the presence of ac energization can disturb the normal operation of power transformers. If large enough, they cause half-cycle saturation of a power transformer’s core which could lead to overheating due to excessive stray flux. Finite element matrix (FEM) modelling software is of considerable use in transformer engineering as it is able to solve electromagnetic fields in transformers. For many problems, typically involving only specific parts of a transformer, fairly accurate solutions can be reached quickly. Modelling the effects of GIC or leakage currents from dc systems, however, is more complex because dc components are superimposed on ac in transformers with nonlinear electrical core steel parameters. At the beginning of the investigation, FEM models of different bench-scale laboratory transformers and a 40 MVA three-phase three limb power transformer were investigated, but the results did not sufficiently represent the measurement data due to the application of widely used modelling assumptions regarding the transformer joints. Following the preliminary analyses, practical measurements and FEM simulations were carried out using three industrially made model single-phase four limb transformers (1p4L) without tanks. These test transformers resemble a real power transformer because they have high-quality grain oriented electrical core steel and parallel winding assemblies. Practical laboratory measurements recorded during ac testing were used to calibrate 2D FEM models by adding “equivalent air gaps” at the joints. The implementation of this joint detail helped to overcome the shortcomings of the preliminary FEM simulation. Analyses of the electrical and magnetic responses of the FEM models using simultaneous ac and dc then followed. A refined 3D FEM simulation with more detailed modelling of the core joints of 1p4L model transformers agreed more closely with the practical measurements of ac only no-load conditions. Further, the depiction of stray flux leaving the transformer’s saturated core under simultaneous ac and dc excitation showed an improvement in the approach as measured in the physical model. Saturation inductance (Lsat) is an important parameter for input into mid- to low-frequency lumped parameter transformer models that are used in electromagnetic transients software such as PSCAD/EMTDC, but it is not easily measured and is seldom provided by manufacturers. Some Lsat measurements on the 1p4L test transformers are presented in this thesis, along with some 3D FEM analyses. The measurements and FEM analyses investigated “air core inductance” which represents a transformer without a core, and “terminal saturation inductance” which represents deep saturation due to dc excitation. An important finding in this thesis is that “terminal saturation inductance” is the more useful of the two for topological transformer models investigating realistic GIC excitation. Further to this, a new composite depiction of half-cycle saturation with a multi-parametric relationships supported by measurement and simulation is presented. The main contribution of this thesis is that it gives more accurately the electrical response and distribution of the leakage flux under conditions such as those caused by GIC or other sources of leakage dc excitation, as well as including of joint details in the FEM models through calibration with physical models. This calibration can aid transformer modelling and design in industry for mitigation of the effects of GICs, contributing to improved transformer survival during significant geomagnetic disturbances.
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    Present day challenges in understanding the geomagnetic hazard to national power grids
    (2010) Thomson, A W P; Gaunt, Charles T; Cilliers, P; Wild, J A; Opperman, B; McKinnell, L-A; Kotze, P; Lotz, S I
    Power grids and pipeline networks at all latitudes are known to be at risk from the natural hazard of geomagnetically induced currents. At a recent workshop in South Africa, UK and South African scientists and engineers discussed the current understanding of this hazard, as it affects major power systems in Europe and Africa. They also summarised, to better inform the public and industry, what can be said with some certainty about the hazard and what research is yet required to develop useful tools for geomagnetic hazard mitigation.