57 research outputs found
Photovoltaic system with multilevel converter coupled to a compressed air energy storage system for grid integration.
No full textM. Sc. Eng. University of KwaZulu-Natal, Durban 2014.Electricity demand is continuously increasing and nations including South Africa, are looking to exploit renewable energy sources to augment conventional electricity generation. An analysis of electricity demand and supply, the electricity infrastructure and the status of renewable electricity including the progress and plans made thereof in South Africa were carried out. A review of the challenges affecting the bulk exploitation of renewable energy (RE) resources and its future prospects are discussed to determine the sustainability of these efforts.
This research investigation focuses on a simulation model designed to harness the energy from the sun through a photovoltaic system. Based on empirical data of environmental conditions, a photovoltaic (PV) system model to generate 30 MW of electricity at Witkop substation, Polokwane (South Africa) was developed and to be fed into the grid. A maximum power point tracker (MPPT) control scheme is utilised to ensure that maximum power can be derived from the PV plant. A modular multi-level converter (MMLC) is utilised to convert the electricity generated by the PV system from direct current (DC) to alternative current (AC). The MMLC coupled to compressed air energy storage (CAES) stores the electricity generated during the day and injects it into the grid during peak periods of electricity demand.
Mathematical models of the PV system, the MMLC, the CAES and the grid integration were developed, modelled and simulated to describe the electrical behaviour and to establish the ideal operational parameters of the various systems components. Furthermore, validation of the performance of the system components in the simulation model were carried out against manufacturers’ data sheets for similar studies and prototypes. The simulation model were used to combine all the system components effectively into the grid based on the electricity generation system configurations, electricity demand and the environmental conditions of the selected site.
More importantly, this investigation seeks to increase the effort of development of PV generation models in the field of renewables when compared to other alternative energy sources such as wind energy generation
Network studies and mitigation of high 132 kV fault currents in eThekwini electricity.
No full textMaster of Science in Electrical Engineering. University of KwaZulu-Natal, Durban 2016.The growth of the world population has led to an increase in the demand for electricity. This has resulted in the expansion of electric power networks and this evolution brought with it many challenges. One of which is that power networks are experiencing increased fault current levels. This is as a result of growth in demand which has led to interconnected networks and increases in generation capacity. Fault current levels have been increasing steadily and are at a point where mitigation measures have to be evaluated to ensure that equipment operate within designed limits. Alternatively, equipment would have to be replaced with adequately rated equipment. In some cases, replacement would have to take place prematurely, since equipment would not have reached their “end of life”. This study investigates the problem at a 132 kV sub-transmission voltage, and the various factors involved with increasing fault levels and mitigation methods being used. Essentially, mitigation measures increase the impedance in the network, thereby reducing fault currents. Mitigation measures are classified as passive or active, and have varied degrees of effectiveness, usage and network losses. Active measures do not have any effect on the network under normal operating conditions, and only operate during a fault. An example is the superconducting fault current limiter. Passive measures operate under normal and abnormal conditions and affect network parameters. These are usually topological changes which increase the system impedance. Passive measures were chosen for the network studies since active measures are in the developmental stage at the 132 kV voltage level. In this research investigation, the measures tested include: network splitting by creating sub-grids, network reduction, high impedance transformers, introducing a higher voltage network and current limiting reactors. Reducing the 132 kV interconnectivity by creating a northern, southern and central grid reduced the fault levels significantly and does not require any capital investment. However, under abnormal conditions the grids are reconnected to ensure that there is no loss of supply. A solution is to construct a network at a higher voltage level that will support the 132 kV sub grids. A reduction in 275/132 kV transformation lowers the fault levels, while a reduction in generation had little effect on the network. High impedance transformers and current limiting reactors increase the losses in the network, but can be used to limit fault currents to pre-determined values. Electric utilities have to investigate the various measures in order to ascertain the most beneficial to that particular network, given the high cost of infrastructure, the ability to experience outages, space constraints in substations, and the electrical losses that might be incurred. The results obtained from this study carried out on the 132 kV eThekwini Network is presented and discussed
Technical performance and stability analysis of eskom power network using 600kv, 800kv, and 1000kv hvdc.
No full textMaster of Medical Science in Electrical Engineering. University of KwaZulu-Natal, Durban 2016.In designing electric power networks or implementing major expansions to existing networks, a number of the key issues regarding the technical performance of the network at both transmission and distribution level must be ascertained, namely: voltage regulation, voltage fluctuations, electrical losses, transmission/distribution plant loading and utilization, fault level, generation stability, harmonics, phase balancing, supply availability and system security. System studies and analysis conducted from time to time to ascertain the operating state of a network, taking into account, load growth projections for the future. Undue stresses on the system or anticipated problems are determined from power flow analysis or during operation and maintenance. Using a modified Eskom network (KwaZulu-Natal sub-grid) as a case study, the technical and stability analysis for different high voltage direct current (HVDC) transmission voltages: 600kV, 800kV and 1000kV were carried out using DIgSILENT PowerFactory engineering software tool, as an alternative for bulk power transfer using high voltage alternating current (HVAC) link along the major corridors. Static analysis using PV and QV curves; dynamic analysis using RMS time domain and electromagnetic EMT analysis were carried out. Dynamic analyses were performed to determine the system fault levels and critical fault clearing time. Results obtained from this investigation show that 600kV and 800kV HVDC transmission systems have greater power capacity than equivalent HVAC line. HVDC delivery systems were observed to have lower electrical losses, better voltage profile, increase fault clearing time, enabling robust protection schemes to be installed. Voltage distortion due to harmonic content and imperfect current waveform in Cahosa-Bassa LCC-HVDC link were also investigated, and re-engineering with the use of VSC-HVDC technology has been proposed. This option provides reduced harmonic content, excellent sinusoidal waveform and minimal vulnerability to commutation failure. A financial and economic analysis of a 500kV HVAC double circuit and ±600kV HVDC transmission network were compared. HVDC system was proposed the most suitable scheme for bulk transmission of electric power over long distances due to high efficiency and better economics
A comparative study and analysis of PHES and UGPHES systems.
No full textMaster of Science in Power and Energy Systems. University of KwaZulu-Natal, Durban, 2015.Underground Pumped Hydroelectric Energy Storage (UGPHES) is a similar energy
storage concept to the conventional Pumped Hydroelectric Energy Storage (PHES) with
the major difference being that the lower reservoir is in an underground cavern system.
Electricity is stored in the form of gravitational potential energy between a surface reservoir
and an underlying subterranean reservoir. In this study, various existing energy storage
systems are examined with the UGPHES introduced as an alternative technology for bulk
energy storage in South Africa to contribute to the constrained electricity network with
environmental and economic benefits. The use of existing infrastructure for the
implementation of UGPHES systems is explored, which includes the use of aquifers and
abandoned mines. South Africa has large amounts of groundwater as well as
transboundary aquifers which may be used for UGPHES systems. A mathematical model
is presented which highlights the considerations for the implementation of an aquifer
UGPHES system including head and aquifer transmissivity. The use of abandoned mines
in South Africa is also explored as it presents an existing underground cavern as well as
large amounts of groundwater. Finally, a mathematical model is presented to provide an
analysis of the water hammer phenomenon as well as an economic analysis for the use of
abandoned mines for UGPHES systems
Spatial modeling and dynamics of a photovoltaic generator for renewable energy application.
No full textThesis (M.Sc.Eng.)-University of KwaZulu-Natal, Durban, 2006.Photovoltaic systems alongside energy storage systems are a recognized distributed generation
(DG) technology deployed in stand-alone and grid connected system for urban and rural
applications. DG system ranging in size from a few kilowatts up to 50 MW refers to a variety of
small, modular power-generating technologies connected to the electric grid, and combined with
energy management and storage systems to improve the operation of electricity delivery
systems. DG provides solutions to two long standing problems of power system operation: non-availability
at all times of sufficient power generation to meet peak demands and the lack of
capacity of existing transmission lines to carry all the electricity needed by consumers. Installing
DG at or near a customer load can eliminate the need to upgrade existing
transmission/distribution networks to handle the extra power requirement. Since these
distributed energy systems are inertia-less and possess large time constants (response times),
there are significant interactions between these systems, the power converters and the
distribution networks. This precipitates new dynamics and control limitations, which are
unknown in the conventional electric power distribution networks. To perform effective load
scheduling, high performance control and optimal operation of these energy systems require an
understanding of the dynamic and steady state characteristics of the DG system. This thesis
report presents a mathematical model for a Photovoltaic (PVG) generator system, including the
energy-storage system. Laboratory test results for steady state performance analysis using
various loads are presented and discussed. It concludes with a fundamental economic evaluation
of system
Dynamic analysis of the Southern Africa power pool (SAPP) network.
No full textMaster of Science in Electrical Engineering. University of KwaZulu-Natal, Durban 2016.Synchronous generators have been connected through overhead transmission lines and interconnected to a regional power system network to improve reliability, enhance the security of supply, trade electricity and share the available natural resources for energy fuel supply. The interconnected power system experiences disturbances during normal operation such as load variations and faults, causes stress on the generators to control and remain in synchronism. This dissertation analyses the natural damping oscillations that will emanate during a disturbance in the interconnected power system and provide understanding to the system operator to monitor and operate effectively the Southern African Power Pool (SAPP). It is required to carry out the performance analysis and characteristics of the generators during the disturbances in order to identify the synchronizing and damping torque in respect of rotor angle and speed deviations. In power system control, the frequency is monitored continually since the speed of the generators is synchronized into the transmission lines. Any small variation on the interconnected system will affect the others machines. The effect can either be the system maintaining its stability or loss of synchronism. The latter can be avoided by identifying the nature and behaviour of oscillations and determining effective means to minimize them in interconnected power pool. It can also notify the system operator of an impending power outage. In this research investigation, a simplified model of the Southern African Power Pool is modeled using DIgSILENT Powerfactory power systems analysis software tool, using input data of the primary plant (synchronous generators) and associated interconnected power system network. Nodal and modal analysis tools were used to determine the dynamic status of the interconnected power network. A dynamic analysis will enable participating members of the power pool understand the nature of oscillations when affected by different types of events with continuous monitoring of the modes and eventually assist in re-tuning of secondary control equipment to improve the service delivery of electricity of a pool such as of the Southern African region.
The study has identified the focal points of power oscillations in the modelled SAPP grid through simulations that affects the behaviour of system voltages during a disturbance and require to control damping oscillations on the synchronous generators
Utilisation of line surge arrestors to improve overhead HVAC and EHVDC line performance under lightning conditions.
No full textDoctoral Degree. University of KwaZulu-Natal, Durban.In high lightning areas, lightning strokes play an important role in the performance of overhead EHV AC and DC lines. A single lightning stroke, that terminate on the earth wire and/or tower can lead to back flashovers. This flashover depends on factors such as conductor type, tower, soil resistivity and magnitude of the stroke. The flashover across the insulator and the resultant fault current surge will propagate along the line, until it is extinguished or the breaker operates. This movement of the surge currents tend to damage and reduce the life span of associated equipment such and circuits breakers, insulators, transformers and impact network performance adversely. Furthermore, this operation of the protective devices leads to power interruption to consumers on that network, and loss of production, thus negatively impacting the economy.
This thesis investigates the incidences of network failure due to lightining strokes occuring on Eskom HVAC network as well as HVDC networks, considering soil resistivity, tower footing resistance and factors that influence the earthing resistances. Tower footing resistance needs to be kept uniform and as low as possible to extinguish the surge across the tower and hence reducing the back flashovers across the insulator under lightning conditions. Theoretical simulations were conducted on the different methods that are available to improve the tower footing resistance values. A case study was undertaken to ascertain the tower footing resistance of an 88kV Eskom line. The crows earthing configuration was then utilized to reduce the footing resistance to a value less than 30 ohms, using line surge arrestors (LSA) which are devices that can drain power surges to ground, if placed adequately and in sufficient numbers.
Furthermore the thesis determines the relationship between the magnitude of the lightning stroke, the tower top voltage, tower footing resistance and hence the back flashover voltage that would appear on the line, which would lead to power interruptions. Surge arrestors were modelled using MATLAB software. The required number of surge arrestors per phase is thus determined that is required to drain the surge current down to earth., thus preventing power interruptions. EHV AC and DC cases studies are simulated and results are presented snd discussed.Publications listed on page iii
The safety risk assessment and mitigation measures of the LV networks with embedded generators.
No full textMaster of Science in Electrical Engineering.Electricity industry liberalization across the world has seen a significant growth in the utilization of autonomous- and distributed power sources deployed at sub-transmission (132 - 33 kV) and reticulation levels (<33kV) in stand-alone or grid connection notations. With the electricity industry reform, an open access regime is a standard policy governing the transmission grid, and this provides for full competition at generation and distribution end of the delivery value chain. The National Electricity Regulator of South Africa (NERSA) is currently examining a roll out plan for a nation-wide rooftop photovoltaic (PV) system. Most of these roof top PV systems are expected to be connected on the low voltage (LV) networks (<1kV). The widespread deployment of such PV installations have associated risks to personnel and could pose challenges to system operations. Most utility field service engineers are not aware of the dangers posed by such installations. Dangers may include but are not limited to reverse power flow from installed PV systems should the anti-islanding protection fail after the loss of utility supply. This research investigation presents results from the analyses of the impact of statutory requirement, load demand and load type on the embedded generator (EG) grid–tied inverter anti-islanding protection settings and anti-islanding non-detection zone to minimize or reduce LV network operating safety risk upon the loss of utility supply
Technical evaluation and life cycle cost analysis of transmission and distribution assets.
No full textMaster of Science in Electrical Engineering. University of KwaZulu-Natal, Durban 2016.Electric Power Transmission and Distribution (T&D) Asset Managers spend on average 30% of their capital expenditure on the procurement of primary and secondary plant and equipment. Furthermore, T&D Asset Managers spend on average 50% of their operating expenditure on the maintenance and operation of plant and equipment over their useful lives which is generally 40 years for primary plant and 15 years for secondary equipment. The privatisation of T&D in many countries and emerging markets means that shareholder return is now a major performance indicator for these companies. Regulatory bodies are becoming stricter in the pursuit of efficiency and productivity, constraining expenditure. This has the effect of reducing shareholder return if not managed appropriately. In order to meet shareholder expectations whilst maintaining consumer and regulatory requirements, T&D Asset Managers must apply innovative techniques to lower their capital and operating cost while meeting regulatory requirements. Therefore, T&D Asset Managers must take optimum advantage of every opportunity for improvement. The major items for cost reduction or productivity improvement are: procurement optimization, delivery efficiency and organisational overheads. Procurement Optimization relates to the procurement of equipment, materials and services. Plant and equipment costs are a major chunk of this spend. Delivery efficiency refers to the design, construction and maintenance of T&D network assets. Opportunities for improvement can exist in design and construction process as well as smart contracting strategies. Lastly, organisational overheads relate to the organisation’s cost for achieving the company’s outcomes. The major costs here are the cost of internal labour and the cost of capital. This research investigation focusses on asset management, asset strategy and equipment evaluation and specification. It involves a technical evaluation of T&D assets and a life-cycle cost analysis of plant and equipment with the goal of minimizing or reducing life cycle cost and hence, reducing risk exposure. A deliberate focus on asset strategy, assessment, specification, and the supply chain will ensure that T&D asset managers deploy fit for purpose assets at the lowest life-cycle cost. Based on the results obtained from this investigation, Asset Managers must apply a structured approach and have a long term view in order to achieve the lowest life-cycle cost whilst meeting regulatory and consumer requirements, within an acceptable risk exposure. This research study provides context and proposes tools and methodologies which can be utilised for effective decision making across the full supply chain for primary and secondary T&D equipment as applicable to the electricity supply industry
Application of distance protection for transformers in Eskom transmission.
No full textM. Sc. University of KwaZulu-Natal, Durban 2014.Eskom is South Africa’s state owned utility who is responsible for the generation, transmission and distribution of electricity. The transmission network in Eskom consists of thousands of kilometres of lines operating at voltages from 220kV to 765kV. Three winding transformers, two winding transformers and autotransformers are employed in Eskom’s transmission network.
High Voltage (HV) Inverse Definite Minimum Time (IDMT) overcurrent protection and Medium Voltage (MV) IDMT overcurrent protection are employed to provide backup for these transformer’s differential protection and for uncleared through faults. Eskom’s Transmission setting philosophy states “that the HV and MV IDMT overcurrent elements must be stable at 2 x full load current of the transformer”. This has resulted in MV and HV over-current protection not detecting MV multiphase busbar faults in substations with low MV fault levels which are located far away from generating stations.
In such cases a possible solution is to use distance protection for transformers. This research study investigates how the different vector groups of the power transformer affect the impedance measured by the protection relay, and how standard distance algorithms in protection relays respond to faults located on the MV side of the power transformer. The study consists of a literature review of current practices of transformer distance protection.
Autotransformers and distance relays are discussed with manual fault calculation examples. The effects of tap-changers and transformer inrush current on transformer distance protection are also discussed. DigSilent Power Factory software version 15.0.2 was used in the modelling and simulation of faults. The response of distance elements for various faults located on the MV side of transformers are analysed and summarised in two tables which indicate which loops will measure the precise distance to fault through the various transformers and which loops will measure the distance to fault with a slight error.
Multifunction Intelligent Electronic Devices (IEDs) with both distance and differential functions are now being commissioned in the Eskom transmission network for the protection of transformers. The distance elements employed in transformer IEDs are similar to distance elements found in a line distance relay. These distance functions can be set to provide local backup protection for uncleared HV and MV busbar faults in the Eskom Transmission network
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