Browsing by Author "Chowdhury, S"

Now showing 1 - 8 of 8
  • Thumbnail Image
    Item
    Open Access
    Comparison of low voltage ride through capabilities of synchronous generator with STATCOM and DFIG based wind farms
    (2015) Appadoo, Kulisha W; Chowdhury, S
    Increase in wind generation and grid-integration of wind energy technologies has resulted from an increasing demand of cheap and clean electricity across the globe. Wind generators are available as small, medium and large scale electric generators, usually in the range of 1kW to 100MW and are usually installed in areas rich in wind resource which may or may not be located close to the load centres. Wind energy penetration has increased since the 1970s with the total worldwide capacity of installed wind power reaching about 282,275 MW. Apart from technical issues of grid-integration, research is also being done to investigate the participation of wind energy systems to enhance grid performance through fault ride-through capabilities, providing voltage control and power quality improvement etc. The goal of a Fault Ride Through (FRT) or Low Voltage Ride Through (LVRT) system is to enable a wind farm (WF) to withstand a severe voltage dip at the connection point and still stay connected to the power system as long as the fault persists. Wind turbine designs are required to incorporate LVRT capability as per Grid Code’s requirements only if they are technically needed for a reliable and secure power system operation. The basic requirement for LVRT is that the wind turbines must maximise their reactive power injections to the network without exceeding the turbine limits. The maximisation of reactive current must continue for at least 150msafter the fault clearance or until the grid voltage is recovered within the normal operation range. It is important here to discuss here the immediate impact of the voltage dip on the wind farm (WF) operation. During the voltage dip caused by the fault, the active power provided to the grid by the WF is instantaneously reduced. This power becomes at least temporarily lower than the mechanical power available at the rotor hence the rotor speed of the wind generator increases. It is required for the LVRT capability of the WF, that the wind generators of the WF must not disconnect from the grid during fault persistence, either due to over-speeding or under voltage protections. After the clearing of the fault that led to the voltage dip, the voltage at the wind turbine bus would increase. It is also required that the wind generators should resume their power supply to the network without losing stability.
  • Thumbnail Image
    Item
    Open Access
    Grid integration of distributed renewable energy sources: a network planning perspective
    (2014) Ramdhin, Avinash; Chowdhury, S
    With the drive for cleaner energy, Independent power producers (IPP’s) have to find suitable potential land sites that meet their renewable project needs and that prove to be technically feasible to integrate into the nearest distribution electrical infrastructure. Project feasibility for utility grid connection can in certain instances be directed to a specific area due to resource availability and existing electrical plant capability. This invariability leads to multiple establishments of renewable energy plants in the same geographic location. Distribution substations and high voltage (HV) lines in the South African National utility, Eskom, are planned and constructed based on simulation models derived from power system models built in DIgSILENT Powerfactory analysis software. For a Network Planning Engineer, planning for this integration can be become quite complex in a multi-machine scenario as above. This dissertation provides network planning criteria that a planning engineer in the utility can successfully use to plan for this integration. Three sets of criteria are established. With the inclusion of widespread distributed generation in close proximity of each other, sharing the same grid electrical infrastructure, a critical path of HV electrical elements exists, which the effects of the combined generation control. The first set of planning criteria is derived from the analysis of locating this critical path. This is determined by means of using iterative programming and calculations. Grid voltage stability is one the most important factors in determining the feasibility of generator grid integration. The voltage stability effects of the Eskom Distribution network to which these generating plants connect to, are analysed and tabulated results established. This will enable the utility to determine the location of a specific size of renewable plant, just by knowing the grid strength and not going into detail voltage stability studies. For the second set of planning criteria three sets of network range strengths are identified with corresponding ratios of grid strengths to generator short circuit current contributions. Successfully integrating DG to the grid also has many technical and cost solutions of network configurations. The third set of planning criteria identifies four generic network configurations and the building blocks of physically costing the engineering integration. Solar density maps provide an indication of proposed MW output in a particular area. In this research, solar density maps are used to identify the maximum connecting generation to the electrical grid in feasible geographic areas. The results derived from this study enable the planning engineer and/or developer to better plan the optimal location of a PV project wrt the chosen geographic area of KZN. This study case may be extended to other technologies leading to a more concise framework of network planning for renewable project integration.
  • Thumbnail Image
    Item
    Open Access
    Investigating the effect of solar modelling using different solar irradiation data sets/sources within South Africa
    (2011) Dekker, Justin; Chowdhury, SP; Chowdhury, S
    When designing a solar energy system, accurate solar data for the specific site in which one plans to install the system is required to accurately determine the sizing of the system components based on the available amount of energy. Both the source of the data and the method used for measuring the solar irradiation data are key. This paper specifically deals with the modelling of an off grid photovoltaic power supply system using three different sources of solar irradiation data for two specific geographical locations within South Africa. The paper then goes on to investigate the financial implications in terms of using free solar irradiation data which is available to the public versus accurate ground measured data for a specific site and how it affects the systems component sizing.
  • Thumbnail Image
    Item
    Open Access
    The optimal placement of phasor measurement units and their effects on state estimation
    (2011) Yuill, William; Chowdhury, S; Chowdhury, SP
    Phasor measurement units (PMUs) are a key new technology for use in electric power systems as a backbone for sensing and measurement and to improve interface and decision support using instantaneous PMU data which will drive faster simulations and advanced visualisation tools that will help system operators assess dynamic challenges to system stability. The two main objectives of this work are to investigate and develop 1. a method for the algorithmic placement of a minimum number of PMUs into a system to ensure full observability, 2. conventional, hybrid and linear state estimation techniques to incorporate and utilize PMU measurement data to perform state estimation and to study the effects that differing PMU placement positions have on the accuracy of the resultant state estimator solution.
  • Thumbnail Image
    Item
    Open Access
    Optimal placement of phasor measurement units using the Advanced Matrix Manipulation algorithm
    (2013) Fish, Adbul-Aziz; Chowdhury, S; Chowdhury, SP
    This thesis investigates the problem of the Optimal Placement scheme of Phasor Measurement Units in electrical power systems for State Estimation to facilitate improved monitoring and control of the system parameters. The research work done for this thesis begins with review of Supervisory Control and Data Acquisition systems (SCADA). SCADA-based systems are currently employed for condition monitoring and control of industrial and utility electrical power systems. For utility power networks, the main problem with voltage and current phasor data captured by SCADA systems is that they are not synchronised with respect to each other in a present-time or Real-time framework. This implies that both magnitude and phase angle of the measured phasors tend to get affected by slow data flow provided by SCADA to the points of utilization and also by differences in time instants of data capture. These factors inhibit theefficiency and quality of the power system monitoring and control. “Phasor Measurement Unit” (PMU) is a relatively new technology that, when employed in power networks, offers real-time synchronised measurements of the voltages at buses and currents along the lines that connect them. This is accomplished by using a GPS based monitoring system which facilitates time synchronisation of measurements and unlike SCADA, makes the measured data available in Real-Time format. SCADA is not able to provide Real-time data due to the low speeds at which RTUs (Remote Terminal Units) provide data. Availability of time-stamped phasor measurements makes PMUs preferable for power system monitoring and control applications such as State Estimation, Instability Prediction Analysis, Real-time Monitoring of the system conditions, Islanding Detection, System Restoration and Bad Data Detection.
  • Thumbnail Image
    Item
    Open Access
    Optimal sizing of hybrid renewable energy systems for rural electrification
    (2011) Coppez, Gabrielle; Chowdhury, SP; Chowdhury, S
    This project has the objective of creating a tool for feasibility assessment and recommendations of sizing of hybrid renewable energy systems in rural areas in South Africa. This involves the development of a tool which would analyse information input about the climate of the area and the load demand.
  • Thumbnail Image
    Item
    Open Access
    Technical and economic analysis of parabolic trough concentrating solar thermal power plant
    (2012) Kariuki, Kibaara Samuel; Chowdhury, S; Chowdhury, SP
    This thesis reports on the technical and economic analysis of wet and dry cooling technologies of parabolic trough CSTP plant. This was done through modelling and simulation of a standalone and grid connected parabolic trough using the System Advisor Model (SAM).
  • Thumbnail Image
    Item
    Open Access
    The Nainital-Cape Survey: IV. A search for pulsational variability in 108 chemically peculiar stars⋆
    (2016) Joshi, S; Martinez, P; Chowdhury, S; Chakradhari, N K; Joshi, Y C; van Heerden, P; Medupe, T; Kumar, Y B; Kuhn, R B
    Context. The Nainital-Cape Survey is a dedicated ongoing survey program to search for and study pulsational variability in chemically peculiar (CP) stars to understand their internal structure and evolution.