Stability studies of Sasol Synfuels Transmission and Distribution network under fault conditions and N-1 supply contingency

Includes abstract.Includes bibliographical references (leaves 129-130).The aim of the work is to perform a transient stability analysis of the Sasol Synfuels Transmission and Distribution network when the power system is subjected to fault conditions and N-1 supply contingency conditions. The work provides an overview of the problem of power system stability as well as discussing issues related to the problem of power system stability; which include power system control and power system modelling

Setting frequency relays and voltage relays to protect synchronous distributed generators against islanding and abnormal frequencies and voltages

This study concerns frequency relays and voltage relays applied to the protection of synchronous distributed generators operating in reactive power control mode without a frequency regulation function. The effect of active and reactive powers combination, load power factor, and reactive power imbalance are investigated for their implication for the anti-islanding setting of the frequency relay. Results reveal that the effect of these factors must be considered when setting the relay for islanding detection. For the voltage relay, results reveal that the effect of active and reactive powers combination, load power factor, and active power imbalance must be considered when setting the relay for islanding detection. The effect of multi-stage tripping on the frequency relay ability to detect island was also investigated. Results show that multistage tripping can improve the anti-islanding performance of the frequency relay.Electrical EngineeringM. Tech. (Electrical Engineering

Loss of mains detection and amelioration on electrical distribution networks

Power system islanding is gaining increasing interest as a way to maintain power supply continuity. However, before this operation become viable, the technical challenges associated with its operation must first be addressed. A possible solution to one of these challenges, out-of synchronism reclosure, is by running the islanded system in synchronism with the mains whilst not being electrically connected. This concept, known as 'synchronous islanded operation' avoids the danger of out-of-synchronism reclosure of the islanded system onto the mains. The research in this thesis was based on the concepts presented in [1-3] and specifically applied to multiple-DG island scenarios. The additional control challenges associated with this scenario are identified and an appropriate control scheme, more suited for the operation of multiple-DG synchronous islands, is proposed. The results suggest that multiple-DG synchronous islanded operation is feasible, but a supervisory controller is necessary to facilitate the information exchange within the islanded system and enable stable operation.For maximum flexibility, the synchronous island must be capable of operating with a diversity of generation. The difficulties become further complicated when some or all of the generation consists of intermittent sources. The performance of the proposed control scheme in the presence of a significant contribution of renewable sources within the island is investigated. Two types of wind technologies were developed in PSCAD/EMTDC for this purpose, they are a fixed speed induction generator (FSIG) based wind farm and a doubly-fed induction generator (DFIG) based wind farm. The results show that although synchronous islanded operation is still achievable, the intermittent output has an adverse effect on the control performance, and in particular limits the magnitude of disturbances that can happen in the island without going beyond the relaxed synchronisation limits of ±60o.Energy storage is proposed as a way to reduce the wind farm power variation and improve phase controller response. A supplementary control is also proposed such that DFIG contributes to the inertial response. The potential of the proposed scheme (energy storage + supplementary control) is evaluated using case studies. The results show massive improvement to the load acceptance limits, even beyond the case where no wind farm is connected. The benefit of the proposed scheme is even more apparent as the share of wind generated energy in the island grows.EThOS - Electronic Theses Online ServiceThe Engineering and Physical Sciences Research CouncilSchool of Electrical and Electronic EngineeringGBUnited Kingdo

Impact of intergrating teebus hydro power on the unbalanced distribution MV network

Small hydro power sources have been identified as one of the renewable energy technologies that the South African government is focusing on in order to generate more electricity from renewable/independent resources. Due to the low carbon output of most renewable energy technologies and the carbon intensive power generation technologies that are currently being used in South Africa e.g. Hydro, coal, gas, and etc. further pressure is increasing to incorporate cleaner forms of generation. In 2002 a study focusing on the hydropower potential was compiled providing an assessment according to conventional and unconventional possibilities for all the provinces. Nowadays, the power electricity demand is growing fast and one of the main tasks for power engineers is to generate electricity from renewable energy sources to overcome this increase in the energy consumption and at the same time reduce environmental impact of power generation. Eskom Distribution Eastern Cape Operating Unit (ECOU) was requested to investigate the feasibility of connecting a small hydro power scheme located in the Teebus area in the Eastern Cape. The Eastern Cape in particular, was identified as potentially the most productive area for small hydroelectric development in South Africa for both the grid connected and off grid applications. These network conditions are in contrast to the South African electricity network where long radial feeders with low X/R ratios and high resistance, spanning large geographic areas, give rise to low voltages on the network. Practical simulation networks have been used to test the conditions set out in the South African Grid Code/NERSA standard and to test the impact of connecting small hydro generation onto the unbalanced distribution network. These networks are representative of various real case scenarios of the South African distribution network. Most of the findings from the simulations were consistent with what was expected when comparing with other literatures. From the simulation results it was seen that the performance of the variable speed generators were superior to that of the fixed speed generators during transient conditions. It was also seen that the weakness of the network had a negative effect on the stability of the system. It is also noted that the stability studies are a necessity when connecting the generators to a network and that each case should be reviewed individually. The fundamental cause of voltage instability is identified as incapability of combined distribution and generation system to meet excessive load demand in either real power or reactive power form

Design, Implementation and Evaluation of a Microgrid in Island and Grid Connected Modes with a Fuel Cell Power Source

The ability to connect a microgrid to the grid is an important step in the development and evolution of the modern power system. The principle objectives of this research are (1) to simulate a simple microgrid consisting of a PEM hydrogen fuel cell, load and connection to the grid and (2) to evaluate the resulting microgrid control system on a corresponding experimental microgrid. The microgrid simulation demonstrated that the control algorithms can operate the microgrid in both islanded (VSC with voltage and frequency regulation) and grid connected (VSC with current control for power transfer). The experimental laboratory microgrid was constructed and operated in real-time performing its black start and managed transitions between island and grid connected modes of operation. The synchronization method adjusted the island microgrid to become in phase with the grid and tracked well under steady state and load changing conditions. The synchronization process brought the island in phase with the grid within 400 ms. Passive island detection was demonstrated with the restoration to grid operation. The grid connected voltage and current THD were under 1%