Conventional power system stabilisers (PSS) are designed to eliminate poorly damped, low frequency power oscillations that occur between remote generating pools or power stations, due to different types and settings of the automatic voltage regulators at different power stations. The supplementary control of the PSS is exerted on the power system through a generator's excitation system to which the PSS is attached. In order to design these conventional power system stabilisers , requires accurate system data and an in-depth knowledge of classical control theory. This thesis investigates the use of an intelligent, non-linear PSS that utilises fuzzy logic techniques. Others have proposed the concept of such a PSS, since it does not require accurate system data. This thesis describes the basic aspects of power system stability . Thereafter the methods of modelling synchronous machines in a multi-machine power system are presented. The sample power system being studied and the simulation packages used in the investigations are introduced and the methods involved to design and tune a conventional power system stabiliser using classical control theory and design methods proposed by others, are discussed. The general concept of fuzzy logic is introduced and the application of fuzzy logic techniques to controller design is explained. Using the principles of fuzzy logic controller design, a fuzzy logic power system stabiliser utilising 9 rules is designed and tuned for the multi-machine power system under investigation. The fuzzy logic stabiliser is then applied to a synchronous motor in a pump storage scheme. Previous work has applied fuzzy logic stabilisers only to synchronous generators . To further compare the performance of the 9 rule fuzzy stabiliser, a 49 rule stabiliser developed by other researchers, and adapted to operate on the synchronous motor, is evaluated. Computer simulated results of each of the stabiliser's performances are presented. The results of the 9 rule fuzzy stabiliser are compared with the performance of a conventional linear stabiliser as well as with a 49 rule fuzzy stabiliser. The robustness properties of the fuzzy stabilisers are evaluated. The results further prove that with proper membership function selection, a simple fuzzy stabiliser that demands very little computational overheads can be achieved to provide adequate system damping. / Thesis (M.Sc. Eng.)-University of Natal, Durban, 2003.

This thesis investigates the design of damping controllers to alleviate the problem of low frequency electro-mechanical oscillations in power systems. The operating point and network parameters of power systems are continually changing, resulting in changes in system dynamics. The conventional controller design methodology has therefore come under increasing scrutiny for its lack of considerations for robustness. The thesis first outlines the conventional design of a power system stabilizer (PSS) and then applies two robust techniques (Hoo and Quantitative Feedback Theory, QFT) to the design problem. The single machine infinite bus (SMIB) model is used to illustrate the procedure for all three design techniques. The final design is undertaken to illustrate the more important problem of robust multi-machine PSS design using QFT. The design requires linearised models of the multi-machine system. A brief discussion is given on how these can be obtained. An introduction to decentralized control design in QFT is included to support the multi-machine design. Chapter three proceeds through the design steps required to generate a conventional PSS. The technique is shown to be simple for a given set of operating conditions. The controller is shown to be adequately robust over the given set of operating conditions albeit not by design. Chapter four introduces a design technique that directly addresses robustness issues during the controller design. For a restricted range of operating conditions the designed controller demonstrates the desired robustness and performance characteristics. The inherent difficulties with Hoo in PSS design become more apparent as the operating range is extended. Chapter five introduces the second robust controller design technique. QFT is shown to be more adept at dealing with increased operating ranges and changing specifications in the single-machine infinite-bus case. The controller is easy to generate and performs well over the entire range of operating conditions. QFT is also applied to the controller design for a four-machine study system. The design is a marginally more complex than in the single machine case but is still easily accomplished. This thesis confirms previous attempts at solving the design problem using the methods outlined above. The performance of all controllers is assessed for small and large disturbances using non-linear time domain simulations with models developed using PSCAD/EMTDC and MATLAB. / Thesis (M.Sc.)-University of Natal,Durban, 2002.

The present thesis tackles the problem of on-line steady state security assessment in electric power transmission networks. The contingencies examined include generation shift as well as line (transformer) outages. / The methodology developed is Pattern Recognition-motivated although not entirely within the frame of traditional statistical Pattern Recognition. / Due to the fact that training samples are rather expensive to obtain in electric power engineering, our first concern was to develop and implement algorithms carrying out the task of intelligently acquiring training points. It is found that these algorithms, permit to substantially reduce the amount of off-line computational effort while, at the same time, the coherency and impartiality of the information contained in the training sets is enhanced. / A new scheme for security assessment (equally applicable for real time security screening) was developed based on the concept of the hyperellipsoids of confidence. It is shown that by proper utilization of the hyperellipsoids of confidence, uncertainty in real time decision making (directly related to the misclassification error) is circumvented. The results of the new methodology were verified by full scale ac simulations. / Finally, the usefulness and potential applicability of the new scheme is demonstrated for EHV equivalents. Its merits are simplicity and reliability in real time environment.

The presence of inter-area oscillations has long affected stability constraints, and therefore, limited the power transfer capacity of interconnected power systems. Adequate damping of these inter-area oscillations is, thus, necessary to secure system operation and ensure system reliability while increasing power transfers. Power system stabilizers (PSS) are the most common devices used to enhance the damping of such oscillations. Many studies have demonstrated that PSSs using remote signals may perform better than using local signals. The advent of phasor measurement units (PMU) makes remote or wide-area signals become available, which enables various important applications. Of particular interest is wide-area damping control (WADC), which aims to utilize remote or wide-area measurements to damp the inter-area oscillations. However, two main challenges in WADC design are (1) feedback controller input signal selection (which PMU signal is best to use?), and (2) latency (which is inherent in the transmission of the measurements) considerations. In response to the first challenge, this thesis proposes a concept called dominant inter-area oscillation path, which serves to pinpoint a set of candidate signals that can be used as the feedback controller inputs by locating the interconnected corridors where the inter-area modal contents are the most observable. Derivation, identification, and use of the dominant inter-area oscillation paths are demonstrated throughout the thesis. Extensive analysis on the relationships between the proposed set of signals and system properties regarding stability and robustness is presented. To tackle the second challenge, the impacts of time delays on the system performance when using the dominant path signals are investigated. To date, several studies have proposed different control design methods using various oscillation dampers to design WADC. Nevertheless, neither a systematic method nor a concept that encompasses fundamental knowledge on power system dynamics has yet been offered. The objective of this thesis is, thus, to propose an analytical framework based on the dominant path concept which is built upon fundamental principles for feedback controller input signal selection in WADC. With this framework, a proper and systematic approach is developed. The proposed method allows to select appropriate signals and use them to effectively mitigate the inter-area oscillations that constrain power transfer capacity and affect system stability. / <p>QC 20150414</p>

The rotor shaft of a synchronous machine can experience severe mechanical stress due to torque pulsations during a pole-slip condition. All pole-slip protection relays currently on the market use the impedance pole-slip protection method to detect a pole-slip. No commercial relay currently available can predict accurately when a generator is about to experience a damaging pole-slip. All the relays will only trip a generator after it has pole-slipped one or more times. Severe mechanical damage could be caused to a machine after only one pole-slip. It is therefore essential to enhance pole-slip protection relays to such an extent that it can trip a generator before it pole slips. The proposed pole-slip protection function must predict when a generator will become unstable during a network fault. As soon as instability is predicted, the generator must be tripped before the fault is cleared to avoid damaging post-fault torque effects. Conventional impedance pole-slip protection methods are are also discussed and the shortcomings of impedance pole-slip protection are investigated. The new pole-slip protection function was designed by using PSCAD. Detailed PSCAD simulations on different network configurations proved that the new pole-slip protection function will trip a generator before a damaging pole-slip occurs. The new pole-slip protection function was also implemented on an ABB REM543 multifunctional protection relay and tested on a RTDS. The concept of the new pole-slip function was successfully demonstrated on the protection relay. The operation of conventional impedance scheme relays was compared with the proposed pole-slip function for different fault conditions. Although the new pole-slip protection function is more complex than the existing impedance functions, it was concluded that similar skills are required to test and commission the new protection function. The new pole-slip function outperforms the impedance protection methods, since the new protection function can trip the generator before it pole-slips. / PhD (Electrical Engineering), North-West University, Potchefstroom Campus, 2011

The rotor shaft of a synchronous machine can experience severe mechanical stress due to torque pulsations during a pole-slip condition. All pole-slip protection relays currently on the market use the impedance pole-slip protection method to detect a pole-slip. No commercial relay currently available can predict accurately when a generator is about to experience a damaging pole-slip. All the relays will only trip a generator after it has pole-slipped one or more times. Severe mechanical damage could be caused to a machine after only one pole-slip. It is therefore essential to enhance pole-slip protection relays to such an extent that it can trip a generator before it pole slips. The proposed pole-slip protection function must predict when a generator will become unstable during a network fault. As soon as instability is predicted, the generator must be tripped before the fault is cleared to avoid damaging post-fault torque effects. Conventional impedance pole-slip protection methods are are also discussed and the shortcomings of impedance pole-slip protection are investigated. The new pole-slip protection function was designed by using PSCAD. Detailed PSCAD simulations on different network configurations proved that the new pole-slip protection function will trip a generator before a damaging pole-slip occurs. The new pole-slip protection function was also implemented on an ABB REM543 multifunctional protection relay and tested on a RTDS. The concept of the new pole-slip function was successfully demonstrated on the protection relay. The operation of conventional impedance scheme relays was compared with the proposed pole-slip function for different fault conditions. Although the new pole-slip protection function is more complex than the existing impedance functions, it was concluded that similar skills are required to test and commission the new protection function. The new pole-slip function outperforms the impedance protection methods, since the new protection function can trip the generator before it pole-slips. / PhD (Electrical Engineering), North-West University, Potchefstroom Campus, 2011

Orust Kretsloppsakademi is a nonprofit organisation, with a goal of annually generate the same amount of electrical energy that is consumed. Orust is an island on the west coast of Sweden, north of Gothenburg. The population of 15 000 reaches 40 000 during summer, due to the large amount of vacationer. The total electricity demand is 174 GWh a year with a maximum power need of 32 MW. This report presents an analysis for the plausibility of their plan and from a power system stability perspective, the effects on the electrical grid. The conclusion is that the restraints for development of power generation from wind, solar and wave generation, are the power systems capability to transfer power, primarily in the transformers of the grid. Various actions, such as constraints of power output at certain times, and clever location of generation facilities, reduces the utilisation rate of the line segments. In order to substantially decrease the utilisation rate of the line segments, the actions need to be combined. Executed simulations showed that Orust needs to be provided with reactive power, even if Orust is self-sufficient of active power, through its connection to the Swedish power system. The need for reactive power decreased when the feeding transformer allowed a reduced voltage in the regional network. Additionally, generation of reactive power could further increase the possibility for Orust to become self-sufficient on electricity generation.

Generators in an interconnected power system normally remain in synchronism with one another. However, severe faults that lead to loss of heavily loaded generators or large load blocks can cause oscillations in the generator rotor angles that are large enough to result in a pole slip in which a generator, or a group of generators, loses synchronism with the rest of the power system. When a generator pole slips and falls out-of-step with the power system, the generator and system voltages sweep past one another at a slip frequency, producing a pulsating current, which can be greater than a three-phase fault at the generator terminals. An out-of-step generator should therefore be isolated from the power system to prevent damage to the generator, generator transformer and the turbine. This dissertation analyses the dynamic performance of generator-pole-slip protection during various stable and unstable power swing events. For the purpose of this dissertation, the Siemens 7UM622 machine protection relay is used to test the response of generator-pole-slip protection. This is done in two stages, firstly, within the DigSilent PowerFactory software by modelling the Siemens 7UM622 relay and then applying simulated time domain stable and unstable power swing conditions to the relay model to evaluate its response. Secondly, the actual 7UM622 hardware relay is injected with currents and voltages, which are produced during the time domain pole-slip simulations to determine if the relay hardware device operates in accordance with the Siemens relay technical manual. The power system analysed in the dissertation was heavily interconnected and a generator pole slip was rather unlikely. If an unlikely generator pole slip were to occur when the system is operating in a normal configuration (all power station outgoing feeders in service), the generator-pole-slip protection was able to detect and disconnect the generator after a single pole-slip cycle. v The critical fault clearing time decreases when an outgoing power station feeder is out of service (n-1 contingency) and therefore the probability of a generator pole slip increases. If a generator pole slip occurs when operating the network under a n-1 contingency, the pole-slip system electrical centre is usually located within the transmission network. In practice, the generator-pole-slip protection settings that are implemented at the power station do not reach into the transmission network (zone 2 disabled). Therefore, if a pole slip were to occur under a n-1 contingency, the generator-pole-slip protection would not be able to detect this condition. The zone 2 generator-pole-slip protection should rather reach into the transmission network, but the trip should only be issued after the third or fourth pole-slip cycle to allow the transmission line out-of-step protection sufficient time to separate the network into islands. The pole-slip function of the Siemens 7UM622 relay model within DigSilent PowerFactory operated in accordance with the Siemens relay technical manual and can be used in future to optimise and test generator-pole-slip protection settings. In the majority of cases, the Siemens 7UM622 relay hardware device operated in accordance with the Siemens relay technical manual. The only time that the relay operated incorrectly was when the measured impedance trajectory of a three-phase fault lingers on the inside and outside edge of the pole-slip impedance characteristic before exiting the pole-slip impedance characteristic. The stable and unstable power swing COMTRADE files that were generated for the tests performed in this dissertation can be used in future to test the generator-pole-slip protection at Kendal power station since it is rather difficult to test the pole-slip protection function properly without a COMTRADE file. / Thesis (M.Sc.Eng.)-University of KwaZulu-Natal, Durban, 2013.

Thesis (PhD) -- University of South Australia, 1993

Bibliography: leaves 238-248 / xxix, 248 leaves : ill. ; 30 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / This thesis is concerned with the design and coordination of linear, fixed parameter controllers for the purpose of enhancing the dynamic performance of a multimachine power system. The studies are based on linear control theory and involve state space analysis, modal analysis, eigenanalysis and conventional frequency response techniques. The emphasis is on the small-signal performance of the system / Thesis (Ph.D.)--University of Adelaide, Dept. of Electrical and Electronic Engineering, 1997?