Continuous Monitoring of Neutral Grounding Resistors and Reactors

Electrical power system components are designed three-phase balanced and symmetric with the internal connection of wye or delta. The common point of the wye-connected equipment, which is called neutral, is impedance grounded for many reasons such as fault ride through by controlling transient overvoltages, and limiting the ground overcurrents. Depending on the application, different neutral impedance grounding methods exist that employ resistors or reactors with/without neutral grounding transformers. These apparatuses are known as Neutral Grounding Devices (NGD). The most well-known sort of NGDsarethe Neutral Grounding Resistor (NGR) and Neutral Grounding Reactor (NGL) which are the main focus of this research work. As said, NGDs provide many benefits; however, they fail due to many reasons such as corrosion, lightning, and extended service life. Upon this failure, the advantages of impedance grounding are replaced by disadvantages of the ungrounded or solidly grounded traditional systems. Consequences of such a failure are the false sense of security, ungrounded system, transient overvoltages, overcurrents, line-to-ground voltage test non-safety, and so on. In order to prevent these issues, the intactness and integrity of the neutral-to-ground circuit shall be ensured. However, this cannot be done easily since the neutral-to-ground circuit is dead or de-energized during the steady-state condition. However, there has to be a continuous and online monitor, which without it there is no guarantee or indication that these apparatuses have failed. That is why the Canadian Electric Code (CEC) mandates monitoring of the neutral-to-ground circuit in industrial and commercial networks. Accordingly, this research work first reviews the existing monitoring methods to understand the fundamentals, and performance of these techniques. The performed literature survey results in a conceptual classification of the existing methods into three categories called passive, active, and passive-active. This part of the carried-out research highlights the advantages and disadvantages of the methods on one hand, and the evolution trend of the methods on the other. It also reveals that all of the existing methods suffer from one shared issue which is the hard-to-achieve continuous monitoring. In fact, they cannot provide continuous or uninterrupted operation in all system conditions, i.e., normal, faulted, and de-energized. It is this major shortcoming of the literature which motivates towards making a difference. Therefore, the mission is to resolve this issue relying on the existing measurement instruments and protection installations. As the results, three new or enhanced methods are achieved. The first technique is a cost-effective combination of two existing techniques resulted in a better performance. The performance of this proposed method is comprehensively studied using software analysis, and a fabricated prototype of the invented mechanism for full-range neutral voltage measurement. The resulted method provides reliable monitoring during both faulted and unfaulted conditions of the power system which is the most prominent advantage of the proposed technique since none of the existing methods, with the same measurements, provide the such a performance. The second proposed technique is an economical solution that employs the third harmonic of neutral and residual voltages for monitoring the NGR installed at the neutral of the unit-connected generators. The proposed technique is comprehensively studied including further hardware validations using an available industrial generator protective relay. The required measurement instruments and protection infrastructures are readily available which means that the proposed method could be implemented with no additional cost. In fact, the proposed method could be easily incorporated into the core of the existing digital protective relays. Lastly, the third technique employs an existing sub-harmonic injection based generator stator ground protection for monitoring the neutral-to-ground circuit of the same generator, which is equipped with either the neutral grounding resistor or neutral grounding reactor. This alternative is also a money-saving solution since it only demands a current sensor to measure the injected current. It is also easily retrofitted to installed digital protective relays. The other advantage of this proposed method is its functionality in de-energized condition of the power system besides its reliable performance in both faulted and unfaulted operation conditions. It is this one last accomplishment that brings the mission to completion

Studies in Electrical Machines & Wind Turbines associated with developing Reliable Power Generation

The publications listed in date order in this document are offered for the Degree of Doctor of Science in Durham University and have been selected from the author’s full publication list. The papers in this thesis constitute a continuum of original work in fundamental and applied electrical science, spanning 30 years, deployed on real industrial problems, making a significant contribution to conventional and renewable energy power generation. This is the basis of a claim of high distinction, constituting an original and substantial contribution to engineering science

Renewable Energy

Renewable Energy is energy generated from natural resources - such as sunlight, wind, rain, tides and geothermal heat - which are naturally replenished. In 2008, about 18% of global final energy consumption came from renewables, with 13% coming from traditional biomass, such as wood burning. Hydroelectricity was the next largest renewable source, providing 3% (15% of global electricity generation), followed by solar hot water/heating, which contributed with 1.3%. Modern technologies, such as geothermal energy, wind power, solar power, and ocean energy together provided some 0.8% of final energy consumption. The book provides a forum for dissemination and exchange of up - to - date scientific information on theoretical, generic and applied areas of knowledge. The topics deal with new devices and circuits for energy systems, photovoltaic and solar thermal, wind energy systems, tidal and wave energy, fuel cell systems, bio energy and geo-energy, sustainable energy resources and systems, energy storage systems, energy market management and economics, off-grid isolated energy systems, energy in transportation systems, energy resources for portable electronics, intelligent energy power transmission, distribution and inter - connectors, energy efficient utilization, environmental issues, energy harvesting, nanotechnology in energy, policy issues on renewable energy, building design, power electronics in energy conversion, new materials for energy resources, and RF and magnetic field energy devices

A novel assessment of unintentional islanding operations in distribution networks

This thesis aims to investigate an unexpected islanding operation (IO) which has been identified in a real distribution network. The process of recording and processing the data obtained from the field measurements in the distribution network (DN) has been the starting point of this research. It has to be underlined that this IO raised a problem and became a major challenge for the distribution operator. Therefore, the aim of this thesis is twofold; solving a real problem as well as further enhance the current research studies about IOs in DNs. IOs have been object of study during the recent years due to the rapid proliferation of the distributed generation (DG) within the so-called smart grids (SGs). Commonly, the power of these DG resources ranges between hundreds of kW and few MW and are allocated at either low voltage or medium voltage levels. One of the significant issues that these resources are raising is, undoubtedly, the IOs. These situations occur when a portion of the grid operates in parallel with the main grid following a disconnection. Thereby IOs, where the DG is energising the grid after a CB opening, must be identified and tripped in the minimum time possible. Failure to do so, the list of hurdles may include; power quality (PQ) disturbances (e.g., frequency and voltage out of range), a safety hazard for the network personnel or out-of-phase reclosings. That is the reason why the research towards the anti-islanding protection methods has elicited great interest. Fundamentally, the substantial improvement of this thesis lies in the fact that, in this IO, there are no DG resources, but large induction motors. In fact, the grid remains energised after the CB disconnection due to the induction motors (IMs) which transiently, act as generators. The island begins with the CB operation and ends when the CB recloses the circuit to restore the electrical supply. This rapid reclosing operation is widely adopted in DNs to avoid manual operations in self-extinguished faults and typically ranges between 0.5 and 1s. Given the fact that usually IOs are originated in the presence of DG, indeed, this IO is utterly unexpectedly for the DSO. Due to the phenomenon mentioned above, the specific goals of this thesis are described down below: 1. The first goal of this thesis focuses on developing a model suitable for validation purposes. To make a proper model validation, the simulations results obtained with this model will be compared with those obtained from field measurements. Thus, once the model has been validated, a thorough investigation regarding the most influential factors will be carried out. 2. The second goal of this thesis falls within the scope of the PQ. During the IO mentioned above, a new voltage sag topology is observed. Consequently, the efforts will be focused on modelling this new type of sag. 3. The third goal of this thesis emerges from the protective point of view. Once the IO has been defined and characterised, the need for identifying and preventing it becomes the main concern. In such a way, the third pillar of the thesis is targeted at implementing a suitable tool to prevent this particular IO. Besides, this new tool will be compared with the currently available methods for ID developed for scenarios with DG.Aquesta tesi te com a objectiu investigar una operació en illa no intencional, que ha set identificada en una xarxa de distribució real. El procés de registre i processament de les dades obtingudes a partir de les mesures de camp en la xarxa de distribució, ha estat el punt de partida d’aquesta investigació. Cal subratllar que aquesta operació en illa va plantejar un problema i es va convertir en un repte important per l’operador de distribució. Per tant, l'objectiu d'aquesta tesi és doble; resoldre un problema real, així com millorar els estudis de recerca actuals sobre les illes no intencionals en xarxes de distribució elèctrica. El fenomen de les illes dins una xarxa elèctrica, han estat objecte d’estudi durant els darrers anys a causa de la ràpida proliferació de la generació distribuïda. Habitualment, la potència d’aquests recursos distribuïts oscil·la entre centenars de kW i pocs MW i s’assignen a nivells de baixa tensió o mitja tensió. Una de les qüestions importants que plantegen aquests recursos és, sens dubte, les illes. Aquestes situacions es produeixen quan una part de la xarxa elèctrica funciona en paral·lel amb la xarxa principal després d’una desconnexió. Per això, les illes no intencionals es donen quan la generació distribuïda energitza la xarxa després de la obertura d’un interruptor. Principalment, l’objectiu es identificar aquesta situació i desconnectar dites fonts en el mínim temps possible. En el cas de que això no succeeixi, els següents disturbis poden produir-se; pertorbacions de la qualitat de potència (PQ) (per exemple, freqüència i tensió fora del rang), un perill per a la seguretat del personal de la xarxa o bé reconnexions fora de fase. Aquesta és la raó per la qual la investigació vers els mètodes de protecció “anti-islanding” han despertat un gran interès. Essencialment, la millora substancial d’aquesta tesi rau en el fet que, en aquesta illa, no hi ha recursos energètics distribuïts, sinó grans motors d’inducció. Així, la xarxa elèctrica continua energitzada després de la desconnexió del interruptor a causa dels motors d’inducció, que actuen de forma transitòria com a generadors. L’illa comença amb l’obertura del interruptor i finalitza quan aquest tanca el circuit per restablir el subministrament elèctric. Aquesta operació de reconnexió ràpid es freqüent en xarxes de distribució per evitar operacions manuals en faltes temporals i generalment oscil·la entre 0,5 i 1s. Tenint en compte que generalment les illes tenen l'origen en presència de generació distribuïda , realment, la illa elèctrica objecte d’aquesta tesi és inesperada per l’operador de distribució. A causa del fenomen esmentat anteriorment, els objectius específics d'aquesta tesi es descriuen a continuació: 1. El primer objectiu d'aquesta tesi se centra a desenvolupar un model adequat per la validació. Per fer una validació adequada del model, es compararan els resultats de les simulacions obtinguts amb aquest model amb els obtinguts de les mesures de camp. Així, un cop validat el model, es durà a terme una investigació completa sobre els factors més influents. 2. El segon objectiu d'aquesta tesi entra dins de l'àmbit d'aplicació del PQ. Durant l’esmentada illa, s’observa una nova topologia de forat de tensió. En conseqüència, els esforços se centraran en modelar aquest nou tipus de forat. 3. El tercer objectiu d'aquesta tesi s’emmarca en el punt de vista de proteccions. Un cop definida i caracteritzada l’illa, la necessitat d’identificar-la i prevenir-la esdevé la principal preocupació. D’aquesta manera, el tercer pilar de la tesi té com a objectiu la implementació d’una eina adequada per prevenir aquesta particular illa. A més, es compararà aquesta nova eina amb els actuals mètodes utilitzats per a identificar les illes en escenaris amb generació distribuïda

A novel assessment of unintentional islanding operations in distribution networks

This thesis aims to investigate an unexpected islanding operation (IO) which has been identified in a real distribution network. The process of recording and processing the data obtained from the field measurements in the distribution network (DN) has been the starting point of this research. It has to be underlined that this IO raised a problem and became a major challenge for the distribution operator. Therefore, the aim of this thesis is twofold; solving a real problem as well as further enhance the current research studies about IOs in DNs. IOs have been object of study during the recent years due to the rapid proliferation of the distributed generation (DG) within the so-called smart grids (SGs). Commonly, the power of these DG resources ranges between hundreds of kW and few MW and are allocated at either low voltage or medium voltage levels. One of the significant issues that these resources are raising is, undoubtedly, the IOs. These situations occur when a portion of the grid operates in parallel with the main grid following a disconnection. Thereby IOs, where the DG is energising the grid after a CB opening, must be identified and tripped in the minimum time possible. Failure to do so, the list of hurdles may include; power quality (PQ) disturbances (e.g., frequency and voltage out of range), a safety hazard for the network personnel or out-of-phase reclosings. That is the reason why the research towards the anti-islanding protection methods has elicited great interest. Fundamentally, the substantial improvement of this thesis lies in the fact that, in this IO, there are no DG resources, but large induction motors. In fact, the grid remains energised after the CB disconnection due to the induction motors (IMs) which transiently, act as generators. The island begins with the CB operation and ends when the CB recloses the circuit to restore the electrical supply. This rapid reclosing operation is widely adopted in DNs to avoid manual operations in self-extinguished faults and typically ranges between 0.5 and 1s. Given the fact that usually IOs are originated in the presence of DG, indeed, this IO is utterly unexpectedly for the DSO. Due to the phenomenon mentioned above, the specific goals of this thesis are described down below: 1. The first goal of this thesis focuses on developing a model suitable for validation purposes. To make a proper model validation, the simulations results obtained with this model will be compared with those obtained from field measurements. Thus, once the model has been validated, a thorough investigation regarding the most influential factors will be carried out. 2. The second goal of this thesis falls within the scope of the PQ. During the IO mentioned above, a new voltage sag topology is observed. Consequently, the efforts will be focused on modelling this new type of sag. 3. The third goal of this thesis emerges from the protective point of view. Once the IO has been defined and characterised, the need for identifying and preventing it becomes the main concern. In such a way, the third pillar of the thesis is targeted at implementing a suitable tool to prevent this particular IO. Besides, this new tool will be compared with the currently available methods for ID developed for scenarios with DG.Aquesta tesi te com a objectiu investigar una operació en illa no intencional, que ha set identificada en una xarxa de distribució real. El procés de registre i processament de les dades obtingudes a partir de les mesures de camp en la xarxa de distribució, ha estat el punt de partida d’aquesta investigació. Cal subratllar que aquesta operació en illa va plantejar un problema i es va convertir en un repte important per l’operador de distribució. Per tant, l'objectiu d'aquesta tesi és doble; resoldre un problema real, així com millorar els estudis de recerca actuals sobre les illes no intencionals en xarxes de distribució elèctrica. El fenomen de les illes dins una xarxa elèctrica, han estat objecte d’estudi durant els darrers anys a causa de la ràpida proliferació de la generació distribuïda. Habitualment, la potència d’aquests recursos distribuïts oscil·la entre centenars de kW i pocs MW i s’assignen a nivells de baixa tensió o mitja tensió. Una de les qüestions importants que plantegen aquests recursos és, sens dubte, les illes. Aquestes situacions es produeixen quan una part de la xarxa elèctrica funciona en paral·lel amb la xarxa principal després d’una desconnexió. Per això, les illes no intencionals es donen quan la generació distribuïda energitza la xarxa després de la obertura d’un interruptor. Principalment, l’objectiu es identificar aquesta situació i desconnectar dites fonts en el mínim temps possible. En el cas de que això no succeeixi, els següents disturbis poden produir-se; pertorbacions de la qualitat de potència (PQ) (per exemple, freqüència i tensió fora del rang), un perill per a la seguretat del personal de la xarxa o bé reconnexions fora de fase. Aquesta és la raó per la qual la investigació vers els mètodes de protecció “anti-islanding” han despertat un gran interès. Essencialment, la millora substancial d’aquesta tesi rau en el fet que, en aquesta illa, no hi ha recursos energètics distribuïts, sinó grans motors d’inducció. Així, la xarxa elèctrica continua energitzada després de la desconnexió del interruptor a causa dels motors d’inducció, que actuen de forma transitòria com a generadors. L’illa comença amb l’obertura del interruptor i finalitza quan aquest tanca el circuit per restablir el subministrament elèctric. Aquesta operació de reconnexió ràpid es freqüent en xarxes de distribució per evitar operacions manuals en faltes temporals i generalment oscil·la entre 0,5 i 1s. Tenint en compte que generalment les illes tenen l'origen en presència de generació distribuïda , realment, la illa elèctrica objecte d’aquesta tesi és inesperada per l’operador de distribució. A causa del fenomen esmentat anteriorment, els objectius específics d'aquesta tesi es descriuen a continuació: 1. El primer objectiu d'aquesta tesi se centra a desenvolupar un model adequat per la validació. Per fer una validació adequada del model, es compararan els resultats de les simulacions obtinguts amb aquest model amb els obtinguts de les mesures de camp. Així, un cop validat el model, es durà a terme una investigació completa sobre els factors més influents. 2. El segon objectiu d'aquesta tesi entra dins de l'àmbit d'aplicació del PQ. Durant l’esmentada illa, s’observa una nova topologia de forat de tensió. En conseqüència, els esforços se centraran en modelar aquest nou tipus de forat. 3. El tercer objectiu d'aquesta tesi s’emmarca en el punt de vista de proteccions. Un cop definida i caracteritzada l’illa, la necessitat d’identificar-la i prevenir-la esdevé la principal preocupació. D’aquesta manera, el tercer pilar de la tesi té com a objectiu la implementació d’una eina adequada per prevenir aquesta particular illa. A més, es compararà aquesta nova eina amb els actuals mètodes utilitzats per a identificar les illes en escenaris amb generació distribuïda

A novel assessment of unintentional islanding operations in distribution networks

This thesis aims to investigate an unexpected islanding operation (IO) which has been identified in a real distribution network. The process of recording and processing the data obtained from the field measurements in the distribution network (DN) has been the starting point of this research. It has to be underlined that this IO raised a problem and became a major challenge for the distribution operator. Therefore, the aim of this thesis is twofold; solving a real problem as well as further enhance the current research studies about IOs in DNs. IOs have been object of study during the recent years due to the rapid proliferation of the distributed generation (DG) within the so-called smart grids (SGs). Commonly, the power of these DG resources ranges between hundreds of kW and few MW and are allocated at either low voltage or medium voltage levels. One of the significant issues that these resources are raising is, undoubtedly, the IOs. These situations occur when a portion of the grid operates in parallel with the main grid following a disconnection. Thereby IOs, where the DG is energising the grid after a CB opening, must be identified and tripped in the minimum time possible. Failure to do so, the list of hurdles may include; power quality (PQ) disturbances (e.g., frequency and voltage out of range), a safety hazard for the network personnel or out-of-phase reclosings. That is the reason why the research towards the anti-islanding protection methods has elicited great interest. Fundamentally, the substantial improvement of this thesis lies in the fact that, in this IO, there are no DG resources, but large induction motors. In fact, the grid remains energised after the CB disconnection due to the induction motors (IMs) which transiently, act as generators. The island begins with the CB operation and ends when the CB recloses the circuit to restore the electrical supply. This rapid reclosing operation is widely adopted in DNs to avoid manual operations in self-extinguished faults and typically ranges between 0.5 and 1s. Given the fact that usually IOs are originated in the presence of DG, indeed, this IO is utterly unexpectedly for the DSO. Due to the phenomenon mentioned above, the specific goals of this thesis are described down below: 1. The first goal of this thesis focuses on developing a model suitable for validation purposes. To make a proper model validation, the simulations results obtained with this model will be compared with those obtained from field measurements. Thus, once the model has been validated, a thorough investigation regarding the most influential factors will be carried out. 2. The second goal of this thesis falls within the scope of the PQ. During the IO mentioned above, a new voltage sag topology is observed. Consequently, the efforts will be focused on modelling this new type of sag. 3. The third goal of this thesis emerges from the protective point of view. Once the IO has been defined and characterised, the need for identifying and preventing it becomes the main concern. In such a way, the third pillar of the thesis is targeted at implementing a suitable tool to prevent this particular IO. Besides, this new tool will be compared with the currently available methods for ID developed for scenarios with DG.Aquesta tesi te com a objectiu investigar una operació en illa no intencional, que ha set identificada en una xarxa de distribució real. El procés de registre i processament de les dades obtingudes a partir de les mesures de camp en la xarxa de distribució, ha estat el punt de partida d’aquesta investigació. Cal subratllar que aquesta operació en illa va plantejar un problema i es va convertir en un repte important per l’operador de distribució. Per tant, l'objectiu d'aquesta tesi és doble; resoldre un problema real, així com millorar els estudis de recerca actuals sobre les illes no intencionals en xarxes de distribució elèctrica. El fenomen de les illes dins una xarxa elèctrica, han estat objecte d’estudi durant els darrers anys a causa de la ràpida proliferació de la generació distribuïda. Habitualment, la potència d’aquests recursos distribuïts oscil·la entre centenars de kW i pocs MW i s’assignen a nivells de baixa tensió o mitja tensió. Una de les qüestions importants que plantegen aquests recursos és, sens dubte, les illes. Aquestes situacions es produeixen quan una part de la xarxa elèctrica funciona en paral·lel amb la xarxa principal després d’una desconnexió. Per això, les illes no intencionals es donen quan la generació distribuïda energitza la xarxa després de la obertura d’un interruptor. Principalment, l’objectiu es identificar aquesta situació i desconnectar dites fonts en el mínim temps possible. En el cas de que això no succeeixi, els següents disturbis poden produir-se; pertorbacions de la qualitat de potència (PQ) (per exemple, freqüència i tensió fora del rang), un perill per a la seguretat del personal de la xarxa o bé reconnexions fora de fase. Aquesta és la raó per la qual la investigació vers els mètodes de protecció “anti-islanding” han despertat un gran interès. Essencialment, la millora substancial d’aquesta tesi rau en el fet que, en aquesta illa, no hi ha recursos energètics distribuïts, sinó grans motors d’inducció. Així, la xarxa elèctrica continua energitzada després de la desconnexió del interruptor a causa dels motors d’inducció, que actuen de forma transitòria com a generadors. L’illa comença amb l’obertura del interruptor i finalitza quan aquest tanca el circuit per restablir el subministrament elèctric. Aquesta operació de reconnexió ràpid es freqüent en xarxes de distribució per evitar operacions manuals en faltes temporals i generalment oscil·la entre 0,5 i 1s. Tenint en compte que generalment les illes tenen l'origen en presència de generació distribuïda , realment, la illa elèctrica objecte d’aquesta tesi és inesperada per l’operador de distribució. A causa del fenomen esmentat anteriorment, els objectius específics d'aquesta tesi es descriuen a continuació: 1. El primer objectiu d'aquesta tesi se centra a desenvolupar un model adequat per la validació. Per fer una validació adequada del model, es compararan els resultats de les simulacions obtinguts amb aquest model amb els obtinguts de les mesures de camp. Així, un cop validat el model, es durà a terme una investigació completa sobre els factors més influents. 2. El segon objectiu d'aquesta tesi entra dins de l'àmbit d'aplicació del PQ. Durant l’esmentada illa, s’observa una nova topologia de forat de tensió. En conseqüència, els esforços se centraran en modelar aquest nou tipus de forat. 3. El tercer objectiu d'aquesta tesi s’emmarca en el punt de vista de proteccions. Un cop definida i caracteritzada l’illa, la necessitat d’identificar-la i prevenir-la esdevé la principal preocupació. D’aquesta manera, el tercer pilar de la tesi té com a objectiu la implementació d’una eina adequada per prevenir aquesta particular illa. A més, es compararà aquesta nova eina amb els actuals mètodes utilitzats per a identificar les illes en escenaris amb generació distribuïda.Postprint (published version

Harmonic domain modelling and analysis of the electrical power systems of onshore and offshore oil and gas field /platform

This thesis first focuses on harmonic studies of high voltage cable and power line, more specifically the harmonic resonance. The cable model is undergrounded system, making it ideal for the harmonics studies. A flexible approach to the modelling of the frequency dependent part provides information about possible harmonic excitations and the voltage waveform during a transient. The power line is modelled by means of lumped-parameters model and also describes the long line effect. The modelling depth and detail of the cable model influences the simulation results. It compares two models, first where an approximate model which make use of complex penetration is used and the second where an Bessel function model with internal impedance is used. The both models incorporate DC resistance, skin effect and their harmonic performances are investigated for steady-state operating condition. The methods illustrate the impotance of including detailed representation of the skin effect in the power line and cable models, even when ground mode exists. The cable model exhibit lower harmonics comparable to overhead transmission lines due to strong influence of the ground mode. Due to the application of voltage source converter (VSC) technology and pulse width modulation (PWM) the VSC-HVDC has a number of potential advantages as compared with CSC-HVDC, such as short circuit current reduction, independent control of active power and reactive power, etc. With these advantages VSC-HVDC will likely be widely used in future oil and gas transmission and distribution systems. Modular multilevel PWM converter applies modular approach and phase-shifted concepts achieving a number of advantages to be use in HVDC power transmission. This thesis describes the VSC three-phase full-bridge design of sub-module in modular multilevel converter (MMC). The main research efforts focus on harmonic reduction using IGBTs switches, which has ON and OFF capability. The output voltage waveforms multilevel are obtained using pulse width modulation (PWM) control. The cascaded H-bridge (CHB) MMC is used to investigate for two-level, five-level, seven-level, nine-level converter staircase waveforms. The results show that the harmonics are further reduced as the sub-module converter increases. The steady-state simulation model of the oil platform for harmonic studies has been developed using MATLAB. In order to save computational time aggregated models are used. The load on the platforms consists of passive loads, induction motors, and a constant power load representing variable speed drives on the platforms. The wind farm consists of a wind turbine and an induction machine operating at fixed speed using a back-to-back VSC. Simulations are performed on system harmonics that are thought to be critical for the operation of the system. The simulation cases represent large and partly exaggerated disturbances in order to test the limitations of the system. The results show low loss, low harmonics, and stable voltage and current. With the developments of multilevel VSC technology in this thesis, multi-terminal direct current (MTDC) systems integrating modular multilevel converters at all nodes may be more easily designed. It is shown that self-commutated Voltage Source Converters (VSC) is more flexible than the more conventional Current Source Converter (CSC) since active and reactive powers are controlled independently. The space required by the equipment of this technology is smaller when compared to the space used by the CSCs. In addition, the installation and maintenance costs are reduced. With these advantages, it will be possible for several oil and gas production fields connected together by multi-terminal DC grid. With this development the platforms will not only share energy from the wind farms, but also provide cheaper harmonic mitigation solutions. The model of a multi-terminal hypothetical power system consisting of three oil and gas platforms and two offshore wind farm stations without a common connection to the onshore power grid is studied. The connection to the onshore grid is realized through a High Voltage Direct Current (HVDC) transmissions system based on Voltage Source Converter (VSC) technology. The proposed models address a wide array of harmonic mitigation solutions, i.e., (i) Local harmonic mitigation (ii) semi-global harmonic mitigation and (iii) global harmonic mitigation. In addition, a computationally-efficient technique is proposed and implemented to impose the operating constraints of the VSC and the host IGBT-PWM switches within the context of the developed harmonic power flow (HPF). Novel closed forms for updating the corresponding VSC power and voltage reference set-points are proposed to guarantee that the power-flow solution fully complies with the VSC constraints. All the proposed platform models represent (i) the high voltage AC/DC and DC/AC power conversion applications under balanced harmonic power-flow scenario and (ii) all the operating limits and constraints of the nodes and its host modular converter (iii) three-phase VSC coupled IGBT-PWM switches

Intelligent autoreclosing for systems of high penetration of wind generation with real time modelling, development and deployment

COPYRIGHT Attention is drawn to the fact that copyright of this thesis rests with its author. A copy of this thesis has been supplied on condition that anyone who consults it is understood to recognise that its copyright rests with the author and they must not copy it or use material from it except as permitted by law or with the consent of the author. This thesis may be made available for consultation within the University Library and may be photocopied or lent to other libraries for the purposes of consultation. ii This thesis presents investigations into the effect of modern wind farms on grid side short circuits using extensive real time digital simulation. Particular reference is made to adaptive autoreclosing algorithms using artificial neural networks. A section of 132kV transmission grid in Scotland, including DFIG wind farms, is modelled on a real time digital simulator. An algorithm is then developed and tested using this model to show that this autoreclosing technique is feasible in systems with high penetration of wind generation. Although based on an existing technique, an important innovation is the use of two neural networks for the separate tasks of arc presence and extinction. The thesis also describes a low-cost, real time, relay development platform. Executive summary of key achievements- The effect of wind turbines on transmission line short circuit transients, with a comparison of the other significant parameters- Treatment of unbalanced faults and realistic arc modelling in this context- Feasibility studies on RTDS development of AdTAR using primary arcing and inter-circuit coupling- Development of robust AdSPAR autoreclosing algorithm using twin neural networks- A critical discussion of the use of AI in power system protection- A low cost, IEC 61850 compliant, real time relay development platfor