In order to decarbonize the electricity grid, renewable energy sources must be utilised in con- junction with energy storage to provide ancillary services, which maintain electricity supply quality, reliability and restorability, whilst remaining aordable. Due to a lack of knowledge about the potential of stacking UK ancillary services and electricity markets to improve service aordability, this study of a wind farm with a co-located battery system compares the UK Black Start service, Firm Frequency Response static low frequency secondary and dynamic high frequency services, alongside the day-ahead market as sources of revenue, both provided individually and stacked, with all mismatches handled in the balancing market, to identify the most protable method of operation. A model of the wind farm - battery system power and energy ows is used to assess availability of Black Start and two Firm Frequency Response services, as well as operation in the day-ahead and balancing market, for a one-year period. Internal rate of return and levelized cost of electricity are used to measure nancial perfor- mance, with a weighted average cost of capital (WACC) of 7.75%. Is is found that no service or market provision is protable compared to the WACC, and the most protable method of operating the system is to sell all wind energy forecast on the day-ahead market, not using storage and not stacking services. The most protable method of providing the BS service is when stacked with the FFR static low frequency secondary service. The most protable method of providing either the FFR static low frequency secondary service or FFR dynamic high frequency service is alone, not stacked. The protability of stacks are most sensitive to the changing of BS requirements, although the protability rank order of stacks doesn't change. A single bad wind year has a very small eect on BS availability, and the eect of increased frequency deviations doesn't aect the stacks of FFR services due to limited income from FFR service energy provision compared to the balancing market or from FFR service availability.

The last decade has seen an immense growth in solar PV systems (both large-scale solar PV systems and distributed solar PV systems). It is expected that this growth will continue due to environmental concerns. Since conventional generators are defined by their physics and control, and solar PV systems are defined solely by their control algorithms, this transition has brought with it challenges for preservation of power system stability. Presently, solar PV systems are not modelled in detail in the current dynamic grid model of TenneT. However, due to the flourishing of solar PV systems and lessening of synchronous generators, the role of solar PV systems on the dynamic behaviour of power systems keeps increasing hence an increased need for detailed modelling is necessary. In this thesis report, solar PV systems i.e. large-scale solar PV systems and aggregation of distributed solar PV systems, are modelled according to the requirements of the Dutch gridcode (netcode) and the European 'Requirements for Generators'. Additionally, a standard modelling approach, including proper selection of models and a default parameter set, for representation of large-scale and aggregated PV systems is developed. Following this, the analysis of transient- and voltage stability is firstly conducted on an IEEE 9 bus network with different PV penetration levels. In addition, several case studies are selected based on TenneT's investment plan scenario to determine the impact of a high penetration of PV systems on transient- and voltage stability in a larger, more extensive network.

Comparative study on the necessary upgrade in European interconnections to sustain solar and wind sources uptake in the energy mix. Grid Development for most difficult borders, and planning recommendations, to reach Paris compatible scenario by 2040.

The Paris Agreement, which calls for countries to channel their efforts to limit global warming would require the deployment of large scale offshore wind energy in the North Sea. This includes the possibility of developing offshore infrastructure for deploying offshore wind power generation with installed capacity ranging from 70 to 150 GW by 2040 and increasing up to 180 GW by 2045. Presently, the Voltage Source Converter (VSC) based - High Voltage Direct Current (HVDC) transmission is considered the most suitable for transfer of offshore wind power from distant offshore wind farms (OWFs) to the onshore system. Amidst the available VSC topologies, Modular Multi-level Converter (MMC) topology is the most appropriate solution for the transfer of offshore wind power to onshore systems due to their enhanced performance during offshore and onshore disturbances. However, the currently deployed state-of-the-art MMC-HVDC transmission has a maximum capacity of 1.2 GW. Compatibility of this available technology for complex systems, with the working of parallel units contributing to the increase in power transfer capacity is still unknown. Hence, this demands the development and analysis of a generic model with parallel operation of MMC-HVDC transmission systems to transfer the bulk amount of power from large scale OWFs.

Additionally, the implementation of large scale offshore networks leads to an increase in the penetration of power electronic (PE) converters in the electrical power system. The increase in PE converters causes technical challenges (e.g. due to unprecedented fast dynamic phenomena) related to voltage and frequency stability, and power flow coordination in the power system. In OWFs, the currently available current injection-based voltage control for PE converters are not suitable for voltage control in large scale PE dominated systems due to the absence of continuous voltage control and ineffectiveness during islanding. Moreover, in such power systems, the conventional controllers are not suitable for frequency control due to the absence of dynamic frequency control. Therefore, better control strategies are required in large scale offshore networks to enhance the dynamic characteristics of the power system.

Conventionally, the OWFs are coupled to an AC collector platform through 33 kV High Voltage Alternating Current (HVAC) cables. The voltage is stepped-up to 145 kV at the collector platform, and power is transferred to the offshore converter station using 145 kV HVAC cables. However, in the upcoming projects, the rated voltage levels are expected to increase from 33 kV to 66 kV to avoid the use of such a collector platform and directly transfer power from OWFs to the offshore converter station using 66 kV HVAC cables. Hence, it would be better to understand the performance of large scale offshore networks developed with 66 kV voltage rating.

This thesis proposes a digital twin model of a 2 GW offshore network with the parallel operation of two MMC-HVDC transmission links connecting four OWFs to two onshore systems representing a large scale power system. The MMCs are connected to a common bus on the AC side of the network, with one MMC creating the voltage reference for the common bus and the other MMC following this reference. Additionally, to mitigate the challenges corresponding to voltage and frequency stability in large scale offshore networks, a Direct Voltage Control (DVC) strategy is implemented in the Type-4 Wind Generators (WGs) representing the OWFs. After analyzing the need for 66 kV HVAC transmission from the OWFs to the offshore converter stations, a 66 kV offshore network is developed to achieve 2 GW offshore wind power transfer. The electrical power system is developed in the power system simulation software, RSCAD Version 5.011.1, in order to perform Electro-Magnetic Transient (EMT) based simulations.

Initially, a single OWF with DVC implemented in the WG connected to an AC equivalent system is modelled to test the performance of DVC in a digital twin of a 66 kV HVAC network. The DVC provides continuous voltage control that improves the dynamic performance of the power system. As mentioned in most of the grid codes, the important requirement of reactive power injection by the OWF during dynamic conditions is satisfied by the controller. DVC also avoids the need for an external controller to perform such an action. To validate the working of the implemented DVC in RSCAD, a similar 66 kV HVAC network with the benchmark DVC model is developed in DIgSILENT PowerFactory 2019 SP2 (x64), for EMT simulations and tested under severe dynamic conditions. Both the models provide similar results, confirming the validation of the RSCAD model. Moreover, the RSCAD model provides a better representation of the real-world operation.

To achieve the overall goal of developing a 2 GW offshore transmission network, a hybrid system with the hub-and-spoke principle is utilized in this thesis. The 2 GW offshore network is achieved by a modular approach, connecting four OWFs to a common bus, to which two MMCs are connected in parallel. The coordination between the implemented DVC in WGs and the control structures in MMCs is evaluated for different scenarios in the network. The performance of the 2 GW network in terms of short-term voltage stability and power flow during severe dynamic conditions in the grid is analyzed. The two most severe dynamic conditions chosen for assessment are; the disconnection of one OWF, and a three-phase fault in the middle of an HVAC cable. In the analysis, it is observed that even after the loss of generation from one OWF, the voltage at Point of Common Coupling (PCC) of other OWFs remains stable within the tolerance limit of $\pm$ 10 \%. Additionally, the loss of generation decreases the active power flow in MMC-1 since it is the one that creates the voltage reference. The power flow in MMC-2 is maintained with the corresponding active power reference. For the event of a three-phase fault, the OWF is islanded by the operation of a circuit breaker. During this event, with implemented DVC, the important requirement of reactive power injection from the islanded OWF as stated in most of the grid codes is achieved. This leads to the conclusion that the voltage control in MMC-1 provides the voltage reference in the network during the pre-fault and post fault conditions. However, DVC implemented in the WGs of OWFs take up the role of providing the voltage reference at corresponding PCCs when the OWFs are islanded from the network during the time of the fault.

A dynamic power system model cannot perfectly predict the behaviour of a physical power system. Model validation tries to answer the question whether the model predicts the behaviour of the physical system sufficiently. This study evaluates if and how a dynamic power system model of the Dutch power grid can be validated using PMU measurements. For this, two approaches to validation of dynamic power system models are compared. They are validation using System Wide Simulation and validation using Hybrid Dynamic Simulation. Both approaches use measurements of disturbances in the power system as a basis for the comparison of the measured and the simulated behaviour of the system. With System Wide Simulation, comparison can be done using measured voltage magnitude, active power flow and reactive power flow. With Hybrid Dynamic Simulation, comparison can be done using measured active power flow and reactive power flow. Identification of model inaccuracies is limited by inaccuracies that are the result of the simulation approach. Inaccuracies are introduced by poor representation of the pre-disturbance operating conditions of the model and poor representation of the disturbance in the simulation. System Wide Simulation is more strongly affected in both cases and is therefore less accurate than Hybrid Dynamic Simulation. System Wide Simulation can be used to gain rough insight into the validity of a model. For accurate model validation and subsequent calibration however, System Wide Simulation falls short, and Hybrid Dynamic Simulation is required. Hybrid Dynamic Simulation however requires PMU measurements to be taken in specifically targeted locations.

The connection of offshore wind turbines to the European grid has been growing in the recent years. Many European countries are adopting this renewable energy and are increasing the number of wind power plant additions into their electrical transmission networks. Due to the phase out of conventional power plants (e.g. fossil fuel fired), new challenges are arising in terms of inertia, frequency stability, voltage stability and power quality, being the latter the main focus in the present work. It is important to study the harmonic frequencies that the wind parks are going to introduce in the electrical grid and how the grid is going to respond to this sustainable energy addition. The classical methods to identify the harmonics frequencies and to assess the stability in an electrical power system are performed by considering single-input single-output (SISO) systems. Nevertheless, when modelling a power system as a SISO system, information about the dynamics of the elements in the system is neglected. To overcome this disadvantage, a representation with more than one input and one output, a multiple-input multiple-output (MIMO) system, can be considered. The present works concerns with the development of a method for studying the harmonic frequencies of any electrical power system. Since the main elements in the grid that contribute to the creation of harmonic frequencies are the inductances and the capacitances of the transmission lines and underground cables, the present work will focus on these passive elements and it will represent the transmission lines as PI sections and the underground cables as ``fitted PI'' sections. These representations are SISO systems, because the have only a voltage signal, measured in the sending end of a transmission branch, as input; and a voltage signal, measured in the receiving end of a transmission branch, as output. Therefore, it is necessary to find an approach to build a MIMO system. This is done via a concatenation of SISO linear-time-invariant (LTI) systems to create a MIMO system. Afterwards, the MIMO system is studied with a powerful mathematical tool called the singular value decomposition that not only will give information about the harmonic frequencies in the system, but it will show it is also possible to study which input of the system is affecting the system the most and which output will be the most affected. To finish the research, a sensitivity analysis is performed with respect to the variation of the capacitances and inductances in the transmission lines and the underground cables. This analysis will evaluate possible variations in the harmonic response of the MIMO system.

The proposed method to investigate the harmonic frequencies of an electrical power system can be applied to any power system. For sake of illustration of application, two different power system models are addressed. First, to understand each step in the method a small size test system is studied. This study shows how to apply the method and illustrates how to interpret the evaluation outcomes. Subsequently, a synthetic model of the Randstad regional transmission network is used to test the method in a relatively larger system model. This case study is of great importance due to the new wind parks that are going to be connected to this region in the coming years. Therefore, the harmonic frequencies observed in the synthetic model of the Randstad region will be obtained and an assessment of which transmission line or underground cable is the most affected by the harmonics in the system will be performed.

The increasing penetration of PE converter interfaced generation units in electrical power systems have given rise to many challenges in the power system operation. Two of the most important challenges are the voltage control and frequency control in the absence of conventional generation units. Furthermore, the PE converters can interact with the power system elements causing the power system to become unstable.

In this thesis, the effect of the wind turbines modified with grid-forming capability is analysed on the transmission networks as well as on the Offshore VSC-HVDC converter station. The dynamic response of the WTs is studied considering the high share of the power electronic converter interfaced generation.

It is shown when the wind turbine power converters are equipped with the implemented control strategy, they can provide voltage and frequency stability to the system and further upgrades can be added to enhance the system response. The control strategy implemented employs the direct voltage control which is upgraded with voltage dependent active current control for improving the transient voltage recovery of the system. The inertial response based on modifying the machine side converter is also added which extracts kinetic energy from the wind turbine rotor that improves the frequency response of the system following load change.

In the end, an offshore wind farm network is modeled which includes the offshore wind park connected to an offshore MMC HVDC converter station for delivering bulk power to the DC source connected via the HVDC cable. The developed wind turbine model is employed for integration in the offshore wind farms which has shown to eliminate the transient overvoltages occurring in the offshore network during the blocking of the HVDC converter.

Until recent times, electrical power grids have been dominated by conventional power plants run by fossil or nuclear fuels in order to cater to the electrical load demand. These power plants employ large generators that operate in synchronous with each other to maintain a stable frequency and voltage across the power grid. The frequency and voltage stability, which are respectively linked to active and reactive power serves as a backbone for a secure operation of the power system. Furthermore, since these classical generation sources promised support of ancillary services during unstable conditions, along with power generation, they were characterized as a reliable solution for maintaining the security of the power system. But, due to the high emission of carbon by-products from these fossil-fuelled generators, challenges of global warming and climate change have made it inevitable to decommission them. And more emphasis has been embarked on the adaptation of renewable energy sources (RES) which offer minimum carbon footprint. Geothermal heat, wind, sunlight, and tides constitute some of the Renewable energy sources since their availability are unlimited and involve the least emission of greenhouse gasses, hence Renewable Energy Sources have a minimal impact on the environment compared to traditional energy sources and can effectively tackle the problems which arise with fossil fuel usage. For all these reasons, during the last decades, there is fierce research on finding ways to produce the needed energy in a sustainable fashion. Synchronous Generators, which are dominant in the existing power grid, have the inherent characteristics to relate system’s frequency with load balance. This considerable advantage is found missing from Power Electronic interfaced renewable energy resources due to the following reasons. Firstly, since active power support was earlier the main purpose of using these devices, they were operated at Maximum power point tracking (MPPT). Secondly, in wind energy technology, isolation between electrical and mechanical circuits had to be introduced due to their variable behavior of energy production, and this has led to no inertia backing from the synthetically produced frequency. So with high penetration of RES in the future grids, the aforementioned problems pose huge risks for grid stability and reliability. The current research mainly focuses on the development, implementation, testing, and validation of frequency regulation strategies under the umbrella of Fast Active Power Regulation controllers specifically to support during large load frequency variation in low inertia power system grid. These controllers developed are very generic and can be implemented with slight modifications in all the renewable energy devices with ease. In order to simulate more real-time behavioral conditions, dynamic simulation studies are performed in RSCAD software interfaced with a Real-Time Digital Simulator (RTDS). Two Test benches have been considered in this thesis, one being an IEEE 9 bus system modified with 52% wind share and another is the North of Netherlands Network. In the first stage of the project, FAPR controller’s proof of concept has been tested on a Type-4 Wind generator setup connected to the modified IEEE 9 bus system. Here wind penetration is scaled up to 52% and a low inertia grid have been simulated. Later, the results obtained here were validated by Hardware in Loop setup utilizing a mock-up grid side converter. The next stage of the project aims at making FAPR controllers more generic. For this the North of Netherlands network was modified by adding FAPR integrated 300MW solar farm, FAPR integrated 82MW full converter based Type-4 Wind Turbine and lastly, a responsive load (Electrolyser) was modified to accommodate FAPR controllers. All together formed a Multi-Energy Hub and simulations were performed to check the practical feasibility and boundaries of operation of FAPR controllers in the future power grid. The results prove that the proposed topology and control strategies can effectively provide frequency ancillary services to the grid by providing support during dynamic load frequency variations.

Power systems have been subjected to several changes due to a constant evolution over the last years. The changes that come along with this evolution include several aspects such as the introduction of variable energy generation from renewable sources, changes in the network's topology, storage, new regulation policies, liberalization of markets, constant trading of electrical energy between countries among others. These changes, combined with a context of growing demand and aging network infrastructure can result in more stressed power systems, uncertainty and potentially more risks that could lead to blackouts. These new conditions have to be taken into account when assessing the reliability of the transmission system in order to have a complete insight of what is happening in the network and to identify potential causes of problems. This thesis provides a methodology using state enumeration to assess reliability in the transmission network in the context of long term planning using a probabilistic approach with the aim to identify potential improvements for current practices based on deterministic approaches. This methodology considers three main aspects: i) Failure probabilities of individual components (i.e transmission lines) based on historical data and operational conditions. The failure probability originated from operational conditions is obtained by combining expert's opinion and available data by applying Bayesian data analysis; ii) Contingency selection to obtain a representative list of contingencies to be analyzed. The screening of contingencies for the list is performed based on the failure probabilities and accepting a certain level of residual risk. The residual risk is calculated by assuming a lost load and finding the probability of the contingency that leads to that lost load; iii) Determination of the effect and the associated risk of contingencies. The purpose of this part is to quantify line overloadings in terms of money to obtain the total cost linked to a certain set of contingencies.The monetization of the effect is performed by using a value of lost load (VoLL). This monetization is first performed without the implementation of re-dispatch actions assuming that overload is lost load. Later on, re-dispatch actions for conventional generators are considered, the new cost of re-dispatch plus lost load is obtained. Furthermore, a comparison between the two costs is performed. Re-dispatch actions are implemented by using a linear programming approach with the selection of an objective function for the minimization of the amount of conventional generation. Risk of lost load is obtained in terms of money by the multiplication of the probability of the contingency times the cost. The proposed methodology obtains reliability in terms of system adequacy by investigating line overloads and lost load. Further on, this methodology is tested on a test model for the 380/220kV grid topology of the transmission grid of the Netherlands. The results show the variation of indicators of risk of lost load and guidelines to continue developing probabilistic approaches for reliability analysis. The computational burden and the time employed for this kind of approaches is still a challenge to be tackled.

Recent projections estimate that the Netherlands needs circa 33 GW of offshore wind capacity in the North Sea to meet the goals of the Paris Agreement. To this end, the Dutch government has very ambitious plans to create new wind sites far from shore and integrate that power generation to the high-voltage power grid in the next years. Due to the challenges of connecting future massive amounts of offshore wind power into the grid TenneT operates it becomes urgent to investigate new alternatives for this purpose. A grid topology with transmission capacities above 1 GW connecting offshore wind farms at distances close to 100 km in a standardized, modular, and cost-efficient manner is the focus of this thesis.

With eight point-to-point HVDC links in operation in Germany and more expected in near future, TenneT TSO is analysing new offshore grid connection concepts to achieve a reliable and secure operation of the infrastructure connecting wind energy both in Germany and the Netherlands. A solution is presented in this thesis report in which new wind farms are connected with 66-kV cables to a centralised platform with a connection capacity of 1050 MW. This platform will utilise HVDC technology based on VSC conversion techniques and MMC topology. It is expected that the 66-kV cables will not be connected to a single busbar through paralleled converter transformer, but that this will be done with at least three converter transformers connected to each other on the valve side but not connected on the 66-kV side.

A dynamic performance study of a test network with the novel connection topology developed in PSCAD has been done. Each component of the system was studied to obtain a complete overview and understanding of the overall behaviour. All the associated control loops for the MMC terminals and wind turbines were modelled in detail. Through several simulations based on eight cases and scenarios the performance of the offshore 66-kV ac grid and the MMC-HVDC link using the control schemes of MMC converters as in a typical grid connection topology for OWFs was assessed.

The progressive phase out of fossil fuel power plants and the integration of variable renewable energy sources, driven by environmental directives striving for the reduction of CO2 emissions, is reshaping how electricity Transmission System Operators (TSOs) plan and operate the power system. The mitigation of uncertainty, which imperils the balance between generation and demand, urges the search of new sources of ancillary services, traditionally provided by bulky synchronous generators. In particular, the coupling of the electricity and gas sectors reveals promising flexibility solutions for power systems through energy conversion and hydrogen storage. The conversion of electrical energy into hydrogen, commonly known as power-to-gas, is enabled by water electrolysis in electrolyzers. Specifically, the Proton Exchange Membrane (PEM) technology can react very quickly to demand variations and thus it holds a strong potential for the procurement of ancillary services. This thesis investigates the viability of the integration of large scale PEM electrolyzer capacity into ancillary services markets in the context of the European initiative “Synergy Action TSO 2020”. The current framework of Dutch frequency balancing markets, voltage control and congestion management is reviewed, as well as the future European plans for the implementation of a harmonized and common frequency market. The conducted research includes the assessment of the technical adequacy of PEM electrolyzers with respect to existing prequalification requirements and the proposal of recommendations for the optimal participation in these markets. To illustrate the value of PEM electrolyzer support for electrical networks, a case study based on a realistic representation of the transmission grid of the Groningen-Drenthe-Overijssel (GDO) area in the north of the Netherlands for the year 2030 is presented. The case study is principally intended to examine the effectiveness of the provision of primary frequency control with PEM electrolyzers. The obtained results highlight how this technology can improve the frequency stability of the power system in comparison with synchronous generators, and more importantly for the future, how it can help alleviate the negative effects attributed to the reduction of inertia in the system.

The search for new sources of ancillary services and the projected demand for hydrogen as a medium of energy storage has aroused considerable interest in the use of large scale electrolysers for power system ancillary services. As the number of large scale electrolysers is projected to grow, it is important that the dynamics of these plants are well understood in order to integrate them successfully. In line with this objective, suitable models must be developed to aid studies of electrical power system dynamics with electrolysers configured as sources of ancillary services. This thesis report provides an overview on implementing practical models of large scale electrolysers (>1 MW) for real time digital simulation and also proposes a control scheme to extend the basic capabilities of large scale electrolysers in order to provide ancillary services to the electrical power system.To illustrate the feasibility of creating such models, case studies are built on a one megawatt-scale plant connected to a high voltage infinite grid via step-down transformers. Real time simulations are performed by using the Real-Time Digital Simulator (RTDS) platform to investigate the response of the electrolyser model to external command signals and power system disturbances. The 1 MWmodel is also scaled to 300 MW with the view to qualitatively assess its performance, with respect to grid code compliance. The results show that the generic 1 MW model in RTDS can replicate the step response profile of a real electrolyser. The results also support the view that high level control schemes are a key enabler for ancillary services using large scale electrolysers. High level control schemes can enable an optimal operation of the electrolyser load on the basis of market and power system conditions.

Industries such as chemical companies need a continuous power supply and the fast transfer relay Siemens 7uv68 is designed to transfer frompresent feederwhich encounters a fault to an auxiliary feeder and minimizes the transient torque of the induction motors during transfer. The relay will be installed in a DOW power plant in South Tarragona, and it should be validated that the relay can operate well in all kinds of fault scenarios and no mis-operation would occur in such power plant.
To perform the relay testing, first, the fault signals which reflect the dynamic performance of DOW Tarragona are generated by ATP-EMTP. The EMTP model of the DOWpower plant has two main parts: the Tarragona power plant and auxiliary relays (overcurrent 50/50N, differential 87T) which send tripping and blocking command to 7UV68. Besides, in order to track the frequency and phase deviation between auxiliary feeder bus and the motor bus during transfer, the frequency measurement is accomplished bya zero-crossingmethod and phase angle ismeasured byClarke transformation. The test setup is made by 2 Omicron Amplifiers and a PLC which is used to simulate breakers’ behavior formain-tie configuration.
Based on the testing requirements, the relay settings are tuned to ensure the motor bus transfer can be initiated by all kinds of faults in feeder bus, and there is no mal-operation if blocking signal is sent. The motor bus can also be transferred to the auxiliary bus when a fault occurs in transmission grid with the help of relay self-start function. Furthermore, the trip delay of differential relay 87T and the communication delay affects the transfer time and the transfer inrush behaviors.

Due to the shift in electrical energy generation from thermal synchronous generators towards various renewable sources, power system stability will become a more pressing issue in the near future. In this thesis, we explore possible improvements to the dynamic grid model currently used by TenneT TSO for large-disturbance stability studies, specifically the addition of motor load, wind, solar PV and HVDC transmission modelling. Thus we pave the way for future, more in-depth research that can contribute to the development of a more sophisticated dynamic grid model for operational and planning use. Our results indicate that motor load modelling has a strong negative influence on grid dynamic performance (compared to a static representation of the same load), and that wind and PV models have a strong positive influence, but that particularly for wind models, the choice of appropriate model parameters remains a challenge.

As the primary protection of high voltage (HV) and Extra high voltage (EHV) transmission networks, distance protection needs to operate properly under all possible fault conditions. It needs to operate as fast as possible for internal fault, while it also must be able to discriminate between the internal and the external faults to prevent unnecessary trip of the normal system. In real life application, the operational characteristic of commercial distance relays such as operating time and reach accuracy are usually defined using the steady state conditions. This leads to difficulty in understanding the operational characteristic of the relay under the dynamic conditions such as faults.
In this thesis, a dynamic test tool based on the latest IEC 60255-121 standard, suitable for performance analysis of distance protection during dynamic condition was developed and validated. The tools are built by using the ATP-EMTP Software and the Omicron secondary injection kit. The test results of two distance relays show that depending on the dynamic conditions, the operational performance of the relay might be affected. In some situations, the operating time of the relays was delayed, while, in other conditions, the accuracy of impedance measurement is affected causing the relay to overreach. Furthermore, this delayed tripping or overreach of distance protection could cause both security and dependability issue in power transmission protection. The dynamic test tool which has been developed can be expanded further to study other dynamic conditions that are not covered in this thesis.

European countries are showing their willingness to reduce their greenhouse gases emissions in the coming years. For example, the Paris agreement within the United Nations Framework Convention on Climate Change (UNFCCC) is one of the most crucial steps that countries have signed recently. The aim is to cause a lower global temperature increase, and thus, to reduce the resulting climate risks.
North Sea countries are working on a greener future in a national level, as well; and these are in fact, the countries which are the most concerned about the climate change globally. Moreover, these are affluent in terms of opportunities for using greener energy sources, due to their climatic and geographic conditions. Clear examples are hydropower plants in the Nordic region or offshore-wind in the North Sea.
Nevertheless, these countries need also of infrastructure to achieve their objectives, such as a Power System which will enable to integrate green generation sources properly and to satisfy the societies’ energy needs successfully. Power Systems are in fact, needed key enablers of this energy transition.
The topic of this Master Thesis is transmission expansion planning in the North Sea for the year 2030. PowerGIM and PowerGAMA are used. The objective is to find the socio-economically beneficial grid design which will help achieve these future ambitions that the North Sea countries have and at the same time, which will be robust w.r.t. renewable energy sources’ development uncertainty. The main finding of this Master Thesis is that Dogger Bank hub is obtained as part of the most socio-economically beneficial offshore-grid layout for the year 2030, in all implemented scenarios. Each scenario refers to one implemented ENTSO-E Vision (Visions 1-4) with some additional assumptions.
In short, in this Master Thesis, four different offshore-grid layouts are obtained, one per each implemented scenario; and all of them have the same core. The core is Dogger Bank hub’s interconnection with Great Britain, Belgium, Germany, Netherlands, Norway and Denmark. Nevertheless, there are some variations which depend on the implemented scenario and on the implemented assumptions. Overall, the obtained Dogger Bank hub could also integrate between 13-32 GW offshore-wind in the North Sea. Then, a reference grid layout is created, as well. This design embraces the previously mentioned four grid layouts in a conservative way, i.e. the repeated lines in all four obtained grid layouts are taken with the lowest capacity value among all four designs.
The grid layout obtained after the implementation of the second scenario is the most robust grid layout w.r.t. different future energy prospects. Its operational cost saving throughout the lifetime of 30 years w.r.t. the reference grid layout is of 20-33 bn €, depending on the implemented future scenario; and the investment cost increase is of 5.5 bn € w.r.t. the reference grid layout.

Power systems have undergone major changes the past few decades, leading to an increase in the frequency of occurrence and severity of blackouts. Intentional controlled islanding constitutes the final resort to rescue the system from a blackout by separating the network into islands in a controlled manner. Various post-separation control action such as generation rejection and load shedding have to be considered in order to restore the active power balance in the created islands.
The transient stability of the constructed islands can be enhanced by identifying and grouping together the coherent generators of the power system. This can be achieved by representing the electrical network as an undirected graph and performing constrained graph partitioning with respect to the generator nodes.
If the demand is higher than the active power produced, the frequency of the formed island starts declining. To deal with this problem and keep the frequency within acceptable limits, it often becomes necessary to curtail a proportion of the load. An advanced underfrequency load shedding scheme can dynamically adjust the shedding steps based on accurate power deficiency estimation and thus minimize the total load shed.
In this thesis, the coherent generator groups are identified for several power systems. Then constrained graph partitioning is used to split these networks into islands, while forcing the coherent generators to remain in the same island. For this step, three different algorithms performing constrained clustering are implemented in Matlab and compared for two different study cases. Moreover, an advanced underfrequency load shedding scheme is applied on various constructed islands by utilizing PowerFactory and Python. Its objective is to minimize the load shedding amount, while keeping the frequency within the predefined limits. The amount of load that needs to be curtailed is estimated based on the frequency gradient of the generators in the island with an excess in power demand.