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A novel method to reduce the impact of wide area blackouts in transmission networks is presented. Millions of customers are affected each year due to blackouts. Splitting a transmission system into smaller islands could significantly reduce the effect of these blackouts. Large blackouts are typically a result of cascading faults which propagate throughout a network where Intentional Controlled Islanding (ICI) has the advantage of containing faults to smaller regions and stop them cascading further. Existing methodologies for ICI are typically calculated offline and will form pre-determined islands which can often lead to excessive splits. This thesis developed an ICI approach based on real time information which will calculate an islanding solution quickly in order to provide a ‘just-in-time’ strategy. The advantage of this method is that the island solution is designed based on the current operating point, but well also be designed for the particular disturbance location and hence will avoid unnecessary islanding. The new method will use a power flow tracing technique to find a boundary around a disturbance which forms the island that will be cut. The tracing method required only power flow information and so, can be computed quite quickly. The action of islanding itself can be a significant disturbance, therefore any islanding solution should aim to add as little stress as possible to the system. While methods which minimise the power imbalance and total power disrupted due to splitting are well documented, there has been little study into the effect islanding would have on voltage. There a new approach to consider the effects that islanding will have on the voltage stability of the system is developed. The ICI method is based on forming an island specific to a disturbance. If the location of a source is known along with information that a blackout is imminent, the methodology will find the best island in which to contain that disturbance. This is a slightly different approach to existing methods which will form islands independent of disturbance location knowledge. An area of influence is found around a node using power flow tracing, which consists of the strongly connected elements to the disturbance. Therefore, low power flows can be disconnected. This area of influence forms the island that will be disconnected, leaving the rest of the system intact. Hence minimising the number of islands formed. Finally the methodology is compared to the existing methods to show that the new tool developed in this thesis can find better solutions and that a new way of thinking about power system ICI can be put forward.

The use of insulation such as paint coatings has grown rapidly over the past decades. However, defects and corrosion under insulation (CUI) still present challenges for current non-destructive testing and evaluation (NDT&E) techniques. One of such challenges is the large lift-off introduced by thick insulation layer. Inaccessibility due to insulation leads corrosion and defects to be undetected, which can lead to catastrophic failure. Furthermore, lift-off effects due to the insulation layers reduce the sensitivities. The limitations of existing NDT&E techniques heighten the need for novel approaches to the characterisation of corrosion and defects under insulation. This research project is conducted in collaboration with International Paint®, and a radio frequency non-destructive evaluation for monitoring structural condition is proposed. High frequency (HF) passive RFID in conjunction with microwave NDT is proposed for monitoring and imaging under insulation. The small-size, battery-free and cost-efficient nature of RFID makes it attractive for long-term condition monitoring. To overcome the limitations of RFID-based sensing system such as effective monitoring area and lift-off tolerance, microwave NDT is proposed for the imaging of larger areas under thick insulation layers. Experimental studies are carried out in conjunction with specially designed mild steel sample sets to demonstrate the detection capabilities of the proposed systems. The contributions of this research can be summarised as follows. Corrosion detection using HF passive RFID-based sensing and microwave NDT is demonstrated in experimental feasibility studies considering variance in surface roughness, conductivity and permeability. The lift-off effects introduced by insulation layers are reduced by applying feature extraction with principal component analysis and non-negative matrix factorisation. The problem of thick insulation layers is overcome by employing a linear sweep frequency with PCA to improve the sensitivity and resolution of microwave NDT-based imaging. Finally, the merits of microwave NDT are identified for imaging defects under thick insulation in a realistic test scenario. In conclusion, HF passive RFID can be adapted for long term corrosion monitoring of steel under insulation, but sensing area and lift-off tolerance are limited. In contrast, the microwave NDT&E has shown greater potential and capability for monitoring corrosion and defects under insulation.

This Thesis presents an investigation on the technical impacts caused by the steady state operation of Small-Scale Embedded Generators (SSEGs) and also introduces the Small Scale Energy Zone (SSEZ) concept which aims to remove the technical barriers associated with SSEGs through intelligent coordination of large numbers of customerowned SSEGs, energy storage units and controllable loads. This approach represents a move away from the conventional passive, “fit-and-forget” philosophy under which the majority of Low Voltage (LV) distribution networks are currently operated and towards a higher degree of network operational management. The employment of a distributed management and control approach for an SSEZ, realised through the Multi Agent Systems (MAS) technology, is proposed due to the advantages that can potentially be realised in the areas of: (i) scalability and openness, (ii) reliability and resilience and (iii) communications efficiency. A FIPA-compliant MAS-based control approach is designed, developed and evaluated based on the specific SSEZ control requirements. The MAS is composed of three types of agents: direct control agents, indirect control agents and utility agents, exchanging information through the employment of a common ontology. In addition, a relational database management system is also designed and developed in order to be coupled with the developed MAS for data management purposes.

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Power cables represent an increasingly important asset in urban transmission and distribution networks. The increasing use of power cables brings technical challenges to the power system operators and maintenance engineers. One of these challenges is early detection of cable faults before they turn into failures. During the service life of power cables, they are vulnerable to various stresses which can turn any cable faults or defects into failures through different mechanisms. However, in the process leading to failure, condition monitoring techniques such as partial discharge (PD), distributed temperature and sheath current in the power cables can be applied to detect the existence of faults. This thesis focuses on, and makes contribution to the field of research, the modelling and analysis of sheath current under normal and abnormal operating conditions, and develops a set of criteria for use in the sheath current monitoring system. Numerical models have been developed to calculate the sheath currents in a cross-bonded cable system. Among these models, the one which contains both the inductive and capacitive components of sheath current, is presented in detail and then taken as the basis of the numerical model to be applied in the current research. Through an iterative process proposed in this thesis, the inductive component of the sheath circulating current is determined with consideration of the effect of sheath current itself due to self-coupling. Based on the presented model, sheath currents in a practical cross-bonded cable sheath using co-axial cable to connect sheaths and link box are simulated · in an example cable tunnel located in Wuhan, China. The effects of influencing factors such as self-coupling effect, capacitive current and power factors on sheath currents are, for the first time, analysed in details.

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The primary goal of this thesis is to investigate the small-signal stability of transmission networks with wind generation and high voltage direct current (HVDC) transmission integrated in them. The topic reflects a number of concerns of transmission network operators in the U.K. and beyond over how stability is maintained as networks evolve. Damping low frequency power oscillations using wide-area signals are illustrated for both line commutated based current source converter (interchangeably referred as LCC or CSC) and self commutated voltage sourced converter (VSC) based HVDC links integrated within host AC networks. With VSC HVDC offering flexibility greater than LCC HVDC in terms of modulating both active and reactive power, it was shown that optimally allocating/sharing the control duty among the multiple control options that exist within a VSC HVDC link, ensures that the overall control duty is reduced, and hence, the dynamic ratings of the expensive converters is minimised. An important consideration in the design of power oscillation damping (POD) controllers is to ensure that the controller is robust across a range of practical operating conditions. To achieve this, an analytical control design technique is introduced in which all the control loops for a VSC HVDC link, are designed simultaneously in a multi-variable framework. The method results in a set of decentralized, robust single-input-singleoutput (SISO) controllers at the two ends of a VSC HVDC link, which ensures coordinated control action and an acceptable performance level in the event of loss of a remote feedback signal. Damping contribution from remote offshore wind farms connected via VSC HVDC is an important consideration for systems with high penetration of wind energy. The effectiveness of coordinating the supplementary control of the wind farm and the onshore HVDC converter is shown in terms of dynamic variations in wind farmreal power output, DC link voltage and turbine speed. Having examined the damping contribution, frequency support from offshore wind farms is also explored. A method using appropriate droop control on the offshore and onshore HVDC converters is proposed which enables offshore wind farms connected through VSC HVDC link to contribute to system inertia and primary frequency control without having to rely on remote communications. The effectiveness of the proposed approaches is illustrated through detailed frequency domain analysis and extensive time-domain simulation results in DIgSILENT PowerFactory on two test systems.

This thesis aims to strengthen the bridge between mathematical and practical research into the transient stability of power systems. Literature that exploits the mathematical parallels between models for transient dynamics in power systems and the phenomenon of synchronisation in complex networks is explored. However, it is contended that research at the intersection of complex systems and power system stability can limit its applications to practical issues in power engineering. This thesis focuses on the measurement of transient stability in power systems in terms of a traditional stability metric for short-circuit faults on a power network, the critical clearing time (CCT). The CCT provides an upper bound on the duration of a short circuit on a power network before it is removed - cleared - by the action of protection mechanisms to isolate the faulted circuit such that the system will regain synchrony once the fault is cleared. Approaches that use energetic methods for assessing the transient stability of a power system are extended by developing metrics that can measure stability trends for different scenarios in a power system via the numerical continuation of equilibrium configurations under the variation of system parameters. An analytical CCT (ACCT) approximation is derived from this energetic framework in order to capture trends in stability with respect to a system parameter. The performance of the ACCT is compared to more accurate computations of CCT that use slower numerical simulation techniques. Attention is given to how well the ACCT approximation can capture stability trends under variation of key network design parameters such as load admittance and generator inertia. It is found for a two-machine infinite bus (TMIB) system that load parameter values that can improve stability can be identified using the ACCT. Also, the general dependence of a fault's CCT on the inertia of a generator in a TMIB power system is identifiable using the ACCT. For power systems with stationary generator inertia values, a method to provide a contingency analysis of fault locations is proposed. The method ranks the locations of short-circuit faults by their CCT; the more severe a fault the shorter its CCT. It is found in a TMIB system that the ACCT can identify the general location of severe faults under different inertia scenarios. It is shown that in larger power systems, energetic methods can be used to accurately identify the locations of faults with short CCTs. These results, together with relevant literature are used to suggest possible strategies to monitor transient stability within modern power systems.