High penetration levels of distributed renewable generation has brought considerable issues and challenges to the operation and control of power systems for countries and regions where there are abundant, but geographically distributed, renewable energy resources. One of such challenging issue is the Loss-of-mains (LOM) and islanding detection. This thesis aims at developing a variety of monitoring methods to tackle this problem. Principal Component Analysis (PCA) method is a linear method which assumes that data follows a normal Gaussian distribution. Therefore, for a Gaussian distributed frequency variable, a PCA model can be calculated with corresponding confidence limits, which is then used for detecting abnormal transients and identifying the islanding sites occurring in the UK utility network. In order to monitor the dynamic characteristics of power systems, a dynamic PCA (DPCA) approach is proposed by incorporating time lags at the modelling stage, thus the auto- and cross-correlations can be extracted. Moreover, power system processes are time-varying, thus a recursive PCA (RPCA) monitoring scheme is also proposed as a reliable extension of PCA to achieve adaptive updating of training data and confidence limits. A novel radial basis function neural network (RBFNN) model-based PCA method is then proposed to monitor non-Gaussian variables in power systems, combing with the newly developed Teaching-Learning-Based-Optimisation (TLBO) method to tune the non linear parameters of RBF neurons. This research has shown that statistical process control methods such as PCA and its extensions can be successfully applied to power system loss-of-mains detection, so that large volumes of PMU data can be efficiently processed and an adequate monitoring model can be built for a given confidence limit. They further provide a wide-area view and early accurate warning of the network for system operators, with the length of time to identify faults and the risks of damaging connected equipment being reduced.

No description available.

No description available.

This thesis details the development of an application specific processor for the transmission line matrix (TLM) method. The application of TLM to the modelling of wave propagation in two and three dimensions is introduced with the discussion focusing on the concept of computational efficiency. Methods for improving computational efficiency are reviewed, in particular the implementation of TLM on large scale parallel computers. It is shown that these methods, while increasing throughput, make inefficient use of available resources. The review of existing methods is used to define a set of goals for a new class of application specific TLM processor. The development of an application specific processor based upon the two dimensional shunt node is presented. This gives rise to an efficient, bit serial scatter processor. The implementation of this processor within a complete, application specific TLM system is discussed. The system is based around a unique mapping of the TLM connect routine to hardware. The bit serial scatter processor is modified to allow the modelling of inhomogenous and three dimensional media using the stub loaded shunt node, the symmetrical condensed node and the symmetrical super condensed node TLM schemes. It is shown that all four TLM schemes may be implemented within a single architecture without the introduction of redundant elements through the use of reconfigurable logic. The implications of interfacing this system to a host PC using the PCI bus are discussed. The processor designs are reviewed within the context of the goals set for the work. It is shown that all of the goals were successfully met. The implications and limitations of the processor are discussed. The thesis concludes with recommendations for areas worthy of further study.

This thesis concerns the study of a novel method of power system digital distance protection, which may provide the breakthrough required for the implementation of faster and more accurate protection schemes than presently available. The method employs a frequency domain impedance measurement technique based upon a simplified line model and the use of finite Fourier transform coefficients in the analysis of very small amounts of information. Unlike previously proposed methods, the algorithm does not rely on any periodicity in the relaying signals and, as a result, it is capable of performing in high transient conditions using data of short duration. Operating times of 10 msec and less can be achieved and it is envisaged that the method will have considerable advantages in short and long line distance protection. The work embraces considerations of the general philosophy behind digital protection schemes, performance studies of the new method and the investigation of various implementation proposals. The performance of the finite transform technique is studied in some detail and, in the analysis, a quasi-optimal relationship is developed by which conditions may be chosen to ensure acceptable response in the presence of noise and various numerical errors. The studies show that offset fault current conditions can cause some problems in the performance of the algorithms. These conditions are studied in detail and a number of practical solutions are investigated. Recently developed frequency domain power system simulation techniques are used in studying the performance of the new method and the importance of such facilities in the development of fast operating protection schemes is demonstrated. The implementation studies are concerned with the practical requirements of hardware and software for protection schemes employing the new method. A brief investigation of data acquisition techniques and signal levels is made and consideration is given to the speed of the various software procedures based on currently available processing equipment.

With the continuous decline in the price of second-generation (2G) high temperature superconducting (HTS) tapes, the 2G HTS cables are a promising candidate to significantly improve the electrical power transmission capacity and efficiency. In order to make the HTS cable competitive to its counterparts in the power market, much ongoing research work have made considerable contributions to the HTS cable design. In this thesis, the challenges of electrical issues of superconducting power cable using 2G HTS tapes have been addressed. The specific contributions of the thesis include: the influence of anisotropic characteristics of 2G HTS is investigated in order to increase critical current of HTS cable; For improvement of transmission efficiency and safety, the homogenization of HTS cable current distribution is achieved considering the influence of contact resistances and HTS layer inductances; AC loss of HTS cable is obtained through experimental measurement for cooling system design; and the impact of HTS cable on power grids is analysed for safe integration of HTS cable into grids. This thesis starts with a literature review of superconductivity and developments of 2G HTS cable. Following the literature review is the critical current investigation of HTS cable considering the anisotropy of 2G HTS tape. 2G HTS tapes were placed in a highly uniform electromagnetic field and the in-field critical currents were measured with various magnitudes and orientations of the magnetic field. The anisotropic characteristics of 2G HTS tape were determined by non-linear curve fitting using measured in-field critical currents and further implemented into the HTS cable finite element method (FEM) modelling. The modelling results indicate that the gap distances among the tapes in the HTS cable affect the critical current of the HTS cable due to the anisotropic characteristics. In order to investigate the critical current of HTS cable with respect to gap distances, an HTS cable circuit model with adjustable gap distances among the parallel placed HTS tapes was designed and built. Extensive experimental and FEM modelling were performed and the results indicate that the minimized gap distance among the neighboring HTS tapes can be beneficial to increase the overall cable critical current. With DC transporting current, the homogenization of current distribution of HTS cable is achieved by controlling the contact resistances. A 1.5 m long prototype HTS cable consisted of two HTS layers was fabricated and tested as a further investigation of the HTS cable circuit model. The magnitude of the contact resistance related to each HTS layer was measured to quantitatively calculate the current distribution. It is found that only a few micro-ohms difference of contract resistances can still cause severe imbalanced current distribution. The FEM modelling work was carried out to obtain the balanced current distribution by varying the contact resistances. With AC transporting current, the inductances of HTS layers in the cable also pose a significant influence on current distribution issues. An optimal algorithm was developed to achieve homogeneous current distribution by optimal design of the cable diameter, pitch angle and winding direction. Another short prototype cable wound with two HTS layers was built according to the optimal design and the current distribution was experimentally measured between the two layers. It is found out that the optimal algorithm is effective to homogenize the AC current distribution. A reliable AC loss measurement was carried out on the 1.5 m long prototype HTS cable in order to quantify the AC loss of the HTS cable for cooling system design. The experimental measurement method is based on the electrical four probe method adopting a compensation coil to cancel the large inductive component of the cable. The HTS cable with long geometry is easily influenced by the surrounding electromagnetic field so that the measured AC loss signal can be influenced. In order to overcome this problem, a symmetrical current return path was utilized in order to eliminate the electromagnetic interface surrounding the HTS cable. The AC loss measurement results are stable and low-noise for a set of AC frequencies, which proves the accuracy of the measurement technique. Finally, a new superconductor component in PSCAD/EMTDC (Power System Computer Aided Design/Electromagnetic Transients including DC) was developed in order to investigate the impact of the HTS cable integrated into the meshed power network. The superconductor component developed in PSCAS/EMTDC takes into account the heat exchange with the HTS cable cryogenic envelope and the detailed configuration of YBCO HTS tape so that HTS cable model is able to accurately predict the power flow, fault current level and grid losses of the power grid with HTS cables.

Distributed generation (DG) refers to electricity generating plant that is connected to a distribution network rather than the transmission system. At present, small-scale DGs are mostly treated as ‘negative demand’ to the transmission system. However, if their contribution to transmission levels are fully understood and properly assessed, these generators can make into valuable assets to improve operational efficiency and substitute major infrastructure investment. This PhD research aims to addresses this challenge from three key aspects: 1. On assessment methodologies, our current industrial practices to evaluate DG-to- transmission-contribution reveal inherent defects. The method given in the transmission system (SQSS) is not sufficient to reflect today’s dispersed generation technologies; while the method for the distribution system (P2/6) fails to reflect and discriminate between different characteristics of distribution networks that DGs are connected. Overcoming these drawbacks, enhanced frameworks to evaluate DG contribution have been developed in this research. 2. On generator’s contribution, little attention has been paid to photovoltaic (PV) outputs characterization and their integration to the overall evaluation process. Neither SQSS nor P2/6 pays sufficient attantion to evaluating PV’s contribution to system. In this regard, an approach aiming at characterizing PV seasonal outputs is proposed. Integrating with the proposed frameworks, this part of the research completes the DG contribution evaluation architecture. 3. On commercial arrangements, conventional business models largely rely on network investment to meet customer demand. Earning a fixed rate of return on invested capital, incumbent distribution network operator (DNO) businesses are encouraged to invest in network assets, very little has been done to support third party service providers for more efficient network development. In the third part of this research, alternative DNO business models and market mechanisms are proposed to further unlock the potential of DG, substantially increase the potential of their contributions to the transmission system.

Renewable energy connection to power systems has been growing worldwide, which brings more challenges to power systems than ever before and correspondingly, the investment in wind farms is increasing rapidly. Instead of connecting single wind turbines or small wind farms to the distribution network, energy companies and manufactures tend to connect large wind farms to the transmission network. These wind farms can contain 200 plus turbines and have a rated capacity of 100 MW up to several GW. Consequently, significant new challenges appeared in the transmission system. Wind intermittency is one of the biggest issues in power systems in that it affects both frequency and system power flow. This project has focused on the transmission system power flow issue that was caused by wind intermittency, and defined it as Wind Intermittency Constraint (WIC). To avoid studying the whole system, WIC was used as a new method in this project to calculate and identify the problematic circuits that were caused by wind intermittency only. These circuits will be calculated in the Power Transfer Distribution Factor (PTDF) method, which is the key part of WIC calculation, and will be defined as WIC. WIC for each circuit in transmission system will be ranked, and circuits with higher WIC ranking over 20% are wind intermittency circuits and will be closely monitored. Smart grid technology has been considered as an effective way to improve system visibility and controllability when attempting to overcome difficulties caused by renewable energy. There are three major parts for this project, which are flexible demand mechanism, generator participation and Flexible AC Transmission (FACTs) equipments. To have a more accurate FACTs control and calculation for wind intermittency only, this project uses a new concept of DI (Dynamic Impedance) to contribute to the controller algorithm. A novel algorithm has been introduced to build three controllers of demand, generation and impedance. To achieve different goals, these three controllers will take instruction from the central selector. The three goals identified in this project are economical, green and secure functions, where economical function is to minimise system cost during different wind scenarios, green function is to maximise system renewable energy output, and security function is to make sure the system is secure when it minimizes cost and maximizes renewable energy. The algorithm will also calculate different wind scenarios and produce a 24 hour profile for system demand, generation and impedance. This profile will be achieved by the three controllers (Demand, generation and impedance controller) A new model for wind scenarios is also used in this project which is called A to B model. It calculates a continuous 24 hour wind profile and find out the system stress points. These points are define as A and B. The controller algorithm will download wind scenario and calculate the best strategy to move from period A to period B. During the A to B process, cost, green and security factors are considered and the best strategy will be presented. 6-node, 9 nodes and 39 nodes IEEE standard models are used across the project to prove the concept of WIC (Wind Intermittency Constraint), DI (Dynamic Impedance), A to B wind profiles and controller algorithm. A simplified UK model has also been used to test real weather data and produce the best strategy to achieve economical, green and security goal. For thermal and voltage study, standard IEEE models are used. For stability study, a dynamic model is used to monitor rotor angle.

In recent years, the capacity of electrical power systems (EPS) has been growing in order to match an increasing demand for electrical power. The expanding power source especially the penetration of the renewable energy makes the systems more difficult to manage and operate. Thus the task of protecting these systems especially for the extra-high-voltage (EHV) transmission line can no longer be handled using the traditional protection schemes, which were designed for simple power system configurations and therefore are not suitable for modern power systems. Also, the protection of EHV transmission line should take into account the increasing penetration of renewable energy generation such as wind farms and the effects of such generations on protection schemes. This thesis describes a novel phase selection and fault detection scheme using current signal data from one end only of a typical UK 400kV transmission system. Firstly, the measured current signals are decomposed using the wavelet transform to obtain the necessary frequency details and then the spectral energy for a chosen number of wavelet coefficients are calculated using a moving short time window; this forms the feature extraction stage, which in turn, defines the inputs for the artificial neural network which is used for classifying the types of fault. After the fault type is identified, the proposed scheme selects the specific neural network of the fault type to distinguish between internal and external faults by utilizing the same patterns features extracted from the previous stage. The input features comprise both the high and low frequency components to enhance the performance of the scheme. An extensive series of studies for a whole variety of different system and fault conditions clearly show that the performance of the scheme both for phase selection and detection is accurate and robust. For testing the robustness of the scheme and also as this research project is a UK-China jointly funded EPSRC project, this designed scheme is also applied to a typical 500kV Chinese transmission system with only traditional power generations and with both traditional and renewable generations (wind farms). The effect of the penetration of wind farms on the performance of the proposed protection scheme is thus investigated. For both systems, promising results from the new protection scheme for the phase selection and fault detection are achieved.

In this thesis a new analytical technique for the evaluation of fault initiated transients has been developed. The technique is very general and is applicable to both the transposed and untransposed polyphase multi-conductor lines of any configuration, and, can take into account the frequency dependence of the parameters of the system. On the basis of this technique the following types of faults can be easily studied: (a) shunt faults (b) series faults (c) simultaneous shunt or series faults or their combination at one or multiple locations. The post fault transient behaviour of ehv ac transmission line has been simulated by using digital computer. The faiilt transient response at the relaying points are presented for a number of interesting cases. This information is of particular interest for the design and development of super-speed protective schemes ehv lines. The phenomenona of fault induced overvoltage has also been investigated briefly. The results for fault induced overvoltage show excellent agreement with Kimbark's field test results. Digital simulation of the transient behaviour has been achieved by a very efficient programming technique.