Protection Fault Location Control In High Voltage Multi Terminal Direct Current Hv Mtdc Grids

In its concluding section, the thesis also outlines a few possible avenues of further research in this area.

The increasing global energy needs and the high integration of renewable energy generation require long-distance power transmission and multi-terminal complex grids. High-voltage direct current (HVDC) is an appealing alternative for future grids. Recent HVDC research has focused on voltage-source converter (VSC) technology. However, VSC is unable to handle DC contingencies. Thus far, AC breakers have been the only way to clear DC faults, though with significant economic and societal consequences. Other protection concepts include multi-level converters and faulty line identification methods. Still, DC breakers are necessary to isolate the faulty line from the network. The goal of this work is to investigate multi-terminal grid topologies under fault cases and analyze the impact of current limiting measures and control strategies on the developing DC fault currents. DC breaker technologies are studied and compared based on the total fault interruption time and the system post-fault operation restoration. With the analyzed concepts, HVDC system designers will be able to understand and tackle DC faults to facilitate an uninterruptible power flow amongst several different AC grids.

Multi-terminal high voltage direct current (MT-HVDC) grids enable integration of large-scale renewable energy resources and facilitate flexible bulk power transfer for energy markets extending over political boundaries. Preserving the integrity of MT-HVDC grids during DC faults remains a major challenge, primarily due to the lack of effective DC circuit breakers (DCCBs) capable of interrupting the expected fault currents. These DCCB limitations and stringent reliability requirements mandate identification of faulted transmission lines and the faulty conductors at extreme speeds with highly sensitivity. Two techniques were developed to improve the sensitivity and the reliability of fault discrimination while meeting these speed requirements. The first technique introduces directional properties for line and bus protection algorithms that rely on the rate of change of local voltage measurements to improve the fault discrimination. The second technique uses locally measured conductor currents to quickly identify the fault type and faulted conductors. This algorithm makes the decisions based on the ratios of the rate of change of currents computed considering a pair of conductors at a time, and therefore, independent of the fault resistance. Versatility and reliability of the proposed fault type discrimination algorithm was demonstrated by applying it to different transmission configurations. Fault recovery aspects of a novel class of hybrid LCC-VSC MT-HVDC transmission systems in which a number of VSC inverters and rectifiers are connected to an LCC HVDC link was investigated. Two possible fault clearing schemes were proposed. The first approach avoids DCCBs, employs series-connected high power diodes at VSC inverter terminals to block the fault current contributions, and clears faults by de-energizing VSC rectifiers and applying force retardation to LCCs. The second approach utilizes DCCBs installed on the branch lines. These DCCBs activated by the proposed fault discrimination schemes minimize the disruption of power flow through the LCC HVDC link due to faults on the lines branched out to connect VSCs. The capability, speed, and sensitivity of each fault clearing scheme were evaluated considering practical designs.

This book discusses HVDC grids based on multi-terminal voltage-source converters (VSC), which is suitable for the connection of offshore wind farms and a possible solution for a continent wide overlay grid. HVDC Grids: For Offshore and Supergrid of the Future begins by introducing and analyzing the motivations and energy policy drives for developing offshore grids and the European Supergrid. HVDC transmission technology and offshore equipment are described in the second part of the book. The third part of the book discusses how HVDC grids can be developed and integrated in the existing power system. The fourth part of the book focuses on HVDC grid integration, in studies, for different time domains of electric power systems. The book concludes by discussing developments of advanced control methods and control devices for enabling DC grids. Presents the technology of the future offshore and HVDC grid Explains how offshore and HVDC grids can be integrated in the existing power system Provides the required models to analyse the different time domains of power system studies: from steady-state to electromagnetic transients This book is intended for power system engineers and academics with an interest in HVDC or power systems, and policy makers. The book also provides a solid background for researchers working with VSC-HVDC technologies, power electronic devices, offshore wind farm integration, and DC grid protection.

This book discusses HVDC grids based on multi-terminal voltage-source converters (VSC), which is suitable for the connection of offshore wind farms and a possible solution for a continent wide overlay grid. HVDC Grids: For Offshore and Supergrid of the Future begins by introducing and analyzing the motivations and energy policy drives for developing offshore grids and the European Supergrid. HVDC transmission technology and offshore equipment are described in the second part of the book. The third part of the book discusses how HVDC grids can be developed and integrated in the existing power system. The fourth part of the book focuses on HVDC grid integration, in studies, for different time domains of electric power systems. The book concludes by discussing developments of advanced control methods and control devices for enabling DC grids. Presents the technology of the future offshore and HVDC grid Explains how offshore and HVDC grids can be integrated in the existing power system Provides the required models to analyse the different time domains of power system studies: from steady-state to electromagnetic transients This book is intended for power system engineers and academics with an interest in HVDC or power systems, and policy makers. The book also provides a solid background for researchers working with VSC-HVDC technologies, power electronic devices, offshore wind farm integration, and DC grid protection.

This book discusses novel methods for planning and coordinating converters when an existing point-to-point (PtP) HVDC link is expanded into a multi-terminal HVDC (MTDC) system. It demonstrates that expanding an existing PtP HVDC link is the best way to build an MTDC system, and is especially a better option than the build-from-scratch approach in cases where several voltage-sourced converter (VSC) HVDC links are already in operation. The book reports in detail on the approaches used to estimate the new steady-state operation limits of the expanded system and examines the factors influencing them, revealing new operation limits in the process. Further, the book explains how to coordinate the converters to stay within the limits after there has been a disturbance in the system. In closing, it describes the current DC grid control concept, including how to implement it in an MTDC system, and introduces a new DC grid control layer, the primary control interface (IFC).

Power systems have been developing over the past few decades, especially in terms of increasing efficiency and reliability, as well as in meeting the recent rapid growth in demand. Therefore, High Voltage Direct Current (HVDC) systems are considered to be one of the most promising and important contenders in shaping the future of modern power systems. A number of trends demonstrate the need to implement Multi-terminal Direct Current (MTDC) systems, including the integration into the conventional grid of renewable energy resources such as photovoltaic (PV) and offshore wind farms. The transmission of power from or to remote areas, such as the North Sea in Europe, is another initiative that is required in order to meet the high demand for power. The interconnection between countries with different levels of frequencies over a long distance is a fundamental application of HVDC grids as well as hybrid AC/DC transmission systems. The industry has also played an essential role in the accelerated progress in power electronics devices regarding cost and quality. Consequently, Voltage Source Converter based-High Voltage Direct Current (VSC-HVDC) systems has recently attracted considerable attention in the research community. This type of HVDC systems has a significant advantage over the classic Current Source Converter based-HVDC (CSC-HVDC) in terms of the independent control of both active and reactive power. Since VSC-HVDC is now being implemented in various applications, this requires a close examination of the behavior of both the economic and operational issues of both VSC-HVDC stations and MT-HVDC systems. This thesis proposes an optimal power-sharing control of MT-HVDC systems using a hierarchical control structure. In the proposed control scheme, the primary control is decentralized and operated by a DC voltage droop control. This method regulates the voltage source converters (VSCs) and guarantees a stable DC voltage throughout the system even in the presence of sudden changes in power flow. A centralized optimal power flow (OPF) is implemented in the secondary control to set the droop gains, and voltage settings in order to fulfil a multi-objective function. This aims at minimizing the losses in DC grid lines and converter stations by an optimization algorithm, namely Semidefinite Programming (SDP). Therefore, an optimal power-sharing result is achieved taking into consideration the losses of both transmission lines and converters, as well as failure intervals of the system. The proposed control scheme was tested on a modified CIGRE B4 DC grid test system based on the PSCAD/EMTDC and MATLAB in which the primary control was designed and simulated in the former, whereas the latter was used to run the SDP algorithm.

This part of GB/T 22390 specifies the technical requirements, test methods, inspection rules, packaging, transportation, storage, signs, labels, instructions for use, and the complete set of supply for the DC line fault location device of the ±500 kV HVDC transmission system. And quality assurance, etc.  This section applies to the DC line fault location device (hereinafter referred to as the device) of ±500 kV HVDC transmission system.

In a near future, multi-terminal High Voltage Direct Current grids (MT-HVDC grids) appear to be a suitable solution for the integration of power electricity produced by remote offshore windfarms into the AC transmission system. Though the recourse to HVDC point-to-point links is well-known, challenges still remain for a safe operation of HVDC grids. Protection is the main technical field still under study and reliable protection strategies ensuring the best technological and economic ratio are investigated. This thesis focused on a full selective protection philosophy similar to the one applied to AC transmission systems. The consideration of cable links, Half-Bridge VSC-MMC converters and hybrid DC circuit breakers defines the frame of the study. An association of two algorithms for the identification of faults is suggested. The time available for the fault clearing process has been investigated. Simulations performed with EMTP software have been used to evaluate the reliability of the suggested strategy.

The modern electric power system has evolved into a huge nonlinear complex system due to the interconnection of thousands of generation and transmission systems. The unparalleled growth of renewable energy resources (RESs) has caused significant concern regarding grid stability and power quality, and it is essential to find ways to control such a massive system for effective operation. The controllability of HVDC and FACTS devices allows for improvement of the dynamic behavior of grids and their flexibility. Research is being carried out at both the system and component levels of modelling, control, and stability. This Special Issue aims to present novel HVDC topologies and operation strategies to prevent abnormal grid conditions.