IMPACT OF DFIG-BASED WIND FARMS ON GENERATOR DISTANCE PHASE BACKUP PROTECTION

Renewable energy technologies are clean sources of energy that have a lower environmental impact than conventional energy technologies. Among all the renewable energy sources, wind energy is clean and plentiful compared to nonrenewable energy sources like fossil fuels and cost-effective compared to other renewable energy sources such as nuclear. Therefore, the potential for wind energy is immense. Nowadays, wind farms are increasingly employed in power systems in order to meet the growing demand of energy as well as the growing environmental awareness. Grid integration of large capacity of wind energy requires, however, new approaches for system operation, control, dynamic enhancement and protection. This thesis reports the results of digital time-domain simulation studies that are carried out to investigate the effect of Doubly-Fed Induction Generator (DFIG)-based wind farms on the performance of generator distance phase backup protection element (Relay (21)) in order to identify important issues that protection engineers need to consider when designing and setting a generator protection system. Such investigation is achieved through incorporating a large DFIG-based wind farm in a study system that inspired from an actual power system. The incorporation takes place under different Relay (21) zone settings. In this context, comparative studies between the relay performance with and without the presence of the DFIG-based wind farm during different faults are presented. The effects of fault location, fault type, generator loading, power flows in the transmission lines in conjunction with wind farm rating and location are also investigated. For validation purposes, time-domain simulations are conducted on benchmark models using the ElectroMagnetic Transients program (EMTP-RV). The results of the investigations carried out in this thesis reveal that DFIG -based wind farm has an effect on the generator distance phase backup protection that leads to error in measured impedance by the generator distance phase backup protection element. This effect varies according to fault type, fault location, generator loading, power flows on transmission lines as well as DFIG-based wind farm rating and location

IMPACT OF WIND ENERGY CONVERSION SYSTEMS ON GENERATOR DISTANCE PHASE BACKUP PROTECTION

The need for clean, renewable energy has resulted in new mandates to augment, and in some cases replace conventional, fossil based generation with renewable generation resources. Wind generation is among those resources that have been at the center of attention. These resources are environmentally friendly, renewable, and they do not produce green-house gases. Therefore, there has been a significant growth in the integration of wind power into power systems networks in recent years. This structural change in power systems results, however, in new concerns regarding the reliable and secure operation of the power system with high penetration of wind energy conversion systems. This thesis investigates the impact of large doubly-fed induction generator- and full- frequency converter-based wind farms on the performance of generator distance phase backup protection (Relay (21)) and the generator capability curves. In this context, comprehensive studies are conducted on a sample power system incorporating large DFIG- and FFC-based wind farms tapped to the transmission system. The results of these studies which provide an in-depth assessment of Relay (21) performance in the presence of this type of wind energy conversion systems show that a wind farm tapped to a transmission line has an adverse effect on the distance phase backup protection of a nearby generator. The severity of such an impact varies according to the fault type and its location. Moreover, the adverse effect of the wind farms on Relay (21) performance extends to affect the coordination between generator distance phase backup protection and the generator overexcited capability limits. Such an impact varies also according to the fault type, fault location and generator loading. The time-domain simulation studies are carried out using the ElectroMagnetic Transient Program (EMTP/RV)

Protection of Transmission Lines Connected to IG-Based Wind Farms

Over the last few decades, renewable energy sources have been attracting great attention due to the increased cost, limited reserves, and the adverse environmental impact of fossil fuels. Among them, wind energy is one of the fastest-growing renewable energy sources worldwide. Wind farms (WFs) comprise a considerable share of the installed capacity of renewable sources in the power grids. With the large integration of WFs in the power grid, the fault ride-through (FRT) requirement has become an essential part of the modern grid codes to increase grid reliability and stability. WFs with FRT capability are required to remain connected to the power grid during fault conditions for a specific period. This will result in WFs contributing to the fault current and changing the system fault current characteristics. Such changes in the fault current characteristics significantly affect the operation of the protection systems. This dissertation will mainly focus on doubly fed induction generator (DFIG)-based WFs and will study their negative impacts on the operation of conventional protection relays, particularly the ones that protect the transmission lines connected to DFIG-based WFs. Considering different negative impacts of DFIG-based WFs on protection systems due to their large slip range, the short-circuit behaviour of a DFIG is evaluated in two different aspects: 1) close-to-zero slip operation and 2) large slip operation. During close-to-zero slip operation of a DFIG-based WF, the short-circuit behaviour of the DFIG is similar to that of a fixed-speed squirrel cage induction generator (SCIG); therefore, fixed-speed SCIG-based WFs are also evaluated in this dissertation. In this situation, a conventional distance relay located at the fixed-speed SCIG or DFIG terminal fails to operate correctly and loses its coordination with the downstream relays for a balanced fault in its backup zone due to the negligible magnitude of the fundamental component of the fault current after several hundred milliseconds. Regarding DFIG-based WFs with FRT capability during large slip operation, the fault current frequency fed by DFIG-based WFs deviates from the nominal frequency during a fault, which affects the operation of conventional protection relays with distance or frequency elements. In this dissertation, two new relaying schemes based on distance elements for the protection of transmission lines connected to the fixed-speed SCIG- and DFIG-based WFs are presented to overcome the aforementioned challenges. To overcome the protection problem associated with the operation of distance relays at the terminal of fixed-speed SCIG- or DFIG-based WFs in case of a balanced fault in the backup zone, a new relaying algorithm requiring only local measurements called modified distance element type I is presented. To detect a fault, the modified distance element type I uses the impedance measured at the relay location together with the fault current waveform injected by the SCIG or DFIG. The reliable performance of the modified distance element type I under different types of faults is verified on a 4-bus test system. The obtained results demonstrate the robustness of the modified distance element type I against fault impedances and system disturbances such as power swing and overload conditions. To overcome the protection challenges associated with the operation of distance relays at the terminal of DFIG-based WFs during large slip operation of DFIGs, a new pilot protection scheme with minimum bandwidth requirements called modified distance element type II is also presented. The developed algorithm relies on the frequency tracking of the fault current injected by the DFIG-based WF. By implementing the modified distance element type II in a 4-bus test system, it is verified that the new relaying algorithm provides reliable protection over the entire length of the transmission line connected to the DFIG-based WF. Moreover, the modified distance element type II accompanied by the modified distance element type I provides proper backup protection for the adjacent lines

Fault analysis and protection for wind power generation systems

Wind power is growing rapidly around the world as a means of dealing with the world energy shortage and associated environmental problems. Ambitious plans concerning renewable energy applications around European countries require a reliable yet economic system to generate, collect and transmit electrical power from renewable resources. In populous Europe, collective offshore large-scale wind farms are efficient and have the potential to reach this sustainable goal. This means that an even more reliable collection and transmission system is sought. However, this relatively new area of offshore wind power generation lacks systematic fault transient analysis and operational experience to enhance further development. At the same time, appropriate fault protection schemes are required. This thesis focuses on the analysis of fault conditions and investigates effective fault ride-through and protection schemes in the electrical systems of wind farms, for both small-scale land and large-scale offshore systems. Two variable-speed generation systems are considered: doubly-fed induction generators (DFIGs) and permanent magnet synchronous generators (PMSGs) because of their popularity nowadays for wind turbines scaling to several-MW systems. The main content of the thesis is as follows. The protection issues of DFIGs are discussed, with a novel protection scheme proposed. Then the analysis of protection scheme options for the fully rated converter, direct-driven PMSGs are examined and performed with simulation comparisons. Further, the protection schemes for wind farm collection and transmission systems are studied in terms of voltage level, collection level wind farm collection grids and high-voltage transmission systems for multi-terminal DC connected transmission systems, the so-called “Supergrid”. Throughout the thesis, theoretical analyses of fault transient performances are detailed with PSCAD/EMTDC simulation results for verification. Finally, the economic aspect for possible redundant design of wind farm electrical systems is investigated based on operational and economic statistics from an example wind farm project

Large Grid-Connected Wind Turbines

This book covers the technological progress and developments of a large-scale wind energy conversion system along with its future trends, with each chapter constituting a contribution by a different leader in the wind energy arena. Recent developments in wind energy conversion systems, system optimization, stability augmentation, power smoothing, and many other fascinating topics are included in this book. Chapters are supported through modeling, control, and simulation analysis. This book contains both technical and review articles

The Protection of Transmission Lines Connected to DFIG-Based WTGs

Recently, many countries have proposed various plans to address the issue of climate change, and increasing the capacity of renewables is one of the major common components of such plans. The uncertainty and variability of generation, introduced by renewable energy sources (RESs), pose significant protection challenges to the power systems. Although many studies have identified the challenges associated with the protection of power systems with RESs and have proposed various algorithms to address these challenges, only a few of them comprehensively discuss all the protection challenges within one system. To begin with, a single test system is developed and used to illustrate the protection challenges and to provide a review of the existing protection schemes, which have been proposed in the literature to tackle the protection challenges associated with power systems with RESs. After introducing the protection challenges associated with the integration of RESs in the power system, this thesis focuses on the protection of transmission lines connected to doubly-fed induction generator (DFIG)-based wind turbine generators (WTGs). DFIG-based WTGs, or namely Type III WTGs, which connect to the power systems via reduced-size converters, raise additional protection challenges such as the maloperation of distance relays due to the frequency deviation of the current measurement caused by the short-circuit characteristics of the DFIGs, and the impact of the fault resistance on the calculated impedance. The protection challenge associated with the frequency deviation caused by the short-circuit characteristics of DFIG is further discussed in detail, and a modified permissive underreaching transfer trip (PUTT) scheme is presented to address the challenge. With the addition of a frequency tracking element, the modified scheme correctly prevents the maloperation of the distance elements during external faults and enables the trip of the relay during internal faults. Besides, the protection challenges associated with conventional distance relays at the terminal of DFIG-based WTGs that are caused by the fault resistance and the frequency deviation associated with the short-circuit characteristics of the DFIG, are addressed and investigated. A modified distance protection scheme is presented to address these protection challenges by using an averaging filter to correct the current phasors and removing the error term caused by the fault resistance in the measured impedance. Pure-fault circuits are used to calculate the pure-impedance of the WTG and pure-fault sequence networks are used to estimate the fault current flowing through the fault resistance. Simulation results show that, for various fault scenarios with different fault resistances, the developed modified distance protection scheme is able to accurately estimate the positive-sequence impedance between the fault and relay location, with fast operations