Modelling of the Protection Relays of STATCOM

Selective, fast and reliable protection measures are essential for the electric power system, particularly for the transmission network operating at high power levels. Due to the dependence of the society on electric power, the protection systems are critical in minimizing the risks of personal injuries, economical losses and interruptions in the supply of electricity. For the same reason, the power quality is another important issue in the modern transmission systems. To compensate reactive power and reduce the harmonic content in the grid, power electronic solutions such as static synchronous compensators (STATCOMs) and static VAr compensators (SVCs) have been developed. The complex control systems of these compensators require an efficient design method, and simulations with Matlab and Simulink are used widely for this purpose. However, the protection system is still often designed conventionally by verifying the setting calculations with intensive stability tests in laboratory. Moreover, the effect of the trips on the control system must be analysed manually. In this thesis, Simulink models for overcurrent and differential protection functions were implemented to reduce the need for testing. Two different commercial protection relay models were analysed for both functions with the results compared to each other and the standards defining the functions. For the overcurrent protection, a simplified simulation model was also created according to the standard. Particularly, operating characteristics of the functions as well as the differences between the relay models were examined by visualising them with the Simulink modelling. In the comparison of the performance of the relays, the focus was on the operating speed. The models were verified first with idealized unit test schemes and finally with a control system model from an actual STATCOM project. In the tests performed, the simulation models succeeded in detecting the simulated problems and tripping the circuit accordingly to the specifications from manuals and standards. The harmonic blocking of differential protection, the reset process of the timers, as well as the sampling were identified as the main differences between the relay models. However, limited information is often available on these features. Therefore, the further development of them will require more detailed modelling of their structures and applications. Another challenge related to the stability simulations was found to be the large computational capacity required by the control system model. Based on the successful results from this thesis, the simulation models will be developed further with the stability simulations in future commercial projects. In addition, new models will be developed to cover more typical functions found in STATCOM and SVC applications, as well as to include the setting calculations

Modelling of the Protection Relays of STATCOM

Selective, fast and reliable protection measures are essential for the electric power system, particularly for the transmission network operating at high power levels. Due to the dependence of the society on electric power, the protection systems are critical in minimizing the risks of personal injuries, economical losses and interruptions in the supply of electricity. For the same reason, the power quality is another important issue in the modern transmission systems. To compensate reactive power and reduce the harmonic content in the grid, power electronic solutions such as static synchronous compensators (STATCOMs) and static VAr compensators (SVCs) have been developed. The complex control systems of these compensators require an efficient design method, and simulations with Matlab and Simulink are used widely for this purpose. However, the protection system is still often designed conventionally by verifying the setting calculations with intensive stability tests in laboratory. Moreover, the effect of the trips on the control system must be analysed manually. In this thesis, Simulink models for overcurrent and differential protection functions were implemented to reduce the need for testing. Two different commercial protection relay models were analysed for both functions with the results compared to each other and the standards defining the functions. For the overcurrent protection, a simplified simulation model was also created according to the standard. Particularly, operating characteristics of the functions as well as the differences between the relay models were examined by visualising them with the Simulink modelling. In the comparison of the performance of the relays, the focus was on the operating speed. The models were verified first with idealized unit test schemes and finally with a control system model from an actual STATCOM project. In the tests performed, the simulation models succeeded in detecting the simulated problems and tripping the circuit accordingly to the specifications from manuals and standards. The harmonic blocking of differential protection, the reset process of the timers, as well as the sampling were identified as the main differences between the relay models. However, limited information is often available on these features. Therefore, the further development of them will require more detailed modelling of their structures and applications. Another challenge related to the stability simulations was found to be the large computational capacity required by the control system model. Based on the successful results from this thesis, the simulation models will be developed further with the stability simulations in future commercial projects. In addition, new models will be developed to cover more typical functions found in STATCOM and SVC applications, as well as to include the setting calculations

Optimal overcurrent relay coordination in wind farm using genetic algorithm

Wind farms are ones of the most indispensable types of sustainable energies which are progressively engaged in smart grids with tenacity of electrical power generation predominantly as a distribution generation system. Thus, rigorous protection of wind power plants is an immensely momentous aspect in electrical power protection engineering which must be contemplated thoroughly during designing the wind plants to afford a proper protection for power components in case of fault occurrence. The most commodious protection apparatus are overcurrent relays (OCRs) which are responsible for protecting power systems from impending faults. In order to employ a prosperous and proper protection for wind farms, these relays must be set precisely and well-coordinated with each other to clear the faults at the system in the shortest possible time. These relays are set and coordinated with each other by applying IEEE or IEC standards methods, however, their operation times are relatively long and the coordination between these relays are not optimal. The other common problem in these power systems is when a fault occurs in a plant, several OCRs operate instead of a designated relay to that particular fault location. This, if undesirable can result in unnecessary power loss and disconnection of healthy feeders out of the plant which is extremely dire. It is necessary to address the problems related inefficient coordination of OCRs. Many suggestions have been made and approaches implemented, however one of the most prominent methods is the use of Genetic Algorithm (GA) to improve the function and coordination of OCRs. GA optimization technique was implemented in this project due to its ample advantages over other AI techniques including proving high accuracy, fast response and most importantly obtaining optimal solutions for nonlinear characteristics of OCRs. In addressing the mentioned problems, the main objective of this research is to improve the protection of wind farms by optimizing the relay settings, reducing their operation time, Time Setting Multiplier (TSM) of each relay, improving the coordination between relays after implementation of IEC 60255-151:2009 standard. The most recent and successful OF for GA technique has been used, unique parameters for GA was selected for this research to significantly improve the protection for wind farms that is highly better compared to any research accomplished before for the purpose of wind farm protection. GA was used to obtain improved values for each relay settings based on their coordination criteria. Each relay operation time and TSM are optimized which would contribute to provide a better protection for wind farm. Thus, the objective of this work which is improving the protection of wind farms by optimizing the relay settings, reducing their operation time, Time Setting Multiplier (TSM) of each relay, improving the coordination between relays, have been successfully fulfilled and solved the problems associated with wind farm relay protection system settings. The new approach has shown significant improvement in operation of OCRs at the wind farm, have drastically reduced the accumulative operation time of the relays by 26.8735% (3.7623 seconds)

Matlab

This book is a collection of 19 excellent works presenting different applications of several MATLAB tools that can be used for educational, scientific and engineering purposes. Chapters include tips and tricks for programming and developing Graphical User Interfaces (GUIs), power system analysis, control systems design, system modelling and simulations, parallel processing, optimization, signal and image processing, finite different solutions, geosciences and portfolio insurance. Thus, readers from a range of professional fields will benefit from its content

Modeling relays for power system protection studies

Numerical relays are the result of the application of microprocessor technology in relay industry. Numerical relays have the ability to communicate with its peers, are economical and are easy to operate, adjust and repair. Modeling of digital and numerical relays is important to adjust and settle protection equipment in electrical facilities and to train protection personnel. Designing of numerical relays is employed to produce new prototypes and protection algorithms. Computer models of numerical relays for the study of protection systems are greatly enhanced when working along with an electromagnetic transient program (emtp). A literature survey has revealed that previous modeling techniques presented a lack of automation in the generation of relay models, or show high complexity in linking the numerical relay models with the power system modeled in the emtp. This thesis describes a new approach of modeling and designing of numerical relays. The proposed methodology employs a Visual C++-based program (PLSA) to obtain from the user the specifications of the relay to be designed, and to process this information to generate the FORTRAN code that represents the functional blocks of the relay. This generated code is incorporated in a PSCAD/EMTDC case using a resource called component, which facilitates the creation of user-custom models in PSCAD/EMTDC. Convenient electrical and logical signals are connected to the inputs and outputs of the PSCAD/EMTDC component. Further additions of digital relay models into the PSCAD/EMTDC case constitute the protection system model. The thesis describes a procedure for designing distance and differential relay models, but the methodology may be extended to design models of other relay elements. A number of protection system studies were performed with the structure created with the proposed methodology. Adjustment of distance and differential relays were studied. Relay performance under CT saturation and the effects of the removal of anti-aliasing analog filter were investigated. Local and remote backup distance protection of transmission lines was simulated. The adjustment of differential protection of power transformer to overcome the effects of inrush current was performed. Power transformer differential protection responses to internal and external faults were considered. Additionally, a set of tests were performed to investigate the consistency of the relay models generated with the proposed methodology. The results showed that the numerical relay models respond satisfactorily according with the expected results of the tests

Influence of instrument transformers on power system protection

Instrument transformers are a crucial component of power system protection. They supply the protection system with scaled-down replicas of current and voltage signals present in a power network to the levels which are safe and practical to op- erate with. The conventional instrument transformers are based on electromagnetic coupling between the power network on the primary side and protective devices on the secondary. Due to such a design, instrument transformers insert distortions in the mentioned signal replicas. Protective devices may be sensitive to these distortions. The inuence of distortions may lead to disastrous misoperations of protective devices. To overcome this problem, a new instrument transformer design has been devised: optical sensing of currents and voltages. In the theory, novel instrument transform- ers promise a distortion-free replication of the primary signals. Since the mentioned novel design has not been widely used in practice so far, its superior performance needs to be evaluated. This poses a question: how can the new technology (design) be evaluated, and compared to the existing instrument transformer technology? The importance of this question lies in its consequence: is there a necessity to upgrade the protection system, i.e. to replace the conventional instrument transformers with the novel ones, which would be quite expensive and time-consuming? The posed question can be answered by comparing inuences of both the novel and the conventional instrument transformers on the protection system. At present, there is no systematic approach to this evaluation. Since the evaluation could lead to an improvement of the overall protection system, this thesis proposes a comprehensive and systematic methodology for the evaluation. The thesis also proposes a complete solution for the evaluation, in the form of a simulation environment. Finally, the thesis presents results of evaluation, along with their interpretation

Communications for smart grid substation monitoring using WIMAX protocol

The SMARTGRID is a general term for a series of infrastructural changes applied to the electric transmission and distribution systems. By using the latest communication and computing technology, additional options such as Condition Monitoring can now be implemented to further improve and optimise complex electricity supply grid operation. Lifecycle optimisation of high voltage assets and other system components in the utility provide a case in point. Today Utility experts agree that application of scheduled maintenance is not the effective use of resources. To reduce maintenance expenses and unnecessary outages and repairs of equipment due to scheduled maintenance, utilities are adopting condition based approaches. Real time online monitoring of substation parameters can be achieved by retrofitting the existing substation with SMARTGRID technology. The IEC 61850 is a common protocol meant for Substation Automation Systems, designed for the purpose of establishing interoperability, one that all manufacturers of all different assets must comply with. This thesis advocates the estimation of bandwidth required for monitoring a substation after retrofitting the existing substation with smart communication technologies. This includes establishing a latest wireless communication infrastructure from the substation to the control centre and evaluating the performance modelling and simulating the physical layer of communication technologies such as WIMAX (IEEE802.16) and MICROWAVE point to point using MATLAB SIMULINK and RADIO mobile online simulation software. Also, link budget of the satellite communication for the same application is calculated. Satellite communication in this case is considered as a redundant or back up technology to ensure that the communication between entities is continuous. On performing the simulation on different environments the results prove that the selected protocols are best suited for condition monitoring. The measured Latency could be the best approximated value which complies with the current objective. However the white noise that exists in the substation has significant hazard with respect to the security of the wireless network. To compensate this constraint whole substation is hard wired by means of plastic fibre optics and the data sent to the base station located near the substation

Engineering Education and Research Using MATLAB

MATLAB is a software package used primarily in the field of engineering for signal processing, numerical data analysis, modeling, programming, simulation, and computer graphic visualization. In the last few years, it has become widely accepted as an efficient tool, and, therefore, its use has significantly increased in scientific communities and academic institutions. This book consists of 20 chapters presenting research works using MATLAB tools. Chapters include techniques for programming and developing Graphical User Interfaces (GUIs), dynamic systems, electric machines, signal and image processing, power electronics, mixed signal circuits, genetic programming, digital watermarking, control systems, time-series regression modeling, and artificial neural networks

IMPACTS OF POWER SYSTEM-TIED DISTRIBUTED GENERATION ON THE PERFORMANCE OF PROTECTION SYSTEMS

The dispersed integration of smaller power units in the existing utility grid is the new trend. This is largely due to changes in the power generation and distribution markets. The combination of rising cost of new construction, deregulations and improved newer power equipment technologies suitable for deferred expansions make the new trend very attractive to power companies and independent investors. Until recently, other contributions to power distribution systems from such sources as standby units were considered negligible and therefore unaccounted for during the design and operation of power systems. This view has drastically changed, largely due to the increasing penetration levels of these newer technologies termed Distributed Generation Resources. This thesis work is a continuation of ongoing work in the validation of the benefits and pitfalls of grid integrated Distributed Generation using modern modeling and simulation techniques. The proposed simplified but more robust symmetrical components based protection relay system is shown to be immune to the mis-coordination, mis-operation and blinding caused by the bidirectional power flow resulting from the high shares of Distributed renewable resource integration