629 research outputs found

    An Adaptive Overcurrent Coordination Scheme to Improve Relay Sensitivity and Overcome Drawbacks due to Distributed Generation in Smart Grids

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    Distributed Generation (DG) brought new challenges for protection engineers since standard relay settings of traditional system may no longer function properly under increasing presence of DG. The extreme case is coordination loss between primary and backup relays. The directional overcurrent relay (DOCR) which is the most implemented protective device in the electrical network also suffers performance degradation in presence of DG. Therefore, this paper proposes the mitigation of DG impact on DOCR coordination employing adaptive protection scheme (APS) using differential evolution algorithm (DE) while improving overall sensitivity of relays . The impacts of DG prior and after the application of APS are presented based on interconnected 6 bus and IEEE 14 bus system. As a consequence, general sensitivity improvement and mitigation scheme is proposed

    Application of evolutionary algorithms for optimal directional overcurrent relay coordination

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    Includes bibliographical references.Relay coordination is necessary to ensure that while protection relays operate as fast as possible, they are also able to isolate only the faulted parts of the system from the network, ensuring that a power system disturbance does not result in interruption of the power supply to a larger part of the power system network. Optimal relay coordination for overcurrent relays depends on two parameters, namely, Time Multiplier and Pickup Current Setting. The conventional method of setting these two parameters for overcurrent relays applied on the power system network is to first determine the main and backup relay pairs which form part of the clockwise and anti-clockwise loops around the power system network. The relays are then set through an iterative process to ensure coordination. Initially, a general rule of setting relays to operate in 0.2 seconds for faults in the primary zone, to ensure fast operation, and in 0.2 seconds plus additional grading time, to ensure coordination, for faults in the backup zone is applied. The next relay in the loop is tested to check if it fulfils the requirements of the initial general rule. If the conditions of the general rule are not met, the previous relay’s setting is adjusted to meet the requirements. This process is repeated until all the relays around the loop are set. Conventional relay coordination process has a limitation in the sense that it is deterministic and the settings of subsequent relays depend on the initial guess of the settings of the initial relay. Therefore, this method does not necessarily provide solutions which guarantee optimal relay coordination but the best of the solutions tried

    INTELLIGENT METHODS FOR OPTIMUM ONLINE ADAPTIVE COORDINATION OF OVERCURRENT RELAYS

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    During the operation in a modern power distribution system, some abnormal events may happen, such as over-voltage, faults, under-frequency and overloading, and so on. These abnormal events may cause a power outage in a distribution system or damages on the equipment in a distribution system. Hence these abnormal events should be identified and isolated by protection systems as quickly as possible to make sure we can maintain a stable and reliable distribution system to supply adequate electric power to the largest number of consumers as we can. To sum up, we need stable and reliable protection systems to satisfy this requirement. Chapter 1 of the dissertation is a brief introduction to my research contents. Firstly, the background of a distribution system and the protection systems in a power system will be introduced in the first subchapter. Then there will be a review of existing methods of optimum coordination of overcurrent relays using different optimal techniques. The dissertation outline will be illustrated in the end. Chapter 2 of the dissertation describes a novel method of optimum online adaptive coordination of overcurrent relays using the genetic algorithm. In this chapter, the basic idea of the proposed methods will be explained in the first subchapter. It includes the genetic algorithm concepts and details about how it works as an optimal technique. Then three different types of simulation systems will be used in this part. The first one is a basic distribution system without distributed generations (DGs); the second one is similar to the first one but with load variations; the last simulation system is similar to the first one but with a distributed generation in it. Using three different simulation systems will demonstrate that the coordination of overcurrent relays is influenced by different operating conditions of the distribution system. In Chapter 3, a larger sized distribution system with more distributed generations and loads will be simulated and used for verifying the proposed method in a more realistic environment. In addition, the effects of fault location on the optimum coordination of overcurrent relays will be discussed here. In Chapter 4, the optimal differential evolution (DE) technique will be introduced. Because of the requirement of the online adaptive function, the optimal process needs to be accomplished as soon as possible. Through the comparison between genetic algorithm and differential evolution on the optimum coordination of overcurrent relays, we found that differential evolution is much faster than the genetic algorithm, especially when the size of the distribution system grows. Therefore, the differential evolution optimal technique is more suited than the genetic algorithm to realize online adaptive function. Chapter 5 presents the conclusion of the research work that has been done in this dissertation

    Hardware-In-Loop Evaluation of Microgrid Protection Schemes

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    Distributed energy resources are becoming more common in distribution systems. Higher energy prices and increased interest in alternative energy sources are two of the driving forces behind this trend. Local utilities, however, anticipate very serious distribution system protection problems resulting from high penetration of these resources. The microgrid concept has been proposed as a possible solution to integrating distributed energy resources without adversely impacting the distribution system. Protection schemes have been proposed to work within this microgrid structure, but very little testing with real hardware is available. Without a practical solution for microgrid protection, backed by extensive studies, microgrids are unlikely to receive wide acceptance. This thesis outlines modeling of microgrids for protection testing using a real time digital simulator. In addition, the construction of a low voltage, low power, hardware-in-loop test bed using relays and an automation controller is detailed. The results of testing possible microgrid protection schemes using this apparatus are presented along with conclusions and suggestions for future work

    3D Multi-Objective Deployment of an Industrial Wireless Sensor Network for Maritime Applications Utilizing a Distributed Parallel Algorithm

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    Effective monitoring marine environment has become a vital problem in the marine applications. Traditionally, marine application mostly utilizes oceanographic research vessel methods to monitor the environment and human parameters. But these methods are usually expensive and time-consuming, also limited resolution in time and space. Due to easy deployment and cost-effective, WSNs have recently been considered as a promising alternative for next generation IMGs. This paper focuses on solving the issue of 3D WSN deployment in a 3D engine room space of a very large crude-oil carrier (VLCC), in which many power devices are also considered. To address this 3D WSN deployment problem for maritime applications, a 3D uncertain coverage model is proposed with a new 3D sensing model and an uncertain fusion operator, is presented. The deployment problem is converted into a multi-objective problems (MOP) in which three objectives are simultaneously considered: Coverage, Lifetime and Reliability. Our aim is to achieve extensive Coverage, long Lifetime and high Reliability. We also propose a distributed parallel cooperative co-evolutionary multi-objective large-scale evolutionary algorithm (DPCCMOLSEA) for maritime applications. In the simulation experiments, the effectiveness of this algorithm is verified in comparing with five state-of-the-art algorithms. The numerical outputs demonstrate that the proposed method performs the best with respect to both optimization performance and computation time

    Application of optimization techniques to solve overcurrent relay coordination.

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    Masters Degree. University of KwaZulu- Natal, Durban.Distribution systems continues to grow and becoming more complex with increasing operational challenges such as protection miscoordination. Initially, conventional methods were favoured to optimize protection coordination; however, the implementation process is laborious and time-consuming. “Therefore, recent studies have adopted the utilisation of particle swarm optimization and genetic algorithms to solve overcurrent relay coordination problems and maximise system selectivity and operational speed. Particle swarm optimization and genetic algorithms are evolutionary algorithms that at times suffer from premature convergence due to poor selection of control parameters. Consequently, this thesis aims to present a comprehensive sensitivity analysis to evaluate the effect of the discrete control parameters on the performance of particle swarm optimizer and genetic algorithms, alternatively on the behaviour of overcurrent relays. The main objectives of this research work also include modelling and simulation of distribution system protection scheme, employment of evolutionary algorithms with control parameters that perform efficiently and effectively to maximise protection coordination between relays, optimize relay operating time and maintain the stipulate coordination time interval, and lastly, to outline future recommendations. The distribution network understudy was modelled and simulated on a real-time digital simulator to validate protection settings, and the verification of evolutionary algorithms performance was displayed on Matlab/Simulink. An extensive parametric sensitivity analysis was conducted to understand the impact of the individual control parameters and their respective influence on the performance of evolutionary algorithms. The findings indicate that particle swarm optimization is more sensitive to inertia weight and swarm size while the number of iterations has minimal effect. The results also depict that genetic algorithms’ performance is mostly influenced by crossover probability, mutation probability, and population size. Sensitivity analysis results were verified by comparing the performance of particle swarm optimizer with genetic algorithms, which demonstrated that particle swarm optimization performs efficiently and robustly in solving the considered problem, especially in terms of convergence speed. Furthermore, overcurrent relays were more sensitive, selective, and the operational speed was reduced for particle swarm optimizer compared to other algorithms. The optimal protection coordination achieved using particle swarm optimization showed superiority of the algorithm, its ability to circumvent premature convergence, consistency, and” efficiency

    Optimizing the protection of an auto-recloser in a DG integrated distribution network.

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    Masters Degree. University of KwaZulu-Natal, Durban.The integration of distributed generation into distribution networks is growing as most of the distributed generators have a sustainable power supply and can be used to improve the voltage profile. However, the type of a distributed generator and location in the distribution network can determine how a voltage profile behaves in a distribution feeder. They also contribute fault current in a new or same direction as the fault current from the utility. With this change in the fault current, the existing protection scheme may maloperate since the protection scheme was designed for fault current from the utility generator. One of the protection devices that can mal-operate is the auto-recloser. This is a device used for the self-remediation of the distribution network when there is a temporary fault. The IEEE and IEC standard for the international use of auto-reclosers in voltages between 1000 V and 38 kV states that the minimum tripping current shall be stated by the manufacturer with a tolerance not exceeding +/- 10% or 3 A, and the preferred operating sequence for auto-reclosers shall be; open – time delay of 0.5 seconds - close and open-second time delay 2 seconds - close and open - third-time delay of 5 seconds - close and open then lock out. However, these parameters can be violated when distributed generators are introduced into the distribution network. The change in the fault current may vary the operating time of the auto-recloser and it may not operate in this manner. The inverse time-current characteristics of the auto-recloser relay cause this. However, the operating time problem can be optimized. The inverse time-current characteristic of the auto-recloser relay can be used to formulate the auto-recloser operating time problem. The settings can be optimized to reduce the time and mitigate mal-operations such as protection blinding, fuse and auto-recloser losing coordination, and sympathetic tripping. To optimize the settings, optimization algorithms can be applied. In this research, the development of a single-shot auto-recloser is conducted. The IEEE 13-node and 34- node radial distribution feeders are used as a passive distribution network. The Wind Turbine and Solar Photovoltaic systems are distributed generators. MATLAB/Simulink is used for simulations, and the results obtained show that the integration of the distributed generators into a passive distribution network causes mal-operations in the auto-recloser when there is a fault. The factors that contribute to these mal-operations is the fault location, fault type, distributed generator type, distributed generator penetration and location. However, the auto-recloser shows improvement when the settings are optimized in these conditions

    Improved differential evolution based on mutation strategies

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    Abstract: Differential Evolution (DE) has been regarded as one of the excellent optimization algorithm in the science, computing and engineering field since its introduction by Storm and Price in 1995. Robustness, simplicity and easiness to implement are the key factors for DE’s success in optimization of engineering problems. However, DE experiences convergence and stagnation problems. This paper focuses on DE convergence speed improvement based on introduction of newly developed mutation schemes strategies with reference to DE/rand/1 on ac-count and tuning of control parameters. Simulations are conducted using bench-mark functions such as Rastrigin, Ackley and Sphere, Griewank and Schwefel function. The results are tabled in order to compare the improved DE with the traditional DE

    Real time coordination of overcurrent relays by means of optimization algorithm.

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    Protection is widely used in all different voltage levels of the electrical power system: generation, transmission, sub-transmission and distribution etc. An overcurrent relay is a protection that is widely implemented in the sub-transmission and distribution systems due to its competing cost. Depending on the operative conditions and fault locations in a mesh system, the load or fault currents can circle in or out of the overcurrent relay's protective zone. Hence directional overcurrent relays are used to discriminate whether the fault is located in or out of the protective zone. The propose of coordinating the overcurrent relays is to encounter settings that minimize the operation time for faults within the protective zone and at the same time offering pre-specified timed backup for relays that are in the adjacent zones. So the maximum fault current that the relay detects in its protective zone must be greater than the fault currents in the adjacent zones. The above condition is met in radial systems, one source mesh systems and two source mesh systems where the sources are located symmetrically at the end. But the above condition is not always met in the multi-source mesh systems due to the numerous operative configurations. Since the systems cannot operate in the absence of protection, other protection principles must be used, i.e. impedance relay. It is then said that for certain operative configurations of mesh system, overcurrent protection principle is out of range or in other words reaches the limit of its protection principle [1]
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