Optimization of nonstandard Tripping Protection Scheme for radial and meshed power networks with distributed generation systems
Authors
Abeid, SalimaAdvisors
Hu, YantingCounsell, John
Publication Date
2023-05
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The operation of modern distribution networks (DNs) tackles serious challenges due to the integration of distributed generations (DGs). The protection scheme is one of these challenges. Particularly, the occurrence of bi-directional short-circuit current flow that affects the reliability, sensitivity and selectivity of traditional overcurrent relays (OCRs). In addition, the future distribution system with DGs is expected that will be occupied by the meshed networks alongside the classical radial design and alternating between the grid-connected and islanded mode, for enhancing their reliability. The purpose of the present thesis is to introduce practicable protection proposals for such implementations and address pertinent protection issues. In this context, a comprehensive literature review has been introduced in the present thesis critically. The main contribution of this thesis is the introduction of advanced non-standard methods for addressing the coordination problem of OCRs in DNs with a growing integration of DGs in the power system. Firstly, this thesis presents a novel optimal OCR coordination scheme developed using the non-standard current characteristics (NSTCCs) approach. This approach is specifically designed to adjust OCRs. The proposed equation is contingent on a variable dynamic coefficient based on a logarithmic function curve for improving the flexibility of the curve, thus the optimal coordination between OCRs has been obtained throughout different fault modes. For enhancing the performance of the proposed approach on the OCRs coordination in the DNs, two optimization techniques, namely, the genetic algorithm (GA) and hybrid gravitational search algorithm–sequential quadratic programming (GSA-SQP) have been employed. Moreover, Due to the proposed equation including only one variable coefficient, the NSTCCs has efficaciously contributed to reducing the number of constraints to eliminate significant constraints numbers in the coordination between the overcurrent protective relays. Radial networks, including IEEE 9-bus and IEC MG systems as benchmark as well as meshed networks, namely, IEEE 9 and 30-bus systems have been used to test the proposed protection scheme. The results of the proposed optimal OCRs coordination scheme have been compared to standard and nonstandard characteristics reported in the literature. The results showed a significant improvement in terms of the protection system selectivity and reliability by minimizing the operating time (OT) of OCRs, ensuring the coordination between primary and backup relays and demonstrating the effectiveness of the proposed method throughout minimum and maximum fault modes. For radial networks based on GA, the reduction percentages of tripping time by using NSTCCs for IEC MG benchmark without DGs (mode 1), DN with DGs (mode 2) and islanded mode (mode 3) compared to the lowest OT value obtained from literature are 42.24%, 60% and 54.74%, respectively. In addition, for the IEEE9-bus radial network, the comparison is between the proposed NSTCCs, standard current characteristics (STCCs) and nonstandard scheme (NSS) recorded in the literature. The overall OT of proposed NSTCCs on mod 1, mode 2 and mode 3 is reduced by 12.06%, 17.33% and 13.55%, respectively compared to STCCs, while it is reduced by 7.05%, 9.91% and 11.42%, respectively compared to NSS. For meshed networks based on the hybrid GSA–SQP algorithm, the NSTCC approach improves the coordination interval time (CTI) between the primary and backup relays. For IEEE 9-bus system meshed network, the sum of CTI values is reduced compared to the sum of CTI values in ref from literature by 16.87%. The OT of proposed NSTCCs is reduced by 78.97% compared to STCC and 21.33% compared to NSS. Furthermore, the NSTCC decreased the total OT in the meshed 30-bus test system by 54.4% and 37.9% compared to the literature methods STCC and NSS, respectively. The suggested NSTCC technique is an important development that could greatly enhance the reliability and selectivity of power systems. Secondly, this thesis investigates the impact of immoderate fault current owing to the presence of DGs on traditional IEC characteristics. The shape of these characteristics has been adjusted to obtain such characteristics. The non-standard characteristics approach (N-SCA) has been proposed for optimal coordination of OCRs installed in DNs by extending the IEC normal inverse characteristics to fifty plug setting multiplier (PSM). Furthermore, an artificial intelligence hybrid algorithm based on water cycle moth flame optimization (HWCMFO) has been proposed as a new optimization technique in OCRs coordination protection to optimize the maximum PSM limits. Several modes have been implemented and tested with an IEC MG benchmark and carried out in MATLAB and NEPLAN software, the obtained results have illustrated the effectiveness and applicability of N-SCA based on the HWCMFO technique considering the limitation of IEC characteristics. The N-SCA outperforms the conventional approach for various fault locations in the several operational modes. For mode 1, mode 2 and mode 3, the total OT is reduced by 6.32%, 5.61% and only 0.35%, respectively. Particle swarm optimization (PSO) technique is used for comparative purposes. Using the HWCMFO technique reduced the computing speed compared to PSO by 86.59% for mode 1, 29.69% for mode 2 and 89.18% for islanded mode. Moreover, the best cost function values of the proposed HWCMFO technique is reached at less than the PSO technique for all operational modes. For mode1, mode 2 and mode 3, it is reduced by 74.26%, 63.39% and 65%, respectively. Therefore, it is demonstrated that the presented HWCMFO algorithm is suitable for identifying the global minimum objective function value in the OCR coordination.Citation
Abeid, S. (2023). Optimization of nonstandard Tripping Protection Scheme for radial and meshed power networks with distributed generation systems [Unpublished doctoral thesis]. University of Chester.Publisher
University of ChesterType
Thesis or dissertationLanguage
enCollections
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