Optimal coordination of DOCRs in interconnected networks using shifted user-defined two-level characteristics

• Published in: International journal of electrical power & energy systems 2022-11, Vol.142, p.108298, Article 108298
• Main Authors: Bassiouny Fayoud, A., Sharaf, H.M., Ibrahim, Doaa K.
• Format: Article
• Language: English
• Subjects: Directional Overcurrent Relays (DOCRs); Multi-Objective formulation; One-level Characteristics; Primary, and Backup Relays; Relays Coordination; Time-Current Characteristics; Two-level Characteristics
• ISSN: 0142-0615; 1879-3517
• DOI: 10.1016/j.ijepes.2022.108298

•The paper proposes two characteristics for DOCRs utilizing the flexibility of digital relaying to achieve optimum DOCRs coordination.•The proposed user-defined two-level characteristics and shifted user-defined two-level characteristics are generated by the combination of non-standard settings.•Optimum DOCRs coordination depends on MATLAB m-files for short circuit calculations, fmincon optimization as a simple tool besides formulating multi-objective functions with proper weighting factors.•The proposed characteristics can successfully achieve optimum DOCRs coordination in the interconnected IEEE 30 bus system while satisfying the constraints.•A comparative analysis for applying different multi-objective functions is also carried out to evaluate the effectiveness of the proposed characteristics. This paper introduces a protection scheme for interconnected networks based on proposed Directional Overcurrent Relays (DOCRs) with user-defined two-level characteristics. By getting usage of the capabilities available in modern digital DOCRs, the proposed relay will have two user-defined characteristics; one for its primary operation and another for its backup operation (two-level characteristics) to fit a specific application or system. The coordination between the proposed relays is formulated and solved as a non-linear optimization problem to minimize their operating time and reduce the thermal impact caused by short circuit currents through electrical equipment while maintaining the technical constraints. Extensive comparative studies have been performed to ensure the effectiveness of the proposed protection scheme. Firstly, the performance of the traditional one-level characteristic relay (COLC) with two settings is compared to the conventional two-level characteristic relay (CTLC) with three settings. Then a further investigation is carried out by suggesting increasing the number of settings to seven, named as the user-defined two-level characteristic relay (UDTLC), and then to nine settings, named as the shifted-user-defined two-level characteristic relay (SUDTLC). Finally, different multi-objective functions with proper weighting factors are investigated to determine the most effective one with the best performance for the proposed idea. The distribution portion of the IEEE 30-bus system has been used to test and verify the proposed characteristics extensively. The optimal coordination problem is solved using thefminconfunction in MATLAB. Based on the ach