New Protective Relay Characteristics for Meshed Distribution Systems

  • Khaled A. Saleh

Student thesis: Master's Thesis

Abstract

Directional overcurrent relays (DOCRs) are commonly used for protecting meshed distribution systems. An inverse time-current characteristic is generally used to model such relays where the optimal relay settings are determined by formulating a protection coordination problem with an objective of minimizing the total relays operating time. The problem involves non-linear constraints that assure proper coordination between primary and backup relay pairs. In the literature, the optimal relay settings are determined where coordination constraints are modeled considering only either one fault location (near-end or midpoint) or two fault locations (near-end and far-end) on a feeder. This work first, investigates whether considering one or two fault locations is sufficient to guarantee proper coordination for faults at all other locations on a feeder. The results show that violations, in the coordination constraints, can occur at various points along the feeder if the relays are coordinated considering one or two fault locations. In addition, considering multiple fault locations while determining the optimal relay setting can avoid such problem but on the expense of the overall relay tripping time. Moreover, with the integration of Distributed Generation (DG), the operating time of the protective system becomes of even more concern to avoid nuisance DG tripping. Thus, this thesis proposes two new tripping characteristics for DOCRs that can achieve a higher possible reduction of the overall relay operating time in meshed distribution networks. The proposed tripping characteristics are denoted as a time-current-voltage and a dual-setting characteristics respectively. Both of the proposed DOCR tripping characteristics are described in details. A microprocessor based DOCR prototype is constructed to experimentally implement the two proposed tripping characteristics. Moreover, the protection coordination problem is formulated as a constrained non-linear programming problem to determine the optimal relay settings. The proposed characteristics are tested on several meshed power distribution systems with inverter based and synchronous based DG units. The outcome of the performed studies reveal that the two new tripping characteristics proposed for DOCRs, can achieve notable reduction in total relay operating time over the conventional characteristic while attaining proper coordination across a broader range of possible fault locations.
Date of Award2014
Original languageAmerican English
SupervisorHatem Zein El din (Supervisor)

Keywords

  • Protection
  • Meshed Distribution Systems; Distribution Networks.

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