Because of society's full dependence on electricity and high cost of system outages, one important goal is to increase the reliability of the power system, which means that a salient attractive feature of smart grid is its self-healing ability. Smart grids will develop and enhance the automation of distribution by operating in a distributed manner through new digital technologies such as monitoring, automatic control, two-way communication, and data management. In this work, the smart grid concept and technologies have been applied to construct a self-healing framework for use in smart distribution systems. The proposed multiagent system is designed to locate and isolate faults, then decide and implement the switching operations to restore the out-of-service loads. The proposed control structure has two layers: zone and feeder. The function of zone agents in the first layer is monitoring, making simple calculations, and implementing control actions. Feeder agents in the second layer are assigned to negotiation. The constraints include voltage limits, line current limits, and radial topology. Load variation has been taken into consideration to avoid the need for further reconfigurations during the restoration period. The results of the simulation conducted using the new framework demonstrate the effectiveness of the proposed control structure.

A Cooperative Multiagent Framework for Self-Healing Mechanisms in Distribution Systems

Microgrid is a distribution system composed of a set of micro-generators which are added to a network. One serious challenge facing a microgrid network is designing a proper protection scheme. This is because the fault current in a microgrid is constantly changing due to the presence of distributed generation (DG) resources at all levels of the distribution network and to the fact that they can operate in two islanding and normal modes. This makes the conventional methods inappropriate for microgrid protection. That is, new schemes should be developed for this purpose. This paper is a summary of studies recently carried out in the field of microgrid protection. Along this line, the structure and topology of microgrids are reviewed first. Afterwards, the protective challenges facing DG-equipped distribution networks are discussed. Then, the innovative methods proposed to solve these problems are analyzed. These methods can be divided up into six main categories: changing settings of protective devices at presence of DG units, disconnecting pertinent DG units when faults occur, creating a balance among different DG technologies, using fault current limiter, using smart transformers, and adaptive protection. In so doing, we consider the factors involved in selecting each method. The factors identified are microgrid type and topology, DG type, communication type and delay time, method of fault detection and analysis, relay type, fault type, method of grounding, and use of smart transformers in microgrid. It is hoped that this work will be useful to the researchers in the field of microgrid protection in finding relevant references and designing appropriate methods.

An overview of microgrid protection methods and the factors involved

Distribution networks (DNs) gradually become more active and flexible with the massive integration of renewable resources. The conventional protection methods are unsuitable for the promising active DNs. This paper proposes a protection scheme on the basis of measured impedance, which includes an impedance differential method and an inverse-time low-impedance method. The former approach identifies fault instant and provides time reference for the exchanged data. As primary protection, it is able to clear different types of faults as soon as possible. The latter method operates in an automatic coordination way with inverse-time characteristic. It can be used as backup protection or provide protection for single-end lines alone. Both of the methods are independent of operation modes and are able to clear faults with high sensitivity. The efficiency of the protection scheme is validated by PSCAD/EMTDC.

An Impedance Protection Scheme for Feeders of Active Distribution Networks

The smart power grid blends the bidirectional energy with information flow. Compared to the traditional power grid, it requires more intelligent and faster control, protection, automation, and communication techniques. Ultimately, power system protection, fault location, and isolation have to go through an immense modernization process since the previously used protection techniques are no longer usable in the smart grid. This is due to the bidirectional flow of energy and dynamics of the network configuration in the smart grid. Multiagent Systems (MAS) techniques can enable the power system to become smarter, reliable, self-healing, and robust. Its decentralized nature and operational robustness make the MAS application a leading technology. In this paper, the MAS architecture that suits the smart grid application is proposed. Besides, a detailed systematic review on the application of MAS to smart grid protection is conducted. The MAS application for self-healing of the smart grid through Fault Location, Isolation, and Service Restoration (FLISR) is also investigated. Furthermore, based on the MAS architecture, fault identification technique, simulation, and verification methods implemented, a comparison is made among the ongoing research activities on power system protection and FLISR. Consequently, the research gap on power system protection, FLISR, and self-healing is indicated. Finally, the use of IEC 61850 for implementing the MAS technique is discussed. As a result, the use of MAS for adaptive smart grid protection, the challenges in the implementation of the communication among the agents and outside laboratory application of the MAS for the power systems are the research topics that require further work.

Multiagent systems application for the smart grid protection

In this paper, a Multi Agent System (MAS) based on sequence current magnitudes and current direction is proposed for fault location and isolation in a smart microgrid system. Each of the fault types has a different impact on the sequence current components, which along with the direction of the current during a fault can be used for fault location. The microgrid has been implemented by adding Distributed Generation at various locations of the 37-bus IEEE benchmark system and its fault simulation has been done in OpenDss which is an open source distribution system simulation software.

Multi Agent System based fault location and isolation in a smart microgrid system

On the premise of future improvement of information infrastructures, we proposed a multi-agent based protection scheme for distribution systems with high penetration of distributed generators (DGs) In the proposed protection scheme, various relays designed as relay agents cooperate to locate and isolate fault zone Binary state signal, eg current direction, magnitude, etc is determined autonomously just by sensing a sudden change of the current at the relay Each relay simultaneously utilizes binary state signals provided by the other relays at breakers involved to the same zone for detecting a fault location By using PSCAD/EMTDC, the proposed protection scheme is tested with a distribution system which has loop structure and is divided into several protection zones Extensive simulation studies show that the proposed protection scheme can be adopted for various conditions of distribution structure and DGs operation, and may contribute to a selective and quick disconnection of faulted zone with less coordination between relays

Y. Suzuoki

Papers

Multi-Agent based Control and Protection of Power Distributed System - Protection Scheme with Simplified Information Utilization -