Protection coordination in power system with distributed generations

Pao Yue-kong Library Electronic Theses Database

Protection coordination in power system with distributed generations


Author: Wan, Hui
Title: Protection coordination in power system with distributed generations
Degree: Ph.D.
Year: 2007
Subject: Hong Kong Polytechnic University -- Dissertations.
Electric power systems -- Protection.
Department: Dept. of Electrical Engineering
Pages: v, 181 leaves : ill. ; 31 cm.
Language: English
InnoPac Record:
Abstract: Protective equipment is one of the most important secondary devices and has great effect on the operation of power system. Relay coordination is therefore an absolutely necessary work in the process of designing and operating power system. The objective of this thesis is to analyze the changes in power system protection after the distributed generations (DG) are connected to the power system and then search for a new protection coordination scheme and the necessary options for the power systems. A coordination study consists of the selection or setting of all series protective devices from the load to the power supply upstream. A great deal of effort has been devoted to the automation of the solution of the coordination problem, which mainly apply topological, optimal, adaptive and intelligent techniques. Distributed generation (DG) is currently attracting both distribution utilities and electricity users. DG can provide meaningful advantages for not only its owner, but also the utility to which it is connected. The advantages of DG are of both engineering and economic view points. The presence of DG tends to affect the protection coordination. Evidently, the short circuit current would be altered due to the contribution of DG, especially the aggregate contributions of several DG sources. Unacceptable operation of protective device may occur. Since the protection coordination will be lost if the fault current flowing through any protective device is changed, this may lead to the large damage in system and the decrease in system reliability. Over the past decades, many researchers and engineers have focused their efforts on intelligent system applications to various problem areas in power engineering. The reason for attracting their attention is that the technology has great potentials to handle large and complex systems. One of the important application area for intelligent systems is the monitoring and control of complex systems such as power grids. A number of intelligent techniques have been applied to the analysis, control and decision making of power systems. Knowledge-based systems, neural network, fuzzy logic, and other qualitative reasoning techniques have been developed. Most conventional intelligent control systems are centralized and supervised in a top-down fashion. These systems may not be able to appropriately respond to rapid changes in the power systems. Note that the computational effort involves a large amount of information and data. In addition, maintenance of the existing intelligent control systems has become more important since the complexity and uncertainty of the power systems are increasing. A multi-agent approach to pair-to-pair relay coordination has been proposed in this thesis. The proposed multi-agent system consists of a number of relay agents, DG agents and equipment agents. Coordination strategy is embedded in every relay agent to facilitate the relay agents to be coordinated under different system situations. In the coordination strategy, relay settings and time will not be the only parameters that will decide the relay coordination. Relay agents communicate themselves in the relay society and also with DG agents and equipment agents in order to obtain a successful coordination. The validity and effectiveness of the proposed multi-agent system have been demonstrated by applying it to an agent-based platform-"JADE". The communication simulation shows that the successful information communication between agents has been achieved indicating that the proposed multi-agent system is a feasible approach in protection coordination. Further works are carried out by proposing the multi-agent approach to substation protection coordination. The proposed multi-agent system takes the substation as one JADE Agent Container which consists of a substation management agent and a number of relay agents, DG agents and equipment agents. Intertripping and power flow control are the options that can be applied as the coordination strategy. Pre-fault constraints, fault constraints and post-fault constraints have been taken into the consideration in coordination strategy. Relay agents communicate themselves in the relay society and also with substation management agent, DG agents and equipment agents in order to obtain a successful coordination. Based on the substation coordination system, a multi-agent approach to power system protection coordination has been extended. Coordination strategy is embedded both in substation management agent and relay agents. Both intertripping and power flow control are applied as coordination strategy. The substation management agent communicates not only with the agents within one substation, but also with other substation management agents. The coordination between different substations is achieved by the substation management agent. This communication simulation is obtained by the agent communication between different JADE containers. The communication simulation shows that the successful information communication has been achieved not only between agents within one JADE container but also between different JADE containers. The agent based relay coordination has the ability to self-check, self-correct, and rapidly acts while achieving highly selective fault regions backup function when either primary protection or circuit breakers fails. The subsequence work to be continued is to improve the performance of multi-agent system in order to cope with protection coordination in a more complex system.

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