AN EXPERT SYSTEM FOR POWER PLANTS Seminar

[born_for seminars]

AN EXPERT SYSTEM FOR POWER PLANTS


DEPARTMENT OF ELCTRICAL & ELECTRONICS ENGINEERING


Abstract: An intelligent fault diagnosis and operator support system targeting in the safer operation of generators and distribution substations in power plants is introduced in this paper. Based on Expert Systems (ES) technology it incorporates a number of rules for the real time state estimation of the generator electrical part and the distribution substation topology. Within every sampling cycle the estimated state is being compared to an a priori state formed by measurements and digital signaling coming from current and voltage transformers as well as the existing electronic protection equipment. Whenever a conflict between the estimated and measured state arises, a set of heuristic rules is activated for the fault scenario inference and report. An included SCADA helps operators in the fast processing of large amounts of data, due to the user-friendly graphical representation of the monitored system. Enhanced with many heuristic rules, being a knowledge based system, the proposed system goes beyond imitation of expert operators’ knowledge, being able to inference fault scenarios concerning even components like the power electronic circuits of generator excitation system. For example, abnormal measurements on generator’s terminals can activate rules that will generate fault hypothesis possibly related to an excitation thyristors abnormal switching operation.

Introduction
Artificial Intelligence is a branch of informatics that was widely adopted in industrial automation during the past fifteen years. AI programs are developed and used in computer science since the early days of digital computers. Only during the last two decades though industry has taken advantage of those special features that make AI so unique in modeling and representing knowledge, as well as imitating the common sense reasoning. The continuous augmentation of available computational strength and the low cost of modern microprocessors on one hand, and the software tools recently developed on the other, leaded in a remarkable expansion of AI applications in the domain of electrical power systems and power electronics.



Expert Systems:
Among others is a very popular AI technique in industry. According to the working group D10 of the line protection subcommittee , An Expert System (ES) is a computer program that uses knowledge and inference procedures to solve problems that are ordinarily solved through human expertise. The main components of an ES are: a) inference engine, b) database, c) user-interface. ES incorporate rule kind of programming. They are currently being used in many applications in the area of power systems and power electronics. Several systems for the short or long term load forecasting have been already introduced based on ES technology .Intelligent SCADA and offline training systems for non-expert operators is another application where ES are often used. All these offline applications are nevertheless not critical for the power system robustness and stability. More and more applications are currently using ES in real time monitoring and/or control, and AI turns to be a common practice in industrial automation. Regarding the category of real time monitoring and control systems, many applications have already been proposed, focusing mainly on topology estimation and fault diagnosis in distribution substations , and on the fault diagnosis and restoration strategies for transmission networks.

Knowledge Based Systems: Go beyond Expert systems in sense that except for imitating the experts’ problem solving behavior, they enrich problem solving strategy with methods that are not originally employed by human experts. Systems that use domain knowledge to guide searches that differ from the experts’ are known as Knowledge Based Systems (KBS).
Intelligent Decision Support Systems: Decision Support Systems (DSS) are computerized tools derived from decision theory used to enhance user ability to make decisions efficiently. They are not intended to offer the final solution, but rather to explore and seek alternative solutions. The intimate decision is left to the user. Intelligent Support Systems (IDSS) add intelligence to existing systems to enhance problem solving
ability and help maintain a broad range of knowledge about a particular domain. They are used for capturing, organizing and reapplying knowledge including decision rules and criteria.
Artificial Neural Networks : That simulate the neural activity of the human brain, deserve the same recognition at the same level as the AI methodologies mentioned above. ANN have already been broadly classified under the AI domain. They do not have some of the AI properties but can be placed under the umbrella of AI technologies. Expert Systems basically mimic the problem solving behavior of experts using domain knowledge acquired through interviews during the knowledge acquisition phase. Knowledge based ES as mentioned go beyond in a sense that they enrich problem-solving strategy with methods that are not ordinarily employed by human experts . The proposed system is designed for the generators and distribution substations protection in power plants. Especially in weak interconnected power systems, operation of plants with over than 1000MVA of installed power can be of great importance for the stability and efficiency of the whole system. An unhandled fault can have a significant impact on power availability for an expanded area of the transmission network. Besides, damage on
a generator would add a very high financial overhead, as generators of this size cost several million Euros. Such unhandled faults have though been reported in the past and can lead even to human casualties. The system is designed to instantly recognize and report abnormalities that can be related to a mechanical equipment failure or to an electrical, or electronic equipment malfunction, or even to a mistaken human operator control instruction.

System Overview

Distribution substations are the interlocking connection points of power plants to the electrical power grid. The state of all substation components (circuit breakers, disconnectors, protection relays etc.) is monitored and recorded to Digital Fault Recorders (DFR) while the electrical values of every circuit breaker, bus, transformer and generator terminal are measured by ad hoc installed current and Voltage-transformers.