A centralized electrical equipment expert maintenance system is bringing order, reduced costs, and a standardized approach to equipment maintenance throughout Minas Gerais state in Brazil. Recognizing inherent problems in a decentralized maintenance system, Companhia Energetica de Minas Gerais S.A. (Cemig), the electrical utility serving the area, is developing a centralized, microcomputer-based maintenance system that builds on the existing records and knowledge of its technicians and engineers to provide full control of the maintenance process. The result is the RME Maintenance Expert System.

Cemig's power system comprises 45 power plants and more than 300 substations scattered throughout the state. Maintenance performed in these several stations is carried out by decentralized regional divisions located in strategic towns. A Central Maintenance Engineering Department is in charge of specific approaches for the whole company as, for example, periodic maintenance, statistical interpretation of maintenance results, maintenance costs and obsolescence.

Such an organizational structure formerly had some problems: - Difficulty in piecing together data generated by the regional divisions. - Lack of test standardization (for instance, what to do? How to do it?). - Lack of a common reference for the record of measurements accomplished.

Until then, there was no efficient tool to warrant such standardization, or to create a common reference and facilitate the analysis of much of the data generated by such maintenance.

Taking into account that thousands of pieces of equipment and hundreds of models exist in Cemig facilities and that there are numerous calculations to be accomplished for the maintenance tests, an idea arose to use computers in maintenance management in order to increase reliability.

The RME Purpose To achieve the standardization desired and the efficiency possible with computers, Cemig's maintenance engineering developed the RME Maintenance Expert System for use with a PC microcomputer.

The main goal of this system is the loading of a Central Database with Results of Measurements and Experiments (RME) of field maintenance. The purpose of the database is to permit engineering maintenance studies at a global level in the enterprise, such as periodic maintenance, maintenance costs, performance statistics, lifetime, obsolescence and statistical investigation. To accomplish this, maintenance tests must be standardized across the decentralized Regional Divisions.

The ultimate goal is the total automation of maintenance tests in the state-of-the-art RME Expert System. Through direct connections of a microcomputer, via an RS232 interface, to an intelligent test set, the RME Expert System automatically carries out the standardized maintenance tests on old equipment as well as on the new digital technology.

The Main Menu The Main Menu of the RME Expert System offers the users the following options: - Printing of standardized test sheets for each piece of equipment, which describe what to do during maintenance. All test values are calculated automatically from technical information (equations, curves, tables) existing in a standardized library and from data entered by customers. This reduces the work in the field and increases reliability of meaningful maintenance data. - Printing of technical maintenance instructions for each model of equipment, which describe how to do the maintenance tests. They also include test diagrams and pictures of the equipment. - Entering of all results obtained from standardized tests carried out during the maintenance program as well as technical features and settings of the equipment. - Queries on the equipments' records are faster and easier than with conventional files. It also reduces the amount of paper consumed. - Reports, which provide managers with a more efficient means of control of service in the field. - Automatic maintenance tests carried out by the system on the old equipment as well as new digital technology.

Standardized Library The RME Expert System is applied to the following areas: protection, switching, transformers, generation and telecommunication equipment. It has first been applied to protective relaying, then to switching and then to transformer equipment. In the future it will be applied to other areas.

Each area has its own standard library, which makes the RME an expert system. These standard libraries are also considered the original source of information for the RME. The contents of this library were compiled from manufacturers' instructions and from experience and know-how acquired along the years by Cemig's maintenance staff. This enables the RME to become a powerful expert system that preserves Cemig's technical knowledge, even when its experts retire.

>From this standard library, standardized test sheets are printed for each device. The sheets describe what to do during maintenance. The maintenance technical instructions for each model of equipment describe how to do the maintenance tests.

Protective Equipment For protective and control equipment, the RME Expert System includes technical information on more than 750 relay models by several manufacturers. Also included in this library are approximately 200 technical maintenance instructions, which cover the 750 relay models.

This library also contains specific algorithms to implement calculations of expected values, admissible range and magnitude of the quantities to be applied in tests. Even very sophisticated and complex relays, and chiefly those of the most up-to-date technology, have been included in this library.

Several relay models have already been standardized, e.g.: IAC, JBC, GCX, BDD, MOD III, SLS, TLS, DGP, etc. by General Electric; L8a, LZ32, LZ92, RAZOA, RADSE, REL511, etc. by Asea-Brown Boveri; CO, CV, IRD, IRV, etc. by Westinghouse.

Switching Equipment For switching equipment, the standard library includes technical features and maintenance tests for more than 419 equipment models of circuit breakers, disconnecting switches, arresters and reclosers. Also included in this switching equipment library are 97 maintenance technical instructions that cover these models.

Much of the equipment has already been standardized: - Circuit Breakers: PK, OR by Dele-Alsthom, HPF by Sprech & Schuh. - Disconnecting Switches: MARK by Brown Boveri, MSM by Magrini; - Reclosers: R, W. - Arresters: XRA50 by Asea, BHF6E by Sprech & Schuh.

Transformation Equipment The standard library for the transformation equipment includes technical features and maintenance tests for more than 47 equipment models of transformers, VTs, CTs and reactors. Also included are 30 maintenance technical instructions that cover these models.

Several pieces of equipment have already been standardized: - Transformers: TMY66 by ABB, HTR-15 by Toshiba. - CTs: AOK and AOT, IMBD by ABB. - VTs: ET by General Electric, PO by Hitachi Line, MPO by Serta.

Automation of Maintenance Tests The state-of-the-art and future trends of the RME Expert System are shown in Fig. 3. This figure shows protective equipment as an example, but the pattern applies to other equipment as well.

The first intelligent test instrument used with the RME Expert System was the F2500 source and later the F2253, both by Doble, Boston, Massachusetts, U.S. These sources can be controlled remotely by using the F2000 communication protocol named DobleCoL, as described below and shown in Fig. 4.

Through direct connections of a microcomputer, by RS-232 interface, to a network of F2000 family sources, the RME running on the microcomputer carries out automatically the standardized maintenance tests on the old equipment as well on the new digital-based technology.

>From the settings entered by users and the specific algorithms for each model of relay included in the standardized library, the RME implements the calculations of expected values and determines the admissible range and the magnitude of the signals to be applied in the tests.

Instead of printing the test sheets, in the option "automatic maintenance tests" the RME formats the commands to the network of F2000 instruments with the calculated values and with some functions developed in Clipper language, which create the sequence of source operations using the DobleCoL protocol, such as required for dynamic tests and fault simulation.

An interrupt-driven communication routine of the RME, developed in C language, controls the full duplex communication between the computer and the sources, sends the formatted commands to instruments and receives messages from instruments via the RS-232 link.

After these received messages have been translated, they are shown on the video and are entered into a database without needing any digitation. If the values are inside the admissible range, they will be shown in green numbers; otherwise, they will be shown in red.

Distributed Information System The RME-Protection standard library has been installed in every Regional Division since February 1992 and in the RME switching and transformation libraries since June 1994.

These RMEs are decentralized and are coordinated and controlled by Central Maintenance Engineering. An efficient coordination and control of these RMEs distributed all over Cemig is obtained through the standard libraries, which are files of standardized and protected data, not accessed by the user, but only by Central Maintenance Engineering. Maintenance Engineering coordinates the RME Expert System and is responsible for adding and updating standardized data in the protected files.

The information system distributed in the microcomputers is made up of the various RME systems installed in the regional departments of the enterprise. Each installed RME loads a regional maintenance database resulting from the corresponding regional maintenance tests being entered in the system. Data transmission to the central maintenance engineering department is done via modem or diskettes through Cemig's internal mail.

Central Maintenance Database A systemic-level central maintenance database is mounted in the Central Maintenance Engineering department. Only a global standardized database like this can guarantee the reliability of various maintenance engineering studies that might include periodicity, average time, costs, performance, obsolescence and equipment lifetime.

The only limit is the maintenance engineering professionals' imagination. Statistical studies as well as research and investigations about this database are carried out through friendly commercial database management systems, such as Foxpro and Access by Microsoft among others.

Benefits - Reduction in maintenance costs due to reduction in maintenance time. - Leverage of experts' knowledge in preventive maintenance. - Better operational performance of the equipment as a result of greater reliability of the tests. - Guarantee of technical superiority because the RME system, with its standardized technical library, contains and expert system that preserves the technical expertise even when specialists of the enterprise leave the company or retire. - Even when performed by third parties, the RME system guarantees that maintenance will be done according to standardized methodology. - Full control of the maintenance process is obtained by standardizing processes and control items through the systemic maintenance database.

Conclusion The RME is considered a new maintenance tool that has an extra-ordinary potential to eliminate old problems in maintenance engineering, such as absence of standardized maintenance tests, difficulty in data acquisition and absence of a common reference for statistical analysis.

Little information exists about similar systems, which causes us to believe we have an original product in the global marketplace.

Due to independence of RME in the company organization, its independence of programming of services, and because it focuses only on the equipment, the RME transcends Cemig's environment and is available for use by other electrical utilities and industries.

With its proposal of a Total Quality Control program, Cemig recently set a goal to be among the best companies in the world in its niche. The RME Expert System is contributing to this goal in the maintenance area.

Dilmar G. Cunha received the electrical engineering degree from Pontifical Catholic University of Minas Gerais, Brazil, in 1979. He was employed by Cemig from 1976 to 1997. He has worked at protective equipment maintenance from 1979 to 1984 and from 1985 to 1997 in the maintenance engineering area. He became a system analyst and since 1989 has been working at the development of the RME Expert System. In 1995 on The First National Seminar of Electrical System Maintenance (I SEMASE) he received the Best Work of the Seminar award. This year he began to develop the automation of maintenance tests. He was a member of the CIGRE Working Group 34-06 and has written several papers about equipment maintenance. He is working as a consultant developing a Windows 95 version of the RME System.

Andre L. M. Costa received the electrical engineering degree from Pontifical Catholic University of Minas Gerais, Brazil, in 1993. He has worked at Cemig since 1978 performing protective equipment maintenance and in maintenance engineering area. Since 1990 he has been working on methodology standardization that is included in the library of the RME Expert System. Recently, he began to use his experience in the algorithms of dynamic tests and fault simulation of the maintenance automation process.

Joao L. O. Gomes received the B.Sc in 1993 from Newton de Paiva Faculty. Esp. in advanced math in 1996 from Pontifical Catholic University of Minas Gerais, Brazil. He has the M.Sc. in electrical engineering (in course) also at Pontifical Catholic University of Minas Gerais. He has worked at Cemig since 1982 in protective equipment maintenance and in maintenance engineering. His activities over the last six years include the standardization of methodology in the RME Expert System and in user support and management of the Systemic Maintenance Database. He recently began to work on the maintenance automation process.