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When applying computer aids to engineering problems, a major difficulty is data handling. We have used a database management system as the central strucutre for a package of computer-aided-engineering (CAE) software for utility engineers concerned with transmission system protection. This paper discusses the design of the database and its role in the CAE package. The use of database management systems in all such CAE tools is discussed. L THE PROTECTION ENGINEERING PROBLEMThe utility engineer responsible for protection of the transmission system is concerned with the design, operation and maintenance of the protection equipment. The task is described in considerable detail in Ref.[1]. We can summarize his activities as: 1. 2.3. 4.to design adequate protection schemes and select the necessary equipment; to adjust the equipment for proper operation, especially to coordinate primary and backup relays;to insure that the protection system continues to operate satisfactorily; to maintain the necessary records on the protection equipment and on the system operation. This task is time consuming and can be rather tedious. For example, relays are coordinated if the backup relay operates slower than the primary by at least some fixed amount (typically 0.3 seconds) so that the primary relay has an opportunity to function before the backup relay operates. Unnecessary backup relaying would remove more of the network from service. All primary/backup relay pairs must satisfy this condition for all network faults and for all credible, abnormal network conditions such as a line outage. Furthermore, once a relay setting is changed, the operation of other relays is affected and the engineer must check all relay pairs again. Clearly, the engineer will benefit from computer aids and a number of such aids have been developed [2,3]. The authors are currently involved in developing a computer-aided-engineering (CAE) tool to assist the protection engineer [1,4].One of the characteristics of the protection engineer's work is the massive quantities of data. For example, in coordinating a modest 10 bus, 15 line network, we encountered 885 primary/backup fault curThis paper was sponsored by the IEEE Power Engineering Society for presentation at the IEEE Power Industry Computer Application Conference, San Francisco, California, May 6-10, 1985. Manuscript was published in the 1985 PICA Conference Record. rent pairs. This data must be extracted from a much larger quantity of fault data for the entire network.Further, each circuit breaker (at all line ends) can be operated by many relays, often of both overcurrent and distance tjpes and each relay is controlled by many parameters. The engineer also needs data describing the network equipment (e.g. line parameters, transformers), the network loading conditions and the maintenance and performance history of the protection equipment.In this paper we describe how we have applied modern database management techniques in developing our CAE tool for protection engineers. We initially incorporated databa...

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