-The task of systematically choosing the s e t t i n the relays in a protection scheme is facilitated by the identification of a suitable break point set and the corresponding relative sequence matrix. The concept of functional dependency is used as a means o f developing algorithms for the accomplishment of these sub-tasks. These algorithms are seen to be computationally more efficient than the existing algorithms of the graph theoretic schemes.
INTROOUCTIONProtection engineers select the settings of the relays in a protection scheme on the basis of certain assumptions with regard to the power system topology and the load conditions. Whenever these assumptions lose their validity, such as after a drastic change in the load values, or the removal of a line from service, the relay settings may no longer be appropriate. Hence, it is desirable that these settings be reviewed before any major alterations in the power network are brought about. However, since the manual design of the relaying scheme is a tedious and time-consuming task, the relay settings are not modified as often as is warranted, and there is a consequent degradation in the performance of the protection scheme. The availability of computer-aided design tools has led to efforts in developing automated re lay coordination techniques , which would take the tedium out of the design of protection schemes, thereby encouraging more frequent adjustments in the relay settings, with a consequent improvement in performance. Recent work in this direction is reported by Damborg et a1 [l], Rao and Rao [2], and Damborg and Venkata [3].In this paper, we develop more efficient technique for the automatic coordination of directional overcurrent and distance relays.The earlier work in the field of automatic relay coordination employed graph theoretic schemes [1,2,4,5].Although these schemes do achieve their objective, they require a computation time which is an exponential function of the number of relays, and hence the computation cost is prohibitive when the number of relays is large [2]. In this paper, the concept of functional dependency will be used as a means for the development of algorithms which complete the same tasks in a computational time which is a polynomial function of the number of relays.90 I C 559-5 PWRD A paper recommended and approved by t h e IEEE Power System Ftelayini, Committee of t h e IZEE Power Engineering Society f o r p r e s e n t a t i o n a t t h e 1990 IEEEIPES I n t e r n a t i o n a l ?ower ileeting-Indis, dew Delhi, I n d i a , October 28 -November 1 , 1990.Ilanuscript submitted !larch 30, 1989; mlde a v a i l a b l e f o r p r i n t i n g July 13, 1990.Functional dependency is a concept which arises in data base systems [6,7,8].In the context of power system protection, the setting of each directional overcurrent or distance relay has a functional dependency on all the primary relays for which this relay serves as a backup relay. Hence, all the constraints on the relay settings can be expressed through a set o f functiona...