Supplement to Recent Practices and Trends in Protective Relaying

This paper is a supplement to ``Recent Practices and Trends in Protective Relaying´´ and includes topics not covered in the previous paper. The evolution in the use of static devices and semiconductors in relay circuits is treated briefly, and some of the benefits and problems in the utilization of these devices are mentioned. The static relays available at present are described, together with some of their advantages and disadvantages. In evaluating the previous paper, it was felt that a section on backup relaying and on the use of digital computers by relay engineers should be included.