Integrated Protection and Control Systems with Continuous Self-Testing

The design of substation protection, metering, and control systems using integration technologies has been developing ever since the advent of microprocessor-based devices. Modern relays include many auxiliary functions beyond their primary function of power system protection. Local and remote metering, local and remote control and status reporting, alarm functions and annunciation, interlocking, oscillographic and sequence-of-event recording are all features that have been required in a substation protection, metering, and control system that can all be provided by modern protective relays when integration technologies are applied. A power system cannot be operated without protection, thus the protective relays are the foundation to build an integrated system upon. Integrated substation protection and control system design has not yet reached the maturity of traditional nonintegrated design architectures. One reason for this is the rapid change inherent in computer and communications technologies. However, if we apply well-developed concepts used for protection system design to the entire integrated protection, metering, and control system, we can create an inherently fault-tolerant and robust system- regardless of the integration technologies used. Unless properly designed, integrated systems can be designed such that inherent redundancies are lost. If the design is approached from the beginning with consideration for integrating protection, metering, and control upon a foundation of modern multifunction programmable relays, we can not only eliminate these deficiencies, we can create a system that has built-in continuous self-test features. We can extend the concept of continuous self-test, which we have enjoyed in the relays themselves, to the entire system. The design concepts discussed in this paper can make problems and failures, which would be hidden in a traditional design, readily apparent so that they can be corrected before undesired operation can occur. These features do not generally require increased cost; instead they are obtained by making use of the capabilities available in the powerful relays currently in use. This paper covers the general design architecture of a protection and control system using powerful multifunction programmable relays. It does not cover power system protection in detail, and it does not cover integration in detail. Rather, the focus of this paper is to discuss design concepts that will help the reader to design a fault-tolerant, robust protection and control system, with continuous self-test features, that takes advantage of the attributes of modern protective relays