Case study comparison of serial and ethernet digital technologies for remedial action schemes

While special protection systems (SPSs) often shed load, recent sophisticated remedial action schemes (RASs) reduce or terminate generation output during an emergency condition. Under certain load conditions, generation newly added to previously balanced transmission grids creates system conditions that violate accepted reliability criteria. At Southern California Edison (SCE), RAS systems are implemented to ensure reliable power system performance following outages on a transmission grid network. They include fast, automatic control actions to mitigate thermal overloads and system instability upon the loss of one or more transmission lines. With these automatic protection features, RAS systems are used in place of expensive alternative measures, which include reconductoring transmission lines, building new lines, and/or adding new transformers. Testing at SCE demonstrates the successful use of IEC 61850 GOOSE (Generic Object-Oriented Substation Event) messages over a distance up to 720 kilometers to collect analysis and arming data and transfer status and control indications. Complete detection, alarming, calculation, and remediation are completed in well under the 50-millisecond benchmark. These methods of mitigation are intended to be used throughout the SCE area of operation as well as at all interties to neighboring utilities to facilitate dynamic load shedding/generation tripping and improved load management. SPSs and RASs must be put in place to protect existing systems that are called upon to serve new generation and load, are intertied with weak systems, or have geographical characteristics that reduce stability. Once protected, the automatic load and generation control ensures stability while improving production and reliability. Once these are in place, wide-area monitoring and control are safely added via