Numerical Generator Protection Offers New Benefits of Gas Turbines

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This article describes the benefits offered by a new type of numerical protection system, applied to gas turbine generators. World-wide more than 100 different generators with a total rating of about 6000 MW are equipped with this type of protection system. This protection system is completely independent of other power plant equipment, with its own DC power supplies, input isolating auxiliary current and voltage transformers and optocoupler or relay type binary input/output devices as well as serial communication links. The heart of the system is a multiprocessor high speed bus capable of handling the communication between the measuring inputs, the protection algorithm processor (s) and the output units. The system makes use of a large library of modular, pretested protective functions. Continuous self-monitoring enhances the availability of the complete protective system. Modern, well coordinated protection and turbine control systems offer new advantages to the user such as faster handling of emergency situations through the availability of more and better information together with the possibility of faster and more detailed fault analysis. In addition, a reduction in the time required for commissioning, e.g. for cables and instrument transformers, can be realized. This paper is presented to provide some understanding of the application of the protection system introduced here, in particular in connection with the ABB gas turbine generator unit type GT11N. Also introduced are the main components involved, such as numerical protective functions, self-monitoring of protection systems, and data exchange.