Coal, Nuclear

Advantages of Distributed Control Systems

Issue 4 and Volume 9.

A distributed control system (DCS) centralizes plant operations to provide flexibility and simplicity by allowing central control, monitoring and reporting of individual components and processes. A DCS is designed to control complex processes that can be geographically disseminated using networked control elements that are distributed throughout the system. These features, along with redundancy that is designed into the overall structure to facilitate high system availability and reliability, drive operators of large, complex facilities and processes, such as those used in nuclear power plants, to choose DCS.

Unlike programmable logic controllers, DCS use a suite of configuration tools to set up the database, control logic, graphics and system security. Control applications are distributed to system controllers that are dedicated to specific plant processes utilizing field devices. Control logic can be created and dispersed across the system controllers. This allows changes that must be made to meet new requirements and/or the addition of new controllers or field devices, to be made efficiently and accurately, easing and simplifying updates and new equipment integration.

The controllers and associated inputs/outputs are connected through a redundant communications network to operating and engineering stations. The stations have graphical, easy-to-use displays for data monitoring, data logging, alarming and control. Field devices, such as actuators and sensors, are directly connected to input/output modules that communicate with assigned controllers while reading and reporting real world information, such as pressure and temperature.

DCS are scalable. A DCS can be deployed in an initial installation as a large, integrated system, or as a standalone system that can be added to as planned or needed. New controllers and inputs/outputs can be added throughout a plant. When new systems are added, they become part of the integrated DCS and are automatically updated by the controlling database.

The Westinghouse DCS of choice is the Ovation® DCS platform. The Ovation DCS has the ability to integrate system security models and cybersecurity, advanced alarm capabilities, system-wide diagnostics and multiple simulation solutions that are extended to every new system added. There is redundancy at all levels, from the inputs/outputs to the controllers, at the network level and to the user interface workstations. Operating experience from more than 3,000 power generation installations worldwide has demonstrated system reliabilities in excess of 99.9 percent. The system is also favored for its forward design. It uses many commercially available, off-the-shelf technologies. This facilitates a secure, powerful architecture that avoids obsolescence by enabling system progression to adjust to rapidly advancing computer technologies. Deployment to operating and new nuclear units solidifies a 25 year working forward compatibility.

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