Digital implementation of a feedwater control system for a 500MW boiler

For reasons of obsolescence and increased flexibility to meet National Grid requirements, Didcot Power Station is being refurbished with distributed microcomputer control systems. In addition to modulating control and remote manual control, the scheme provides diverse monitoring facilities. The computer system for each 500MW unit comprises twenty DEC PDP11-73 microcomputers linked by dual Ethernet. The distribution of functions amongst them was chosen for reasons of flexibility, reliability and graceful degradation. Such a distribution ensures that, should a processor fail, control is available from other processors. A hardwired control panel is retained to provide back-up facilities in the event of a computer failure. An in-house, real-time multitasking operating system and high level language were used. Generic software allows for easier maintenance, development and commissioning. A computer simulation and display system has been developed to facilitate the design and analysis process and to test off-line the software to be installed