Multivariable boiler superheat control at a nuclear power station using PLCs

Two of the four main control systems, the boiler feedwater control system and the steam pressure control system, at a magnox nuclear power station, have been refitted using programmable logic control (PLC) equipment. The work was initiated after a series of tests were conducted which showed that the original control systems could not adequately cope with certain transients, including gas circulator and turbine trips without manual intervention. The author discusses the plant configuration and the need for new control systems. The basic operation of the feedwater control system is discussed as is noninteracting control. The plant matrix is identified and the compensating matrix discussed. Incremental control is also discussed