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Automatic load following by fossil-fired generating units requires the control of the flow of air and fuel to the boiler, and of the steam flow to the turbine. Prototype load controllers designed to achieve this have been installed at coal and oil-fired power stations within the CEGB. The principle behind their design is that boiler-stored energy is made available only for system frequency regulation. This policy helps to maximise the regulation capability available to the grid system while minimising the cyclic damage inflicted on the plant. Test results and operating experience show that both coal and oil-fired units equipped with such load controllers respond successfully to both loading and frequency regulation demands. Evidence of improved coal-fired combustion efficiency has also been obtained.