Improving the Incremental Regulation of Steam Turbines Equipped With Mechanical Hydraulic Control (MHC) Systems

Prior to 1970, mechanical hydraulic control (MHC) systems were used as the industry standard for operating steam turbine generators in the USA. These systems were primarily designed for safe, reliable, efficient base load operation close to nameplate rating. Today, most steam turbine generators rated at 400 megawatts (MW) or below are required to operate in some form of automatic load following central dispatch control mode. This mode of operation necessitates the need to provide a predictable linear output response to a specific demand input signal within a wide load range. A typical MHC system “Fig.1” performs multiple proportional response functions. The contents of this paper focus on the proportional relationship of the hydraulic operating cylinder stroke relative to the steam flow resulting from control valve lift specific to steam turbines manufactured by the General Electric Co. and Allis Chalmers Co. The purpose of this paper is to raise the level of awareness to: 1. The reasons why most MHC systems have difficulty operating in automatic load following mode. 2. The major factors contributing to this operating problem. 3. A proven methodology to quantify the influence of these major factors. 4. A proven cost effective approach to improving non-linear steam flow without major modifications.