Method for the short-term adjustment of the output of a combined-cycle power plant steam turbine, for primary frequency control

A method for brief power matching of a steam turbine of a gas and steam power plant, for primary regulation, which turbine has pressure stages comprising at least a high-pressure stage, a medium-pressure stage and a low-pressure stage, comprising:

• opening or closing a medium-stage turbine valve of the medium-pressure stage of the steam turbine in a manner dependent on a required change in power,
• comparing a predefined pressure target value with a pressure measurement, upstream of the medium-stage turbine valve, which provides a measurement of the pressure of a first steam mass flow flowing into the medium-pressure stage,
• opening or closing of a feed for introducing a variable water fraction into the first steam mass flow of the medium-pressure stage or into a second steam mass flow of the high-pressure stage as soon as the pressure measurement has fallen below or has exceeded the pressure target value,
• wherein the variable water fraction is introduced into the steam mass flow until a steam temperature target value is reached, which is determined from a difference between a predefined basic steam temperature target value and an output value of a regulator which has at least proportional action and which evaluates and compensates for the difference between the pressure measurement and the pressure target value.