For example: the design is based on the life of 10,000 times. If it is used improperly and the thermal stress is large, the actual life may be only a few thousand times. Therefore, automatic control is required to ensure the service life of the unit. ATC is the automatic start control that guarantees the life of the unit. The imported units have special life control curves and calculation procedures.
ATC detects the temperature at each point of the unit through the ATCI/O channel of the DEH control cabinet, calculates the actual stress of the high-pressure and medium-pressure rotor, and then compares it with the allowable stress to obtain the difference. It is then converted into the target command and rate of change of the speed or load, and the DEH is used to control the speed increase and variable load of the unit. In the whole start-stop group or load change process, the closed-loop automatic control is carried out to keep the rotor stress within the allowable range. In addition to closed-loop control of stress, ATC has complete logic control and closed loops for cranking, warming up, valve switching, grid connection, etc., and for eccentricity, differential expansion, vibration bearing metal temperature, axial displacement and motor of the steam turbine. Various safety parameters such as the cooling system are also automatically monitored.
For the imported unit, the rate of rise is divided into 10 levels from 50 to 500r/min per minute, and the stress of each level of 50r/min per minute can be expressed by the temperature difference △T. When the actual temperature difference is <72°F, the rate is increased by one level every 3 minutes, and the maximum rate is 500r/min per minute; when the temperature difference is greater than 72°F, the rate is reduced by one level per minute, and the minimum rate is 50r/min per minute. The temperature difference is around 70°F, and the rate does not change. The load-increasing rate divides 1.395～13.95MW/min into 10 grades. Each level is 1.395MW/min, and the rising and falling law is the same as the rising rate. If the temperature difference is <72°F, increase the load rate by one step every 3 minutes, and the maximum load rate is 13.95MW/min. The thermal stress can be controlled by controlling the steam change speed of the first stage of the steam turbine, which can be achieved by controlling the load change and the change rate.