Steam Turbine Startup Torque Control via Generator Cooling
Solution Overview
Problem
Steam turbines face challenges during startup and shutdown, including insufficient steam flow leading to temperature issues, excessive rotational speed, and potential shutdowns due to high temperatures, as well as increased heating and reduced availability.
Innovation Solution
A method that utilizes a torque-coupled electrical generator with adjustable cooling air pressure to control torque transmission to the steam turbine rotor, increasing gas friction losses and allowing for controlled steam flow and pressure without excessive rotational speed, thereby improving startup and shutdown processes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If steam mass flow is increased during startup, then steam turbine heating is improved, but radial pressure drop increases causing separation and blade heating
Solution Approach 1:
The invention applies preliminary anti-action by introducing a counterbalancing force (braking torque from the generator) to offset the harmful effects of increased steam flow during startup. The generator is operated in braking mode to create a counter-torque that compensates for the separation and reverse flow caused by high steam mass flow, thereby preventing blade heating while maintaining the heating benefit.
Solution Approach 2:
The invention converts the harmful radial pressure drop and separation effects into a beneficial control mechanism. By operating the generator in braking mode, the system transforms the potentially harmful reverse flow and friction losses into a useful braking torque that controls rotor acceleration and prevents excessive speeds, while the associated steam flow increases turbine heating efficiency.
2Speed
If pressure drop in high-pressure section is increased to reduce temperature, then rotational speed control is improved, but power output decreases
Solution Approach 1:
The invention converts the loss of power output into a beneficial braking torque. By operating the generator in braking mode rather than power-generating mode, the system transforms what would normally be a power loss into a useful control mechanism for limiting rotational speed during startup and shutdown, while the associated pressure drop effectively reduces outlet temperatures.
3Temperature
If generator cooling air pressure is increased, then cooling effectiveness is improved, but gas friction losses and torque increase
Solution Approach 1:
The invention exploits parameter changes by intentionally varying the cooling air pressure in the generator as a control mechanism. By adjusting the cooling air pressure, the system simultaneously controls both the cooling effectiveness and the gas friction torque, using the latter as a beneficial braking force during startup and shutdown operations.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This method enhances plant availability, reduces blade fatigue, and allows for faster startup by managing steam flow and temperature, increasing braking power and condensation temperature, thus extending blade service life and minimizing ventilation-related wear.
Implementation Method 1
the generator rotor exerts a torque on the steam turbine rotor
Implementation Method 2
the generator is cooled with a cooling medium, in particular air
Implementation Method 3
the steam thermally expands, and in the process cools, on a flow path within the steam turbine, wherein the thermal energy is converted into rotational energy of the steam turbine rotor
Implementation Method 4
a hot steam with relatively high thermal energy is conducted via inflow regions into the steam turbine, wherein the steam thermally expands
Data Source
AI summary
A method for operating a steam turbine, wherein the pressure of the cooling medium in the generator is changed not only for cooling but also for increasing or decreasing the torque of the generator on the steam turbine, this being utilized for the purpose of the start-up or shut-down process.