The steam turbine is a core power device that converts the thermal energy of steam into mechanical work. Its components are designed around four main principles: 'steam energy conversion – mechanical energy transmission – operational control – safety assurance.' Each part works together to achieve efficient and stable energy output. The specific components and their functions are as follows:
1. Core Energy Conversion Section: Steam Flow System
This is the core of a turbine's transformation from "thermal energy → kinetic energy → mechanical energy" and directly determines the unit's efficiency. It mainly includes three key components: nozzles, rotor blades, and diaphragms:
- Nozzles (stator blades): The "first energy converter" for steam entering the turbine. As high-pressure steam passes through the nozzle, the channel narrows, causing the steam pressure to drop and velocity to rise sharply (converting the steam's thermal energy into kinetic energy), forming a high-speed steam flow that prepares for the subsequent work done by the rotor blades.
- Rotor blades: The "executing components" of energy conversion. When the high-speed steam flow strikes the rotor blades, it generates lateral thrust, driving the rotor blades and the connected shaft to rotate (converting the steam flow's kinetic energy into the rotor's mechanical energy). They are the direct source of turbine output power. The shape of rotor blades (e.g., twisted type) must precisely match the steam flow direction to minimize energy loss.
- Diaphragms: The "support and positioning structure" for nozzles. Diaphragms are fixed to the cylinder wall with a central hole for the rotor to pass through. Their main function is to divide the turbine into multiple pressure stages (each stage consisting of a set of nozzles and a set of rotor blades), allowing the steam to expand and do work progressively through multiple "nozzle-rotor blade" sets, achieving stepwise energy utilization and improving overall efficiency.
2. Mechanical Energy Transmission Part: Rotating System
Responsible for transmitting the rotational mechanical energy generated by the moving blades to the generator (or other loads), while ensuring stability during high-speed rotation. The core component is the rotor, with supporting components including the main shaft, couplings, and impellers (or drums):
- Rotor: The "rotating core" of the steam turbine. According to the type of unit, it is classified into "impulse rotor" and "reaction rotor":
- Impulse rotor: Consists of the main shaft, impeller, and moving blades. The moving blades are fixed on the impeller, and the impeller is mounted on the main shaft. It is suitable for high-pressure, small-capacity units;
- Reaction rotor: Has no impeller, and the moving blades are directly fixed on the main shaft (or drum). The rotor has higher overall stiffness and is suitable for medium- to low-pressure, large-capacity units (such as thermal power steam turbines of 300MW and above).
- Main shaft and couplings: The main shaft is the "skeleton" of the rotor, supporting the impeller/moving blades; couplings connect the turbine rotor to the generator rotor (or other loads) and transmit rotational torque. High coaxiality must be ensured to avoid vibration during operation.
3. Fixed Support and Sealing Components: Stator System
Provides fixed support for the rotating system, contains steam, and prevents steam leakage (which affects efficiency) and air ingress (which disrupts vacuum). It mainly includes the cylinder, steam seals, and bearings:
- Cylinder: The "shell" of the turbine. Made of cast steel or alloy steel, divided into high-pressure cylinder, intermediate-pressure cylinder, and low-pressure cylinder (for multi-cylinder units). Internally, it houses components such as diaphragms, nozzles, and rotors, forming a closed steam passage. The cylinder must have sufficient strength to withstand high steam pressure and temperature and must be sealed with flanges and bolts to prevent steam leakage.
- Steam Seals: "Key anti-leakage components." Divided into three types:
- Shaft Seal: Installed where the rotor passes through the cylinder, preventing high-pressure steam inside the cylinder from leaking along the shaft end (reducing energy loss) or air from the condenser side from entering (damaging the vacuum).
- Diaphragm Steam Seal: Installed in the gap between the central hole of the diaphragm and the rotor, preventing steam from flowing between adjacent pressure stages (avoiding interstage energy loss).
- Blade Tip Steam Seal: Installed in the gap between the top of the moving blades and the cylinder inner wall, reducing steam leakage over the blade tops and improving stage efficiency.
- Bearings: The rotor's "support and friction-reducing components." Divided into radial bearings and thrust bearings:
- Radial Bearings: Support the rotor's weight, ensuring stable radial rotation of the rotor and preventing friction with stator components.
- Thrust Bearings: Bear the axial thrust on the rotor caused by steam (due to pressure difference), preventing axial movement of the rotor and maintaining stable gaps between the moving and stationary blades.
4. Operation Control Section: Regulation and Protection Systems
Adjust the turbine output according to external load demands (such as changes in power grid electricity consumption) while protecting the unit under abnormal conditions. The core components include the regulation system and the protection system:
- Regulation System: the "Load Control Center." It consists of a governor, hydraulic actuator, control valve, and transmission mechanism:
1. The governor (such as centrifugal or electro-hydraulic type) monitors the rotor speed in real-time. When load changes cause the speed to deviate from the rated value (e.g., a decrease in grid electricity usage → speed increases), it outputs a signal;
2. The signal is transmitted to the hydraulic actuator, which drives the control valve (installed at the turbine steam inlet);
3. The control valve adjusts the steam flow (e.g., if speed rises, the valve closes slightly to reduce steam), restoring rotor speed stability while adjusting unit output to match the load.
- Protection System: the "Safety Line." When the unit experiences conditions that threaten safety (such as overspeed, low lubrication oil pressure, excessive axial displacement, or vacuum loss), protection actions are automatically triggered, such as closing the main steam valve to cut off steam, or opening the emergency trip valve to release oil, forcing the turbine to shut down and preventing equipment damage.
5. Auxiliary Efficiency Enhancement: Condensing and Lubrication Systems
Although they do not directly participate in energy conversion, these systems determine the operational efficiency and equipment lifespan of the unit, serving as the "guarantee system" for stable turbine operation:
- Condensing System (mainly used for condensing turbines): the "key to efficiency improvement." It consists of the condenser, vacuum pump, and condensate pump:
- Condenser: Condenses the turbine exhaust steam (low-pressure steam) into water, creating a high vacuum (exhaust pressure drops to 0.005-0.01 MPa), significantly lowering the exhaust temperature and pressure of the steam, increasing the enthalpy drop of the steam in the turbine (understood as the "energy difference"), and improving unit efficiency;
- Vacuum Pump: Maintains the condenser vacuum by removing air that leaks in during condensation;
- Condensate Pump: Pumps the condensed water (condensate) back to the boiler for reheating into steam, enabling the recycling of the working fluid (water-steam) and reducing water resource consumption.
- Lubrication System: the "guarantee of equipment lifespan." It consists of the oil tank, lubricating oil pump, oil cooler, and oil filter:
- Lubricating Oil Pump: Pressurizes the lubricating oil from the tank and delivers it to rotating components such as radial and thrust bearings, forming an oil film to reduce friction and wear;
- Oil Cooler: Cools the lubricating oil with water (preventing damage to the oil film caused by excessive oil temperature);
- Oil Filter: Filters impurities from the oil to ensure the cleanliness of the lubricating oil.
Summary: The Coordinated Logic of Each Component
High-pressure steam first enters the steam flow system, where it is accelerated by nozzles to drive the rotation of the moving blades; the moving blades drive the rotation system (rotor), transferring mechanical energy to the generator via a coupling; the stator system (cylinder, steam seal) ensures that steam does not leak and the rotor rotates stably; the control system adjusts the steam input according to the load, while the protection system responds to abnormal conditions; the condensing system improves efficiency, and the lubrication system protects the equipment-each part works closely together, ultimately achieving the efficient conversion of "steam thermal energy → electrical energy (or mechanical energy)."
