Pumped-storage power stations (PSPS) function as integrated hydroelectric energy engineering complexes capable of both power generation and energy storage. By utilizing surplus off-peak electrical energy to pump water from lower to upper reservoirs and releasing it back to generate electricity during peak demand periods, these facilities have evolved into an indispensable regulatory cornerstone for modern, resilient power grids.
Within the auxiliary infrastructure of a PSPS, the Compressed Air System (CAS) serves as the critical kinetic source ensuring the operational safety of the hydro-generator units and facilitating high-frequency mode switching. Structurally and technologically, the CAS is categorized into Medium-Pressure Compressed Air Systems (primarily dedicated to water depression for synchronous condenser operation and governor air supply) and Low-Pressure Compressed Air Systems (allocated for mechanical braking and maintenance operations). The transient response capability of these systems directly dictates the dynamic regulation performance of the units within the evolving power grid network.
1. Medium-Pressure Compressed Air System: Core Kinetic Energy and High-Pressure Control Source
Operating typically within a pressure range of 4.0 to 8.5 MPa, the medium-pressure compressed air system generally utilizes reciprocating piston air compressors as its primary supply source. This system is designed to sustain frequent operational mode transitions and high-pressure energy-storage control components. Its high-load consumption points and instantaneous air replenishment demands are subject to stringent technical criteria, spanning five primary application scenarios:
● Pumped-Mode Startup and Water Depression for Synchronous Condenser Operation: When transitioning from standstill to pumped-mode startup, or into a synchronous condenser operating state, the system is required to inject high-pressure air into the runner chamber within an ultra-short interval. This forces the water level down below the guide vanes—a process known as "water depression startup"—effectively eliminating the massive hydraulic resistance caused by the runner rotating in water. Consequently, the medium-pressure source must deliver exceptional instantaneous displacement and volumetric energy storage.
● Replenishment for Air Leakage during Runner Rotation: During synchronous condenser operation, the runner rotates at high speeds in an air-filled chamber. Due to physical tolerances and leakage across the main shaft seals and guide vane clearances, the compressed air within the runner chamber continuously dissipates. The medium-pressure system must perform dynamic, closed-loop air replenishment to maintain the water level safely below the critical threshold, preventing catastrophic vibrations induced by water-runner contact.
● Pressurization of Governor and Inlet Spherical Valve Accumulators: As the power source for the station's core control valve groups, the oil-air accumulators of the governor and the inlet spherical valve must maintain a high-pressure air cushion over prolonged durations. The medium-pressure system provides both initial charging and precise operational replenishment, ensuring that the hydraulic transmission system retains sufficient energy release velocity to meet the required response times for rapid regulation and emergency valve closure.
● System Purging: The system executes routine high-pressure pneumatic purging of critical pipelines and essential valve bodies, eliminating internal impurities to guarantee the cleanliness and operational reliability of the equipment.
2. Low-Pressure Compressed Air System: Mechanical Braking and Utility Power Source
Operating at standard pressures between 0.6 and 1.0 MPa, the low-pressure compressed air system is engineered to satisfy the continuous demands of routine operations, maintenance, and mechanical braking. Rotary screw air compressors are predominantly selected as the supply equipment for this configuration.
● Mechanical Braking of Hydro-Generator Units: Upon execution of a shutdown sequence, as the speed of the motor-generator decelerates to the critical threshold of 30% to 35% of its rated speed, the low-pressure system delivers compressed air to actuate the pneumatic brakes (brakes). By applying mechanical friction, the unit is brought to a rapid, stable, and complete halt, preventing prolonged creeping at low rotational speeds which would otherwise lead to the burning and failure of the thrust bearings.
● Plant-Wide Maintenance and Pneumatic Tool Supply: This subsystem provides a standardized, distributed industrial power source for maintenance junction boxes, pneumatic tools, and auxiliary servicing equipment across all floor levels of the powerhouse.
Although traditionally classified as "auxiliary equipment," the technical performance of the compressed air system directly influences the safety margins of the primary machinery within the macro-context of constructing highly flexible and resilient modern power grids. In strict accordance with industry technical standards promulgated by the National Energy Administration and the China Electricity Council, the transient response accuracy and pressure stability of the CAS represent the core driving metrics determining the success rate of operational mode transitions and the overall quality of frequency and peak regulation services.
