Generator Sealing Oil System: Function and Key Components

 
The generator sealing oil system is vital for maintaining generator performance. Its primary role is to prevent external air or impurities from entering while stopping hydrogen leakage, ensuring stable gas purity and pressure within the generator. This system's reliability directly impacts the generator's efficiency, safety, and lifespan. In hydrogen-cooled generators, effective hydrogen sealing is especially crucial. The system uses a dual-flow-ring design, with independent air-side and hydrogen-side oil circulation systems to supply oil to different sealing zones. The following sections detail the system's working principles, components, and key elements.

Working Principle of the Sealing Oil System

 
The sealing oil system works by introducing two independent oil circuits through a dual-flow-ring seal to the air and hydrogen sides of the generator. The oil pressure is always maintained higher than the internal gas pressure of the generator to ensure that hydrogen does not leak and external air cannot enter. The oil pressures on the hydrogen and air sides are equal, with the pressure difference precisely controlled at around 0.085 MPa. This effectively prevents gas leakage while reducing energy loss due to poor sealing. The system includes an oil cooler to remove the heat generated by the friction between the sealing rings and the shaft, maintaining oil and ring temperatures within the specified range.
In addition, the system includes oil filters to remove impurities from the oil, ensuring the cleanliness of the oil, preventing blockages and wear in the oil circuit, and further enhancing the system's efficiency and service life.

Air-Side Sealing Oil System

 
The air-side sealing oil system is powered by an air-side AC sealing oil pump. This pump draws oil from the air-side oil tank, pressurizes it, and passes it through an oil cooler and filter before sending it to the air side of the sealing ring. This ensures that the oil is fully cooled and filtered before entering the seal. Part of the cooled oil lubricates and seals the ring, while the rest returns to the oil pump inlet through the main differential pressure valve. The differential pressure regulating valve precisely adjusts the air-side oil pressure, ensuring that it always exceeds the generator's internal gas pressure by 0.085 MPa, thus maintaining a stable seal. In case of a failure in the AC pump, a standby DC sealing oil pump takes over, ensuring uninterrupted oil supply.

Hydrogen-Side Sealing Oil System

 
The hydrogen-side sealing oil system is designed similarly to the air side. The hydrogen-side sealing oil pump draws oil from the hydrogen-side return oil control box. After pressurization, the oil is sent through an oil cooler, filter, and balance valve to the hydrogen side of the sealing ring. To ensure that the hydrogen-side oil pressure matches the air-side pressure, the system includes bypass pipes and throttling valves for rough pressure adjustment, while the balance valve provides precise regulation. The hydrogen-side DC sealing oil pump is also in standby mode, ready to take over system operation and maintain normal sealing in any situation.

Defoaming Box Design and Function

 
Oil discharged from the sealing ring first passes through a defoaming box, where the mixed gas escapes by expansion, preventing gas buildup in the system. The defoaming box is installed inside the lower end cap of the generator and is equipped with a direct pipe overflow device to control the oil level, preventing excessive oil accumulation. To avoid oil mist circulation within the generator caused by inconsistent pressure between the fan at the turbine and exciter ends, a U-shaped pipe is installed in the connecting pipelines. This ensures smooth internal oil-gas flow. Additionally, the defoaming box contains a float-type oil-level high alarm switch to monitor the oil level, preventing oil from entering the generator and ensuring system safety.

Function of the Differential Pressure Valves

 
The differential pressure valves are critical control elements within the sealing oil system. Two differential pressure valves are installed: the main differential pressure valve and a backup valve. The main valve is connected to the air-side sealing oil pump inlet and outlet, serving as a bypass pressure regulator. This valve automatically adjusts the bypass oil flow based on changes in the generator's internal gas pressure and air-side oil pressure, ensuring the air-side oil pressure is always 0.085 MPa higher than the generator's internal pressure, effectively preventing hydrogen leakage. The backup differential pressure valve is installed in series with the air-side high and low-pressure standby oil circuits, ensuring that the backup oil pressure always exceeds the generator's internal pressure by 0.056 MPa, providing redundancy to the system. If the primary system fails, the backup system can promptly take over.

System Advantages and Safety Features

 
The generator sealing oil system ensures that the sealing oil pressure is always higher than the generator's internal gas pressure through precise differential pressure control and oil temperature regulation, effectively preventing hydrogen leakage and air ingress. The cooling and filtration devices ensure the temperature and cleanliness of the sealing oil, significantly improving the system's reliability and durability. The defoaming box and U-shaped pipe design further enhance system safety by preventing oil mist circulation within the generator, avoiding potential hazards from oil entering the generator. The dual oil pump design ensures system continuity and stability, as the backup pump can quickly take over in the event of a failure in the primary system.

Conclusion

 
As a critical component of a generator's safe operation, the sealing oil system features a precise structure and advanced design. Through the independent oil circulation systems on the air and hydrogen sides, combined with efficient cooling, filtration, and defoaming devices, the system ensures the stability of the generator's internal gas purity and sealing. This significantly enhances the generator's operational efficiency and safety.