Steam turbines have existed for over 90 years. They are devices that extract thermal energy from the steam and convert it to mechanical work in one or more stages. A steam turbine is usually connected to a drive, most often through a gearbox.
The steam temperature can reach 560°C, and the pressure ranges from 130 to 240 atm. Enhancing efficiency by increasing steam temperature and pressure is a fundamental factor in improving steam turbines. However, high temperatures and pressures increase the requirements for turbine lubricants. Initially, turbine oils were made without additives and did not meet these requirements. Therefore, additives have been used in steam turbines for about 50 years. These turbine oils contain oxidation inhibitors and anticorrosive agents and, subject to certain specific regulations, provide high reliability. Modern turbine oils also contain small amounts of extreme pressure and antiwear additives to protect the lubricated components from wear. Steam turbines are used in power plants to drive electric generators. In conventional power plants, their output capacity is 700-1000 MW, while in nuclear power plants this figure is about 1300 MW.
The requirements for turbine oils are determined by the turbine themselves and the specific conditions of their operation. Oil in the lubrication and control systems of steam and gas turbines must perform the following functions:
- hydrodynamic lubrication of all bearings and gearboxes;
- heat dissipation;
- functional fluid for control and safety contours;
- preventing friction and wear of dedendum in the turbine gearboxes during the shock rhythms of the turbine operation.
Along with these mechanical and dynamic requirements, turbine oils must have the following physicochemical characteristics:
- resistance to ageing during long-term operation;
- hydrolytic stability (especially if additives are used);
- reliable water separation (vapors and release of condensed water);
- fast deaeration - low foaming;
- good filterability and high purity.