Experimental Studies of Honeycomb Seals with Wavy Ridges on the Rotor

Аннотация

During steam turbine operation in transient modes, contact in labyrinth seals is possible. To avoid such contact in the regular stepped labyrinth seals, specialists of the Ural Turbine Works upgraded the end seals during major repairs in several T-250/300-23.5 type turbines of PAO Mosenergo: the regular seals on the rotor were replaced by straight-flow honeycomb seals with wavy ridges. After this upgrading, there were a reduction of air suctions through the end seals of low-pressure cylinder, the normalization of the ejector operation, and oil watering reducing. However, by these indirect indices, it is impossible to evaluate the actual change of leakages through upgraded seals. Therefore, the comparative experimental studies of flow and dynamic characteristics of the straight-flow seals with classic straight and wavy ridges were implemented. According to the investigation results, the flow characteristics of all studied models of straight-flow seals during transition from classical straight ridges to wavy ones deteriorated. The measurements of nonconservative components of the force in the seal models also revealed a deterioration of dynamic characteristics of the models of straight-flow seals during transition from straight ridges to wavy ones. In the end seals, increasing the nonconservative forces capable to cause a self-excited vibration of the shafting of the steam-turbine plant (STP) does not pose a threat owing to their low magnitude. However, in diaphragm seals, especially in the high-pressure section of STP to the supercritical steam parameters, using new honeycomb straight-flow seals with wavy ridges requires special caution, since these forces reach the highest values in the region of high pressures and are capable, in combination with the overbandage forces and forces arising in the oil layer of bearings, to cause low-frequency self-excited vibrations of shaftings. Taking into account that the level of nonconservative forces in the regular stepped seals is by 20% less than in the straight-flow seals, the transition to the straight-flow honeycomb seals with wavy ridges on the rotor in the diaphragm seals appears inappropriate.