Abstract—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.
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