EXPERIMENTAL INVESTIGATION OF THE OXIDATION INFLUENCE ON THE THERMAL CONTACT RESISTANCE AT THE BLADE-ROTOR-CONNECTION IN A STEAM TURBINE
Flexible steam turbines play an important role within the future energy market. Start-up times and lifetime
consumption can be reduced due to steam turbine pre-warming. The consideration of the thermal contact resistance (TCR) is important especially during an operation with low rotational speed. Several analytical approaches for the determination of the TCR in various technical applications are known from literature. However, according to the author's knowledge no investigation, which satisfies the boundary conditions (material properties, contact pressure, surface conditions and temperature level) appropriately to steam turbine operations is known. In the present paper, the TCR at the blade-rotor-connection of a steam turbine is investigated with a focus on the influence of the oxidation layer thickness on the TCR. The oxidation layer usually increases during the operation time and influences the surface properties and thus, the TCR. Therefore, a steam oxidation rig was constructed which allows the successive oxidation of the specimen in an Ar-50vol.%H2O atmosphere at a temperature of 600°C. Several oxidation intervals were conducted with in total more than 700 hours of oxidation time. Between these oxidation intervals the temperature distribution within the blade root specimen was measured in another test rig, in which the contact pressure was varied up to the equivalent value
of a nominal rotational speed and contact temperatures above 250°C. The results for different oxidation layer
thicknesses are shown and discussed in the present paper.