Table of Contents
3.4.1 Operation behavior and operation load
As the low pressure turbine and the power turbine are subject to comparable loads, they will both be handled here under the title -low pressure turbine (LPT). The power turbine only serves the actual power output ( "Ill. 2.1-7", "Ill. 2.1-8" and "Ill. 3.1-2" ) whilst the LPT also /only drives the low pressure compressor.
The LPT serves towards delivering power in stationary use ( "Ill. 2.1-7", "Ill. 2.1-9" and "Ill. 3.1-2"). The generator or the aggregate to be driven (e.g., compressor or pump) is normally attached to the low pressure turbine shaft. At aero engines, the low pressure turbine shaft passes through the hollow shaft of the high pressure turbine ( "Ill. 2.1-9") towards the front to the fan or gear box (helicopter). In derivates for stationary use, the shaft is led frequently towards the rear ( "Ill. 2.1-2" and "Ill. 2.1-7"). The LPT shows a high number of stages, in order to make the exhaust energy available as shaft power as far as possible. Normally the original LPT of an aero engine can not be used without modifications for the drive of a generator or a pump ( "Ill. 2.1-2"). It would be a coincidence if the rotor speed of both engines fits. Therefore they must be interconnected with a gear or an especially designed power turbine must be used. The power turbines are for example common for the drive of generators because of their exact fixed rotation speed. Its many big components represent a considerable cost share of the plant. Because of the long and filigree blades the LPT/power turbine is sensitive for bigger FODs. That means for example, that a blade fracture in the gas generator stream up, causes costly secondary failures.
The low pressure turbine rotates clearly slower in comparison to the high pressure turbine and is thermally less loaded. The gas temperatures lie in the front stages of modern engines at about 950 °C and drop at the end of the turbine to exhaust temperatures of under 600 °C The latter is less heat resistant and /or has less or no cooling, so that these components are often life limited, albeit, over relatively long periods of time. The latest generation of engines have a low pressure turbine whose first stages are already cooled and sometimes possess single crystal or directionally solidified material. In comparison to high pressure turbines, the time area temperature gradients as well as the absolute temperatures are clearly lower. In combination with the relatively low centrifugal force load, the probability of failures are, consequently, substantially less.
Operation experiences show that even low pressure turbines feature typical influences, stimulating particular failure mechanisms. These are types of ‘(sulfidation, "Ill. 3.4-2" and 3.4-3) that become effective at temperatures in the low pressure turbine. It is, therefore, precisely for the low pressure turbine, of especial importance to know whether the inlet air of the compressor shows damaging impurities and which qualities the used fuel has. Gas is almost clear of „suspicion“.
