This paper describes the test rig and the functional tests that have been carried out to define a satisfying solution for the bearing #2 of NovaLT16, the GE Oil & Gas latest high-efficiency Gas Turbine. The bearing #2 is a journal bearing located inside the compressor discharge casing and for this reason it is exposed to high temperatures. As a consequence, the lube oil provided to the bearing should not only lubricate the bearing pads but also cool the bearing housing and for this reason it should be more than what required by the pads. This large amount of oil is gathered by two bearing housing sumps and then drained by gravity through two pipes. Scavenge pumps are not required. The bearing housing also includes two circumferential labyrinth seals able to prevent oil leakage through the gap between the bearing housing and rotor. Both seals are purged by air extracted from the gas turbine compressor; the air not only creates a barrier to oil leakage but facilitate the draining inside the sumps. An insufficient draining system may increase the oil levels in the bearing housing sumps above the safety limit and therefore it may generate oil leakage through the labyrinth seals. If the leakage reaches the external high-temperature zone then it can lead to oil degradation, decrease in GT performances and engine tripe due to smoke in the GT package in the worst case. The draining system was therefore tested with an advanced test rig. The test rig was a 1:1 scale including the bearing housing, the bearing with its pads and also a mock-up of the shaft. The shaft was driven by an electric motor and therefore it was possible to verify the full operating speed range of the gas turbine. The gas turbine discharge compressor casing environment was simulated through electric resistances able to provide heat all around the bearing housing. During the functional tests there have been simulated design and off-design conditions including extreme values of oil pressure, oil temperature, pitch and roll angles (for offshore application), shaft speed and buffering air. The results were mainly evaluated in terms of sump oil levels, shaft temperatures and bearing housing temperatures. The full test campaign allowed to identify and validate a satisfying configuration both for on-shore and off-shore applications and to properly tune all the main bearing parameters in order to guarantee a robust configuration. The NovaLT16 test campaign is part of the continue evolution in the GE O&G bearing #2 area design, started with the previous gas turbines (such as MS5002E and GE10).
展开▼
