Design and Operation of a Low Speed Test Turbine Facility

In order to investigate in detail the performance of steam turbine stages the Low Speed Test rig at Politecnico di Milano has been adapted. As different designs are going to be compared, very accurate measurement system is required. In order to reduce the performance measurement uncertainty, both thermodynamic and mechanic approach, respectively based on total temperature drop and torque measurement, will be applied. The setup consists of a one and an half turbine stage with an inlet guide vane. The idea is to replicate the condition of a stage for different operating points and the IGV is therefore applied to simulate the presence of an upstream rotor while the second stator provides the downstream potential field at the stage exit. The rig operates in close loop condition and the air is delivered by a centrifugal fan with a maximum pressure ratio of about 1.3; the mass flow is then measured by a Venturi tube and after passing through a plenum and a cooler, enters in the turbine section. The turbine shaft drives a two-stage axial compressor, operating as a brake and equipped with two variable pitch guide vanes (VGV). The compressor allows for an additional pressure ratio, while the fine tuning of the power shaft rotational speed is provided by an electrical motor. The maximum rotational speed for this study is limited to 3000 rpm. Depending on the operation mode and stage setup a maximum expansion ratio of about 1.5 and a maximum mass flow around 15 kg/s can be reached. Two kind of experimental approaches are planned on the rig: the first denominated “performance” will be carried out by the OGTL department of GE Oil&Gas Florence, due to their consolidated experience in global measurements. At the same time, Politecnico di Milano will perform detailed inter-stage measurement with steady probes and time resolved fast response pressure probes. Details of both measurements will be given in this paper. The paper will conclude with the presentation of the operability of the rig obtained with the flange to flange global measurement acquired in the commissioning phase of the project.