Power Take-Off for a Shaft-Driven Countra-Rotating Reversible Pump-Turbine

In WP3, the Power Take-Off (PTO) and Machine-Side Control (MSC) are studied and designed. One outcome of task 3.4 was the virtual design of the PTO for the 10 MW shaft-driven contra-rotating RPT. 

For this dual drivetrain PTO, where both runners are coupled to separate Axial-Flux PMSMs, many different configurations are possible and are discussed in this paper.

The virtual PTO comprises coaxial contra-rotating shafts, where the two AF-PMSMs are placed on one side of the RPT, housed inside a bulb. This topology minimises impact on the hydraulic efficiency, while retaining allowable constructional and bearing loads. 

A detailed parametric quasi-static design tool was developed, to allow to scale the PTO design based on different inputs (e.g. RPT designs). First, the Axial-Flux PMSMs are dimensioned based on the rated power and nominal speed of the RPT runners. Some main parameters that influence these dimensions are the cooling method (indirect air cooling, water cooling …), and the relation between the number of phases, rotor pole pairs and stator slots. 

Next, both the short hollow and long solid shaft lengths are determined. Next, based on the radial, axial and moment loads on the shafts and shaft material, the minimum shaft diameters are calculated. Finally, the design tool calculates bearing loads and helps select a suitable bearing, after which the bearing lifetime can be calculated. 

Currently, the quasi-static design for the 10 MW shaft-driven RPT is being validated in FEM. Furthermore, the fatigue lifetime will be evaluated in a realistic case where the RPT is used to provide Frequency Containment Reserve (FCR) to support grid stability.