The heart of a new machine [Powerformer, cable-wound stator machine]

Powerformer (an amalgam of power generator and transformer) is a radically new generator design that could herald a new era in high-voltage generation. The new machine from ABB is a 100 RPM, 11 MVA, 45 kV machine, installed as unit 9 (U9) of the Porjus Hydropower Centre, on the Lule river in northern Sweden. The Powerformer uses a cable-wound stator using XLPE insulated cable. The cable's circular cross section solves the two basic problems arising from the use of conventional, rectangular stator windings. First, within the stator slots, the uniform field in the insulator maximises insulation performance, and hence the voltage rating of the cable. Secondly, bending a cable of circular cross section does not result in the kinks and sharp edges that arise with a rectangular cable. Thus, even in the end regions, where the cable is bent to make the transition from one slot to the next, the electric field within the insulator remains free of singularities. In the end regions of the Powerformer the electric field remains confined within the cable, and the need to control an external electrical field as in a conventional machine, is eliminated.