Conference article

In medium voltage high MVA Turbo-generators, generally Roebel bars are used in slot area. To reduce the circulating current in slot area of Turbo-generators, transposed Roebel bars are located in slots. Because of that large turbo-generators trend to offer a top power density, winding strands being as a Roebel transposition form and strands are insulated against each other. Optimized structure of the Roebel bar can remove the circulating currents which have been generated in the stator windings. The structure of the bar causes an increase in volume of copper used in strands of windings. With increasing the copper volume and length of strands, the rugged magnetic field increases in the slot area. Because of this reason, eddy current losses grow in solid winding strands. Thus there must be a balance between eddy current losses and circulating current losses in Turbo-generators. The optimal transposition way based on a finite analysis model is used to create this balance so to optimize the circulating currents desirably. To reduce circulating current, an optimized transposition should be performed in the end area too. Simulations by finite element confirm the desired effect of transpositions. A 160 MW, 11 KV Turbo-generator has been simulated and the results verified by real data.

Turbo-Generator; circulating current losses; eddy current losses; Roebel bars; copper losses; optimization transposition