Measurements of the currents flowing in the stator frame of a 500 MW turbogenerator

The magnetic leakage fields in large turbogenerators produce currents in the steel frame supporting the stator core. This paper describes measurements undertaken to determine the magnitude and distribution of the currents in the stator frame of a particular generator. Currents are produced mainly by the axial magnetic fields impinging on the core end, and vary linearly with the current in the stator winding. The radial current from the stator core end screen (15 kA per pole) flows mainly through flexible links to the stator frame. A simplified theoretical model is described to demonstrate the effect of different link systems. The results highlight the importance of considering in detail the electrical paths provided to accommodate large currents in the core frame, so that overheating at junctions of components of the frame may be avoided.