Finite element modelling of nonlinear stress grading materials for machine end windings

As machine end windings leave the stator core their surface can be subject to high voltage gradients. The high electric stresses arising here can lead to sparking and erosion. To alleviate the stresses special stress grading materials are applied whose resistivity varies with the applied stress. Since the tape is very thin in comparison with other dimensions a surface representation has been implemented. These materials have been modelled both in the frequency and time domains as an aid to stress grading system design.