Measurement of the voltage distribution along the endwinding stress control layer of a turbogenerator stator conductor bar

The development of a satisfactory stress control system for 500 MW machines was achieved using commercially available SiC loaded materials and a full size stress control endwinding model. This was expensive and restrictive to design, and a project was therefore commenced to model the endwinding stress layers to enable correct design for higher voltage machines up to 40 kV line voltage. The current/voltage characteristics of silicon carbide loaded resins were studied to provide the basis for designing a layer of known characteristics by choosing the type and size of silicon carbide. In parallel with that investigation an electrode arrangement was constructed on a specially made full size 500 MW conductor bar to enable the voltage distribution to be measured in amplitude and phase along the length of the endwinding stress control layer. A mathematical model for the stress layer arrangement was also developed to give the design capability to predict and subsequently stipulate a given voltage distribution. This paper describes the measurement and calculation of the voltage along such a layer