Partial discharge characterization of machine insulation by the transfer of reactive power

In many cases, the electrical degradation of the stator insulation of large machines is preceded by a deterioration in mechanical integrity. Forces on the conductors which result from the interaction of the load current with the leakage slot flux will compress the groundwall insulation. Consequently, delamination or erosion of the structure will result in increased relative movements and concomitant changes in the partial discharge signatures. This paper explores the possibility of detecting mechanical degradation by changing the import or export of reactive power to affect the moment of the application of peak force with respect to the electric stress. Preliminary measurements on hydrogenerators would appear to indicate that this technique does indeed cause some change in the discharge signatures obtained and may permit machines with mechanically deficient slot insulation to be separated from those with intact groundwall structures