3.3 EPOXY RESIN RICH MICA PAPER,AUTOCLAVE PROCESS
The earliest stator winding insulated by this process
involves the Roebel stator bars of Grand Rapids Unit 4
dating from 1968 (Table 9). This stator was re-wedged in
1990. The stator frame was placed on sole plates with radial
dowels in 1993 in an effort to reduce instances of loose
laminations. In February 2010 an unusual pulse-phase
pattern was observed during on-line partial discharge
measurements as shown in Figure 15. In April of that year a
missing core clamping finger was discovered together with
serious damage to the associated stepped lamination packet
as will be seen in Figure 16. It was concluded that the
anomalous PD observed from the 80 pF coupler in B-phase
in phase windows 135o-180o and 315o-360o had been crosscoupled
through the end windings from C-phase [20].