In August 1996 a Long Spruce generator experienced a
phase-to-phase fault between two lower end caps. This had
been preceded 4 days earlier by evidence of phase-to-phase
PD during on-line measurements [20]. Then in 2003 visual
evidence was found, as shown in Figure 20, of reversion of
the epoxy filler of a number of lower end caps. By the use
of infrared scanning it was determined that the lower end
arms were operating at temperatures up to 125oC. This was
corrected by modifications to the air flow to improve the
cooling [24]. All stators at Long Spruce have been rewedged
using radial ripple springs similar to Kettle.
At Limestone there are ten units rated 13.8 kV 156 MVA
90 rpm. The stator core, winding and type of cooling are
similar to Long Spruce. The core has 540 slots. However
IEEE Std 1043 [25] had now been developed which
recommends that voltage endurance tests on the groundwall
insulation be made on the complete stator bar. Previously