At Long Spruce there are ten units rated 13.8 kV 115 MVA
81.8 rpm. The stator core was piled on site and has 684 slots.
The stator winding consists of single turn Roebel bars with three
circuits per phase. Cooling is by means of air-to-water heat
exchangers using water from the Nelson River. Installation of
the units was in the period of 1977/79. The upper end arms are
connected to span jumpers by means of brazed connections and
as installed these were enclosed by a temporary mould which
was filled with epoxy to produce a Blister Pak. In August 1983
two phase-to-phase faults occurred between adjacent Blister
Paks. One such failure is shown in Figure 17. At this time the
river water temperature was 21 oC which was higher than in
previous years. It was concluded that at temperatures of 80oC
and above the insulation resistance and dielectric strength of the
epoxy were greatly reduced. This epoxy was evidently not a
Class F material. The solution was to remove the Blister Paks
from every other connection and to insulate these by hand
applied fully cured mica tape with brushed on epoxy resin as is
shown in Figure 18 and with a minimum air gap of 8 mm. See
also [21].