3 THERMOSETTING INSULATION
Thermosetting insulation is usually Class F (155 oC).
3.1 LARGE FLAKE MICA, POLYESTER RESIN
VPI PROCESS
In Manitoba Hydro the largest number of units with
large flake mica bonded with polyester resin by the VPI
process are the twelve units rated 13.8 kV, 120 MVA 90
rpm installed at Kettle during the period of 1970 to 1974
(Table 5). Each stator has 600 slots with a total of 24
circuits with 25 three-turn coils between line and neutral.
The stator core and frame together with factory installed
stator coils was shipped to site in four sections. There are
normally 38 coils in a lift and these coils are heated to
110 oC at the knuckle. Single coils are heated to between
70 and 80 oC prior to insertion. The coils were supplied
with an asbestos armour tape in the slot section and there
was no side packing. As these coils have a stress control
coating on the end arms in-stator measurements of Tan δ
tip-up are of limited value because guard electrodes
cannot be applied [14].