Power Plant Engineering

Fig. 12.2. Conventionally Cooled Rotor
 Fig. 
12.3. 
Arrangement of Conductors Fop. Direct
Slot and Ducts.
Cooling (General Electric Co.).
methods are being developed for direct contact between the rotor coils and the gas coolant. One such
method is shown in Fig. 12.3. The essential feature is the use of straight rectangular tribes for the slot
conductors, ventilated on a cooling circuit separate from that of the stator, the hydrogen gas coolant
being circulated through the tubes by a centrifugal impeller mounted on the outboard end of the rotor.
The slot tubes are connected at both ends by suitably shaped copper bars forming inlet or outlet ports.
The conductors are hard-drawn electrolytic silver-bearing copper, with synthetic-resin bonded glass
cloth laminate insulation.
(c) Overhang. The appearance and arrangement of the overhang can be seen in Fig. 12.4, which
also shows the spigot on which the retaining ring is
centred. The conductors are sloped conically inward
to provide sufficient space for the thickness of the ring,
and are strongly braced to fit closely within the ring
without movement other than that due to unavoidable
expansion. Non-magnetic, magnesium and magnesium-
nickel steels are used for the retaining rings, the non-
magnetic property being useful for avoiding excessive
magnetic leakage and stray load loss.
(d) Fans. The rotor may carry centrifugal or
axial (propeller) fans, the former being more common.
However, restrictions on rotor diameter and the great
length between bearings may make separate fans es-
sential for large machines. They may be coupled to a
shaft extension or be separately driven.
(e) Slip Rings. Slip rings are required for con-
veying the exciting current to and from the rotor wind-
ing. Rings of steel, shrunk over micanite, may be placed
one at each end of the rotor, or both at one end, inside
or outside the main bearing. Fig. 12.5 shows a typical
completed two-pole rotor.