Power Plant Engineering

Fig. 12.4. Overhang arrangement or
2-Pole Rotor (English Electric).
Fig. 12.5. Completed Rotor (Parsons).

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ELECTRICAL SYSTEM
389
12.2.2 STATORS
Large stator housings comprise a series of annular rings flame-cut from steel plate, joined by
tubes and longitudinal bars, and carrying ribs to take the stator core laminations. Fig. 12.6 shows a
simple stator housing requiring two end plates and four intermediate plates, held apart by tie bars. The
core stampings are built up in the frame, the end plates places in position, and the whole stator clamped
together by bolts. The frame is then covered with sheet steel.
Assembly
End Plate
Centre Plate
Fig. 12.6. Method of Fabrication Turbo-Generator Stator Housing.
(a) Core. The active part of the stator consists of segmental lamina-tions of low-loss alloy steel.
The slots, ventilation holes and dovetails or dovetail keyholes, are punched out in one operation. The
stamp-ings are rather complicated on account of the number of holes and slots that have to be produced.
The use of cold-rolled grain-oriented steel sheet has possibili-
ties in machines as well as in transformers, most particularly in two -
pole machines where the major loss occurs in the annular part of the
core external to the slotting. Here the flux direction is mainly circum-
ferential, and by cutting the core- plate sectors in such a way that the
pre-ferred flux direction is at right-angles to their central radial axis,
Fig. 12.7, a sub-stantial reduction in core-loss can be secured.
It is of great importance that the assembled stator laminations
are uniformly compressed during and after building, and that the slots
are accurately located. The core plates are assembled between end
plates with fingers projecting between the slots to support the flanks
of the teeth. The end plates are almost invariably of non-magnetic
material, for this greatly reduces stray load loss. The end packets of
core plates may be stepped to a larger bore for the same reason.