Fig. 1,574.—Triumph pedestal and brush rigging for large revolving field alternators. Carbon brushes are used, carried in box type brush holders. The stand or pedestal here shown is the kind used with the engine and fly wheel types of alternator. The brush studs are mounted on the stand in such a manner that the brushes are easily accessible. The latter carry only the low voltage direct current necessary for exciting the field.
By repetition, the same grouping will suit for any machine having a multiple of 8 or of 10 poles. These two cases are illustrated in figs. 1,572 and 1,573. In the figures, the coils are represented as occupying two slots each, but they might be further distributed.
Turbine Alternator Winding.—For the reason that steam turbines run at so much higher speed than steam engines, the construction of armatures and windings for alternators intended to be direct connected to turbines must be quite different from those driven by steam engines. Accordingly, in order that the frequency be not too high, turbine driven alternators must have very few poles—usually two or four, but rarely six.
Figs. 1,575 and 1,576.—Westinghouse turbine alternator armature construction. Fig. 1,575. View showing dovetail grooves in armature casting; fig. 1,576, laminæ assembled in dovetail grooves of armature casting.
The following table will show the relation between the revolutions and frequencies for the numbers of poles just designated.
| Frequency | Revolutions | ||
|---|---|---|---|
| 2 pole | 4 pole | 6 pole | |
| 25 | 1,500 | 750 | 500 |
| 60 | 3,600 | 1,800 | 1,200 |
| 100 | 6,000 | 3,000 | 2,000 |
Fig. 1,577.—Armature of Westinghouse turbine alternator with end bells removed showing method of bracing the coil ends.