B12 ALTERNATING GENERATORS AND SYNCHRONOUS MOTORS. 
410. Speed and Flywheel Effect.—The amount of the 
necessary flywheel effect is usually specified by the engine 
maker and the alternator designer has to dispose his 
material accordingly. 
For medium and high speed alternators it is not difficult to 
comply with the specification of the engine maker, but for 
low speed generators the placing of the rotating weight 
inside the magnet wheel becomes a vital question, which 
needs very careful consideration. 
411. Values of Flywheel Effects.—It is a general practice 
to express the flywheel effect by the product of the re- 
volving weight in tons, multiplied by the square of the 
gyration diameter in feet. 
TABLE 24. 
KVA 200 300 > 500 800 
FlywheelEffectin| Nor- | Maxi-| Nor- | Maxi- | Nor- | Maxi-| Nor- | Maxi- 
Ton Feet Square.} mal. | mum.| mal. mum. |] mal. mum.| mal. mum, . 
; 200 110 | 200 | 165 | 295 | 235 | 370 | 410 | 620 
a 
mn 
5 150 235 | 460 | 280 | 510 | 600 | 1,000] 800 | 1,200 
Bs 
e3 125 300 | 620 | 680 | 1,000 | 1,100 | 2150 | 1.450 | 2,450 
ms 
= 107 750 | 1,600 | 1,200 | 2.800 | 1,750 | 3,800 | 2,200 | 4,200 
vo 
3 Bish oa 
a 
D 94. 1,100 | 2,400 | 1,800 | 4,200 | 2.800 | 6.500 | 3,500 | 7,400 
Table 24 indicates for low speed alternators the usual values 
of flywheel effects, as well as the maximum values, which 
may be placed ir the magnet wheel of alternators of 
various sizes and speeds. | 
412. Paralleling and Direct Coupled Sets.—The direct 
coupling of prime mover and generator gives the most 
compact arrangement and a good efficiency. It is found 
