ALTERNATING GENERATORS AND SYNCHRONOUS MOTORS. 213 
advisable to place as much flywheel effect in the alternator 
as possible, or, if it is placed outside it should be close 
to the magnet wheel, which tends to prevent vibration of 
the shaft. It should be noted that the application of solid 
poles or special damping arrangements, such as brass 
bridges between the poles, will considerably assist the 
even parallel running of alternators. 
413. Necessity of Balancing Alternators at Work 
and Causes of Failures.—With modern alternators 
of the rotating field and stationary armature type, there is 
very little trouble connected with their general working, 
provided that the paralleling question is satisfactorily 
solved. 
From a mechanical point of view, it is necessary that the 
magnet wheel should be properly balanced and centred 
inside the armature bore, otherwise a one-sided pull will 
appear, as well as unsymmetry in the magnetic fields and, 
consequently, in the armature E.M.F., which is especially 
troublesome in the case of a closed winding, for instance, 
with a mesh connected, three phase machine, where surging 
eurrents are likely to appear. 
414. Heating and Humming.—Single phase generators 
with solid poles often run cool on a non-inductive load, 
but run hot if the armature earries a lagging current, 
and if wide, open slots are used, a humming noise is 
produced. In both cases the proper rounding of the pole 
shoes, closing of the slots, application of many slots and 
use of a large air gap, will in all probability remedy the 
above defects. 
415. Faults in the Windings.—The most delicate parts of 
an alternator are, of course, the armature and magnet 
windings, but only gross carelessness and inattention will 
cause a breakdown of same. The principal reasons of 
failure are rupture or disconnection of the winding, faulty 
