ELECTRICAL MACHINERY 483 



wound machines there is both a series and a shunt coil 

 surrounding the cores of the field magnets. This style 

 of machine is designed to give automatically a better 

 regulation of voltage on constant-potential circuits than 

 is possible on the shunt-wound machines, and yet pos- 

 sesses the characteristics of both the series and shunt ma- 

 chines. Like the shunt machine a part of the current io 

 shunted from the brushes and around the magnet cores, 

 also the external circuit is thrown around these cores. 

 These machines are designed especially for conditions in 

 which the load is very variable, as street car work, in- 

 candescent lighting and for commercial power purposes. 



648. Classification of dynamos. Dynamos may be 

 classified according to their mechanical arrangement as 

 follows : 



1. Stationary field magnet with revolving armature. 



2. Stationary armature with revo'ving field magnet. 



3. Stationary armature and stationary field magnet with re- 

 volving core. 



They may also be classified by mechanical designs as 

 follows : 



1. Direct-current machines. 



2. Alternating-current machines. 



And by electrical arrangement as 



3. Shunt-wound. 



4. Series-wound. 



5. Compound-wound. 



649. Armatures. The armature core introduced into 

 the magnetic circuit to help lower the reluctance is also 

 an electrical conductor, and when rotated in a magnetic 

 field will have currents set up within itself. These cur- 

 rents are independent of the external circuit, hence are 



