Fig. 695.--Watson armature discs. Each lamination is made from low carbon electrical steel of high magnetic permeability. Each disc is annealed and afterwards varnished.
Ques. What trouble is liable to be encountered in operating after cutting out a coil?
Ans. The remaining coils are liable to heat up to a greater extent than formerly, owing to the increased current, hence it is advisable to proceed cautiously in starting the dynamo, since the temperature may exceed a safe limit. If this occur, a resistance may be put in circuit with the field coils, or the speed of the dynamo reduced.
Fig. 696.--Fort Wayne pedestal type commutator truing device. When this device is used, the armature is revolved in its own bearings by means of a handle clamped to the pulley. The tool has a horizontal travel of 21 ins., (being 3 ins. wide inside the fastening bolt in the base), and a vertical adjustment of 12 ins., adapting it to machines with commutators up to 36 ins. in diameter.
Fig. 697.--Fort Wayne yoke type commutator truing device for machines having brush mechanism mounted on a yoke carried by the field frame. It consists of a carriage for the tool holder having a screw feed and a bracket for attaching to the brush yoke. The bracket replaces two brush holder brackets on the brush yoke, and is made to fit the yoke of the particular machine on which it is to be used.
Ques. What kind of dynamo is affected by breaks in the external circuit?
Ans. A series dynamo.