Special Motors and Generators

Author: E.E. Kimberly

It is the purpose of this chapter to describe some of the more commonly used motors and generators designed with special characteristics to meet the requirements of special duties.

The Arc-Welding Generator. - The characteristics of an arc-welding generator are similar to those of an ordinary direct-current, compound-wound generator with the series field differentially connected, or one in which the armature reaction is very great. A typical circuit diagram for an arc-welding generator is shown in Fig. 29-1. The open-circuit voltage is adjustable between about 40 and 100 volts.

Fig. 29-1. Schematic Diagram of Separately Excited Arc-Welding Generator

This voltage is desirable for striking the arc, but the voltage across the arc when welding must be of the order of 25 to 40 volts at the chosen welding current. The welding current for a particular weld is chosen by the operator in accord with his best judgment. The welding current is sometimes controlled by a multi-blade switch, by which successive portions of the series-field winding may be short-circuited and the drop of the characteristic curve may be controlled. See Fig. 29-2 for typical characteristic curves of generators of one type.

Fig. 29-2. Characteristics of Welding Generators of One Type With Diverter Switch on Various Steps

With some types of welding generators it is necessary to connect a smoothing reactor in series with the line, to aid in stabilizing the arc. With others, stability is achieved by the design of the generator alone. Every builder of arc-welding generators uses a special circuit scheme and welder design.