Field Excitation of Shunt Generator

Author: E.E. Kimberly

The field poles may be magnetized or excited by current from any suitable d-c source, but the current is usually taken from the generator itself. A generator whose field-winding current is obtained from its own armature is said to be self-excited. This may be done by using field coils of many turns of small wire connected in series with a control rheostat across the generator terminals (called shunt connected). The series type of connection in which the field coils are in series with the armature is unsuited to most applications and will be discussed later. The shunt connection is so called because the armature supplies current to its field circuit in shunt with the load circuit if there is one.

The circuit diagram of Fig. 10-13 shows the connections of a self-excited shunt generator with field rheostat.

Fig. 10-13. Diagram of self-excited shunt generator. The field circuit is connected directly across the armature.

A field rheostat is illustrated in Fig. 10-14. The field rheostat is used to vary the terminal voltage within limits. The field circuit has many turns of small wire, and its resistance is high enough to permit its safe connection to the generator at rated voltage without protective resistance.

Fig. 10-14. Shunt Field Rheostat