The performance of a DC motor is closely tied to its method of excitation. Typically, there are four types of DC motor excitation: separately excited, shunt-excited, series-excited, and compound-excited. It is essential to understand the specific characteristics of each of these four methods:
1. Separately Excited DC Motor: The excitation winding has no electrical connection to the armature; the excitation circuit is powered by a separate DC source. Consequently, the excitation current remains unaffected by changes in the armature terminal voltage or armature current.
2. Shunt-Excited DC Motor: The circuits are connected in parallel, resulting in current division; thus, the voltage across the shunt winding is identical to the voltage across the armature. However, the shunt winding is wound using fine wire with a large number of turns; this configuration results in high resistance, thereby limiting the excitation current flowing through it to a relatively low value.
3. Series-Excited DC Motor: The circuits are connected in series, resulting in voltage division; the excitation winding is connected in series with the armature. Consequently, the magnetic field within this type of motor varies significantly in response to changes in the armature current. To minimize power losses and voltage drops within the excitation winding, its resistance should be kept as low as possible; therefore, the series winding in a DC motor is typically wound using thick wire with a relatively small number of turns.
4. Compound-Excited DC Motor: The magnetic flux within this motor is generated by the excitation currents flowing through two distinct windings.
