Overview
The supply method for the field winding is called the excitation method. DC motors use the following excitation methods.
Types of Excitation
- Separately excited.
The field winding is powered by a separate source and is not connected to the armature winding. Permanent-magnet DC motors also fall into this category, since their main field is established by permanent magnets and is independent of the armature current.
- Shunt-excited.
The field winding is connected in parallel with the armature winding. The field current in this arrangement depends on the voltage across the armature.
- Series-excited.
The field winding is connected in series with the armature winding.
- Compound-excited.
Compound-excited DC motors have both shunt and series field windings on the same main pole core. The magnetomotive forces of the shunt and series windings can add or subtract; the former is called cumulative compound, and the latter is called differential compound. The shunt winding can be connected to the armature in two ways, known as short shunt and long shunt. In practice, long and short compound motors have similar operating characteristics; only the series winding current differs slightly.
