woundfields

Wound fields are magnetic field sources formed by coils of insulated copper wire wound around a magnetic core to produce flux in electrical machines. The term is used for machines where the field is generated by electromagnets, as opposed to permanent magnets. They are common in DC machines and some synchronous machines.

In DC machines, field windings are energized by a direct current from a separate excitation source, in configurations that can be shunt, series, or compound. The field current sets the magnetic flux, which in turn determines the machine’s generated voltage (in generators) or speed-torque characteristics (in motors). Regulation is achieved by varying excitation current, using resistors, electronic controllers, or brushless exciters. Self-excitation can occur when the machine’s output supplies part of the field current.

Shunt fields are connected in parallel with the armature; series fields in series with it; compound uses both. Shunt fields tend to stabilize speed; series fields provide high starting torque but greater speed variation; compound aims to balance these characteristics. In synchronous machines, the rotor carries a DC field winding supplied through slip rings or brushless excitation, controlling the generated voltage and power angle.

Applications and trends: Wound-field excitation dominates high-power and industrial drives requiring precise control and rapid regulation. Permanent magnets are common in smaller machines but wound-field remains standard for large generators, high-voltage motors, and systems using power-electronic exciters.