Lesson 1/Learning Event 2
Brush arc is an explosion hazard; fuel or oil cannot be used safely as a coolant. The rotor winding
is hard to cool and is relatively unreliable in high-speed or rough-drive applications that cause stress
on rotor windings and insulation. The woundpole alternator has an extensive history of
development but is best suited for low-speed applications in a limited range of environments.
The Lundell rotor develops a field by placing the excitation windings around the axis of the rotor
shaft, resulting in each end of the shaft assuming a polarity. Coupled to each end are interspaced
fingers forming opposite polarities that provide an alternating field when rotated. Field excitation is
achieved through slip ring conduction. Advantages of the Lundell rotor are a simple rotor winding
construction and stationary output current windings. Disadvantages are windage (air resistance)
losses and the use of slip rings and brushes.