Lundell Inductor

Wheeled Vehicle Electrical Systems (Part II)
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This generator type differs from the previously described Lundell type, in that the rotor contains no

windings. Excitation is induced in the rotor poles by stationary field coils located at the ends of the

rotor. This results in elimination of slip rings and rotating windings. Further advantages can be

obtained by casting a nonmagnetic material around the pole fingers, thus producing a smooth rotor

with low-windage losses and high-speed capability. An inherent design requirement of this

stationary field arrangement is the inclusion of an auxiliary air gap in the magnetic circuit. This

requires greater field current for excitation.

A Lundell inductor has several advantages. There are no contamination problems or slip ring wear,

and the unit is inherently explosion proof. The rotor can be solid and permanently balanced. All

windings are stationary and readily accessible for cooling. The low-rotor mass reduces bearing loads

and permits rapid acceleration. The bearing center-to-center distance is minimized by the

elimination of slip rings and this, combined with a large shaft diameter, permits high-speed

operation. The field windings are simple, bobbin-wound coils permitting short mean turn length.

The only disadvantage is that extra air gaps in the magnetic circuit require increased excitation

power.