Transcript Machine Field: Slides to Complement Class Notes

The Magnetic Field of Synchronous
Machines:
Slides to Complement Class Notes
by Constantine J. Hatziadoniu
Stator Carries a 3-phase ac winding, Rotor
carries a dc winding
Machine with Salient Poles
The Rotor is supplied via slip rings
One phase with concentrated winding:
Flux distribution is rectangular
One-phase distributed winding: Flux space
distribution is closer to sinusoidal
Three phase stator: positive sequence
currents
Phase a is excited by a sinusoidal current: Air-gap field is a
sinusoidal (space) distribution pulsating in time
Phase a field is a two-pole magnet; The magnetic axis
passes through the middle (axis) of the winding
Phase b bi-polar field
Phase c bi-polar field
All three fields added in the air-gap: The resulting
field is a rotating sinusoidal distribution
The combined field (dashed line) moving
around the air gap
…Continued
Instances of the rotating field: Field rotates ones
around the air-gap within a complete electric period
The winding arrangement of a four-pole
machine
Phase a of the 4-pole machine: The spatial
distribution varies twice in a full cycle
Phase b of the 4-pole machine
Phase c of the 4-pole machine
The three distributions shown for the 4-pole
machine
Combined field is a rotating distribution
The 4-pole field rotates ½ times around in one electric period—
the machine speed is reduced to half the speed of a 2-pole
machine
The Rotor Field of the 4-pole machine
Rotor and Stator Fields rotate in step inside
the airgap