Main Rotor of Permanent Magnet Generator

Main Rotor of Permanent Magnet Generator

The Main Rotor of PMG

• Is a field that induces voltage in the main stator.

• Powered by the exciter rotor.

• Connected to the (+) and (-) rotating rectifier terminals.

• Coils are connected in series around a core.

• Laminated core is typical

•Solid core with large rotors

• Current flow is directed in a clockwise and CCW rotation to create north and south poles.

• Pressed on a shaft.

Types

Layout

Frequency, RPM, Pole #

If you have a prime mover that runs at 1000

RPM and you wanted 50 Hz, you would need a generator with how many poles?

(50 Hz × 120)/1000 RPM= 6 poles

Damper Cage

• Also called “Amortisseur windings.”

• Copper bars through the pole faces and shorted together by the end plates.

• Standard for all but traction generators, solid rotors.

• Has a very short time constant (effect expressed in datasheets as X”d). 

• Helps with parallel operation

• Helps with load-induced harmonics (non-linear loads).

• Helps reduce initial voltage dip during motor starting.

Magnetism

Magnetic flux paths (i.e. flow of magnetism) for a generator operating at 0.8 PF