Stator Assembly
The Stator is fixed to the housing of the generator and does not turn. It contains three main sets of windings wrapped in slots around a laminated, circular iron frame. Each of the three windings has the same number of coils as the rotor has pairs of north and south poles. The coils of each winding are evenly spaced around the core.
Scheme 34
The three sets of windings alternate and overlap as they pass through the core in order to produce the required phase angles.
Each group of windings occupy one third of the stator, or 120 degrees of the circle.
The voltage produced by each loop of the stator is at a different phase angle, as a result the output of the stator is divided into three phases.
Two common methods of connecting the windings are
- Y Connection.
- Delta Connection.
The parallel path of the Delta connection makes more current available.
Scheme 35
Rotor Assembly
The Rotor Assembly consists of the rotor shaft, a winding around an iron core, two pole pieces and slip rings.
The rotor shaft is pressed into the core, then six-fingered malleable iron pole pieces are assembled on the shaft against each end of the winding core.
The pole pieces are placed so that the fingers mesh but do not touch. When direct current is passed through the field coil winding, the fingers become alternately North and South poles.
Scheme 36
As a result of this arrangement of poles, the magnetic flux lines will move in opposite directions between adjacent poles.
(Flux lines always move from North to South.)
This arrangement provides for several alternating magnetic fields to intersect the stator as the rotor is turning.
Scheme 37
A slip ring pressed on to the rotor shaft is connected to the two ends of the field winding.
Two brushes are held by springs against the slip rings. One brush is connected through a switch to the battery B+, the other to the voltage regulator.
The brushes conduct only the field current (2 to 5 amps).
Scheme 38
Although different in appearance the Stator Assembly in a brushless generator performs the same functions as the brush type.
Scheme 39
The brushless generator Rotor does not contain the field coil. The pole-finger crowns rotate around a fixed field coil and are magnetized by the flux field of the field coil.
The two crowns form claw-pole half sections and are retained by a non-magnetic ring positioned below the pole fingers.
Rectifier Assembly
The Rectifier Assembly consists of six diodes, a pair of diodes for each stator winding. Each pair contain one positive biased diode and one negative biased diode. By using a pair of diodes that are reversed biased to each other, rectification of both sides of the AC sine wave is achieved. The negative biased diodes allow for conducting current from the negative side of the AC sine wave and putting this current into the circuit as positive current. The use of positive and negative biased diodes provide for full wave rectification because both halves of the sine wave are used.