ADVANTAGE OF STATIONARY FIELD, ROTATING ARMATURE

1. Application

• Used in applications involving small amounts of power. With larger amounts of power, a great deal more current flow occurs through the slip rings and brushes. It is difficult and expensive to build slip rings and brushes to carry large amounts of current.

2. Disadvantage

• The slip-ring and brush assembly is in series with the load circuits and, because of worn or dirty components, may interrupt the flow current.

ADVANTAGE OF ROTATING FIELD, STATIONARY ARMATURE

1. Application

• Because the output power is taken from stationary windings, the output may be connected through fixed terminals.

2. Disadvantage

• Load can be connected to the armature without moving contacts in the circuit.

• It is much easier to insulate stator fields than rotating fields.

• Much higher voltages and currents can be generated.

• Larger amounts of currents can be handled because there are no sliding contacts and the whole output circuit is continuously insulated.

STATIONARY FIELD, ROTATING ARMATURE

• Small AC generators usually have a stationary field and a rotating armature.

• Stator provides a stationary electromagnetic field.

• Rotor, acting as the armature, rotates in the field, cutting the lines of force and producing the desired output voltage.

• Output voltage is taken from rotor by slip rings and brushes.

• One slip ring is attached to each end of the rotating loop.

• The brushes make sliding electrical contact with the slip rings.

• The generator's AC output voltage can be transferred from the slip rings through the brushes to an external circuit

ROTATING FIELD, STATIONARY ARMATURE

• Direct current from a separate source is passed through windings on the rotor by means of slip rings and brushes.

• This maintains a rotating electromagnetic field of fixed polarity (similar to a rotating bar magnet).

• The rotating magnetic field of the rotor extends outward and cuts through the armature windings embedded in the surrounding stator.

• As the rotor turns, alternating voltages are induced in the windings because magnetic fields of first one polarity and then the other cut through them

pOLY - PHASE GENERATOR

Most electric power is generated and distributed as threephase rather than single-phase power for the following reasons:

• A three-phase generator has a 180% greater capacity than a single phase generator of the same physical size.

• Single-phase voltage and power is easily available from a three-phase system by merely tapping any two of the power leads.

• The cost of transmission is less than for the same voltage and power in a single - phase system.

3 PHASE GENERATOR

• A three-phase AC generator is designed to produce three-phase AC power by building more coils in the stator around the rotor.

• The 3 coils are equally spaced 120° apart around the inside of the stator.

• The armature coils are wired so that the generator has three separate output voltages that differ in phase by 120°.