AC GENERATORS construction

AC GENERATORS construction

AC GENERATORS consists of a Field Winding, an Armature (Coil), Slip Rings and Brushes as depicted in the below picture:

Field Windings are magnets used to produce the magnetic field in a generator. The magnetic field can be provided by permanent magnets or by Electromagnets. Most AC

Generators have their magnetic field generated by Electromagnets. Electromagnets are supplied with an external current to keep the magnetic field at its desired magnetic strength.

An Armature (Coil) is the movable coil of wire that rotates through the magnetic field. An Armature (Coil) may consist of many coils (similar to the armature in a DC generator). The difference between the DC Generator and the AC Generator is:

o In a DC Generators Armature the ends of the coil(s) are attached to a commutator.

o In n AC Generators Armature the ends of the coil(s) are attached to slip rings.

Slip Rings are metallic rings connected to the ends of the armature coils(s) and are used to connect the induced voltage to the generators brushes. When the armature is rotated in the magnetic field, a voltage is generated in each half of the armature coil. This voltage is illustrated in the below sine wave of one revolution:

An AC Generator uses slip rings, which will allow the output current and voltage to oscillate through positive and negative values. This oscillation of voltage and current takes the shape of a sine wave. This is typical of the AC Voltage we have in our homes and industry throughout the world.

In DC Generators, a commutator is used to provide an output whose current always flowed in the positive direction .

Brushes in an AC Generator are the sliding contact that rides against the slip rings and is used to connect the armature to the external AC Circuit. As the armature is rotated, each half cuts across the magnetic lines of force at the same speed. Thus the strength of the voltage induced in one side of the armature is always the same strength of the voltage induced in the other side of the armature. Each half of the armature cuts the magnetic lines of force in a different direction. As the armature rotates in the clockwise direction, the lower half of the coil cuts the magnetic lines of force from the bottom up to the to the left, while the top half of the coil cuts the magnetic lines of force from the top down to the right. The voltage induced in one side of the coil, therefore, is opposite to the voltage induced in the other side of the coil. The voltage in the lower left half of the coil enables current flow in one direction, and the voltage in the upper half enables current flow in the opposite direction. This means the voltage and current alternates in both directions as is why it is called ALTERNATING CURRENT VOLTAGE (AC Voltage).

Since the two halves of the coil(s) are connected in a closed loop, the voltages add to each other. The result is that the total of a full rotation of the armature is twice the voltage of each coil(s) half. This total voltage is obtained at the brushes connected to the slip rings, and is applied to an external circuit.