Single-phase generator

Single-phase generator (also known as single-phase alternator) is an alternating current electrical generator that produces a single, continuously alternating voltage. Single-phase generators can be used to generate power in single-phase electric power systems. However, polyphase generators are generally used to deliver power in three-phase distribution system and the current is converted to single-phase near the single-phase loads instead. Therefore, single-phase generators are found in applications that are most often used when the loads being driven are relatively light, and not connected to a three-phase distribution, for instance, portable engine-generators. Larger single-phase generators are also used in special applications such as single-phase traction power for railway electrification systems. The design of revolving armature generators is to have the armature part on a rotor and the magnetic field part on stator. A basic design, called elementary generator, is to have a rectangular loop armature to cut the lines of force between the north and south poles. By cutting lines of force through rotation, it produces electric current. The current is sent out of the generator unit through two sets of slip rings and brushes, one of which is used for each end of the armature. In this two-pole design, as the armature rotates one revolution, it generates one cycle of single phase alternating current (AC). To generate an AC output, the armature is rotated at a constant speed having the number of rotations per second to match the desired frequency (in hertz) of the AC output. The relationship of armature rotation and the AC output can be seen in this series of pictures. Due to the circular motion of the armature against the straight lines of force, a variable number of lines of force will be cut even at a constant speed of the motion. At zero degrees, the rectangular arm of the armature does not cut any lines of force, giving zero voltage output. As the armature arm rotates at a constant speed toward the 90° position, more lines are cut.