over single-phase system. Let us see a few of them. . .
Poly-phase AC generator Some AC generators may have more than one coil in the armature core and each coil produces an alternating emf. In these generators, more than one emf is produced. Thus they are called poly-phase generators . If there are two alternating emfs produced in a generator, it is called two- phase generator.
In some AC generators, there are three separate coils, which would give three separate emfs. Hence they are called three-phase AC generators . . .
Three-phase AC generator In the simplified construction of three- phase AC generator, the armature core has slots, cut on its inner rim. Each slot is ° away from one another. Six armature conductors are mounted in these slots. The conductors and are joined in series to form coil .
The conductors and form coil while the conductors and form coil . So, these coils are retangular in shape and are ° apart from one another (Figure . ). Figure .
Construction of three- phase AC generator Coil Coil Coil Initial position 12th - 12th - - - - - Unit ELECTROMAGNETIC INDUCTION AND ALTERNATING CURRENT laminated and is made up of a good magnetic material like silicon steel. Coils are electrically insulated but magnetically linked via transformer core (Figure . ). The coil across which alternating voltage is applied is called primary coil P and the coil from which output power is drawn out is called secondary coil S .
The assembled core and coils are kept in a container which is filled with suitable medium for better insulation and cooling purpose. Working If the primary coil is connected to a source of alternating voltage, an alternating magnetic flux is set up in the laminated core. If there is no magnetic flux leakage, then whole of magnetic flux linked with primary coil is also linked with secondary ) For a given dimension of the generator, three-phase machine produces higher power