Electric Circuit Analysis: Unit IV: Three phase circuits

Generation of 3 Phase Voltage

The 3-phase voltage can be produced in a stationary armature with rotating field or in a rotating armature with a stationary field. 3-phase voltages are generated in three separate but identical sets of windings or coils which are displaced by 120 electrical degrees in the armature.

Unit – IV

THREE PHASE CIRCUITS

 

GENERATION OF 3-PHASE VOLTAGE

The 3-phase voltage can be produced in a stationary armature with rotating field or in a rotating armature with a stationary field. 3-phase voltages are generated in three separate but identical sets of windings or coils which are displaced by 120 electrical degrees in the armature. Hence, the voltages generated in them are 120° apart in time phase. This arrangement is shown in Fig.4.1(a). Here, RR' constitutes one coil (R-phase); YY' another coil (Y-phase) and BB' constitutes the third coil (B- phase). The field magnets are assumed to be rotating in clock-wise direction.

The voltages generated by a 3-phase alternator is shown in Fig.4.1(b). The three voltages are of the same magnitude and frequency. But they are displaced from one another by 120°. The voltages are assumed to be sinusoidal. Counting the time from the instant when the voltage in phase-R is zero, the equations for the instantaneous voltages of the 3-phases are expressed as below:


At any given instant, the algebraic sum of the three voltages is zero. It can be proved by adding the above three equations.


Electric Circuit Analysis: Unit IV: Three phase circuits : Tag: : - Generation of 3 Phase Voltage