Basic Electrical, Electronics And Instrumentation Engineering: UNIT I: Electrical Circuits
Three Phase Supply
A single phase ac voltage can be generated by rotating a turn made up of two conductors, in a magnetic field. Such as ac producing machine is called single turn alternator. But voltage produced by a single turn is very less and not sufficient for practical loads.
THREE
PHASE SUPPLY
A
single phase ac voltage can be generated by rotating a turn made up of two
conductors, in a magnetic field. Such as ac producing machine is called single
turn alternator. But voltage produced by a single turn is very less and not
sufficient for practical loads. So number of turns are increased in series to
form one winding in a practical alternator. Such windings are called armature
windings. OTOS ei tasteni yns is 29gstlov
To
develop a polyphase system, the armature winding in an alternator is divided
into number of phases required. In each section a separate ac voltage gets
induced. A three phase voltage can be generated by using three windings. From
these windings three separate AC voltages will be available having same magnitude
and frequence but they will have a phase difference of 360°/3 = 120° with
respect to each other. All those voltage with a phase difference of 120° will
be available to supply a 30 load such a system is called as three phase system.
Advantage of three phase system:
1.
The output of three phase machine is always greater than single phase machine.
2.
Three phase motors are self starting.
3.
It gives steady output.
4.
Good power factor.
5.
For converting machines like rectifiers, the dc output voltage becomes smoother
if the number of phases are increased.
Generation of Three Phase Voltage
The
armature coils are divided into three groups such that they are displaced by an
angle of 120° from each other as shown in Figure 1.50.
The
phasor diagram of voltage is shown in Figure 1.51. As phasors rotate in
anticlockwise direction, we can say that ey lags eR by
120° and eB lags ey by 120o.
If
we add three voltages vectorially it can be observed that the sum of the three
voltages at any instant is zero.
The
sequence in which the voltages in three phases reach their maximum positive
values is called phase sequence. Generally the phase sequence is R-Y - B.
Basic Electrical, Electronics And Instrumentation Engineering: UNIT I: Electrical Circuits : Tag: : - Three Phase Supply
Basic Electrical, Electronics And Instrumentation Engineering: UNIT I: Electrical Circuits
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