Topics 2 3 multiphase systems topic b23

Solve Problems in Single and Three
Phase Low Voltage Circuits
Topics 2 & 3: Multiphase Systems


Multiphase Systems


The main objective of a multiphase system is to produce a more
efficient source of electrical energy.
 Single-phase system





significant periods of low voltage generation
these periods still require energy from the prime-mover to rotate the
conductor loop past these points.

Multi-phase system



additional conductor loops added inside an alternator
greater electrical energy output can be achieved for each rotation


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eg. a second conductor loop installed onto the alternator of a single-phase

alternator will provide a two-phase system.

Nathan Condie

2


Three-Phase System


Preferred system for electrical energy
distribution in Australia.


Three separate conductor loops installed onto a
alternator shaft and rotated inside a magnetic
field*.


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Provides the most effective generation of voltage for
minimal increase in construction complexity

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3


Three-Phase System: Modern

Arrangement

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Advantages: Three-Phase System
A higher output of electrical energy can be achieved

1.

1.
2.
3.
2.
3.
4.
5.

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1Ø ~ 64%
2Ø ~ 90%
3Ø ~ 96%
Two voltages are available – phase-to-neutral, and phase-tophase
The electrical power delivered is more constant
Three-phase machines are smaller than single-phase machines

for the same power output
For an electrical distribution system, the quantity of copper
material required for three conductors is less than that required
for an equivalent single-phase, active and neutral system.

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5


Generation of a 3Ø Waveform
A Phase B Phase C Phase

North
B2

2400

C1

A1

A2

C2

B1

1200

South

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Generation of a 3Ø Waveform
A Phase C Phase B Phase

North
B2

C1

A1

A2

C2

B1

South

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Phase Sequence (or phase rotation)
Phase sequence
 Determined by the order in which the voltages induced in each
conductor loop reach their positive peak values




Normally A-B-C.

By reversing the direction of rotation of the alternator, the phase
sequence can be reversed to produce a reverse phase
sequence


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Eg. A-C-B.

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8


Phase Sequence (or phase rotation)
Phase sequence

 For generation purposes, a phase sequence of A-B-C is
essential to ensure all alternators are producing waveforms that
are IN-PHASE with each other.


However, for three-phase loads such as motors, the connection
sequence can be selected to produce the desired direction of
rotation.

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Nathan Condie

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