Topics 2 3 multiphase systems topic b23

Bài giảng ngành Điện: Giải các bài toán trong mạch điện điện thế thấp một pha và ba pha (Phần B) gồm các chủ đề sau Solve problems in single and threephase low voltage circuits Part B Content Topic 1: AC power and power factor Topic 23: Multiphase systems Topic 4: Threephase STAR connection Topic 5: Threephase, Fourwire systems Topic 6: Threephase DELTA connection Topic 7 Interconnected Star and Delta Devices Topic 8 Energy and Power Requirements of AC Systems Topic 9: Harmonics

Solve Problems in Single and Three Phase Low Voltage

Circuits

Topics 2 & 3: Multiphase Systems

20/07/24 Nathan Condie 2

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

 eg a second conductor loop installed onto the alternator of a single-phase alternator will provide a two-phase system.

Three-Phase System

distribution in Australia.

alternator shaft and rotated inside a magnetic

field*.

 Provides the most effective generation of voltage for

minimal increase in construction complexity

20/07/24 Nathan Condie 4

Three-Phase System: Modern

Arrangement

Advantages: Three-Phase

System

1. A higher output of electrical energy can be achieved

1. 1Ø ~ 64%

2. 2Ø ~ 90%

3. 3Ø ~ 96%

2. Two voltages are available – neutral, and

phase-to-phase

3. The electrical power delivered is more constant

4. Three-phase machines are smaller than single-phase machines

for the same power output

5. For an electrical distribution system, the quantity of copper

material required for three conductors is less than that required

20/07/24 Nathan Condie 6

Generation of a 3Ø Waveform

North

South

B1

B2 C

1

240 0

A Phase B Phase C Phase

Generation of a 3Ø Waveform

North

South

B1

B2 C

1

C2

A Phase C Phase B Phase

20/07/24 Nathan Condie 8

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

 Eg A-C-B.

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