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Three-Phase circuits

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Three-Phase circuits Prof. Siripong Potisuk Three-phase Voltage Sources Balanced Y-connected Voltage Source Balanced phase voltages are equal in magnitude and are out ... – PowerPoint PPT presentation

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Title: Three-Phase circuits


1
Three-Phase circuits
  • Prof. Siripong Potisuk

2
Faradays Law
The EMF induced in a circuit is directly
proportional to the time rate of change of
magnetic flux through the circuit.
The EMF can be produced by changing B
(induced EMF) or by changing the area, e.g., by
moving the wire (motional EMF).
  • It is the relative movement between the coil
    and
  • the magnet that matters

3
Magnet
Magnetic Flux lines
DC source
brush
Coil
Conductor loop
Slip ring
4
¼ Cycle
Start
½ Cycle
¾ Cycle
½ Cycle
¾ Cycle
¼ Cycle
5
(No Transcript)
6
(No Transcript)
7
Phase 1
Phase 2
Phase 3
Start
¾ Cycle
½ Cycle
¼ Cycle
8
Three-phase Voltage Sources
Y-connected Source
D-connected Source
9
Balanced Y-connected Voltage Source
  • Balanced phase voltages are equal in magnitude
    and are out of phase with one another by 120
    degrees.
  • Phase voltages sum up to zero.
  • Two possible combinations

acb or (?) sequence
abc or () sequence
10
Balanced Y-connected Voltage Source
  • Balanced line voltages are equal in magnitude and
    are out of phase with one another by 120 degrees.
  • Line voltages sum up to zero.
  • The magnitude of line voltages is 1.732 times the
    magnitude of the phase voltages
  • Line Voltages lead their corresponding phase
    voltages by 30 degrees

11
Balanced Three-phase Load Configurations
A balanced load is one in which the phase
impedances are equal in magnitude and in phase.
D-connected Load
Y-connected Load
12
Balanced Y-Y Connection
ZY ZS Zl ZL
13
Example Calculate the line currents in the
three-wire Y-Y system as shown.
14
Balanced Y-D Connection
15
  • Example A balanced abc-sequence Y-connected
    source with V is connected to a
    D-connected balanced load of 8j4 ? per phase.
    Calculate the phase and the line currents.

16
Balanced D-D Connection
17
Example A balanced ?-connected load having an
impedance of 20-j15 ? is connected to a
?-connected, positive sequence generator
having
V. Calculate the phase
currents of the load and the line currents.
18
Balanced D-Y Connection
19
  • Example A balanced Y-connected load with a phase
    impedance of 40j 25 ? is connected to a
    balanced, positive sequence D-connected source
    with a line voltage of 210 V. Calculate the phase
    currents. Use Vab as reference.
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