This ppt is more useful for Civil Engineering students. I have prepared this ppt during my college days as a part of semester evaluation . Hope this will help to current civil students for their ppt presentations and in many more activities as a part of their semester assessments. I have prepared this ppt as per the syllabus concerned in the particular topic of the subject, so one can directly use it just by editing their names.

1. Vishvakarma
Government Engineering
College, Chandkheda
Name –Darshil Vekaria(150170106061)
Branch–Civil Engineering
Subject- EEE
Topic –Three Phase AC. Circuit

2.  Three Phase System:
◦ A generator consists of three coils placed 120 apart.
◦ The voltage generated are equal in magnitude but,
out of phase by 120.
 Three phase is the most economical polyphase
system.
Circuit or system in which AC sources operate at
the same frequency but different phases are
known as polyphase.

3.  All electric power is generated and
distributed in three phase.
◦ One phase, two phase, or more than three phase
input can be taken from three phase system rather
than generated independently.
◦ Melting purposes need 48 phases supply.

4.  Uniform power transmission and less vibration
of three phase machines.
◦ The instantaneous power in a 3 system can be
constant (not pulsating).
◦ High power motors prefer a steady torque especially
one created by a rotating magnetic field.
 Three phase system is more
economical than a single
phase.

5. THREE-PHASE WAVEFORM
Phase 2 lags phase 1 by 120. Phase 2 leads phase 3 by 120.
Phase 3 lags phase 1 by 240. Phase 1 leads phase 3 by 240.
Phase 1 Phase 2 Phase 3
120 120 120
240
120 120 120
240

6.  Balanced three phase voltages:
1) same magnitude
2) 120 phase shift
 
 
   


120cos240cos)(
120cos)(
cos)(
tVtVtv
tVtv
tVtv
MMcn
Mbn
Man



BALANCED 3 CURRENTS
•Balanced three phase
currents:
1) same magnitude
2) 120 phase shift
 
 
 


240cos)(
120cos)(
cos)(



tIti
tIti
tIti
Mc
Mb
Ma

7.  
 


120cos)(
120cos)(
cos)(
tVtv
tVtv
tVtv
Mcn
Mbn
Man






120
120
0
Mcn
Mbn
Man
VV
VV
VV



120
120
0
Mcn
Mbn
Man
VV
VV
VV
POSITIVE
SEQUENCE
NEGATIVE
SEQUENCE

8.  Balanced Phase Voltage: all phase voltages
are equal in magnitude and are out of phase
with each other by 120.
 Balanced Load: the phase impedances are
equal in magnitude and in phase.

9.  Phase voltage is measured between the
neutral and any line: line to neutral
voltage
 Line voltage is measured between any
two of the three lines: line to line
voltage.
PHASE CURRENTS and LINE
CURRENTS• Line current (IL) is the current in each
line of the source or load.
• Phase current (I) is the current in
each phase of the source or load.

10. SOURCE LOAD CONNECTION
Wye Wye Y-Y
Wye Delta Y-
Delta Delta - 
Delta Wye -Y

11.  Common connection of source: WYE
◦ Delta connected sources: the circulating current
may result in the delta mesh if the three phase
voltages are slightly unbalanced.
 Common connection of load: DELTA
◦ Wye connected load: neutral line may not be
accessible, load can not be added or removed
easily.

13. ZY
ZY
ZY
a
c
b
n
Load
ZY
ZY
Z Y
a
b
c
Load
n
OR

14. BALANCED-
CONNECTION

15.  Phase voltage is
measured between the
neutral and any line: line
to neutral voltage
n
a
b
c
Vab
Vbc
Vca
Vbn
Vcn
Van
Ia
Ib
Ic
Van
Vbn
Vcn

16.  Line voltage is
measured between any
two of the three lines:
line to line voltage. n
a
b
c
Vab
Vbc
Vca
Vbn
Vcn
Van
Ia
Ib
Ic
Vab
Vbc
Vca

17.  30VVL 
Magnitude - VL LEAD their
corresponding V by 30
LV 3 V
•POWER
–The instantaneous power is
constant.
 
)cos(3
cos
2
3
)()()()(


rmsrms
MM
cba
IV
IV
tptptptp




18.  Phase voltages are equal to the voltages
across the load impedances.



19. BCCAc
ABBCb
CAABa
III
III
III






120II
120II
30I3I
ac
ab
ABa
RELATIONSHIP BETWEEN I and IL
IIL 3
 30IIL 
1. Magnitude 1. Phase
- IL LAG their
corresponding I by
30

20.  The line currents are obtained from the phase
currents by applying KCL at nodes A,B, and C.



21. THANK YOU