Lecture 03 - 3phase
-
Upload
rachit-khanna -
Category
Documents
-
view
14 -
download
0
description
Transcript of Lecture 03 - 3phase
-
7/21/2019 Lecture 03 - 3phase
1/31
ELEN 3441 Fundamentals of Power Engineering Spring 2008
1
Instructor:
Dr. Gleb V. Tcheslavski
Contact:
Office Hours:
TBD; Room 2030
Class web site: MyLamar
Lecture 3: Three!hase !ower circuits
mailto:[email protected]:[email protected] -
7/21/2019 Lecture 03 - 3phase
2/31
ELEN 3441 Fundamentals of Power Engineering Spring 2008
2
Intro"uction
lmost all ele!tri! power generation and most of t"e powertransmission in t"e world is in t"e form of t"ree#p"ase $
!ir!uits% t"ree#p"ase $ s&stem !onsists of t"ree#p"ase
generators' transmission lines' and loads%
("ere are two ma)or ad*antages of t"ree#p"ase s&stems o*er
a single#p"ase s&stem+
1,-ore power per .ilogram of metal form a t"ree#p"ase
ma!"ine;
2,Power deli*ered to a t"ree#p"ase load is !onstant at all time'instead of pulsing as it does in a single#p"ase s&stem%
("e first t"ree#p"ase ele!tri!al s&stem was patented in 1882
/& o"n op.inson #ritis" p"&si!ist' ele!tri!al engineer'
Fellow of t"e Ro&al So!iet&%
-
7/21/2019 Lecture 03 - 3phase
3/31
ELEN 3441 Fundamentals of Power Engineering Spring 2008
3
#. Generation of three!hase
volta$es an" currents
t"ree#p"ase
generator !onsists of
t"ree single#p"ase
generators wit"
*oltages of eualamplitudes and
p"ase differen!es of
1200%
-
7/21/2019 Lecture 03 - 3phase
4/31
ELEN 3441 Fundamentals of Power Engineering Spring 2008
4
#. Generation of three!hase
volta$es an" currents
Ea!" of t"ree#p"ase
generators !an /e
!onne!ted to one of t"ree
identi!al loads%
("is wa& t"e s&stem would
!onsist of t"ree single#p"ase
!ir!uits differing in p"ase
angle /& 1200%
("e !urrent flowing to ea!"
load !an /e found as
VI
Z
= 3%4%1,
-
7/21/2019 Lecture 03 - 3phase
5/31
ELEN 3441 Fundamentals of Power Engineering Spring 2008
5
#. Generation of three!hase
volta$es an" currents
("erefore' t"e !urrents flowing in ea!" p"ase are
0
0
0
0
120120
240240
A
B
A
V
I IZ
VI I
Z
VI IZ
= =
= =
= =
3%5%1,
3%5%2,
3%5%3,
-
7/21/2019 Lecture 03 - 3phase
6/31
ELEN 3441 Fundamentals of Power Engineering Spring 2008
6
#. Generation of three!hase
volta$es an" currents
7e !an !onne!t t"e negati*e ground, ends of t"e t"ree single#
p"ase generators and loads toget"er' so t"e& s"are t"e !ommon
return line neutral,%
-
7/21/2019 Lecture 03 - 3phase
7/31ELEN 3441 Fundamentals of Power Engineering Spring 2008
#. Generation of three!hase
volta$es an" currents
("e !urrent flowing t"roug" a neutral !an /e found as
0 0
0 0 0 0
0 0 0 0
120 240
cos( ) sin( ) cos( 120 ) sin( 120 ) cos( 240 ) sin( 240 )
cos( ) cos( 120 ) cos( 240 ) sin( ) sin( 120 ) sin( 240 )
cos(
N A B CI I I I I I I
I jI I jI I jI
I jI
I
= + + = + +
= + + + + +
= + + + + +
= 0 0 0 0
0 0 0 0
) cos( )cos(120 ) sin( )sin(120 ) cos( )cos(240 ) sin( )sin(240 )
sin( ) sin( )cos(120 ) cos( )sin(120 ) sin( )cos(240 ) cos( )sin(240 )jI
+ + + +
+ + +
1 3 1 3cos( ) cos( ) sin( ) cos( ) sin( )2 2 2 2
1 3 1 3sin( ) sin( ) cos( ) sin( ) cos( )
2 2 2 2
0
NI I
jI
= +
+ +
=
7"i!" is+
3%%1,
3%%2,
-
7/21/2019 Lecture 03 - 3phase
8/31ELEN 3441 Fundamentals of Power Engineering Spring 2008
8
#. Generation of three!hase
volta$es an" currents
s long as t"e t"ree loads are eual' t"e return !urrent in
t"e neutral is 9ero:
Su!" t"ree#p"ase power s&stems eual magnitude' p"ase differen!es
of 1200' identi!al loads, are !alled /alan!ed%
n a /alan!ed s&stem' t"e neutral is unne!essar&:
P"ase Seuen!eis t"e order in w"i!" t"e *oltages in t"e indi*idual
p"ases pea.%
abc acb
-
7/21/2019 Lecture 03 - 3phase
9/31ELEN 3441 Fundamentals of Power Engineering Spring 2008
amined%
4% ("e s&stem power fa!tor at t"at point using t"e
power triangle relations"ip%
5% Line and p"ase !urrents at t"at point%
7e !an treat t"e line *oltage as !onstant and use t"e power triangle met"od to
ui!.l& !al!ulate t"e effe!t of adding a load on t"e o*erall s&stem and power fa!tor%