L22 1 ph-ac
4
ELE101/102 Dept of E&E,MIT Manipal 1 Power in AC circuit Power in AC circuit can be written as jQ P S VI Q VI P jQ P j VI jI I IZ Z I sin ; cos ) sin (cos ) sin cos ( 2 I a along V axis is called active current. I a = I cos. I r is perpendicular to V axis & is called reactive current. I r = I sin Active power P = V I cos = V I a. Reactive power Q = V I sin=VI r Apparent power S = V I - I I then load Z Z 0 V V reference the be Voltage Let ; inductive ˆ
description
Transcript of L22 1 ph-ac
ELE101/102 Dept of E&E,MIT Manipal 1
Power in AC circuit
Power in AC circuit can be written as
jQPS
VIQVIP
jQPjVI
jIIIZZI
sin;cos
)sin(cos
)sincos(2
Ia along V axis is called active current. Ia = I cos.
Ir is perpendicular to V axis & is called reactive current. Ir = I sin
Active power P = V I cos = V Ia.
Reactive power Q = V I sin=VIr
Apparent power S = V I
-II then load ZZ
0VV reference thebe VoltageLet
;inductiveˆ
ELE101/102 Dept of E&E,MIT Manipal 2
Complex Power
I
;I where
;
*
*
Ithen
I
IVIVjQPS
P
Q
S
XC>XLP
SQ
XL>XCI2R =
I2X =
ELE101/102 Dept of E&E,MIT Manipal 3
Power Triangle
Find P1, Q1 and P2, Q2
Draw the Individual Power triangle
Now PT = (P1+ P2) and QT = (Q1+ Q2)
Now Draw the over all Power triangle
ST = (PT +j QT)
VR2XL2
I
2I
Indu
ctiv
e lo
ad
R1XL1
1I
I
V R
XL
zI
Indu
ctiv
e lo
adQT
PT
Q2
P2
Q1P1
ST
S1
S2
1
2
T
ELE101/102 Dept of E&E,MIT Manipal 4
Power Factor Improvement
Need for power factor improvement
Method of Improvement:A capacitor connected in parallel to an inductive load improves the power factor.
Determination of Capacitor Value:T is the over all power angle
F is the final power angle after connecting the capacitor across the load.
ST = PT/CosT & SF = PT/CosF
QT = (PT/CosT) * Sin T
QF = (PT/CosF) * Sin F
QC = (QT - QF) = PT(Tan T - Tan F)
QC = V2/ XC
CI
V R
XL
I
zI
Indu
ctiv
e lo
ad
XC
QT
PT
ST
SF
F
T QF
QC
