Transcript Slide 1

AC POWER CALCULATION
Power Factor Correction
SEE 1023 Circuit Theory
1
Power Factor Correction
I
+
V

V = Vv
Load
I = Ii
As we have seen before (for sinusoidal voltage and current),
pf = cos (vi)
P = V I cos (vi)
The REAL power (or average power) is transformed into useful energy
e.g. heat, mechanical, light, sound, etc
For a given V and P, loads with high power factor draw LESS current
compared with loads with low power factor
2
Power Factor Correction
I2
I1
P
pf = cos 1
V
P
pf = cos 2
V
cos 1 > cos 2
1 < 2
S1
1
Pave
S2
Q2
Q1
2
S1
I1 
V
Pave
I2 
S2
V
For a given V and P, loads with high power factor draw LESS current
compared with loads with low power factor
I1  I 2
3
Power Factor Correction
For a given V and P, loads with high power factor draw LESS current
compared with loads with low power factor
Less current results in LESS losses during transmission
I2 R
+

Source
Load
Utility company (TNB) charge more to loads with LOW power factor
Therefore, it is desirable to increase the power factor
4
Power Factor Correction
How to increase the power factor without altering the voltage
or current of the original load?
IL
QC
+
+
Vs
QL
1
(rms)
VL
QT
2

PL

Before C added, S = PL + jQL
After C added, S = PL + j(QL – QC)
pf = cos 1
pf = cos 2
i.e. increased
(voltage and current of the original load are retained)
5
Power Factor Correction
How do we calculate C?
QC
Voltage across C = Vs (rms)
QL
1
1
Impedance
of C =  j
QT
C
2
PL
Vs 2
Qc
Qc 
C 
1

Vs 2
C
6