it is the knowledge of the electrical circuit 2 that will help us to update our knowledge and encourage the student to gather the knowledge and upgrade themselves

1. Electrical Circuit II
EEE-121

2. Capacitor
A device used to store an electric charge,
consisting of one or more pairs of
conductors separated by an insulator.

3. Capacitor
An electrolytic capacitor (e-cap) is
a polarized capacitor whose anode or
positive plate is made of a metal that
forms an insulating oxide layer through
anodization. This oxide layer acts as the
dielectric of the capacitor.
A fixed capacitor is constructed in such
manner that it possesses a fixed value
of capacitance which cannot be
adjusted. A fixed capacitor is classified
according to the type of material used as
its dielectric, such as paper, oil, mica, or
electrolyte.

4. Capacitor
A variable capacitor is a capacitor
whose capacitance may be
intentionally and repeatedly changed
mechanically or electronically.

5. Capacitor

6. Inductor
 A component in an electric or
electronic circuit which possesses
inductance.

7. Inductor

8. Instantaneous power
Instantaneous power p(t) is defined as
the product of instantaneous voltage
v(t) and instantaneous current i(t).
Assuming the sinusoids waveforms v(t)
= Vm cos (ω t + θ v ) and i(t) = Im cos
(ω t + θi ) represent the voltage and
current, then it can be shown:

9. Active Power
Instantaneous power to a load is p = v
• i.
 In an ac circuit
◦ p may be positive sometimes and
negative other times
 Average value of the power, P
◦ Real power

10. Active Power
 Average value of instantaneous
power, real power, active power, and
average power mean the same thing.

11. Reactive Power
During times when p is negative,
power is being returned from load
This can happen for inductive or
capacitive loads

12. Apparent Power
Power to a load is VI
If load has both resistance and
reactance
◦ Product is neither the real power nor the
reactive power, but a combination of both

13. Apparent Power
 This is called the apparent power, S
 S = VI = I2Z = V2/Z
 Units are volt-amperes (VA)

14. Apparent Power

15. Relationship Between P,Q,
and S
P, Q, and S are related by the “power
triangle”
S
Q
P
22
QPS 

16. Active and Reactive Power
Equations
P = VI cos  = S cos 
Q = VI sin  = S sin 
V and I are RMS values
 is the phase angle between V and I
Q is positive for inductive circuits and
negative for capacitive circuits

17. Power Factor
Ratio of real power to apparent power
is called the power factor, Fp
Fp = P/S = cos 
Angle  is angle between voltage and
current

18. Power Factor
For pure resistance  = 0°
For inductance,  = 90°
For capacitance,  = -90°
For a circuit containing a mixture,  is
somewhere between 0° and 90°

19. Power Factor
Unity power factor
◦ For a purely resistive circuit, the power
factor will be one
For load containing resistance and
inductance
◦ Power factor will be less than one and
lagging
◦ Current lags the voltage

20. Power Factor
For a circuit containing resistance and
capacitance
◦ Fp is less than one and is leading

21. Why Equipment Is Rated in
VA
A highly reactive load
◦ May seem to require a small amount of
power while requiring a large current
Equipment is rated in VA to prevent
overloading the circuit

22. Why Equipment Is Rated in
VA
Size of electrical apparatus required
by a load
◦ Governed by its VA requirements

23. Power Factor Correction
A load with a small power factor can
draw a large current
Can be alleviated by
◦ Cancelling some or all reactive
components of power by adding
reactance of opposite type to the circuit
 This is power factor correction

24. Power Factor Correction
Industrial customers may pay a
penalty for low power factors due to
large currents required for highly
reactive loads

25. AC Power Measurement
To measure power in an ac circuit you
need a wattmeter
Meter consists of
◦ Current-sensing circuit
◦ Voltage-sensing circuit
◦ Multiplier circuit
◦ Averaging circuit

26. AC Power Measurement
This will measure load voltage and
current and find the product and the
angle between these

27. Thank you
for your kind attention
Question ???