1. AC Power

2. AC Power
As in the case with DC power, the instantaneous electric power in an AC circuit is given by P = VI, but these quantities are continuously varying. Almost always the desired power in an AC circuit is the average power, which is given by
Pavg = V I cos 
where  is the phase angle between the current and the voltage and V and I are understood to be the effective or rms values of the voltage and current. The term cos    is called the "power factor" for the circuit.

3. Instantaneous Power
As in DC circuits, the instantaneous electric power in an AC circuit is given by P=VI where V and I are the instantaneous voltage and current.
Since
then the instantaneous power at any time t can be expressed as

4. Average Power the power becomes:
Averaging this power over a complete cycle gives the average power.
Average Power
                                                 
Normally the average power is the power of interest in AC circuits. Since the expression for the instantaneous power is a continuously varying one with time, the average must be obtained by integration. Averaging over one period T of the sinusoidal function will give the average power. The second term in the power expression above averages to zero since it is an odd function of t. The average of the first term is given by

5. Since the rms voltage and current are given by
       
      
and
the average power can be expressed as                       

6. Average Power Integral
Finding the value of the average power for sinusoidal voltages involves the integral
                                                                                                 
The period T of the sinusoid is related to the angular frequency
  and angle   by                                                       
Using these relationships, the integral above can be recast in the form:
Which can be shown using the trig identity:
                                              
which reduces the integral to the value 1/2 since the
second term on the right has an integral of zero over
the full period.

7. RLC Series Circuit
The RLC series circuit is a very important example of a resonant circuit. It has a minimum of impedance Z=R at the resonant frequency, and the phase angle is equal to zero at resonance.

8. Vm = the amplitude of the sinusoid
Single-phase System
The Sinusoidal voltage
v(t) = Vm sin wt
where
Vm = the amplitude of the sinusoid
w = the angular frequency in radian/s
t = time

9. The angular frequency in radians per second

10. Single-phase System v(t) = Vm sin (wt + q) where q is the phase angle
A more general expression for the sinusoid (as shown in the figure):
v(t) = Vm sin (wt + q)
where q is the phase angle

11. Single-phase System sin (ωt ± 180o) = - sin ωt
A sinusoid can be expressed in either sine or cosine form. When comparing two sinusoids, it is expedient to express both as either sine or cosine with positive amplitudes. We can transform a sinusoid from sine to cosine form or vice versa using this relationship:
sin (ωt ± 180o) = - sin ωt
cos (ωt ± 180o) = - cos ωt
sin (ωt ± 90o) = ± cos ωt
cos (ωt ± 90o) = + sin ωt

12. Single-phase System Apparent Power, Reactive Power and Power Factor
The apparent power is the product of the rms values of voltage and current.
The reactive power is a measure of the energy exchange between the source and the load reactive part.

13. Single-phase System
The power factor is the cosine of the phase difference between voltage and current.
The complex power:

14. Three-phase System

15. Generation of Three-phase
In a three phase system the source consists of three sinusoidal voltages. For a balanced source, the three sources have equal magnitudes and are phase displaced from one another by 120 electrical degrees.
A three-phase system is superior economically and advantage, and for an operating of view, to a single-phase system. In a balanced three phase system the power delivered to the load is constant at all times, whereas in a single-phase system the power pulsates with time.

16. Generation of Three-phase
Suppose three similar loops of wire with terminals R-R’, Y-Y’ and B-B’ are fixed to one another at angles of 120o and rotating in a magnetic field.

17. Generation of Three-phase
The instantaneous e.m.f. generated in phase R, Y and B:
vR = VR sin wt
vY = VY sin (wt -120o)
vB = VB sin (wt -240o) = VBsin (wt +120o)

18. Generation of Three-phase
Phase sequences:
RYB or positive sequence
VR leads VY, which in turn leads VB
This sequence is produced when the rotor rotates in
the counterclockwise direction

19. Generation of Three-phase
(b) RBY or negative sequence
VR leads VB, which in turn leads VY
This sequence is produced when the rotor rotates in
the clockwise direction

20. Star and Delta Connection

21. Star Connection
Three wire system

22. Four wire system

23. Wye connection of Load

24. Delta Connection

25. Delta connection of load

26. Wye Connection Line-to-neutral voltages: # Reference: VRN
# Positive sequence

27. The two other can be calculated similarly.

28. The line to line voltages

29. Line-to-line currents:
Delta Connection
Line-to-line currents:
# Reference: IRY
# Positive sequence.

30. The two other can be calculated similarly.

31. The line currents:

32. Vector diagram Phasor diagram is used to visualize the system voltages
• Wye system has two type of
voltages: Line-to-neutral, and
line-to-line
• The line-to-neutral voltages are
shifted with 120 degrees
• The line-to-line voltage leads
the line to neutral voltage with
30 degrees
• The line-to-line voltage is times
the line-to-neutral voltage

33. TNB SUPPLY SYSTEM Voltage 3 phase, 50 Hz
The main transmission and substation network are:
- 275 kV
- 132 kV kV
The distribution are: kV kV kV kV
volts
- 240 volts (single phase) drawn from 415 volts 3 phase
(phase voltage), between line (R, Y, B) and Neutral (N)

34. Supply Method (two types of premises)
SYSTEM
The low voltage system (415/240 V) is 3-phase four wire.
The low voltage system is a mixture of overhead lines and
under ground cables.
The high voltage and extra high voltage system is 3-phase three wire
Configuration. Overhead line and under ground cable system are used.
Supply Method (two types of premises)
1. Single consumer such as private dwelling house, workshop, factory, etc
Single phase, two wire, 240 V, up to 12 kVA max demand
Three phase, four wire, 415 V, up to 45 kVA max demand
Three phase, four wire, C. T. metered 415 V, up to 1,500 kVA max
demand

35. High Voltage and Extra High Voltage
2. Multi tenanted premises, such as high rises flats, commercial,
office blocks, etc
Low Voltage
Three phase, four wire, C.T. metered 415 V, up to 1,500 kVA max
demand
High Voltage and Extra High Voltage
Three phase, three wires, 6,600 and 11,000 V for load of 1, 500 kVA
max demand and above, whichever voltage is available
Three phase, three wires, 22,000 and 33,000 V for load of 5,000 kVA
Three phase, three wires, 66,000 V, 132,000 V and 275,000 for
exceptionally large load of above 20 MVA max demand

36. Standby Supply
Standby generator(s) to be used by the consumer in his premises, in
accordance with the relevant by-laws, may be provided by the consumer
The generator(s) shall remain a separate system from the TNB’s
Distribution system and should be certified and registered by
Suruhanjaya Tenaga (formerly JBE)
This may be used in place of the TNB’s supply source through a suitable,
Approved change over facility under emergency conditions.

37. Berubah setiap masa, hari, minggu dan bulan.
Beban
Berubah setiap masa, hari, minggu dan bulan.
Beban mempengaruhi penjanaan tenaga.
Penjanaan tenaga berdasarkan permintaan beban yang lepas.
Lengkuk beban berubah dalam sehari.