Electrical Power Systems
Hydro
Electrical Units and Definitions
EEE110 Electric Circuits
Anawach Sangswang
Dept. of Electrical Engineering
KMUTT
Gas
Nuclear
Coal
Generations
Transmissions
Distributions
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Introduction
Systems of Units
International System of Units (SI): General
Conference on Weights and Measures in 1960
An electric circuit is an interconnection of
electrical elements
A simple electric circuit
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Powers of Ten
Notation
Determination of the power
Fixed point
Floating point
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Powers of Ten
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Symbols and Meanings
Scientific notation
Engineering notation
Prefixes
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Charge
Charge is an electrical property
of the atomic particles of which
matter consists, measured in
coulombs (C).
The charge e on one
electron is negative
and equal in magnitude
to 1.602 × 10-19 C
Charge
Copper
Hydrogen
The free electron is the charge carrier in a copper wire
or any other solid conductor of electricity
Helium
1 inch3 of Cu @room temperature contains
1.4x1024 free electrons
Other metals that exhibit the similar properties
are silver, gold, aluminum, and tungsten
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Charge
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Current
Random motion of free electrons
Electric current i ≜
The unit of ampere is 1 A = 1C/s
Example: A conductor has a
constant current of 5 A.
How many electrons
pass a fixed point on
the conductor in
one minute?
i
With no external forces applied, the net flow
of charge in a conductor in any one direction
is zero.
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Example
Example
Total no. of charges pass in 1 min is given by
5 A = (5 C/s)(60 s/min) = 300 C/min
The total charge entering a terminal is given
by q = 5t sin4πt mC. Calculate the current at
t = 0.5 s
i = dq/dt = d(5t sin4πt)/dt
= 5sin4πt + 20πt cos4πt mA
At t = 0.5: i = 5 sin2π + 10π cos2π = 0 + 10 π
= 31.42 mA
Total no. of electronics pass in 1 min is given
300 C/min
= 1.87 x10 21 electrons/min
−19
1.602 x10 C/electron
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DC vs. AC
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Voltage
Voltage (or potential difference) is the energy
required to move a unit charge through an
element, measured in volts (V).
A potential difference of 1 volt (V) exists
between two points if 1 joule (J) of energy is
exchanged in moving 1 coulomb (C) of charge
between the two points.
A direct current (dc) is a current that remains
constant with time.
An alternating current (ac) is a current that
varies sinusoidally with time. (reverse
direction)
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Voltage
Mathematically,
Power and Energy
≜
(volt)
w is energy in joules (J)
q is charge in coulomb (C).
Electric voltage, vab, is always across the circuit
element or between two points in a circuit.
Power is the time rate of expending or
absorbing energy, measured in watts (W)
Mathematical expression:
≜
p=
vab > 0 means the potential of a is higher
dw dw dq
=
⋅
= vi
dt
dq dt
p = v ⋅i
than potential of b.
vab < 0 means the potential of a is lower
Absorb: p = +vi (vi > 0)
Supply: p = -vi (vi < 0)
than potential of b.
vab = −vba
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Power and Energy
The law of conservation of energy
∑p=0
Energy is the capacity to do work, measured
in joules (J)
t
t
Mathematical expression: w = ∫t pdt = ∫t vidt
0
0
Example: How much energy does a 100W
electric bulb consume in 2 hours?
w = pt = 100 ⋅ 2 ⋅ 60 ⋅ 60 = 720, 000 J = 720kJ
or
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w = pt = 100 ⋅ 2 = 200 Wh
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Circuit Elements
Active Elements
Independent
sources
Circuit Elements
Example: Obtain the voltage v for i2 = 1A
Passive Elements
•A dependent source is an active
element in which the source
quantity is controlled by
another voltage or current.
Dependant
•There are four different types:
sources
VCVS, CCVS, VCCS, CCCS
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Circuit Elements
Example: Calculate the power at each element
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