Fundamentals of Electrical Engineering 1 Grundlagen der

Transcription

Fundamentals of Electrical Engineering
Fundamentals of Electrical Engineering 1
Grundlagen der Elektrotechnik 1
Chapter: Basic Concepts / Grundlagen
Michael E. Auer
Source of figures:
Alexander/Sadiku: Fundamentals of Electric Circuits,
McGraw-Hill
Michael E.Auer
14.11.2009
GET01
Course Content
Basic Concepts / Grundlagen
Basic Laws / Grundgesetze
Circuit Theorems / Zweipoltheorie
Common Methods of Network Analysis / Allgemeine Netzwerkanalyse
Operational Amplifiers / Operationsverstärker
Capacitors and Inductors / Kapazitäten und Induktivitäten
Basic RC and RL Circuits Switching / Einfache Schaltvorgänge
Michael E.Auer
14.11.2009
GET01
Chapter Content
Introduction / Einführung
Systems and Units / Einheitensysteme
Charge and Current / Ladung und Strom
Voltage / Spannung
Power and Energy / Leistung und Energie
Circuit Elements / Grundelemente
Summary / Zusammenfassung
Michael E.Auer
14.11.2009
GET01
Chapter Content
Voltage / Spannung
Michael E.Auer
14.11.2009
GET01
Electric Circuits
An electric circuit is
an interconnection of
electrical elements.
Radio receiver
Michael E.Auer
14.11.2009
GET01
Chapter Content
Voltage / Spannung
Michael E.Auer
14.11.2009
GET01
System of Units (1)
ISO
Michael E.Auer
Six basic units
Quantity
Basic unit
Symbol
Length
Mass
Time
Electric current
Absolute Temperature
Luminous intensity
meter
kilogram
second
ampere
kelvin
candela
m
kg
s
A
K
cd
14.11.2009
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System of Units (2)
The derived units commonly
used in electric circuit theory
Decimal multiples and
submultiples of SI units
Michael E.Auer
14.11.2009
GET01
Chapter Content
Voltage / Spannung
Michael E.Auer
14.11.2009
GET01
Electric Charges

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 which is called as
electronic charge. The charges that occur in nature are
integral multiples of the electronic charge.
Michael E.Auer
14.11.2009
GET01
Electric Current (1)

Electric current
i = dq / dt

(ampere)
The unit of ampere can be derived as 1 A = 1C/s.
Michael E.Auer
14.11.2009
GET01

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)
Michael E.Auer
14.11.2009
GET01

The direction of current flow
Positive ions
Michael E.Auer
Negative ions
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Example 1
A conductor has a constant current of 5 A.
How many electrons pass a fixed point on the conductor in one
minute?
Solution
Total no. of charges pass in 1 min is given by
5 A = (5 C/s)(60 s/min) = 300 C/min
Total no. of electronics pass in 1 min is given by
300 C/min
21
=
1
.
87
x
10
electrons/min
−19
1.602 x10 C/electron
Michael E.Auer
14.11.2009
GET01
Chapter Content
Voltage / Spannung
Michael E.Auer
14.11.2009
GET01
Electric Voltage (1)

Voltage (or potential difference) is the energy required to
move a unit charge through an element, measured in volts
(V).

Mathematically,
vab = dw / dq
(volt)
– w is energy in Newton meter (Nm) and q is charge in coulomb (C).
Michael E.Auer
14.11.2009
GET01
Electric Voltage (2)

Electric voltage, vab, is always across the circuit element or
between two points in a circuit.
– vab > 0 means the potential of a is higher than potential of b.
– vab < 0 means the potential of a is lower than potential of b.
Michael E.Auer
14.11.2009
GET01
Chapter Content
Voltage / Spannung
Michael E.Auer
14.11.2009
GET01
Power and Energy (1)


Power is the time rate of expending or absorbing energy,
measured in watts (W).
Mathematical expression:
Passive sign convention
i
v
Michael E.Auer
i
+
+
–
dw dw dq
p=
=
⋅
= v ⋅i
dt dq dt
v
p = + vi
absorbing power
14.11.2009
–
p = – vi
supplying power
GET01
Power and Energy (2)
 The law of conservation of energy
∑p=0
 Energy is the capacity to do work, measured in
joules (J).
 Mathematical expression
Michael E.Auer
14.11.2009
t
t
t0
t0
w = ∫ p ⋅ dt = ∫ v ⋅ i ⋅ dt
GET01
Chapter Content
Voltage / Spannung
Michael E.Auer
14.11.2009
GET01
Circuit Elements (1)
Active Elements
Independent
sources
Michael E.Auer
Passive Elements
Dependant
sources
14.11.2009
• An ideal independent source is an active
element that provides a specified voltage or
current that is completely independent of
other circuit elements.
• A dependent source is an active element in
which the source quantity is controlled by
another voltage or current. They have four
different types: VCVS, CCVS, VCCS, CCCS.
GET01
Circuit Elements (2)
i
i
Independent
sources
v = v(t)
v
V = const.
i
Dependant
sources
Michael E.Auer
v
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GET01
Chapter Content
Voltage / Spannung
Michael E.Auer
14.11.2009
GET01
Summary
•
An electric circuit consists of electrical elements connected together.
The international System of Units (SI) is the international measurement language, which
enables engineers to communicate their results. From the six principal units (one of this is
the Ampere), the units of other physical quantities can be derived.
Current is the rate of charge flow:
•
Voltage is the energy reqired to move 1 C of charge through an element:
•
•
i = dq / dt
vab = dw / dq
•
Power is the enrgy supplied or absorbed per unit time. It is also the product of voltage and
current.
p=
•
•
•
dw dw dq
=
⋅
= v ⋅i
dt dq dt
According to the passive sign convention, power assumes a positive sign when the current
enters the positive polarity of the voltage across an element.
An ideal voltage source produces a specific potential difference across its terminals
regardless of what is connected to it. An ideal current source produces a specific current
through its terminals regardless of what is connected to it.
Voltage and current sources can be dependent or independent. A dependent souirce is one
whose value depends on some other circuit variable.
Michael E.Auer
14.11.2009
GET01

Fundamentals of Electrical Engineering 1 Grundlagen der

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