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Electrical Engineering & Telecommunications
Lecturer:Ted Spooner
Lecture -Intro to Circuit Basics
Elec1111Elec1111
Rm 124A EE email: [email protected]
How is the Electrical system of an Aircraft Powered?
One of 4 variable frequency 150kVA generators on the new A380 Airbus Ram Air Turbine
Auxiliary Power Unit (APU)
How do we connect it all?
• How do we go about designing and evaluating the design?– Have to analyse circuits– How do we do that?
Possible Circuit solutions to a simplified aircraft electrical system.
Generator 1 Generator
2
LOAD 1 LOAD 2
LOAD 3
LOAD 4
LOAD 5
Possible Circuit solutions to a simplified aircraft electrical system.
Generator 1
Generator 2
LOAD 1LOAD 2
LOAD 5
LOAD 4
LOAD 3
How do we analyze a circuit like this?
• Audio Power Amplifier
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Electric Circuit VariablesCharge
Current
Voltage
Power
Energy
Need to Understand Concepts
How do we calculate current in each element of this circuit?
10V
1000 10
87 20 3V
currentconstant: direct current (dc)
time-varying: many formse.g. sinusoidal, also called
alternating current (ac)
t (s)
i(A)
0
sinusoid (ac)
rampexponential
Time-varying current
t (s)
i(A)
0
Direct current (dc)
t (s)
i(A)
0
sinusoid (ac)
rampexponential
Time-varying current
t (s)
i(A)
0
Direct current (dc)
VOLTAGE• When charge flows through an element
then energy is transferred either to or from the element
a bi
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• Voltage (potential difference) = measure of the amount of energy transferred per unit of charge.
• Unit: volt, V
• Notation: V, v(t) or v
energy
chargedqdwv =
Voltage
• As charge flows through an element then energy is transferred either to or from the element
a b
vi
+ _
Must have a sense of direction.If i and v are positive then: energy is being transferred to the element.
Voltage
• Element absorbing energy
a bi + _
iv
a bi +_
• Element delivering energy
iv
If i and v are positive.
Voltage is analogous to pressure
PUMP
Resistance to flow
Voltage is like pressure HV transmission lines: up to 500kV
Household supply: 230V
Car battery: 12V – 13V
Flashlight battery: 1.5V
Electroencephalography (EEG):10μV
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Voltage Sign conventions
• Voltage is a measure of potential difference between two points.
• ie Vab is the difference in potential between nodes a and b.
• Vab is the voltage of node a with respect to node b.
a
b
+
_
abvWhen we say voltage of node When we say voltage of node aarelative to node relative to node bb we write it like:we write it like:
Voltage Sign conventionsVoltage is a measure of
potential difference between two points.
Reference Ground
va
+
_
vb
+
_
vab = va - vb
a
b
+
_
bavWhen we say voltage of node When we say voltage of node bbrelative to node relative to node aa we write it like:we write it like:
Now voltage of b with respect to a
Reference Ground
vb
+
_
va+
_
vba = vb - va
a b
+ _
bav
abv
+_
a b
Then :Then :
IfIf 5abv V=
5bav V= −
a b
+ _abv
5abv V=
COM V
+5V Reading
Measuring Vab
Sources = devices that supply energy to circuit
VoltageVoltagesourcessources
CurrentCurrentsourcessources
SourcesSources
2 types
Sources can be independentindependent or dependentdependent.