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Basic Electrical Engineering
Anurag Srivastava
Power Engineering = The Power to Transform and Restore
Basics of Electricity
Signals
Spectrum
Voltage
Current
Resistance
Capacitance
Inductance
Power
Inventors and Their contribution
Inventor Country Invention Remarks
William Gilbert
(1544-1603)
English Physician Magnetic Science
Charles A. Coulomb
(1736-1806)
French Engineer Law of Electrostatics Unit of Charge
James Watt
(1736-1819)
English Inventor Steam Engine Watt is unit of power
Alessandro Volta
(1745-1827)
Italian Physicist Electric Piles Volt is unit of voltage /potential
Andre Marie Ampere
(1775-1836)
French Mathematician Relation between electric
current and magnetic field
Ampere is Unit of current
George Simon Ohm
(1789-1854)
German Mathematician
Relation between voltage and
current
Ohm is unit of
Resistance/Impedance
Michael Faraday
(1791-1867)
English Inventor
Electromagnetic Induction,
Transformer
Unit of capacitance
Joseph Henry
(1797-1878)
American Physicist Self Induction, Telegraph Unit of Inductance
C. F. Gauss
(1777-1855)
German Mathematician
Measurement of Earths
Magnetic Field
Gauss is unit of magnetic
strength
W. Ed. Weber
(1804-1891)
German Physicist
Electromagnetic Telegraph Weber is used as unit of
magnetic flux
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Inventors and Their contribution
Inventor Country Invention Remarks
James. P. Joule
(1818-1889)
British Inventor Mechanical Equivalent of Heat Unit of energy is Joule (J)
James C. Maxwell
(1831-1879)
Scottish Physicist Electromagnetic Theory of light
and law of electrodynamics
E. W. Siemens
(1816-1892)
Germen Inventor Invention and development of
electrical machine
Siemens is the unit of
conductance
C. W. Siemens
(1823-1883)
Gustav Robert Kirchhoff
(1824-1887)
German Scientist Law of circuit analysis (V & I)
Thomas Elva Edison
(1847-1931)
US Engineer Lamp, Motor, phonograph, DC
power system
H. Rudolph Hertz
(1857-1894)
German Scientist Nature of electromagnetic
waves
Hertz is unit of Frequency (H)
Nikola Tesla
(1856-1943)
Croatian Inventor Poly phase AC system,
Induction mtor
Tesla is the unit of Magnetic
flux density (T)
Few Facts Year Fact
1870s Commercial use of Electricity
1881 Edison established first Electric power system at Pearl station, NY
1882 Became operational for generation, transmission and distribution
1884 DC motor invented by Frank Sprague
1886 First AC distribution system by Stanley at Westinghouse
1889 First AC transmission line of 4kV, single phase put into operation in Oregon, north America,
between Willamette Fall and Portland
1893 First 3 phase line in southern California, NA came into operation at 2.3kV, which was 12 km
long.
1960-61 5654MW power generation
2010 159398.49MW = 36863.4 (Hydro) + 102453.98 (thermal from gas, coal, diesel) + 4560
(Nuclear) + 15521.11 (renewable energy sources.
In USA it has gone to 400 times in last 30 years
Upto 1921 AC system voltage were 12kV, 44kV, and 60kV
Increases to 165kV in 1922 ; 220kV in 1923; 287kV in 1935, 330kV in 1953; 500kV in 1965;
735kV in 1966; 765kV in 1969 and 1100kV in 1990
In India It is132kV, 220kV for High Voltage, and 400kV and 765kV for Extra High Voltage
The maximum generating voltage available in world is 33kV, in India it 21kV
National Grid and Regional Grids in India|
Power system Grids
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... a closer view of a power plant ...
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Base Quantity Base Unit Name Symbol Name Symbol
Time
Length
Mass
Temperature
Electric Current
Amount of Substance
Luminous Intensity
t
l
m
T , Ө
I
n
(not in A Level)
second
metre
kilogram
kelvin
ampere
mole
candela
s
m
kg
K
A
mol
cd
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Physical Quantity Defined as : Unit Special Name
velocity
acceleration
density
momentum
force
pressure
work (energy)
power
electrical charge
potential difference
resistance
Homogenous Equations
Ep = m g h
Nm = kg kgms-2kg-1 m
kgms-2 m = kgm2s-2
kgm2s-2 = kgm2s-2
This equation is homogenous
J = kg Nkg-1 m
Homogenous Equations
v2 = u2 +2ax
= +
m2s-2 = m2s-2 + m2s-2
This equation is homogenous
m2s-2 m2s-2 ms-2 m
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Homogenous Equations
F = mv
r
kgms-2 = kgs-1
This equation is not homogenous
Homogenous Equations
What is missing? kgms-2 = kgs-1
The equation should read:
F = mv2
r
ms-1 = v on rhs
Homogenous Equations Try these:
Ek = ½ m v2
and v = u + at2
J = kg m2s-2
N m = kg m2s-2
kg m2s-2 = kg m2s-2 OK
ms-1 = ms-1 + ms-2 s2
ms-1 = ms-1 + m Not OK
s-1 is missing, so equation
should read:
V = u + at
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Homogenous Equations
Homework:
Show that these equations are homogenous
a) x = ut + ½at2
b) T = 2π√l/g
c) v = fλ
d) I = nAve
e) W = ½CV2
What is missing here?
f) F = mv - mu
Scientific Notation
M x 10n
M is the coefficient 1<M<10
10 is the base
n is the exponent or power of 10
Other Examples:
5.45E+6
5.45 x 10^6
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Numbers less than 1 will have a
negative exponent.
A millionth of a second is:
0.000001 sec 1x10-6
1.0E-6 1.0x10^-6
Limits of Measurement
Accuracy and Precision
Accuracy
– a measure of how close a
measurement is, to the true value of
the quantity being measured.
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Example: Accuracy Who is more accurate when measuring a
book that has a true length of 17.0cm?
Susan:
17.0cm, 16.0cm, 18.0cm, 15.0cm
Amy: 15.5cm, 15.0cm, 15.2cm, 15.3cm
Precision
– a measure of how close a series of
measurements are to one another. A
measure of how exact a measurement
is.
Example: Precision
Who is more precise when measuring the same 17.0cm book?
Susan:
17.0cm, 16.0cm, 18.0cm, 15.0cm
Amy:
15.5cm, 15.0cm, 15.2cm, 15.3cm
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Example: Evaluate whether the following are
precise, accurate or both.
Accurate
Not Precise
Not Accurate
Precise
Accurate
Precise
Error
Error= experimental –accepted value
Percent Error
% Error= |experimental –accepted| x100
accepted value
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Ohm’s Law
Every conversion of energy from one form to
another can be related to this equation.
In electric circuits the effect we are trying to
establish is the flow of charge, or current. The
potential difference, or voltage between two points
is the cause (“pressure”), and resistance is the
opposition encountered.
Opposition
Cause Effect
Ohm’s Law
Simple analogy: Water in a tube
Electrons in a copper wire are analogous to water in a hose.
Consider the pressure valve as the applied voltage and the
size of the hose as the source of resistance.
The absence of pressure in the hose, or voltage across the wire
will result in a system without motion or reaction.
A small diameter hose will limit the rate at which water will
flow, just as a small diameter copper wire limits the flow of
electrons.
Ohm’s Law
Developed in 1827 by Georg Simon Ohm
For a fixed resistance, the greater the voltage (or
pressure) across a resistor, the more the current.
The more the resistance for the same voltage, the less
the current.
Current is proportional to the applied voltage and
inversely proportional to the resistance.
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Ohm’s Law
Where: I = current (amperes, A)
E = voltage (volts, V)
R = resistance (ohms, Ω)
R
EI
Plotting Ohm’s Law
Plotting Ohm’s Law
Insert Fig
4.8
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Ohms law,
defines the relationship between voltage, current and
resistance.
These basic electrical units apply to direct current, or
alternating current.
Ohm’s Law is the foundation of electronics and electricity.
This formula is used extensively by electricians.
Without a thorough understanding of “Ohm’s Law” an
electrician can not design or troubleshoot even the simplest
of electronic or electrical circuits.
Ohm established in the late 1820’s that if a voltage was applied
to a resistance then “current would flow and then power would
be consumed”.
Ohm's law magic triangle
Let's see how these equations might work to help us analyze simple circuits:
If we know the values of any two of the three quantities
(voltage, current, and resistance) in this circuit, we can
use Ohm's Law to determine the third.
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calculate the amount of current (I) in a circuit, given values of
voltage (E) and resistance (R):
calculate the amount of resistance (R) in a circuit, given values of voltage (E) and current (I):
calculate the amount of voltage supplied by a battery, given values of current (I) and resistance (R):
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Ohm’s Law power consumption through a resistance
Some every day practical examples of this basic rule are: base
board heaters, electric frying pans, toasters and electric light bulbs. The heater consumes power producing heat for warmth,
the frying pan consumes power producing heat for general cooking,
the toaster consumes power producing heat for cooking toast, and
the electric light bulb consumes power producing heat and more
important light.
A further example is an electric hot water system. All are examples
of Ohm’s Law.
milliamp or just mA
As a milliampere (milliamp or just mA) is 1/1000th of an ampere, we can
convert mA to Amps by just dividing by 1000. Another way is to take the
current in mA and move the decimal to the left three places to accomplish
the division by 1000. Here's the scoop:
275 mA / 1000 = 0.275 Amps
Note that the decimal in 275 is to the right of the 5, and it's written as 275.0
(with a 0 added to show where the decimal is). Moving the decimal to the
left three places gets up to .275 Amps, but we usually hang a 0 in front of the
decimal.
To convert Amps to milliAmps, just multiply by 1000 or move the decimal
to the right three places. Just the opposite of what we did here to convert the
other way.
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Power
Power is an indication of how much work
(the conversion of energy from one form to
another) can be done in a specific amount of
time; that is, a rate of doing work.
Power
Power can be delivered or absorbed as defined by
the polarity of the voltage and the direction of the
current.
t
WP
second / joule 1 (W)Watt 1
Energy
Energy (W) lost or gained by any system is
determined by:
W = Pt
Since power is measured in watts (or joules per
second) and time in seconds, the unit of energy is
wattsecond (Ws) or joule (J)
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Energy
The watt-second is too small a quantity for most practical purposes, so the watt-hour (Wh) and kilowatt-hour (kWh) are defined as follows:
The killowatt-hour meter is an instrument used for measuring the energy supplied to a residential or commercial user of electricity.
1000
(h) time (W) power(kWh)Energy
(h) time (W) power (Wh)Energy
Efficiency
Efficiency () of a system is determined by
the following equation:
= Po / Pi
Where: = efficiency (decimal number)
Po = power output
Pi = power input
Efficiency
The basic components of a generating (voltage) system are depicted below, each component has an associated efficiency, resulting in a loss of power through each stage.
Insert Fig
4.19
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Typical wattage ratings of some common
household items
Insert Table 4.1
Power coming into any facility or item must be limited to ensure that the current through the lines or electrical equipment is not above the rated value.
Fuses or circuit breakers are installed where the power enters the installation. Fuses have an internal metallic conductor which begins to melt if the
current exceeds the fuse rated value on the case.
In recent years fuses have been replaced with circuit breakers.
Circuit breakers have an electromagnet, that, when the current exceeds the rated value, has sufficient strength to draw the connecting metallic link out of the circuit and open the path.
Circuit Breakers, GFCIs, and Fuses
Circuit Breakers, GFCIs, and
Fuses National Electrical Code requires that outlets in the bathroom and
other sensitive areas be of the Ground Fault Circuit Interrupt (GFCI) variety.
GFCIs are designed to trip more quickly than the standard circuit breaker.
GFCI senses differences in input and output currents to the outlet, and trips if they are not the same.
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Applications
Microwave ovens
Most microwaves are rated at 500 W to 1200 W at a
frequency of 2.45 GHz.
Heating occurs because the water molecules in the
food vibrate at such a high frequency that the friction
with neighboring molecules causes the heating effect.
Most microwaves are between 50% and 60% efficient.
Applications
Household wiring
Most older homes, without electric heating, have a 100
A service.
Power is broken down into different circuits utilizing
15 A, 20 A, 30 A and 40 A protective breakers.
o Maximum load on each breaker should not exceed 80% of its
rating (12 A of a 15 A circuit breaker).
Applications
The correct gauge of wire must be used with the
right circuit breaker
#14 wire up to a 15 A breaker,
#12 wire up to 20 A,
#10 wire up to 30 A.
Grounding is a very important part of safety.
The National Electric Code requires that the neutral
wire of a system be grounded to an earth-driven rod, a
metallic water piping system of 10 ft or more, or a
buried metal plate.
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Examples of Conductors
Metals – Gold
– Silver
– Copper (Cat 5 Cable)
Water
Humans
Insulators
Material with a high resistance to electrical
current.
Electron orbits are very close to the nucleus.
Examples:
– Plastic
– Glass
– Wood
– Air and other gases
Multimeter Basics
A Multimeter is used to measure: – Voltage
– Resistance
– Continuity (level of resistance)
When using a Multimeter, you must properly set it to either AC or DC, depending on the voltage you’re trying to measure.
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Current
This is the flow of electrons
which is electricity
Measured in amps (a)
Algebraic Symbol -- I = intensity
Graphic Symbol A = 1 coulomb/s
A
Voltage This is the Force or Push of
electricity, aka. Electro-Motive Force(EMF); amount of work or energy potential (joules/coulombs)
Measured in volts (v)
Algebraic Symbol -- E or V
Graphic Symbol ~
_
+
Resistance This is the property of matter which
opposes the flow of electrons
Measured in ohms ( )
Algebraic Symbol -- R
Graphic Symbol
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Capacitance
This is the property of matter which opposes the change in voltage
Measured in farads (F)
Algebraic Symbol is C
Graphic Symbol
Capacitance - cont’d.
A capacitor acts like a battery. It is
also a DC filter, depending on the
frequency of the voltage. The
dielectric between plates
determines the flow of electrons
between the plates and the
charging capacity of the device.
Capacitance-cont’d
Capacitive reactance resists DC
flow
frequency
Xc Xc = 1/2ƒC
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Inductance
This is the property of matter which
opposes the change in current
Measured in henrys (H)
Algebraic Symbol is L
Graphic Symbol
Inductance-cont’d
Allows DC, filters AC
Electromagnetic
frequency
XL
XL = 2ƒL Inductive Reactance
Inductance - cont’d.
An inductor acts like an AC filter,
again related to frequency. The
inductance increases as the
frequency increases (which is
inverse to that of capacitance’s
relationship to frequency).
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Power
This is the ability of electricity to
perform work
Measured in watts (W)
Algebraic Symbol -- P
No graphic symbol
A Circuit
For electricity to flow, one must
have a complete path.
Complete Circuit
Open Circuit
Short Circuit
A Circuit - cont’d.
Wire (a medium for transmission)
Source (power -- e.g. battery)
Load (resistance)
Control (switch, dial, phone)
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Required Parts
of an Electrical Circuit Source or Battery Complete Path
Resistance
Circuits
Series -- A single path for current to
flow
Parallel -- A single voltage shared
by multiple loads
Complex -- Combinations of series
and parallel
A Series Circuit
_
+
R1
R2
R3
E I
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Series Circuit - Total Value
Rtotal = R1 + R2 + …Rn
R1 = 5, R2 = 15 , and R3 = 7
What is the total resistance of the circuit?
Simple Parallel Circuit
_
+ R1 R2 E
I
I1 I2
Simple Parallel Circuit - cont’d
R1R2
R1 + R2
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A More Complexed Parallel
Circuit
_
+ R1 R2 R3 E
I
I3 I1 I2
Complexed Parallel Circuit
1
1/R1 + 1/R2 + …+ 1/Rn
Total resistance for a complex parallel
circuit.
A Complex Circuit
R2
E
_
+
R1
R7
R3 R4 R5
R8
R9 I
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Two Types of Current
Alternating Current (AC)—electrical
current flows in both directions; positive
and negative terminals continuously
trade places (polarity)
– Example: Electricity provided by Vectren
Direct Current (DC)—electrical current
flows in one direction; negative to
positive
– Example: Electricity provided by batteries
Alternating VS Direct Current
Why AC?
Where AC?
How AC to DC?
Direct Current (DC)
_
+
R1
R2 E I
vo
lts
2
4
6
time
E
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Alternating Current (AC) R1
R2 E I
~
vo
lts
2
4
6
time
E
-6
-4
-2
0
E
Characteristics of AC
Amplitude
– Peak
– Peak-to-peak
– Root Mean Square (RMS)
Frequency/Period
Phase
vo
lts
2
4
6
time
E
-6
-4
-2
0
E
Anurag Srivastava