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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

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