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Page 1: Lecture 1 Basics of Electric Circuits

Lectures on Electrical

and Instrument

Engineering

Focused, To-The-Point and Practical!

Page 2: Lecture 1 Basics of Electric Circuits

Personal IntroductionEngr. Arslan Ahmed Amin is a professional Electrical and

Instrumentation Engineer serving Pakistan’s pioneer Oil and Gas

Organization, Pakistan Petroleum Limited. He obtained his Bachelor's

degree in Electrical Engineering from the prestigious University of

Engineering and Technology, Lahore in 2010 and started his

professional career with Pakistan Petroleum Limited. He has served

this organization for more than 5 years and achieved lots of

accomplishments in the development of the systems of newly installed

210 MMSCFD gas compression facility. He actively contributed his

services in commissioning, testing, maintenance and upgradation of

the E&I systems. He completed his Master’s in Business Administration

(M.B.A.) in 2014 from Virtual University of Pakistan, Lahore through

distance learning and afterwards obtained Masters (M.Sc.) in Electrical

Engineering from University of Engineering and Technology, Lahore in

2015.

Page 3: Lecture 1 Basics of Electric Circuits

M.Sc. Electrical Engineering (University of Engineering

and Technology, Lahore)

M.B.A. Online (Virtual University of Pakistan, Lahore)

B.Sc. Electrical Engineering with Honors (University of

Engineering and Technology, Lahore)

Education

Page 4: Lecture 1 Basics of Electric Circuits

05 years’ experience in industrial process controls and

electrical power systems domain with Pakistan

Petroleum Limited (PPL) in CMMS (SAP) environment.

Experience of commissioning, testing and maintenance

of latest systems regarding Power Generation, Field

Instrumentation, Distributed Control System, Safety

Instrumented System, Gas Turbines, PLCs, Analyzers and

Utility packages.

Experience

Page 5: Lecture 1 Basics of Electric Circuits

‘Circuits and Electronics’ from Massachusetts Instituteof Technology (MIT) USA.

‘Project Management’ from Virtual University ofPakistan (VU).

‘Production and Operations Management’ from VirtualUniversity of Pakistan (VU).

‘Conflict Management’ from Virtual University ofPakistan (VU).

‘Crisis Management’ from Virtual University of Pakistan(VU).

Professional Courses

Page 6: Lecture 1 Basics of Electric Circuits

QMS 9001, ISO 14001 EMS and OHSAS 18001, ERP System, Cost ofQuality, Productivity Improvement Techniques, Process SafetyManagement, Hazard Identification and Risk Assessment, HAZOP,SIL systems, Occupational health and Safety, Permit to worksystem, Safety Modules (Complete), Communication Skills, TeamWork Skills, Decision Making Skills (Organized by PPL)

SAP System (R3P version) Maintenance Work Orders Processing,Contracts Management, Spares and Material.

‘Instrumentation and Controls Fundamentals’ from OMS Institute ofManagement and Technology, Lahore.

Installation, calibration and maintenance of Fire and Gas detectorsby Det-tronics.

Generation, Transmission and Distribution at WAPDAEngineering Academy Faisalabad.

Professional Trainings

Page 7: Lecture 1 Basics of Electric Circuits

Among Top 10 students in the session of 240 students in B.Sc.Electrical Engineering.

Received Dean’s Honor Role award in consecutive fivesemesters for excellent academic performance in B.Sc.Electrical Engineering.

Overall Topped in F.Sc. in Board of Intermediate andSecondary Education, Faisalabad 2006.

Winner of Quaid-e-Azam Scholarship.

Gold medal winner in District Science Quiz CompetitionFaisalabad.

Represented as ‘Talent of Pakistan Youth’ in China in 2007 byMinistry of Youth, Pakistan.

Academic Achievements

Page 8: Lecture 1 Basics of Electric Circuits

Lets Start!

Lecture-1

Basics of Electric Circuits

Page 9: Lecture 1 Basics of Electric Circuits

Electric Circuit

An electric circuit is an interconnection of

electrical elements.

Page 10: Lecture 1 Basics of Electric Circuits

Systems of UNITS

Quantity Basic Unit Symbol

Length meter m

Mass kilogram kg

Time second s

Electric current ampere A

Thermodynamic

Temperature

kelvin K

Luminous

intensity

candela cd

Page 11: Lecture 1 Basics of Electric Circuits

The SI Prefixes

Page 12: Lecture 1 Basics of Electric Circuits

Charge and Current

Page 13: Lecture 1 Basics of Electric Circuits

Electric Current

Page 14: Lecture 1 Basics of Electric Circuits

Electric Current

Current is the flow of

electricity, much like

the flow of water in a

pipe. It is measured in

Amperage as opposed

to gallons per minute

of water.

Page 15: Lecture 1 Basics of Electric Circuits

Conductors

Free Electrons (e)

Easily Directed

Usually metals

Copper

Aluminum

Gold

Platinum

-

-

-

-

-

--

--

-

-

-

-

-

-

-

-

-

-

-

--

--

-

-

-

-

-

-

- +

Page 16: Lecture 1 Basics of Electric Circuits

Semi-Conductors

Dielectrics

4 Valence Electrons

Polarize with Some

Electron Flow due to

Electrical Fields

+

-

Page 17: Lecture 1 Basics of Electric Circuits

Insulators

No Free Electrons

No Current Flow with

Field

+

-

Page 18: Lecture 1 Basics of Electric Circuits

Why Does Current Flow?

A voltage source provides the energy (or work) required to produce a current

Volts = joules/Coulomb = dW/dQ

A source takes charged particles (usually electrons) and raises their potential

so they flow out of one terminal into and through a transducer (light bulb or

motor) on their way back to the source’s other terminal

Page 19: Lecture 1 Basics of Electric Circuits

Voltage

Voltage is a measure of the potential energy that causes a current to flow

through a transducer in a circuit

Voltage is always measured as a difference with respect to an arbitrary

common point called ground

Voltage is also known as electromotive force or EMF outside engineering

Page 20: Lecture 1 Basics of Electric Circuits

Voltage (Volts - V or E)

Voltage is the electrical

pressure in the system,

much like water pressure.

Electrical pressure is

measured in Volts as

opposed to Pounds per

Square Inch. (ie: 110V like

water from a tap, 4160 like

a fire hose)

Page 21: Lecture 1 Basics of Electric Circuits

Voltage

Page 22: Lecture 1 Basics of Electric Circuits

Resistance (Ohms - R or Ω)

Resistance is simply the

restriction of current

flow in a circuit.

Smaller wire

(conductors) and poor

conductors have higher

resistance.

Page 23: Lecture 1 Basics of Electric Circuits

Resistance

ee

e ee

ee

e

e

ee

ee

e

Many Collisions = Heat!

Fewer Collisions = Less Heat!

Page 24: Lecture 1 Basics of Electric Circuits

Ohm’s Law

Current, Voltage, and Resistance relate as follow:

I = E / R

Page 25: Lecture 1 Basics of Electric Circuits

A Circuit Current flows from the higher voltage

terminal of the source into the higher

voltage terminal of the transducer before

returning to the source

+

SourceVoltage

-

I

+ Transducer -Voltage

The source expendsenergy & the transducerconverts it into something useful

I

Page 26: Lecture 1 Basics of Electric Circuits

Passive Devices

A passive transducer device functions only when energized by a source in a

circuit

Passive devices can be modeled by a resistance

Passive devices always draw current so that the highest voltage is present on

the terminal where the current enters the passive device

+ V > 0 -

I > 0

Notice that the voltage ismeasured across the device Current is measured

through the device

Page 27: Lecture 1 Basics of Electric Circuits

Active Devices

Sources expend energy and are considered active devices

Their current normally flows out of their highest voltage terminal

Sometimes, when there are multiple sources in a circuit, one overpowers

another, forcing the other to behave in a passive manner

Page 28: Lecture 1 Basics of Electric Circuits

Power

The rate at which energy is transferred from an active source or used by a

passive device

P in watts = dW/dt = joules/second

P= V∙I = dW/dQ ∙ dQ/dt = volts ∙ amps = watts

W = ∫ P ∙ dt – so the energy (work in joules) is equal to the area under the

power in watts plotted against time in seconds

Page 29: Lecture 1 Basics of Electric Circuits

Power

The power consumed or created is just the Voltage

multiplied by the Current

P = V x I

Eg:

If 3 amps flowing through a component

generate 12 volts across the component

the power is 3 x 12 = 36 watts

Page 30: Lecture 1 Basics of Electric Circuits

Some power calculations

Current

I

Voltage

V

Power

P

2 Amps 5 Volts

9 Amps 36 Watts

10 Watts

4 Volts

Page 31: Lecture 1 Basics of Electric Circuits

Conservation of Power

Power is conserved in a circuit - ∑ P = 0

We associate a positive number for power as power absorbed or used by a

passive device

A negative power is associated with an active device delivering power

I

+

V

-

If I=1 amp

V=5 volts

Then passive

P=+5 watts

(absorbed)

If I= -1 amp

V=5 volts

Then active

P= -5 watts

(delivered)

If I= -1 amp

V= -5 volts

Then passive

P=+5 watts

(absorbed)

Page 32: Lecture 1 Basics of Electric Circuits

Example

A battery is 11 volts and as it is charged, it increases to 12 volts, by a current

that starts at 2 amps and slowly drops to 0 amps in 10 hours (36000 seconds)

The power is found by multiplying the current and voltage together at each

instant in time

In this case, the battery (a source) is acting like a passive device (absorbing

energy)

Page 33: Lecture 1 Basics of Electric Circuits

Energy

The energy is the area under the power curve

Area of triangle = .5 ∙ base ∙ height

W=area= .5 ∙ 36000 sec. ∙ 22 watts = 396000 J.

W=area= .5 ∙ 10 hr. ∙ .022 Kw. = 110 Kw.∙hr

So 1 Kw.∙hr = 3600 J.

Since 1 Kw.∙hr costs about $0.10, the battery costs $11.00 to charge

Page 34: Lecture 1 Basics of Electric Circuits

AC and DC Current

•DC Current has a constant value

•AC Current has a value that changes sinusoidally

Notice that AC current

changes in value and

direction

No net charge is

transferred

Page 35: Lecture 1 Basics of Electric Circuits

AC v DC

• DC can be produced chemically or mechanically; AC must be produced mechanically

• DC can be easily stored; AC cannot

• AC is easier, and thus cheaper, to produce

• AC can easily be transformed to other voltages

• AC can be transmitted more economically

Page 36: Lecture 1 Basics of Electric Circuits

Polarity

• Some components (like a bulb) can be connected either way round – they will still work

Page 37: Lecture 1 Basics of Electric Circuits

Polarity

• Some components (like a diode) can be connected either way round – they work one way but not the other

Page 38: Lecture 1 Basics of Electric Circuits

Passive Sign Convention

Page 39: Lecture 1 Basics of Electric Circuits

PSC: Example I

Page 40: Lecture 1 Basics of Electric Circuits

PSC: Example II

Page 41: Lecture 1 Basics of Electric Circuits

PSC: Example III

Page 42: Lecture 1 Basics of Electric Circuits

Circuit Elements

Ideal Independent Source: provides a specified

voltage or current that is completely independent of

other circuit variables

Ideal Independent Voltage Source:

Page 43: Lecture 1 Basics of Electric Circuits

Circuit Elements

Ideal independent current source

Page 44: Lecture 1 Basics of Electric Circuits

Circuit Elements

Ideal dependent voltage source

Ideal dependent current source

Page 45: Lecture 1 Basics of Electric Circuits

Automotive circuits

Page 46: Lecture 1 Basics of Electric Circuits

Equivalent electrical circuit

Vbatt

(b)

+

Ihead

Ibatt

Itail Istart Ifan Ilocks Idash

Page 47: Lecture 1 Basics of Electric Circuits

Electrical vehicle battery

pack

DC-AC converter(electric drive)

12 V12 V12 V12 V12 V

AC motor

(a)

Vbatt1 Vbatt2 Vbattn

Page 48: Lecture 1 Basics of Electric Circuits

Various representations of an

electrical system

HeadlightCar

battery

+ –

R

i

i

+

–v

So

urc

e

Lo

ad

(a) Conceptualrepresentation

Power flow

(b) Symbolic (circuit)representation

(c) Physicalrepresentation

+_

i

+

vVS

Page 49: Lecture 1 Basics of Electric Circuits

Volt-ampere characteristic of

a tungsten light bulb

0.1

0.2

0.3

0.5

0.4

–0.5

–0.4

–0.3

–0.2

0–20–30–40–50–60 –10 5040302010 60

–0.1

i (amps)

v (volts)

Variablevoltagesource

Currentmeter

+

v

i

Page 50: Lecture 1 Basics of Electric Circuits

The resistance element

i

R v

+

A

l 1/R

i

v

i-v characteristicCircuit symbolPhysical resistorswith resistance R.

Typical materials arecarbon, metal film.

R =l

A

Page 51: Lecture 1 Basics of Electric Circuits

Resistor color code

b 4 b 3 b 2 b 1

Color bands

blackbrownredorangeyellowgreen

012345

bluevioletgraywhitesilvergold

6 7 8 9

10%5%

Resistor value = ( b 1 b 2 ) 10b3;b4 = % tolerance in actual value

Page 52: Lecture 1 Basics of Electric Circuits

The current

1.5 V+_

R

v+ –

v– +

+

vi

R

i flows through each of the four series elements. Thus, by KVL,

1.5 = v1+ v2+ v3

R 1

R 2

R 3

R n

R N

R EQ

N series resistors are equivalent to a single resistor equal to the sum of the individual resistances.

Page 53: Lecture 1 Basics of Electric Circuits

Parallel circuits

+

v

KCL applied at this node

The voltage v appears across each parallel

element; by KCL, iS = i1 + i 2+ i 3

N resistors in parallel are equivalent to a single equivalent resistor with resistance equal to the inverse of the sum of

the inverse resistances.

RN REQR1 R2 R3 Rn

i1 i2 i3

iS R1 R2 R3

Page 54: Lecture 1 Basics of Electric Circuits

Wheatstone bridge circuits

c

R2

R3R1

v S a+_

(a)

Rx

v bva b

d

c

R2

R3R1+_

(b)

R x

v bva b

d

avS

Page 55: Lecture 1 Basics of Electric Circuits

A force-measuring instrument

R2

R3R1

vS

R4

vbva

d

c

+

ia ib

h

w

Beam cross section

R2 , R3 bondedto bottom surface

F

Page 56: Lecture 1 Basics of Electric Circuits

Practical voltage source

R L

rSi S

+_vS

+

v L

Practical

voltagesource

iS =vS

rS + R L

lim iS =vS

rSRL 0

r S i S max

vS

+

vL

The maximum (short circuit) current which can be supplied by a practical voltage source is

iS max = vS

rS

+_

Page 57: Lecture 1 Basics of Electric Circuits

Practical current source

R Li S

+

v Sr S

A model for practical current sources consists of an ideal source in parallel with an internal resistance.

i S

+

v Sr S

Maximum output voltage for practical current source with open-circuit load:

vS max = iS rS

Page 58: Lecture 1 Basics of Electric Circuits

Measurement of current

R2

R1

+_vS

A seriescircuit

R2

R1

+_vS

A

A

Symbol forideal ammeter

Circuit for the measurementof the current i

i i

Page 59: Lecture 1 Basics of Electric Circuits

Measurement of voltage

R2

R1

+_vS

A seriescircuit

R1

+_ VV

Idealvoltmeter

Circuit for the measurementof the voltage v2

i

v2

+

–i

R2v2

+

–v2

+

vS

Page 60: Lecture 1 Basics of Electric Circuits

Models for practical ammeter

and voltmeter

rm

A

Practicalammeter

V

Practicalvoltmeter

rm

Page 61: Lecture 1 Basics of Electric Circuits

Measurement of power

i

R1

+_

Internal wattmeter connections

R2v 2

+

vS

iR1

+_

Measurement of the powerdissipated in the resistor R2:

P2 = v2 i

vS

W

R 2v2

+

V

A

Page 62: Lecture 1 Basics of Electric Circuits

Definition of a branch

a

rm

A

Practicalammeter

Idealresistor

Rv

A battery

A branch

Branchvoltage

Branchcurrent

+

b

i

Examples of circuit branches

Page 63: Lecture 1 Basics of Electric Circuits

Definition of a node

Examples of nodes in practical circuits

Node a

Node b

vS iS

Node c Node a

Node b

Node

Page 64: Lecture 1 Basics of Electric Circuits

Definition of a loop

Loop 1 Loop 2

Loop 3

vS

R

1-loop circuit 3-loop circuit(How many nodes in

this circuit?)

Note how two different loopsin the same circuit may in-clude some of the same ele-ments or branches.

iSR1 R2

Page 65: Lecture 1 Basics of Electric Circuits

Magnetics

NorthSouth

Magnetic Flux

Magnet

Page 66: Lecture 1 Basics of Electric Circuits

Current Flow in Conductor

- +

Current Flowing in a Conductor

Page 67: Lecture 1 Basics of Electric Circuits

Generated Field Around

Conductor

+

Page 68: Lecture 1 Basics of Electric Circuits

Magnetic Field With Coil

+

-

+

-

North Magnetic Pole

South Magnetic Pole

Page 69: Lecture 1 Basics of Electric Circuits

Interaction with Medium

NorthSouth

Magnetic Flux

MagnetMetal NS

Page 70: Lecture 1 Basics of Electric Circuits

Electrical Properties

Frequency

Inductance (L)

Mutual

Inductive Reactance (XL)

Capacitance (C)

Capacitive Reactance (XC)

Phase Angle/Power Factor

Impedance (Z)

Page 71: Lecture 1 Basics of Electric Circuits

Frequency

0 90 180 270 360

Page 72: Lecture 1 Basics of Electric Circuits

Inductance

Stores electromagnetic energy

in its magnetic field

mH

dt

diLV

t

idvL

i0

)0()(1

2

2

1LiW

I lags V

Page 73: Lecture 1 Basics of Electric Circuits

Mutual Inductance

When 2 coils in close

proximity, a changing

current in one coil will

induce a voltage in a

second coil

0 90 180 270 360

N1 = 5 Turns

100 Volts

N2 = 5 Turns

100 Volts

Page 74: Lecture 1 Basics of Electric Circuits

Inductive Reactance XL

Inductive Reactance is

the AC Resistance of a

coil

Presented as a

resistance in Ohms

Frequency and

Inductance Dependant

fLX L 2

Page 75: Lecture 1 Basics of Electric Circuits

Capacitance

Stores energy in an electric field

Dielectric between 2 plates

The charged condition is maintained until a discharge path is present

Causes current to lead voltage

+

-

Page 76: Lecture 1 Basics of Electric Circuits

Capacitive Reactance XC

fCX C

2

1

Page 77: Lecture 1 Basics of Electric Circuits

Phase Angle / Power Factor

In a coil or motor,

current lags behind

voltage

This is represented as

an angle or a fraction

of ‘unity’

Adding C can improve

PF

IV

0 90 180 270 360

Page 78: Lecture 1 Basics of Electric Circuits

Impedance Z

fCX C

2

1fLX L 2

DC

Resistance

Complex

AC

Resistance

22 )( CL XXRZ

Page 79: Lecture 1 Basics of Electric Circuits

Summary

Atomic Structure and Electron Movement

Conductors, Semi-Conductors, Insulators

Basic Electricity: Current, Voltage and Resistance

Electrical and Magnetic Fields

Alternating Current Electricity: L, C, XL, XC, Z

Page 80: Lecture 1 Basics of Electric Circuits

Generation & Distribution

Generator

10.6 KV

GT220 KV

Step down

transformer

Distribution

Power plant Transmission

systemDistribution system

Page 81: Lecture 1 Basics of Electric Circuits

• AC generators (“alternators”) generate

electricity

• Electricity generated at 9-13 KV

• Power generated from 67.5 to 1000 MW

• Power stations: generating transformers

(GTs) to increase voltage to 132-400 KV

• Substations: step-down transformers to

reduce voltage before distribution

Generation & Distribution

Page 82: Lecture 1 Basics of Electric Circuits

Benefits of high voltage transmission

• Less voltage drop: good voltage regulation

• Less power loss: high transmission

efficiency

• Smaller conductor: lower costs

Generation & Distribution

Page 83: Lecture 1 Basics of Electric Circuits

83

Single phase AC circuit:

• Two wires connected

to electricity source

• Direction of current

changes many times

per second

Phase of Electricity

3-phases of an electric system

Three phase systems:

• 3 lines with electricity from 3 circuits

• One neutral line

• 3 waveforms offset in time: 50-60 cycles/second

Page 84: Lecture 1 Basics of Electric Circuits

Star connection

Phase of Electricity

Delta connection

Page 85: Lecture 1 Basics of Electric Circuits

Review of Phasors

Goal of phasor analysis is to simplify the

analysis of constant frequency ac systems

v(t) = Vmax cos(wt + qv)

i(t) = Imax cos(wt + qI)

Root Mean Square (RMS) voltage of sinusoid

2 max

0

1( )

2

TV

v t dtT

Page 86: Lecture 1 Basics of Electric Circuits

Phasor Representation

j

( )

Euler's Identity: e cos sin

Phasor notation is developed by rewriting

using Euler's identity

( ) 2 cos( )

( ) 2 Re V

V

j t

j

v t V t

v t V e

q

w q

q q

w q

Page 87: Lecture 1 Basics of Electric Circuits

Then drop the constant terms

( ) Re 2

V cos sin

I cos sin

V

V

jV

jj t

V V

I I

V V e V

v t Ve e

V j V

I j I

q

qw

q

q q

q q

Page 88: Lecture 1 Basics of Electric Circuits

Advantages of Phasor Analysis

0

2 2

Resistor ( ) ( )

( )Inductor ( )

1 1Capacitor ( ) (0)

C

Z = Impedance

R = Resistance

X = Reactance

XZ = =arctan( )

t

v t Ri t V RI

di tv t L V j LI

dt

i t dt v V Ij C

R jX Z

R XR

w

w

Device Time Analysis Phasor

Page 89: Lecture 1 Basics of Electric Circuits

RL Circuit Example

2 2

( ) 2 100cos( 30 )

60Hz

R 4 3

4 3 5 36.9

100 30

5 36.9

20 6.9 Amps

i(t) 20 2 cos( 6.9 )

V t t

f

X L

Z

VI

Z

t

w

w

w

Page 90: Lecture 1 Basics of Electric Circuits

Complex Power

max

max

max max

( ) ( ) ( )

v(t) = cos( )

(t) = cos( )

1cos cos [cos( ) cos( )]

2

1( ) [cos( )

2

cos(2 )]

V

I

V I

V I

p t v t i t

V t

i I t

p t V I

t

w q

w q

q q

w q q

Power

Page 91: Lecture 1 Basics of Electric Circuits

max max

0

max max

1( ) [cos( ) cos(2 )]

2

1( )

1cos( )

2

cos( )

= =

V I V I

T

avg

V I

V I

V I

p t V I t

P p t dtT

V I

V I

q q w q q

q q

q q

q q

Power Factor

Average

P

Angle

ower

Page 92: Lecture 1 Basics of Electric Circuits

P

Q

S

Power Triangle Inductive Load, lagging Power

Factor.

Page 93: Lecture 1 Basics of Electric Circuits

P

QS

Power Triangle Capacitive load, Leading

Power Factor

Page 94: Lecture 1 Basics of Electric Circuits

*

[cos( ) sin( )

P = Real Power (W, kW, MW)

Q = Reactive Power (var, kvar, Mvar)

S = Complex power (VA, kVA, MVA)

V I V IS V I j

P

I

jQ

V

q q q q

Page 95: Lecture 1 Basics of Electric Circuits

Power Factor (pf) = Cosø

If current leads voltage then pf is leading

If current lags voltage then pf is lagging

Page 96: Lecture 1 Basics of Electric Circuits

1

Relationships between real, reactive and complex power

cos

sin

Example: A load draws 100 kW with a leading pf of 0.85.What are (power factor angle), Q and S?

-cos 0.85 31.8

100117.6

0.85

P S

Q S

kWS

kVA

117.6sin( 31.8 ) 62.0 kVarQ

Page 97: Lecture 1 Basics of Electric Circuits

Conservation of Power

At every node (bus) in the system

Sum of real power into node must equal zero

Sum of reactive power into node must equal zero

This is a direct consequence of Kirchoff’s

current law, which states that the total

current into each node must equal zero.

Conservation of power follows since S = VI*

Page 98: Lecture 1 Basics of Electric Circuits

Conversation of Power

Example

Earlier we found

I = 20-6.9 amps

*

*R

2

*L

2

100 30 20 6.9 2000 36.9 VA

36.9 pf = 0.8 lagging

S 4 20 6.9 20 6.9

1600

S 3 20 6.9 20 6.9

1200var

R

L

S V I

V I

W I R

V I j

I X

Page 99: Lecture 1 Basics of Electric Circuits

Power Consumption in

Devices

2Resistor Resistor

2Inductor Inductor L

2

Capacitor Capacitor C

Capacitor

Resistors only consume real power

P

Inductors only consume reactive power

Q

Capacitors only generate reactive power

1Q

Q

C

I R

I X

jI X X

j C Cw w

2

Capacitor

C

V

X

Page 100: Lecture 1 Basics of Electric Circuits

Example

*

40000 0400 0 Amps

100 0

40000 0 (5 40) 400 0

42000 16000 44.9 20.8 kV

S 44.9 20.8 400 0

17.98 20.8 MVA 16.8 6.4 MVA

VI

V j

j

V I

j

First solve

basic circuit

Page 101: Lecture 1 Basics of Electric Circuits

Example

Now add additional

reactive power load

and resolve

70.7 0.7 lagging

564 45 Amps

59.7 13.6 kV

S 33.7 58.6 MVA 17.6 28.8 MVA

LoadZ pf

I

V

j

Page 102: Lecture 1 Basics of Electric Circuits

Balanced 3 Phase () Systems

A balanced 3 phase () system has

three voltage sources with equal magnitude, but with an angle shift of 120

equal loads on each phase

equal impedance on the lines connecting the generators to the loads

Bulk power systems are almost exclusively 3

Single phase is used primarily only in low voltage, low powersettings, such as residential and some commercial

Page 103: Lecture 1 Basics of Electric Circuits

Balanced 3 -- No Neutral Current

* * * *

(1 0 1 1

3

n a b c

n

an an bn bn cn cn an an

I I I I

VI

Z

S V I V I V I V I

Page 104: Lecture 1 Basics of Electric Circuits

Advantages of 3 Power

Can transmit more power for same amount of

wire (twice as much as single phase)

Torque produced by 3 machines is constant

Three phase machines use less material for

same power rating

Three phase machines start more easily than

single phase machines

Page 105: Lecture 1 Basics of Electric Circuits

Three Phase - Wye Connection

There are two ways to connect

3 systems

Wye (Y)

Delta ()

an

bn

cn

Wye Connection Voltages

V

V

V

V

V

V

+

Page 106: Lecture 1 Basics of Electric Circuits

Wye Connection Line Voltages

Van

Vcn

Vbn

VabVca

Vbc

-Vbn

(1 1 120

3 30

3 90

3 120

ab an bn

bc

ca

V V V V

V

V V

V V

Line to line

voltages are

also balanced

Page 107: Lecture 1 Basics of Electric Circuits

Wye Connection

Define voltage/current across/through device

to be phase voltage/current

Define voltage/current across/through lines to

be line voltage/current

6

3

3 1 30 3

3

j

Line Phase Phase

Line Phase

Phase Phase

V V V e

I I

S V I

Page 108: Lecture 1 Basics of Electric Circuits

Delta Connection

IcaIc

IabIbc

Ia

Ib

a

b

a

3

For the Delta

phase voltages equal

line voltages

For currents

I

3

I

I

3

ab ca

ab

bc ab

ca bc

Phase Phase

I I

I

I I

I I

S V I

Page 109: Lecture 1 Basics of Electric Circuits

Three Phase Transmission Line

Page 110: Lecture 1 Basics of Electric Circuits

Wye Connection Line Voltages

Van

Vcn

Vbn

VabVca

Vbc

-Vbn

(1 1 120

3 30

3 90

3 150

ab an bn

bc

ca

V V V V

V

V V

V V

Line to line

voltages are

also balanced

Page 111: Lecture 1 Basics of Electric Circuits

Wye Connection Line Voltage

Define voltage/current across/through device to be phase

voltage/current

Define voltage/current across/through lines to be line

voltage/current

6

3

3 1 30 3

3

j

Line Phase Phase

Line Phase

Phase Phase

V V V e

I I

S V I

Page 112: Lecture 1 Basics of Electric Circuits

Delta Connection

IcaIc

IabIbc

Ia

Ib

3

For the Delta

phase voltages equal

line voltages

For currents

I

3

I

I

3

a ab ca

ab

b bc ab

a ca bc

Phase Phase

I I

I

I I

I I

S V I

Page 113: Lecture 1 Basics of Electric Circuits

Three Phase Example

Assume a -connected load is supplied from a 3 13.8 kV

(L-L) source with Z = 1020W

13.8 0

13.8 0

13.8 0

ab

bc

ca

V kV

V kV

V kV

13.8 0138 20

138 140 138 0

ab

bc ca

kVI amps

I amps I amps

Page 114: Lecture 1 Basics of Electric Circuits

*

138 20 138 0

239 50 amps

239 170 amps 239 0 amps

3 3 13.8 0 kV 138 amps

5.7 MVA

5.37 1.95 MVA

pf cos 20 lagging

a ab ca

b c

ab ab

I I I

I I

S V I

j

Page 115: Lecture 1 Basics of Electric Circuits

Delta-Wye Transformation

Y

phase

To simplify analysis of balanced 3 systems:

1) Δ-connected loads can be replaced by 1

Y-connected loads with Z3

2) Δ-connected sources can be replaced by

Y-connected sources with V3 30

Line

Z

V

Page 116: Lecture 1 Basics of Electric Circuits

Per Phase Analysis

Per phase analysis allows analysis of balanced 3 systems

with the same effort as for a single phase system

Balanced 3 Theorem: For a balanced 3 system with

All loads and sources Y connected

No mutual Inductance between phases

Page 117: Lecture 1 Basics of Electric Circuits

Per Phase Analysis

Then

All neutrals are at the same potential

All phases are COMPLETELY decoupled

All system values are the same sequence assources. The sequence order we’ve been using(phase b lags phase a and phase c lags phase a) isknown as “positive” sequence; later in the coursewe’ll discuss negative and zero sequence systems.

Page 118: Lecture 1 Basics of Electric Circuits

Per Phase Analysis Procedure

To do per phase analysis

1. Convert all load/sources to equivalent Y’s

2. Solve phase “a” independent of the other phases

3. Total system power S = 3 Va Ia*

4. If desired, phase “b” and “c” values can be

determined by inspection (i.e., ±120° degree phase

shifts)

5. If necessary, go back to original circuit to

determine line-line values or internal values.

Page 119: Lecture 1 Basics of Electric Circuits

Per Phase Example

Assume a 3, Y-connected generator with Van = 10volts supplies a -connected load with Z = -j through a transmission line with impedance of j0.1 per phase. The load is also connected to a -connected generator with Va”b” = 10 through a second transmission line which also has an impedance of j0.1per phase.

Find

1. The load voltage Va’b’

2. The total power supplied by each

generator, SY andS

Page 120: Lecture 1 Basics of Electric Circuits

Per Phase Example

First convert the delta load and source to equivalent

Y values and draw just the "a" phase circuit

Page 121: Lecture 1 Basics of Electric Circuits

Per Phase Example

' ' 'a a a

To solve the circuit, write the KCL equation at a'

1(V 1 0)( 10 ) V (3 ) (V j

3j j

Page 122: Lecture 1 Basics of Electric Circuits

Per Phase Example

' ' 'a a a

'a

' 'a b

' 'c ab

To solve the circuit, write the KCL equation at a'

1(V 1 0)( 10 ) V (3 ) (V j

3

10(10 60 ) V (10 3 10 )

3

V 0.9 volts V 0.9 volts

V 0.9 volts V 1.56

j j

j j j j

volts

Page 123: Lecture 1 Basics of Electric Circuits

Per Phase Example

*'*

ygen

*" '"

S 3 5.1 3.5 VA0.1

3 5.1 4.7 VA0.1

a aa a a

a agen a

V VV I V j

j

V VS V j

j

Page 124: Lecture 1 Basics of Electric Circuits

124

Delta-Star Transformation

Page 125: Lecture 1 Basics of Electric Circuits

125

Start-Delta Transformation

Page 126: Lecture 1 Basics of Electric Circuits

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