Unit1_3 Phase System

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UNIT 1

THREE PHASE SYSTEM

By: INTAN SHAFINAZ BINTI ABD. RAZAK


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Introduction

What is alternating current???

What is single phase system???

What is three phase system???


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Single-phase electric power

In electrical engineering, single-phaseelectric power refers to the distribution of

electric powerusing a system in which allthe voltages of the supply vary in unison.

Single-phase meaning (2) power lines as an

input source; therefore, only (1) primary and

(1)secondary winding is required to

accomplish the voltage transformation.
http://en.wikipedia.org/wiki/Electric_powerhttp://en.wikipedia.org/wiki/Electric_power


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A single-phase load may be powered from a

three-phase distribution system either by

connection between a phase and neutral .

For example, in places using a 415 volt 3

phase system, the phase-to-neutral voltage

is 240 volts, allowing lighting to be

connected phase-to-ground and motors to

be connected to all three phases.
http://en.wikipedia.org/wiki/Ground_and_neutralhttp://en.wikipedia.org/wiki/Ground_and_neutral


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THREE PHASE AND

SINGLE PHASE POWER SYSTEM

R

Y

B

N

3 phase delta system Single phase(R)3 phase wye system

Single phase

(Y)

Single phase

(B)


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THREE PHASE AND

SINGLE PHASE POWER SYSTEM

RED

YELLOW

BLUE

LINES

NEUTRAL

PROTECTING

GEAR 3-Phase

415V, 3-Wires(For Motor and

smallindustrialconsular)

Three separate

single-phase 240Vsupplies (For

lighting, heatingand domestic

consumer)

Single- phase

415V supply

BLACK

IR

IY

IB


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Polyphase system

Polyphase system is the system use

more than one coil to generate the

current. Example: Three phase system


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HOW TO GENERATE THREEPHASE CURRENT???

Rotating magnetic field , static

winding coil. (Medan magnet berputar,

gegelung kekal.)

Rotating winding coil, static magnetic

field (Gegelung berputar, medan magnet

kekal.)


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Three phase motor

The rotating

magnetic field of a

three-phase motor

The winding coil is

static
http://en.wikipedia.org/wiki/Magnetic_fieldhttp://en.wikipedia.org/wiki/Magnetic_field


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THREE PHASE SYSTEMS(THREE PHASE VOLTAGE)

If three separate coils are spaced 120apart, three voltages 120 out of phasewith each other will be produced whenmagnetic field through the coils.

This manner in which a three-phase

voltage is produced.
http://localhost/var/www/apps/conversion/releases/20121120192253/tmp/VIDEO/e_and_m_3phase_gen.swf


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THREE PHASE SYSTEMS(THREE PHASE VOLTAGE)

Three phase voltage cycle

Result of three-phase voltage cycle as shown below:


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The waveform

Three-phasenetworks consistof three simplenetworks, eachhaving the sameamplitude andfrequency, and a120 phase

differencebetween adjacentnetworks


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The phasors diagram

We can also

represent these

voltages withphasors diagram.


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To reduce the number of wires it is usual to interconnectthe three phases.

Two ways solution:

Star/Wye connection : applied on sources of three

phase supplies (alternators). Higher voltage but lower current (amps)

Delta connection : applied on motors and otherloads.

Lower voltage but mores current (amps).

THREE PHASE SYSTEMS(THREE PHASE CONNECTION)


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Introduction to delta and wye

three phase system

When you connect a load to the threewires/ lines it should be done in such

a way that it does not destroy thesymmetry.

This means that you need three equalloads connected across the three pairsof wires.


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Delta and Wye Connections

This looks like an equilateral triangle,

or delta, and is called a delta load.

Another symmetrical connection wouldresult if you connected one side of

each load together, and then the three

other ends to the three wires. Thislooks like a Y, and is called a wye

load.


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Delta and WyeConnections cont

In a three-phase transformer, there is a three-

legged iron core.

Each leg has a respective primary and secondary

winding. As can be seen, the three-phase transformer

actually has 6 windings (or coils) 3 primary and 3

secondary. These 6 windings will be pre-connected at the

factory in one of two configurations: - Delta and WyeConnections/ Configurations.


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Wye Connection


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The Wyeor Y-connection

The Wyeor Y-connection, wherethe negative terminals of eachgenerator or load are connected to form the neutral terminal.

This results in a three-wire system, or if a neutral wire is provided, a

four-wire system.

Ip2Ip1

Ip3 IL3

IL2

IL1

IN


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Phase & Line in Y-connection

In Y-connection, the phase and line

currents are obviously the same, but

the line voltages are greater than thephase voltages.

In the balanced case:


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Phase & Line in -connection

As opposed to a Y-connection, in -

connection the phase and line voltages

are obviously the same, but the linecurrents are greater than the phase

currents.

In the balanced case:


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versus Y

-connection Y-connection

VL= VP

IL

=IP


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POWER IN THREE PHASE SYSTEM (Y AND )ARE THE SAME!!!

P 3 = 3 .VL . IL . cos


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SUMMARY

Symbol Y

Voltage VL = VPH VL = 3 VPH

Current IL = 3 IPH IL = IPH

Steady state

(Keadaanseimbang)

V (closed loop) =VRY + VYB + VBR = 0 IN = IR + IY +IB = 0

Single phase powerfor each coil.

VPH . IPH . cos

Three phase power(phase element)

3 .VPH . IPH . cos

Three phase power(line element)

3 .VL . IL . cos


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Example 2:

Di dalam satu sistem tiga fasa 4dawai, voltan talian ialah 415V dan

beban-beban resistif 10kW, 8kW dan5kW disambungkan di antara ketiga-tiga pengalir talian dan pengalir neutralseperti dalam rajah berikut. Kirakan:

Arus dalam setiap talian. Arus di dalam pengalir neutral


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Kebaikan sistem tiga fasa berbanding sistemsatu fasa

Penggunaan bekalan kuasa AU untuk tujuan pemanasan filamen lampuelektrik adalah memadai dengan menggunakan sistem kuasa satu fasa.

Namun demikian, penggunaan sistem satu fasa untuk tujuan kendalian motorAU mempunyai kelemahannya. Salah satu kelemahan iaitu motor AU satufasa tidak dapat dimulakan putaran dengan sendiri (self-starting), sebaliknyabeza fasa antara gegelung tiga fasa membolehkan motor AU tiga fasamempunyai ciri kendalian permulaan kendiri.

Penjimatan bahan pengalir untuk kehilangan tembaga yang sama, apabilakuasa yang sama dipindahkan dalam sistem tiga fasa berbanding sistem satufasa.

Motor tiga fasa adalah kendalian permulaan kendiri tetapi tidak berlakudalam motor satu fasa.

Motor tiga fasa mempunyai faktor kuasa dan kecekapan yang lebih baik dan

saiz yang lebih kecil, bagi keluaran yang sama berbanding motor satu fasa. Daya kilas yang dihasilkan oleh motor tiga fasa adalah tetap, sementara daya

kilas motor aruhan satu fasa adalah berbentuk dedenyut.


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Alatubah tiga fasa adalah lebih ringan, berkecekapan lebihbaik dan lebih murah berbanding alatubah satu fasa yangsama saiz.

Dalam sistem pengagihan tiga fasa, dua bentuk sambungan

biasanya dilakukan untuk menghasilkan nilai voltan yangberlainan daripada satu sumber bekalan yang sama, tanpapenambahan kos. Sambungan bintang menggunakanvoltan fasaantara fasa-fasa dan neutral yang lebih rendahbiasanya untuk kegunaan domestik;manakala sambungandelta menggunakan voltan yang lebih tinggiiaitu voltantalian(3 kali lebih besar) biasanya untuk kegunaan

perindustrian.


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Copper loss is the term often given to heat produced by electrical currents in theconductors oftransformerwindings, or other electrical devices.

Copper losses are an undesirable transfer ofenergy, as are core losses, which resultfrom induced currents in adjacent components.

The term is applied regardless of whether the windings are made ofcopperor anotherconductor, such as aluminium. Hence the term winding loss is often preferred.

A related term, load loss closely related but not identical, since an unloaded transformerwill have some winding loss. Copper losses result from Joule heating and so are also referred to as "I squared R

losses", in deference to Joule's First Law. This states that the energy lost each second, orpower, increases as the square of the current through the windings and in proportion tothe electrical resistance of the conductors. Copper Loss = I2R

where I is the current flowing in the conductor and R the resistance of the conductor. WithI in amperes and R in ohms, the calculated power loss is given in watts.

With high-frequency currents, winding loss is affected by proximity effect and skin effect,and cannot be calculated as simply.

For low-frequency applications, the power lost can be minimized by employingconductors with a large cross-sectional area, made from low-resistivity metals.
http://en.wikipedia.org/wiki/Heathttp://en.wikipedia.org/wiki/Electrical_currenthttp://en.wikipedia.org/wiki/Electrical_conductorhttp://en.wikipedia.org/wiki/Transformerhttp://en.wikipedia.org/wiki/Induced_currenthttp://en.wikipedia.org/wiki/Energyhttp://en.wikipedia.org/wiki/Core_losshttp://en.wikipedia.org/wiki/Induced_currenthttp://en.wikipedia.org/wiki/Copperhttp://en.wikipedia.org/wiki/Aluminiumhttp://en.wikipedia.org/wiki/Joule_heatinghttp://en.wikipedia.org/wiki/Power_(physics)http://en.wikipedia.org/wiki/Square_(algebra)http://en.wikipedia.org/wiki/Joule%27s_first_lawhttp://en.wikipedia.org/wiki/Proportionality_(mathematics)http://en.wikipedia.org/wiki/Proportionality_(mathematics)http://en.wikipedia.org/wiki/Secondhttp://en.wikipedia.org/wiki/Power_(physics)http://en.wikipedia.org/wiki/Square_(algebra)http://en.wikipedia.org/wiki/Proportionality_(mathematics)http://en.wikipedia.org/wiki/Electrical_resistancehttp://en.wikipedia.org/wiki/Amperehttp://en.wikipedia.org/wiki/Watthttp://en.wikipedia.org/wiki/Proximity_effect_(electromagnetism)http://en.wikipedia.org/wiki/Skin_effecthttp://en.wikipedia.org/wiki/Resistivityhttp://en.wikipedia.org/wiki/Resistivityhttp://en.wikipedia.org/wiki/Skin_effecthttp://en.wikipedia.org/wiki/Proximity_effect_(electromagnetism)http://en.wikipedia.org/wiki/Watthttp://en.wikipedia.org/wiki/Amperehttp://en.wikipedia.org/wiki/Electrical_resistancehttp://en.wikipedia.org/wiki/Proportionality_(mathematics)http://en.wikipedia.org/wiki/Square_(algebra)http://en.wikipedia.org/wiki/Power_(physics)http://en.wikipedia.org/wiki/Secondhttp://en.wikipedia.org/wiki/Joule%27s_first_lawhttp://en.wikipedia.org/wiki/Joule_heatinghttp://en.wikipedia.org/wiki/Aluminiumhttp://en.wikipedia.org/wiki/Copperhttp://en.wikipedia.org/wiki/Induced_currenthttp://en.wikipedia.org/wiki/Core_losshttp://en.wikipedia.org/wiki/Energyhttp://en.wikipedia.org/wiki/Transformerhttp://en.wikipedia.org/wiki/Electrical_conductorhttp://en.wikipedia.org/wiki/Electrical_currenthttp://en.wikipedia.org/wiki/Heat


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Salah satu kelemahan iaitu motor AU

satu fasa tidak dapat dimulakan

putaran dengan sendiri (self-starting). Explain what is self-starting?


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Large industrial synchronous motors

are self started by embedded squirrel

cage conductors in the armature,acting like an induction motor.

The electromagnetic armature is only

energized after the rotor is brought upto near synchronous speed.


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Mini-quiz to check your

understanding


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Wh t d l t i l


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What does an electricaltransformer do?

a) It changes the direction of AC

electricity

b) It changes the voltage of DCelectricity

c) It changes the voltage of AC

electricity


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QUIZ!!!

What is the difference between AC

and DC electricity?

Why do we use AC instead of DC? How do we create AC electricity?


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Unit1_3 Phase System

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