Week02 Chapter 1Three Phase System

7/29/2019 Week02 Chapter 1Three Phase System

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Chapter 1 Three phase system

Week 2

Interconnections of three phase system (star and delta),

Relationship between line and phase valuesBalanced load


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v(t)

Vm

-Vm

t

Phasor

diagram

Which one is:Vm = ?

Vinst = ?

= ?

+V

-V


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3

A three-phase system is superior economically and

advantage, and for an operating of view, to a single-

phase system. In a balanced three phase system thepower delivered to the load is constant at all times,

whereas in a single-phase system the power pulsates

with time.

Three-Phase System

In a three phase system the source consists of three

sinusoidal voltages. For a balanced source, the three

sources have equal magnitudes and are phase

displaced from one another by 120 electrical degrees.


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Advantages of 3- compared to 1- system

High efficiency

For same power at the transmission line,

less conductor and lighter Construction and maintenance, minimum

(cheaper)

Starting behavior and operation of 3-equipment better or more stable than 1-


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5

Generation of Three-PhaseThree separate windings or coils with terminals R-R, Y-Y and B-B are

physically placed 120o apart around the stator.

Y

BY

B

Stator

Rotor

Y

R

B

R

R

N

S


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6

It has 3 conductor loops

that is R (red), Y (yellow) and

B (blue). The conductor loop will

move in circle and then cut

off the magnetic flux.

It will produces the

electromagnetic force e.m.fin the conductor.

Maximum e.m.f is when the

conductor loop is 90 with

magnetic flux line.


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7

v(t)

t

vR

vY

vB

The instantaneous e.m.f. generated in phase R, Y and B:

vR= VRsin tvY= VY sin (t -120

o)

vB= VB sin (t -240o)= VBsin (t +120

o)


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8

Phase sequences : RYB and RBY

120o

-120o

120o VR

VY

VB

o

)rms(RR0VV

o

)rms(YY120VV

o

)rms(B

o

)rms(BB

120V

240VV

VR leads VY, which in turn leads VB.This sequence is produced when the rotor rotates in

the counterclockwise direction.

(a) RYB or positive sequence


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9

(b) RBY or negative sequence

o

)rms(RR0VV

o

)rms(BB120VV

o

rmsY

ormsYY

V

V

120

240

)(

)(

V

VR leads VY, which in turn leads VB.This sequence is produced when the rotor rotates in

the clockwise direction.

V

120o

-120o120

o

VR

VB

Y


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Simulation of current flow in 3 phase system


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3 phase generator
http://localhost/var/www/apps/conversion/tmp/scratch_2/alternator1.swfhttp://localhost/var/www/apps/conversion/tmp/scratch_2/3phase.swf


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12

Connection in Three Phase System Star and Delta

Star Connection ()

Also known as Y connection (wye)

Usually been used in system that needs high voltage and

low current

There are two types of Y connection, i.e:

i) 3 wire star connection

ii) 4 wire star connection


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13

R

Y

B

ZR

ZY ZB

3 wire star connection

Use 3 line wire, that are R, Y and B.

All of the conductor loop source is connected in similar reference

point S.


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14

R

Y

B

ZR

ZY ZB

Star/wye Connectiona)Three wire system

Voltage

source Load

No Neutral wire

E,N S

VRY

VYB

VBR

VRN

VYNVBN

VRS

VBSVYS

IR

IY

IB


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15

VRN

VBN

VYN

ZR

ZY ZB

R

B

NY

4 wire star connection

Use 4 line wire, that are R, Y , B and N.

N wire is connected to reference point S.


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16

Star Connection

b) Four wire system

VRN

VBN VYN

ZR

ZY ZB

R

BN

YNeutral wire

Voltage

source LoadVRY

VYB

VBR

VRN

VBNVYN

N

IR

IY

IB


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17

Star/wye connection of Load

Z1

Z3

Z2

R

B

Y

NLoad

Z3

Z1Z 2

R

Y

B

Load

N

or


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18

Delta Connection ()

Usually been used in system that need high line current and lowphase current.

Connect all the conductor in series.

No neutral line

Generator Load


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19

Delta Connection

R

Y

B

Y

B

R

Voltage

source

Load

VRY VBR

VYB

VRY

VBR

VYB

IYB

IRY

IBR

IRIR

IY

IY

IB

IB

IRY

IYB

IBR


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20

Delta connection of load

Zc

Za

Zb

R

B

Y

Load

Zc

Zb

Za

R

Y

B

Load


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21

Line Voltage (VL) : Potential different between two line.

Phase Voltage (Vph) : Potential different between two

phase or voltage across load in each phase.

Line Current (IL): Current flow in each line.

Phase Current (IPH): Current flow in each phase or load.

3 phase system definition


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22

Line Voltage

Potential between line to line, Star and

Delta

VRY

between line R and Y

VYB between line Y and B

VBR between line B and R


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23

Balance 3 phase systemIn balance three phase system:

The system will have same value of load in

each phase.

Each phase voltage will have same magnitude

and phase different 120.

Each phase current will have same magnitude

and phase different 120.


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24

Star connection

Line Voltage

VRY : Line voltage between R & Y

VYB : Line voltage between Y & B

VBR : Line voltage between B & R

Phase Voltage

VRN : Phase voltage R

VYN : Phase voltage Y

VBN : Phase voltage B


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25

Star connection

VRN is take as the reference point in positive rotation

120120

120120

00

PhBNBN

PhYNYN

PhRNRN

VVV

VVV

VVV

From Kirchhoff Law:

303

1201011200

Ph

Ph

PhPhYNRNRY

V

V

VVVVV


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26

Star connection

1503

903

PRNBNBR

PBNYNYB

VVVV

VVVV

As conclusion :

303 PLVV

For a balance star

connection.

Line voltage (VL) has magnitude 3 Vph and is leading phase voltage (VPH)

with 30.

With the same method ;


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27

Star connection

Phasor diagram for phase voltage and line voltage;


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28

Line Current = Phase Current

Current flow in each line is:

IR : Line current R.

IY: Line current Y.

IB: Line current B.

Phase current : Current that flow through each phase loop or

load.

For star connection;

Star connection

current)(Phasecurrent)(LinePLII


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29

Delta Connection

Line Voltage,

VRY

Voltage across conductor RR.VYB

Voltage across conductorYY.VBR

Voltage across conductorBB.

In delta connection, Line voltage is also thephase voltage , So:

voltage)(Phasevoltage)(LinePLVV

Delta Connection


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30

120120

120120

00

PBRBR

PYBYB

PRYRY

III

III

III

303

1200

:loadAt the

P

PP

BRRYR

I

II

III

Phase current , IRY, IYB dan IBR Current flow through each conductor loop in

each phase.And IRYalways be taken as the reference current, so ;


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31

903

1503

;Then

PYBBRB

PRYYBY

IIII

IIII

Line Current (IL) lagging current phase (IPH) with 30.Magnitude IL = 3 IPH.

303 PLII

For balance delta

connection

Conclusion :


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32

Delta Connection


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Example

A positive phase sequence three-phase

voltage source connected in a balanced Y has

a line voltage of VRY= 415 -45 Vrms.

Determine the phase voltage.

V(t) = Vmax sin (t 45o)


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Example

A balanced Y-connected load is supplied by a

balanced Y-connected source with a phase

voltage of VRN = 220 Vrms . If IR = 5 -30 A.

Determine the phase and line voltages, phaseand line currents. Subsequently, sketch

phasor diagram with positive sequence phase.


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A balanced -connected load issupplied by positive phase sequence

balanced three-phase -connected

source with VRY= 415 Vrms, If thecurrent flowing through phase RY, IRY

= 5 A, determine phase and line

voltages, phase and line currents.Hence sketch the phasor diagram.

35

Example


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Balanced Load Connection in

3-Phase System

Balance Power Supply


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////// 321 ZZZ

321 ZZZ

Y Y connection

Y - connection

- connection - Y connection


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VRN

VBN

Z1

Z2 Z3

R

B

N

Y

VYN

IR

IY

IB

IN

BYRNIIII

For balanced load system,

IN = 0 and Z1 = Z2 = Z3

3

o

BN

B

2

o

YN

Y

1

o

RN

R

Z

120VI

Z

120VI

Z

0VI

BNYNRNphasa

phasaBN

phasaYN

phasaRN

VVVVwhere

120VV

120VV

0VV

Voltage and Current at Star Connected Balanced Loads

a)Four wire system


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Voltage and Current at Star Connected Balanced Loadsb) Three wire system

R

Y

B

Z1

Z 2 Z3

IR

IY

IB

VRY

VYB

VBR S

0IIIBYR

3

o

BS

B

2

o

YS

Y

1

o

RS

R

Z

120VI

Z

120VI

Z

0V

I

BSYSRSphasa

phasaBS

phasaYS

phasaRS

VVVVwhere

240VV

120VV

0VV


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Voltage and Current at Delta-Connected Balanced Loads

Z

Z

Z

R

Y

B

VRY

VYB

VBR

IR

IRY

IBR

IYB

IB

IY

Phase currents:

3

o

BR

BR

2

o

YB

YB

1

o

RY

RY

Z

120VI

Z

120VI

Z

0VI

Line currents:

YBBRB

RYYBY

BRRYR

III

III

III

lineBYR

phasaBRYBRY

IIIIand

IIIIwhere

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Week02 Chapter 1Three Phase System