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Presented By:

Sourabh KanthaliyaB.E. Final YearElectrical Engineering

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INTRODUCTION

GENERAL CAUSES

INTRODUCTION TO VOLTAGE SAGS IN

INDUCTION MOTOR NON RECTANGULAR VOLTAGE SAG

CLASSIFICATION

STUDY & ANALYSIS

OUTPUT

CONCLUSION

2

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3

Voltage sags are short-duration reductions in the r.m.s.voltage magnitude

Sag magnitude range from 10% to 90% of nominalvoltage

Sag duration ranges from cycle-1 min

One of the major power quality problem

A voltage sag is not a complete interruption of power

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ILLUSTRATION OF VOLTAGE SAG

4

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GENERAL CAUSES OF VOLTAGE SAG5

Voltage Sag due to Faul ts

The sag magnitude due to faultsdepends on:

Distance to the fault

Fault impedance

Type of fault

Presag voltage level

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The sag magnitude depends upon:

Characteristics of the induction

motor

Strength of the system at the point

where motor is connected

6

Voltage Sags due to M otor Starting

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The causes for voltage sags due to

transformer energizing are:

Normal system operation, which

includes manual energizing of a

transformer.

Reclosing actions

7

Voltage Sags due to Transformer Energizing

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VOLTAGE SAG IN

INDUCTION MOTOR

In induction motors it has been noticed that voltagesags cause speed loss, peak currents and torquesthat appear with voltage recovery. However, thereare also non-rectangular voltage sags which arebasically caused by starting high power motors thatdemand high currents that lower as speed increases

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NON RECTANGULAR VOLTAGE SAGS

Non-rectangular voltagesags are the result of therecuperation of a motor

steady-state after a faultin the bus at which it isconnected. Theirdifference withrectangular sags is a

reacceleration time thatlasts from the end of thefault that caused thevoltage sag and the

steady state voltage.

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CLASS A

CLASS B

CLASS C

CLASS D

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CLASS A

Voltage sags Type A

are caused mainly

by three-phasefaults, producing

equal voltage drop

in three phases

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CLASS B

Type B sags are

caused by single

phase faults

producing voltage

drop only in the

faulted phase.

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CLASS C

Type C are due to

phase-to-phase

faults which causevoltage drop and

phase-angle

movement in the

faulted phases

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CLASS D

Type D are also due tophase-to-phase faultswhich cause voltage

drop and phase-anglemovement in thefaulted phases. Theseare slightly different

than type C fault i.e.magnitude of thirdphase voltage drops.

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FIRST STEP :

The first stage is togenerate the non

rectangular voltagesag signals. for thissimulation letsmanipulate a

sinusoidal waveparameters in termsof the amplitude,sag duration andrecovery time.

Study and Analysis

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SECOND STEP :

The second stage is to

select a representativemotor. It is convenient tochoose a motor withmiddle-low power inorder to see the effects.

Power 3746 VA

Nominal Voltage 180V

Frequency 60 Hz

Poles 2

Inertia coefficient 0.089 J

Slip 3%

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THIRD STEP :

Finally, different types (A, B, C and D) of sags are applied to

the machine considering the non rectangular voltage sagmodel.

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SPEED

TORQUE

CURRENT

Outputs

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It can be seen that Non rectangular voltage sags type A an D cause a

huge speed loss considering that the duration of the sag is only 0.4seconds. Instead, Type B sags are not as severe as the others in terms ofspeed loss; this is an expected result because in this type of sags thereis only one phase involved during the event.

Sag Type Loss of

speed

A 6.46%

B 2.44%

C 4.01%

D 7.50%

SPEED

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It can be seen from that in alltype of sags there is a counter-torque at the moment that thesag starts. After that, this torquerecuperation occurs until the endof the sag. It can be noticed thatduring this recuperation there isoscillation due to the linearcharacteristic of the sagreacceleration. The oscillationsare more severe in sags type Cprobably because of the

combined effect of voltage dropand phase angle change. Onthe other hand, sags type Acause little oscillation. This isbecause of the remainingequilibrium in voltage amplitude

and phase angle.

tORQUE

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PHASE A

PHASE B

PHASE C

current

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PHASE A

PHASE B

PHASE C

current

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PHASE A

PHASE B

PHASE C

current

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It can be noticed thatphase A is the mostaffected having veryhigh current peak,especially in sags typeA and D. On the otherhand, phase c is theless affected; yet, sag

type A has a strongimpact. In terms ofoscillations, sag type Bcause little effect.

Sag

Type

Ratio

peak

current

to

nominalcurrent

phase

A

Ratio

peak

current

to

nominalcurrent

phase B

Ratio

peak

current

to

nominalcurrent

phase

C

A 4.375 3.375 2.20B 2.875 3.25 2.01

C 2.975 2.125 3.25

D 4.875 4.125 3.00

current

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CONCLUSION

Sags type A and D cause an important loss ofspeed that could become harmful for themechanical work of the machine if sags last more.

At the moment of occurrence of sag there is ahuge counter-torque that results in a high demandof currents. These current peaks cause windingdamage and, as a consequence, a loss of usefullife of the machine.

Sags type A and D also cause high peak currentswhich make them a phenomenon of special care.

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