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Enhancement of Voltage Qualityin Isolated Power Systems

BYP.Balaswamy (11NE1A0239)

TIRUMALA ENGINEERING COLLEGE,

JONNALAGADDA.

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CONTENT INTRONUCTION

VQ PROBLEMS

DESCRIPTION OF VQ PROBLEMSWHO GET AFFECTED

SINGLE LINE DIAGRAM WITH SC

BENEFITS OF VQ MONITORING

CONCLUSION

REFERENCE

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ABSTRACTThe use of series compensators (SCs) in improving voltagequality of isolated power systems is considered.The roles of the compensators are to mitigate the effects of

momentary voltage sags/swells, and to control the level ofharmonic distortions in the networks. A control strategy for the SC is developed to regulatepower flow.This is achieved through phase adjustment of load terminalvoltage. It leads to an increase in the ridethrough capabilityof loads to the voltage sags/swells.

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INTRODUCTION

ISOLATED power systems are commonly found in rural anremote areas of the world. These systems represent thealternative to grid connection, where interconnection to alarge grid is not viable due to high cost and/or geographicalobstacles .

Furthermore, power systems such as those onboard of ships,in oil exploration areas and remote mining districts arecharacterized by limited generating capacity, supplying loadswhich can consist of significant amount of motor drives and

power converters.

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VOLTAGE QUALITY PROBLEMS1.DisturbanceI. Voltage sagII. Voltage interruptionIII. Voltage swellIV. TransientV. Voltage notch2.Imbalance3.Distortion4.Voltage fluctuation

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DESCRIPTION1.DISTURBANCES

A disturbance is defined as the temporary deviation

from the steady state waveform. VOLTAGE SAG

Reduction in voltage magnitude for a short period of

time. VOLTAGE INTERRUPTION

Voltage sag with 100% reduction in amplitude .

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VOLTAGE SWELL

Increase in RMS voltage or current at the power

frequency between 1.1 to 1.9 per unit for a duration of

15milisec to 2sec. TRANSIENT

Voltage disturbance shorter than sag/swell and are

caused by sudden changes in power system . VOLTAGE NOTCH

Periodic transient occuring within each cycle.

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4.VOLTAGE FLUCTUATION

T he rapid change in voltage magnitude in the

allowable limit .

5.FLICKER

Flicker is a term used to describe a random or

continuous voltage fluctuations .

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Why VQ is such a Big Problem?

The sensitivity of todays electronic equipment makes itsusceptible to voltage disturbancesdue to sensitive loads like Digital Computers

Variable Frequency Motor DrivesProgrammable Logic ControllersComputer Numerical Control (CNC)Automated Systems and ProcessesConsumer ElectronicsDigital Clocks

Due to non-linear loads like fluorescent lamp . electric welding machine . Diode rectifier.Motor drives.Power discharging devices

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In order to mitigate the problems and enhancethe voltage quality series compensation is used

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Descriptions of above SC diagram

shows a typical isolated power system supplying aconverter load.The RL load may be used to represent an aggregate ofdc motor drives, supplied via the converter.The converter is often a controlled six-pulse rectifierthrough which the motor torque is regulated byadjusting the firing angle of the rectifier.The motor-drive load is nonlinear and would involvecommutation process within the converter.

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Harmonic power flow in the isolated system: hth harmonic component.

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Description of harmonic power flow

The main converter load is the dominant harmonic sourcein the power system due to its much larger capacity,compared to the SC and sensitive load.The SC is assumed to be ideal in that whatever harmonicsgenerated by the VSI are effectively dealt with by its LCfilter.

The SC is a harmonic sink. In this way, theharmonic power Pdh produced by the nonlinearmain drive load is dissipated in the upstreamsource impedance and is absorbed by the sensitiveload.

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Equivalent circuits of the sensitive load-SC branch for (a) fundamentalcomponent and (b) hth harmonic component.

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(a)Equivalent circuit describing harmonic compensation inpractice and

(b) phasor diagram for the hth harmonic order.

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Conclusion

A method to control the injection voltage of the SC so thatit can mitigate the effects of the harmonics has been

proposed. The SC is also designed to maintain the fundamentalfrequency component of the terminal voltage of protectedsensitive load. In the process of harmonic voltage compensation, it isshown that power exchange exists between the SC and the

external network.A new SC control strategy is then proposed which involvesthe phase adjustment of the fundamental frequencycomponent of the sensitive load terminal voltage.

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BIBILOGRAPHY

[ 1] I. Jonasson and L. Soder, Power quality on ships-a questionnaireevaluation concerning island power system, in

Proc. IEEE Power Eng Soc.Summer Meeting, Jul. 2001, vol. 15 19, pp. 216 221.

[2] J. J. Graham, C. L. Halsall, and I. S. McKay, Isolated power systemsProblems of waveform distortion due to thyristor converter loading, in Proc. 4th Int. Conf. Power Electronics and Variable-Speed Drives , Jul.1990, vol. 17 19, pp. 327 330.

[3] ITI (CBEMA ) Curve Application Note , [Online]. Available:http://www.itic.org., Inf. Technol. Ind. Council (ITI).

[4] J. C. Das, Passive filter Potentialities and limitations, IEEE Trans.Ind. Appl., vol. 40, no. 1, pp. 232 241, Jan. 2004.

[5] H. Akagi, New trends in active filter for power conditioning, IEEE Trans. Ind. Appl ., vol. 32, no. 6, pp. 1312 1322, Nov. 1996.

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THANK YOU