Power Quality - Eeerulez.blogspot.in

8/3/2019 Power Quality - Eeerulez.blogspot.in

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POWER QUALITY

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INTRODUCTION:

´ The power quality problem is defined as any problemmanifested in voltage, current or frequency deviations thatresults in mal-operation of customer equipment.

´ The power quality problem causes the deterioration of

performance of various sensitive electronic and electricequipments. The good quality of power can be specified as

The supply voltage should be within guaranteed toleranceof declared value.

The waveshape should be pure sine wave withinallowable limits for distortion.

The voltage should be balanced in all three phases.

Supply should be reliable i.e continuous availabilitywithout interruption



WHY POWER QUALITY IS SO

IMPOR

TANT?

´ Lost production: Each time production is interrupted, yourbusiness loses the margin on the product that is notmanufactured and sold.

´ Damaged product: Interruptions can damage a partially

complete product, cause the items to be rerun or scrapped.´ Maintenance: Reacting to a voltage disruption can involve

restoring production, diagnosing and correcting the problem,clean up and repair, disposing of damaged products and, insome cases, environment costs.

´ Hidden costs: If the impact of voltage sag is a control error, aproduct defect may be discovered after customer delivery.The costs of losing repeat sales, product recalls and negativepublic relations can be significant and hard to quantify.



THE GOOD QUALITY OF POWER CAN BE

SPECIFIED AS: -

´ The wave should be a pure sine wave within allowable limits fordistortion.

´ Voltage should be balanced in all 3 phases.

´ Supply should be reliable

Causes of poor power quality:

Variations in voltage, magnitude and frequency

Variations in frequency can rise of out of system dynamics orharmonics injection.

´ Consequently the voltage or current waveforms of a power systemceases to be purely sinusoidal in nature but consist of harmonics andother noises.



Voltage fluctuations:

Voltage fluctuations are changes or swings in the steady-state

voltage above or below the designated input range for a piece

of equipment. Fluctuations include both sags and swells.



TRANSIENTS

Transients, commonly called "surges," are sub-cycle disturbances

of very short duration that vary greatly in magnitude.



HARMONICS:

The dynamic power system loads produce a time varying amplitude

in current waveforms depending on the load characteristics which

consists of the fundamental and harmonics components.

For assessing power quality it is important to know the total

harmonic distortion i.e. the voltage and current distortion

factors

V THD = & I THD =

Vk = Voltage of Kth harmonic, Ik = Current of Kth harmonic



HORMONIC ELIMINATION

TECHNIQUES:

. The simplest way of eliminating harmonics of different

orders is to install filters at the location generated by

different loads are connected in two ways in power system

network.

Series connected filter:

Such type of filters are connected in

series with power system network and offer highimpedance at turning frequencies high impedance offered

by filters allow very little harmonics are passed.



SHUNT CONNECTED FILTER:

It is most commonly used filters in A.C. power system network and

offers very low impeda.nce path to harmonics.

Passive filters:

These are LC resonating or parallel resonating circuits which offer

very high or low impedance at tuning frequency.




ACTIVE FILTERS:

Active filters compensates voltage of current harmonic signal

measured. The injected voltage or current harmonic signal

measured.

It comprises power converter and control loop which controlsthe harmonics injection of the filter as the function of harmonic

signal measure.




SOLUTIONS: -

Surge suppressors:

These are small plug-in devices designed to protect

equipment from moderate surges and spikes.

Isolation transformers:These devices electrically separate the electronic

equipment from the incoming power system, reducing

unwanted electrical noise.




CONCLUSION:

Harmonic distortion is increasing day by day at a fasterrate and is a matter of concern to the utility, customerand manufacturers of different equipment.

In India it is necessary first to create awareness regarding

harmonic problems, their effects and eliminationtechniques among the utility, consumers andmanufacturers of different equipments to make powersystem less polluted.

The utility should monitor the installation of high tension

consumers periodically, regarding the harmonic distortionand penalties should be imposed on customers using equipments crossing specified limits.




REFERENCES:

Power quality and Harmonics: JOHN H.

WAGGONER.

Inside PQ: MAX McGRANAGHAN. Grounding and lightening protection: ROBISON,

M.D.

Electric Power Quality: problems and means toimprove them: S.MOHANTY, B.R.MISHRA, Dr.

D.S. CHAUHAN.


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