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The power quality problem is defined as any problem manifested in voltage, current or frequency deviations that results in mal-operation of customer equipment.

The power quality problem causes the deterioration of performance of various sensitive electronic and electric equipments. The good quality of power can be specified as

The supply voltage should be within guaranteed tolerance of declared value.

The waveshape should be pure sine wave within allowable limits for distortion.

The voltage should be balanced in all three phases.

Supply should be reliable i.e continuous availability without interruption

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Lost production: Each time production is interrupted, your business loses the margin on the product that is not manufactured 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, in some cases, environment costs.

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

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The wave should be a pure sine wave within allowable limits for distortion.

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 or harmonics injection.

Consequently the voltage or current waveforms of a power system ceases to be purely sinusoidal in nature but consist of harmonics and other noises.

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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.

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Transients, commonly called "surges," are sub-cycle disturbances of very short duration that vary greatly in magnitude.

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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

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. 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 high impedance at turning frequencies high impedance offered by filters allow very little harmonics are passed.

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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.

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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 controls the harmonics injection of the filter as the function of harmonic signal measure.

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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.

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

In India it is necessary first to create awareness regarding harmonic problems, their effects and elimination techniques among the utility, consumers and manufacturers of different equipments to make power system less polluted.

The utility should monitor the installation of high tension consumers periodically, regarding the harmonic distortion and penalties should be imposed on customers using equipments crossing specified limits.

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