Chap I Power Point

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Chap I. POWER QUALITY AND DISTURBANCES



This voltage is generally subjected to a lot of disruption of two

distinct origins:

� Voltage disturbances caused by interference voltage such as voltageunbalance and voltage dips.

� Voltage disturbances caused by the shift in power grids, disrupting

currents like harmonics current, unbalance and reactive power flow.

TYPES OF VOLTAGE INTERFERENCES

I.1 Voltage fluctuations (Flicker): The slow fluctuations of the

voltage are reduced and rapid variation of the rms voltage of lessthan 10%.



Fig I.2 Example of rapid variation of the rms voltage

The consequences of the slow fluctuations of voltage occur mainly onincandescent lamps, where it causes a flicker of luminous flux (Flicker: Repetitive sags and swells in the electric service voltage,often accompanied by periodic harmonic distortion)

I.2 Unbalanced three-phase system: The system imbalanceoccurs when the three-phase voltages are not equal inamplitude and / or 120 ° out of phase ones relative to theothers.



Fig. I.3 Unbalanced three-phase system

I.3 Voltage Surge: a short-duration (microsecond to millisecond)increase in power line voltage. Also called a spike or an

impulse.



Fig I.5 Example of transient overvoltage

I.3.2 Effect of voltage surge

Their consequences are very different depending on the time of application,repeatability, magnitude, mode (differential or common), the steepness of the rising edge and frequency.

Dielectric breakdown, because of destruction of sensitive equipment(electronics etc ....).

Degradation by aging equipment (non-destructive but repeated surge).

Cutting long due to the destruction of equipment (loss of billing fordistributors, production losses for the industry).

Disruption of the control circuits, control and communications for lowcurrent.



I.4 Voltage dips/sags:

Sags are a sharp decrease in voltage at a point in a network of

electrical energy to a value between 90% and 10% of ratedvoltage, followed by recovery voltage; the duration can rangefrom 10 ms to several seconds.

Fig I.7 Voltage dips



I.4.2 Impact of voltage dips on equipments:

Tab I.1 Impact of voltage dips on some sensitive electrical equipment.



I.5 Voltage Swells:

a voltage or current RMS

value at supply frequency thatincreases for a time period from 0.5 cycles to 1 minute. It can

cause overheating and destruction of components.

Fig I.7.2 Voltage Swell



I.6 Voltage drops:

When transit in a power line is large enough, the current flow in

the line causes a voltage drop. The lower voltage is then

ultimately in its origin, and the line is loaded with power flow,the greater the voltage drop will be significant.

Fig I.8 Voltage drop caused by the supply of a load by a line froma power plant



Fig I.10 For a consumer with multiple distributed powers



I.7 Harmonic Distortion:

Caused by the nonlinear transfer characteristics of a device or circuit. When a

sinusoidal signal of a single frequency (the fundamental frequency) is

applied at the input of a nonlinear circuit, the output contains frequencycomponents that are integer multiples of the fundamental frequency

(harmonics). The resulting distortion is called harmonic distortion.

Fig II.1 Distortion caused by an harmonic (h=3)



I.7.2 Effect of harmonics

The most important effects are interference with

telecommunications networks, and

malfunction of some electrical equipment and

the risk of resonance excitation.



Conclusion:

In this chapter, we introduced various types of

disturbances affecting the voltage waveform of thegrid. As we have seen, the voltage unbalance,harmonics and voltage dips have adverse effects onpower quality and electrical equipment.

Finally, we can say that the disturbances have differentimplications depending on the economic context andscope, discomfort to the loss of the means of production, degradation of the operation until the totaldestruction of equipment.

The traditional compensation of reactive power (seriesand shunt) will be the next chapter as a means of improving power quality in electrical networks.

Chap I Power Point

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