Voltage Fluctuations and Flicker

1. Voltage Fluctuations and Flicker

2. Voltage fluctuations are defined as the cyclic variation of voltage with amplitude that does not exceed 10 %. flicker is defined as the impression of unsteadiness of visual sensation induced by a light stimulus whose luminance or spectral distribution fluctuates with time. DESCRIPTION OF THE Phenomenon

3. Thus, a physiological aspect is involved in the definition offlicker while voltage fluctuations are defined exclusively from an electrical point of view. This means that flicker is a phenomenon due to the combination of two factors: voltagefluctuations causing changes in light intensity and a person exposed to these changes. DESCRIPTION OF THE Phenomenon

4. Flicker is essentially a visual phenomenon that can cause significant malaise to the person exposed to it. • The degree of annoyance experienced by the individuals depends on several factors as: • The amplitude of the fluctuations, • The frequency of the fluctuation, • The duration of the disturbance • The color of the lighting source. • However, sensitivity to flicker is also dependent to a high degree on the individual. Physiology of Flicker Perception

5. In general, it can be said that the origin of flicker is in the devices connected to the electrical system that produce rapid voltage fluctuations. Usually, these voltage fluctuations are caused by variations in the consumed power and, especially, by reactive power fluctuations. Variations of power can be due either to switching on or off large-capacity loads, or to loads with an intrinsically fluctuating behavior (i.e. arc furnace loads). SOURCES

6. Industrial Loads • Arc Furnaces • Welding Machines • Electric Boilers • Capacitor Banks • Electrical Appliances Supplied from LV Networks • Wind Turbine Generation Systems Sources

7. Arc Furnaces Arc furnaces can range from a few MVA to more than 100 MVA and they are one of the major sources of perturbations connected to a HV network from the point of view of flicker. Sources – Industrial loads

8. Sources – Industrial loads

9. Sources – Industrial loads

10. Welding Machines In welding operation, short intervals of welding (with high current flow) are followed by others of no-load operation. In each welding operation, two voltage steps are produced, one at the time of establishing current and another at the instant of disconnection. These voltage variations can cause problems in the nearby loads producing voltage magnitudes outside the voltage tolerances and can even produce flicker. Sources – Industrial loads

11. Electric Boilers Electric boilers are used in industrial applications for generating steam. Thus, the required control of the temperature together with the varying need of steam lead to periods of high power demand followed by periods without energy consumption Sources – Industrial loads

12. Capacitor Banks Switching on and off a capacitor bank produces a voltage step proportional to the reactive power capacity of the capacitor bank and inversely proportional to the short-circuit capacity of the point of connection. In general, the most common power quality problems related to capacitor banks are the appearance of resonance phenomena between the capacitor and inductive elements of the system and the possible overvoltage transients due to the capacitor’s connection. It is only in very rare cases that voltage variations caused by capacitors switching can lead to a noticeable flicker level. Sources – Industrial loads

13. Electrical appliances supplied from LV networks like drives for lifts, pumps, fans, electric boilers, refrigerator chambers, electric cookers or air-conditioning equipment, having a considerable high power and being switched on an off cyclically or irregularly are potential flicker sources. Most of these disturbances are of the motor-start type. Other potential flicker generators in LV systems are X-ray equipment and large copying machines. Sources - Electrical Appliances Supplied from LV Networks

14. In recent years, power systems have experienced a significant increase in wind energy penetration. Wind turbines generate fluctuating power during continuous operation that can lead to voltage fluctuations at the PCC. In this regard, variable speed turbines have some advantages concerning flicker emission. In addition to continuous operation, switching operations of wind turbines are also a potential cause of voltage variations. Sources - Wind Turbine Generation Systems

15. The most important effect of voltage fluctuations is flicker produced by the variations in the fluctuation of illumination of light sources. Tungsten filaments of incandescent lamps of different nominal wattage behave differently when subjected to the same voltage fluctuations because of differences in construction. Compared to incandescent lamps, fluorescent lamps cause less flicker. On the contrary, the use of lamp dimmers substantially increases lamp susceptibility to voltage variations, so electronic dimmers increase the risk of flicker. EFFECTS

16. Flicker is caused by voltage fluctuations. Therefore, any strategy oriented to mitigate flicker must be based on a reduction of voltage fluctuations. Two kinds of approaches can be applied for this purpose: • Decreasing power variations (mainly reactive power variations) of the loads. • Increasing the short-circuit power level. MITIGATION STRATEGIES

17. Decreasing power variations (mainly reactive power variations) of the loads. • Static Var Compensator – SVC • Arc Furnaces • Insertion of a Saturable Inductance • Insertion of a Series Inductance MITIGATION STRATEGIES

18. Increasing the short-circuit power level. • A supplementary line which can be constructed to reinforce the distribution line. • Connection to a network at a higher voltage level. • Parallel connection of the mains transformers. MITIGATION STRATEGIES

19. “Handbook of Power Quality” , Edited by Angelo Baggini, ISBN: 978-0-470-06561-7, John Wiley & Sons Press, 2008. References

20. Thank you & Questions?