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Power Quality in Public Lighting Systems
A. Dolara, Student Member, IEEE, R. Faranda, Member, IEEE, S. Guzzetti and S. Leva, Member, IEEE
Abstract-- The governments are interested in applying energy saving policies. From this point of view, the energy consumption for lighting can catch up 15% of the total electrical energy country bill. As a matter of fact, the lights are often inefficient, they are used when is not necessary and they are also generator of a considerable amount of distortion. A possible method to reduce the energy consumption and to increase the Power Quality (PQ) level can be represented by the substitution of the old lamps and by using new ballast and control systems. The aim of this paper is, with reference to public lighting, to illustrate as the electronic control gear for traditional High Pressure Sodium (HPS) lamp makes possible not only energy saving but also a wide PQ improvement.
driving. It must be noticed that discharge lamps cannot be connected directly to the supply line. In fact, to ignite them it is necessary to provide an extra voltage of some kV. In order to limit the current, a ballast in series with the lamp is typically used. In these conditions, the current absorbed from the supply line is out of phase with the voltage (current is delayed compared with the voltage) and shows a considerable amount of distortion [4]-[6]. In order to obtain an acceptable PF, a compensation capacitor for the fundamental component is commonly used and harmonics filters are required. All these devices, conveniently called control gear, can be replaced with an electronic device.
Index Terms— Power Quality, discharge lamp, lighting design, energy efficiency.
I. INTRODUCTION
T
HE electrical Power Quality (PQ) is regulated by distributors and standards from IEC and EN are used as reference [1]-[2]. In order to respect these technical standards, the power generators have to guarantee voltage levels established by the standards and they have to ensure the supply continuity . The end-user have to guarantee current absorptions with adequate Power Factor (PF) and reduced harmonics contents. In case of non-linear loads, compensation capacitance for the fundamental component is insufficient to compensate non-active power and harmonics filters are required. An inadequate PF and/or insufficient PQ level cause power losses and voltage drop increment and voltage distortion. Public lighting are currently made with High Intensity Discharge (HID) lamps and in particular, the High Pressure Sodium (HPS) types [3]. HPS lamps have particular characteristics that make them suitable for public lighting application.. In fact, the luminous efficiency is quite high and the spectral luminous distribution (see Fig. 1), even if mainly concentrated on yellow, has a certain content of the other colours of the visible spectrum. As a matter of fact, other types of lamps (e.g. Low-Pressure Sodium (LPS), Fig. 1) have greater efficiency, but the luminous emission is concentrated on a single spectral line, preventing therefore the recognition of colours, with obvious problems of security for nocturnal
A. Dolara is with the Department of Energy of Politecnico di Milano, Italy (e-mail:
[email protected]). R. Faranda is with the Department of Energy of Politecnico di Milano, Italy (e-mail:
[email protected]). S. Guzzetti is with the Department of Energy of Politecnico di Milano, Italy (e-mail:
[email protected]). S. Leva is with the Department of Energy of Politecnico di Milano, Italy (e-mail:
[email protected]).
978-1-4244-7245-1/10/$26.00 ©2010 IEEE
Fig. 1. Typical output spectrum emission of a HPS and LPS. With reference to lighting, for both street and residential application, the replacement of conventional mercury vapour lamps (street lighting) or incandescent lamps (residential lighting) with energy efficient electronic lighting system (efficient lamp and electronic control gear) will result in a reduction of the load and a decreased amount of the CO2 emission. Anyway standard control gear and electronic gear without filters can be a source of distortions and the standard concerning the PF and harmonics of loads is becoming more and more restrictive. Furthermore, from the point of view of energy saving, recent European and National standards suggest
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the use of programmable clocks as switching on and off devices and luminous flux reduction. [7]-[8] The continuous decrease in the cost of electronic components and the regulatory directives now applied make the electronic solution more and more competitive. In fact, electronic control gear can be able to offer several advantages both from power quality and efficiency, that can be summarized mainly in quality of lighting service, electrical requirements and energy saving [9]. In the last years same papers deal with the analysis of the performance of street lighting systems and in particular of the control gear both on the points of view of energy saving and of the power quality impact [3]. Thinking that future public lighting will make use of LED technology, this is becoming very and very important. For cost and efficiency reasons LED lamp are not yet competitive with HID lamps. The use of power electronics and of a microcontroller-based supervisor appears to be viable. In particular, it could just be that intelligent control strategies, such as the reduction in lighting power during the hours of lower traffic volumes, will anticipate the entry of LEDs into the market of public lighting systems [10]-[11]. In the present paper a comparative analysis of the performances in terms, both of absorbed power (energy consumption) and of luminous flux, of a 150W HPS street luminaire is presented. The comparative analysis is made supplying the same lamp with an electro-mechanical traditional power supply system (comprehensive of ballast and capacitor) and successively with an electronic ballast. The behaviour of the street luminaire when a sharp decrease of the supply voltage with the two different ballast has also analyzed. In particular, the goals of this study are: to find the performances of the equipment in the two configurations (electro-mechanical and electronic ballast) to the nominal voltage; to evaluate the lighting performance in the two different configurations varying the RMS of supply voltage. Moreover the obtained results are used to analyze power quality problem in a typical street application. II. TESTING ARRANGEMENT AND RESULTS During the tests three quantities have been measured: the illuminance in a point (Ep), the supply voltage and the absorbed current by the lamp. In particular, the illuminance was measured in a point placed perpendicular to the lamp and to a distance of 3.5m from street luminaire; the applied voltage and absorbed current have been measured after a stabilization period from switch-on, equal to 45 minutes (discharge lamps require a period of time to stabilize their light output). The luminous flux is measured by a luxmeter instead the current – corresponding to the supply voltage - are measured connecting the luminaire (lamp and control gear) to an oscilloscope and interposing, between the supply and load, a variable transformer in order to change, within an opportune range, the lamp supply voltage. An outline of the supply and measurement arrangement is sketched in Fig. 2.
Fig. 2. Test arrangement.
In order to characterize the lamp electric behaviour and to evaluate the energy consumption during a typical working day, seven different supply voltage are considered, starting from 200V and growing up to 260V with step of 10 V. Furthermore, the behaviour of the luminaire has been also analysed reducing quickly the voltage from 250 V to 220 V. With the aim to compare the two different technologies of gear the measurements has been made firstly by installing the electro-mechanical traditional control gear and then the electronic ballast with the same lamp and measurement systems. The first set of measurements has been performed using the electro-mechanical traditional power supply of the street luminaire. The results of the test are shown in Table I, where S is the apparent power and P the active power. TABLE I RESULTS OF MEASUREMENTS OF THE FIRST TEST WITH ELECTRO-MECHANICAL TRADITIONAL POWER SUPPLY
Supply Voltage (V)
S (VA)
P (W)
Illuminance EV (lx)
200
132.7
122.7
161
210
147.4
136.7
190
220
165.2
152.3
220
230
182.1
168.3
255
240
201.8
187.1
291
250
223.1
204.2
327
260
245.4
224.6
367
In order to understand the current absorption, Fig. 3 shows the voltage waveform at 230V and the relative current waveform. Fig. 4 represents the harmonic contents of the voltage and current absorbed by the luminaire at all the considered supply voltages, normalized with respect to the fundamental current harmonic. The current absorbed by the luminaire is distorted and characterized by elevated harmonic content.
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TABLE II RESULTS OF MEASUREMENTS OF THE SECOND TEST WITH ELECTRONIC BALLAST POWER SUPPLY
Supply Voltage (V)
S (VA)
P (W)
Illuminance EV (lx)
200
159.3
154.2
256
210
158.9
156.8
256
220
159.7
157.1
256
230
159.0
156.0
256
240
158.5
154.8
256
250
158.7
154.3
256
260
159.0
154.2
256
Fig. 3. Voltage and current waveform absorption at 230V for electro-mechanical traditional power supply.
Fig. 5. Voltage and current waveform absorption at 230V for electronic ballast power supply.
Fig. 4. Harmonic contents at each voltage test for electro-mechanical traditional power supply.
The second test is carried out using the electronic ballast power supply of the street luminaire. The results of this test are reported in TABLE II. Fig. 5 shows the voltage waveform at 230V and the relative current waveform at the same time, respectively. Fig. 6 reports the harmonic contents of the voltage and current absorbed by the luminaire at all the testing voltage. In this case, by using electronic ballast, the current absorbed by the street luminary is constant and independent on the mains voltage. Furthermore, it is characterized by very low harmonic content.
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Fig. 6. Harmonic contents at each voltage test for electronic ballast power supply.
In terms of power consumption (see table I and II), it is possible to observe that the electronic ballast guarantee an energy saving of approximately 7%, with similar illuminace, when the supply voltage is equal to the rated voltage. The energy savings and the variations of illuminance obtained by using electronic ballast fed with voltages different from the rated one are calculated, respectively, as:
∆p =
Pelectronic ballast − Pelectro − mechanical ballast
∆eV =
(1)
Pelectro −mechanical ballast
EVelectronicballast − EVelectro−mechanical ballast
(2)
EVelectro−mechanical ballast
These values (see Table III) are not completely enough to characterize the real behavior of the luminaries. For this purpose, Table III reports the values of relative efficiency, defined as the ratio of the absorbed power and its illuminance, referred to a reference a value. In this case, rated conditions with electro-mechanical ballast (230 V, 168.2 W and 255 lx) are taken as reference.
eq. eff . =
Where the subscript 1 refers to the fundamental harmonic and the subscript H refers to all the other the harmonics. Starting from (4) and (5), the apparent power is decomposed into fundamental apparent power S1, current distortion power DI, voltage distortion power DV and harmonic apparent power SH as indicated in the follow:
P EV Pref EVref
(3)
Electronic ballast ensure an equivalent efficiency of about 109 % with respect to the traditional one in the rated conditions, moreover equivalent efficiency is almost constant with voltage supply level. TABLE III COMPARISON BETWEEN BALLASTS AND LIGHT PERFORMANCES. Equivalnet Equivalnet Supply efficiency efficiency Power Illuminance Voltage for for variation variation (V) traditional electronic ballast ballast 200 25,67% 59,01% 86,60% 109,57% 210
14,70%
34,74%
91,73%
107,76%
220
3,15%
16,36%
95,34%
107,55%
230
-7,31%
0,39%
100,00%
108,31%
240
-17,26%
-12,03%
102,65%
109,15%
250
-24,44%
-21,71%
105,69%
109,50%
260
-31,34%
-30,25%
107,85%
109,57%
S1 = V1 ⋅ I1
(6)
DI = V1 ⋅ I H
(7)
DV = VH ⋅ I1
(8)
SH = VH ⋅ I H
(9)
Fundamental apparent power is composed by the fundamental active and reactive power:
S12 = P12 + Q12
(10)
and it takes into account the power quantities related to the voltage and current fundamental harmonic. Current distortion power is related to the product of the voltage fundamental harmonic with the current harmonic components. Similarly, voltage distortion power is related to the product of the current fundamental harmonic with the voltage harmonic components. Harmonic apparent power is composed by the harmonic active power and harmonic distortion power:
SH2 = PH2 + DH2
(11)
Current distortion power, voltage distortion power and harmonic apparent power are related to the voltage and/or current distortion: the nonfundamental apparent power SN is defined ad follow:
S N2 = DI2 + DV2 + SH2
(12)
With regard to energy conversion, the active power is defined as the mean value over a period of the instantaneous power: P=
1 τ +T v ( t ) ⋅ i ( t ) ⋅ dt T ∫τ
(13)
The fundamental active power P1, defined in (10), is given by:
P1 = V1 ⋅ I1 ⋅ cos ϕ1
(14)
and harmonic active power PH ,defined in (11), is given by:
III. POWER QUALITY ANALYSIS To complete the comparison a power quality analysis has been performed. The apparent power absorbed by the luminaire in both cases is decomposed in 4 parts, as described in [9] with regards to the single phase case. The voltage ad current RMS square values are decomposed, respectively, as follows:
V 2 = V12 + VH2
(4)
I 2 = I12 + I H2
(5)
PH = P − P1
(15)
Finally, the power factor is defined as:
PF =
P S
(16)
It is important to underline that the only way to reduce the apparent with traditional equipment is to place a capacitor in parallel with the load. In the case of distorted load, capacitor can compensate only the reactive power Q1. Moreover, capacitor acts like a high-pass filter for the harmonic currents,
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requiring oversizing. Finally, parallel resonance with the line
inductance can cause an high voltage distortion.
TABLE IV POWER QUALITY ANALYSIS OF THE MEASUREMENTS RESULTS OBTAINED BY ELECTRO-MECHANICAL BALLAST. Supply Voltage (V) 200 210 220 230 240 250 260
Voltage RMS values V (V)
V1 (V)
VH (V)
199.5 209.9 220.1 229.6 240.2 249.4 260.6
199.4 209.7 219.9 229.4 240.0 249.2 260.4
6.9 8.3 9.4 9.4 10.0 9.8 10.2
Apparent Power S THDI (VA)
Current RMS values
THDV
I (A)
I1 (A)
IH (A)
3.5% 3.9% 4.3% 4.1% 4.2% 3.9% 3.9%
0.663 0.702 0.751 0.793 0.840 0.894 0.942
0.617 0.654 0.696 0.737 0.784 0.830 0.879
0.242 0.255 0.281 0.292 0.302 0.333 0.338
39.2% 39.0% 40.5% 39.6% 38.5% 40.1% 38.4%
132.3 147.4 165.2 182.1 201.8 223.1 245.4
Active Power decomposition
Apparent Power Decomposition
P (W)
P1 (W)
PH (W)
S1 (VA)
SN DI DV SH (VA) (VAr) (VAr) (VA)
122.7 136.7 152.3 168.3 187.1 204.1 224.6
122.9 137.0 152.6 168.5 187.3 204.7 225.3
-0.2 -0.3 -0.3 -0.1 -0.1 -0.5 -0.7
123.1 137.2 153.0 169.1 188.1 206.9 228.9
48.5 53.9 62.3 67.4 72.9 83.4 88.4
48.2 53.6 61.9 67.0 72.4 83.0 87.9
4.3 5.4 6.5 6.9 7.8 8.2 9.0
1.7 2.1 2.6 2.7 3.0 3.3 3.5
cos(φ)
PF
0.998 0.998 0.997 0.996 0.995 0.989 0.984
0.928 0.927 0.922 0.925 0.928 0.915 0.915
cos(φ)
PF
0.989 0.988 0.985 0.983 0.979 0.976 0.974
0.988 0.987 0.984 0.981 0.977 0.973 0.970
TABLE V POWER QUALITY ANALYSIS OF THE MEASUREMENTS RESULTS OBTAINED BY ELECTRONIC BALLAST. Supply Voltage (V) 200 210 220 230 240 250 260
Voltage RMS values V (V)
V1 (V)
VH (V)
200.1 209.9 220.4 230.6 241.8 250.4 261.0
199.9 209.8 220.2 230.4 241.7 250.3 260.8
7.7 7.6 8.0 8.1 8.7 8.3 10.0
Apparent Power S THDI (VA)
Current RMS values
THDV
I (A)
I1 (A)
IH (A)
3.9% 3.6% 3.6% 3.5% 3.6% 3.3% 3.8%
0.796 0.757 0.725 0.690 0.655 0.633 0.609
0.795 0.755 0.723 0.688 0.653 0.631 0.606
0.047 0.046 0.044 0.050 0.055 0.057 0.061
5.9% 6.1% 6.1% 7.2% 8.4% 9.0% 10.0%
159.3 158.9 159.7 159.0 158.5 158.6 159.0
All these quantities are calculated with references to the two ballast. The results are shown in Table IV and Table V. and discussed in the following. First of all, in both cases voltage Total Harmonic Distortion (THD) [13] is low and it is between 3% and 4% in the most considered cases: this is due to the harmonic pollution already present in the power network. Instead, the use of electronic ballast reduce the current THD from about 40% to values between 6% and 10%. In both cases, the fundamental power factor cosφ is close to unity and the harmonic active power PH is negligible. The current distortion produced by electromechanical ballast increase the apparent power, reducing the power factor. The input current waveform of electronic ballast is mainly a sinusoid in phase with the voltage waveform and the power factor is very close to the fundamental power factor, that is just a little less of unity. The apparent power of electromechanical ballast is mainly composed by the fundamental active power and by the nonfundamental apparent power. The latter is primarily represented by the current distortion power; fundamental reactive power, voltage distortion power and harmonic apparent power are negligible because voltage distortion is very small and voltage and current fundamental harmonics are essentially in-phase. The strong reduction in the current distortion due to the use of electronic ballast increase the power factor, reducing the current distortion power. The magnitudes of the voltage and current harmonics and the sign of the harmonic active power suggest that the
Active Power decomposition
Apparent Power Decomposition
P (W)
P1 (W)
PH (W)
S1 (VA)
SN DI DV SH (VA) (VAr) (VAr) (VA)
157.4 156.8 157.1 156.0 154.8 154.3 154.2
157.2 156.5 156.9 155.7 154.6 154.1 153.9
0.2 0.2 0.2 0.2 0.3 0.2 0.2
158.9 158.5 159.3 158.5 157.8 157.9 158.1
11.3 11.2 11.3 12.7 14.4 15.1 17.0
9.4 9.6 9.7 11.5 13.2 14.1 15.8
6.1 5.7 5.8 5.6 5.7 5.2 6.1
0.4 0.3 0.4 0.4 0.5 0.5 0.6
electronic ballast under test will produce a current waveform that has the same shape of the voltage waveform. This control method is very simple, but the current absorption is almost sinusoidal only in the case of little voltage distortion. In presence of high voltage distortion, this control method produces a deformed current waveform that includes at least all harmonics present in the voltage waveform. In the latter case, it is better to make use of ballasts controlled as active filter, such as a sinusoidal current in-phase with the voltage fundamental harmonic independently of the harmonics in the voltage waveform. Another advantage of the electronic ballast concerns its behaviour during the rapid voltage changes. This kind of event has been reproduced reducing quickly the voltage from 250 V to 220 V. The electronic ballast maintains the functional performance of lighting equipment even in presence of this type of voltage variation; this feature is not guaranteed by the electromechanical ballast and consequently the lamp shutdowns. This characteristic can play a key role in terms of safety in a real context, such as a lighting plant of a major road. In fact, in case of a sudden voltage rush due to accidental, incidental or unforeseen factors, lighting shutdown could result in a risk factor for users that pass on that road. It is still necessary to underline that this kind of event is quite rare. It is important to note that the electronic ballast absorbs constant power, therefore a voltage reduction will produce an increase in the current. This kind of control opens some issues related to the transmission stability. A fast voltage variation will produce a dynamic response: it is necessary to verify that
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the entire system composed by the electronic ballasts and the supply cables reach the steady state faster and without slightly damped – or even undamped – oscillations and the reached steady state is a stable equilibrium point. Moreover, it is important to consider that the electric grid maximum output power depends on the square of the voltage. A large voltage reduction could create the condition in which the power required by the lighting plant is higher than the maximum output power from the network, leading to a blackout. IV. ENERGY SAVING ANALYSIS An estimation of the light efficiency, calculated as the ratio of the measured illuminance and the power input, is also reported in TABLE III. The results obtained for the electromechanical ballast with a supply voltage of 230 V is taken as reference value: the other cases are expressed in relative terms with respect to this reference. Analysing the data it can be observed that only at voltages higher than 230 V the electromechanical system performances are comparable to those of the electronic ballast. Nevertheless, under this conditions, the emitted flux from the light source is very high and it can be in contradiction with directive or local laws about light pollution and energy saving [7],[8]. In order to compare the energy consumption as a function of the illuminance, the voltage variations of a street lighting during a typical working day have to be considered. Fig. 7 shows, as an example, the main voltages recorded during a day of a mall.
Moreover, high voltage will be present in the period from 24.00 to 8.00, when the standard requires the reduction of the luminous flux of 30%. In this regards it is important to note that the link between luminous flux and power consumption change with the typology and size (in term of power) of lamp. As an example, Figs. 8-10 show the trends of luminous flux and power input, as a function of voltage for some HPS lamps. Form these figures it can be seen that a flux reduction of 30% corresponds to a reduction of power consumption of about 20% for a 150W HPS light source, of 25% for a 250W HPS light source, and approximately 30% for a 400W HPS light source. As a conclusion, a reduction of the luminous flux of 30%, as required by the guidelines for light pollution, may result in an average reduction of power consumption of about 25%.
Fig. 8. Luminous flux (red) and correspondingly power consumption (blue) for a 150 W SAP lamp.
Fig. 7. RMS of supply voltage in a street of a typical working day.
Despite the street luminaire’ switching times changes during the seasons, supply voltage is always higher than the nominal voltage of 230 V during any day of the year when the luminaires have to be powered. Then, using an electromechanical ballast not able to manage appropriately the input power in function of the supply voltage, luminaire would absorb more power than its rated value for the entire period of operation. High voltage, between 243 V and 250 V, results in an increase of both luminous flux and energy consumption. Considering the measurements results, the different public lighting switching times during the year [12], and assuming that the voltage variation during the day is the same for all the days of the year, a luminaire with 150 W lamp powered with an electronic ballast save 170 kWh/year with respect to the same luminaire powered with an electromechanical ballast. This corresponds to an energy savings of about 20%.
Fig. 9. Luminous flux (red) and correspondingly power consumption (blue) for a 250 W SAP lamp.
Fig. 10. Luminous flux (red) and correspondingly power consumption (blue) for a 400 W SAP lamp.
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Considering also that electronic ballast can implement the flux regulation, and considering the results presented in Fig. 8 for a 150 W lamp, it is estimated that the energy reduction grows up to about 240 kWh/year in presence of flux regulation, that corresponds to an energy savings of about 30%. Higher relative energy savings can be achieved by using 250 W (Fig. 9) or 400 W (Fig. 10) lamp that are characterized by higher lighting efficiency. Another aspect that must be considered on the energy efficiency point of view is related to the harmonic contents of current drawn from the lighting system. An electronic ballast absorbs a current that is mainly composed by the fundamental component at 50 Hz and, consequently, presents a reduced harmonic content: this allows a rational use of the lighting plants reducing line losses, voltage drop and voltage distortion. V. CONCLUSIONS From the comparison of the measured data to put in evidence the following aspects can be underlined. The use of the electronic ballast, instead of the electro-mechanical one, guarantees to the lighting both constant power consumption and lighting performance. This result is in agreement with the data shown in [12]: by using electronic ballast the light efficiency is quite independent on voltage. The electronic ballast allows to maintain constant the luminaires’ luminous flux for all the working period: changing the main voltage, the illuminance measured is constant. In this way, the parameters of the lighting design and drivers’ safety can be also guaranteed for all the working period of the lighting. On the contrary, the use of electro-mechanical power supply system determines, inside of the established range, an important oscillation of the emitted luminous flux and therefore of the illuminance (from 161l x at 200 V to 367 lx at 260 V) making the respect of the design lighting performance extremely improbable. Furthermore, electronic ballast can perform luminous flux regulation. Electronic ballast can implement the compensation of all the non-active power components absorbing from the network a sinusoidal current. The input current waveform of electronic ballast is mainly a sinusoid in phase with the voltage waveform and the power factor is very close to the fundamental power factor, that is just a little less of unity. This reduce of the PQ problems and allows a rational use of the lighting reducing line losses, voltage drop and voltage distortion. The use of electronic ballasts in public lighting, in addition to energy savings and PQ ensures lamps greater useful life, as demonstrated by major manufacturers of light sources (eg Osram). This allows a reduction of maintenance costs and an increase road safety. VI. REFERENCES [1]
Electromagnetic Compatibility, Part 3, Section 2. Limits for harmonic current emissions (equipment input current ≤16A per phase), EN 61000-3-2, Ed.3, Nov. 2005
[2]
Electromagnetic compatibility (EMC). Testing and measurement techniques. General guide on harmonics and interharmonics
[3]
[4] [5]
[6] [7] [8]
[9]
[10]
[11] [12] [13] [14]
measurements and instrumentation, for power supply systems and equipment connected thereto, EN 61000-4-7, 2002 E.R. Manzano, M. Carlorosi, and M. Tapia Garzon, “Performance and measurement of power quality due to harmonics from street lighting networks,” in Proc. Int. Conference on Renewable Energies and Power Quality (ICREPQ’09), Valencia (ESP), 15-17 April, 2009 D. Pileggi, T. Gentile, and A. Emannuel, "The effect of modern CFLs on voltage distortion," IEEE Transactions on Power Delivery, July 1993. R. Dwyer, and R. McCluskey "Evaluation of harmonic impacts from compact fluorescent lights on distribution systems," IEEE Transactions on Power Systems, November 1995. R. Verderber "Harmonics from compact fluorescent lamps," IEEE Transactions on Industry Applications, May/June 1993 “Illuminazione stradale. Selezione delle categorie illuminotecniche”, UNI 11248, Oct. 2007 “Misure urgenti in tema di risparmio energetico ad uso di illuminazione esterna e di lotta all’inquinamento luminoso”, L.R. n°17, Mar. 2000 G. Pantaleone, “Power Electronics in Public Lighting Systems,” Power Systems Design Europe, March 2007. Avaible on line on www.powersystemsdesign.com N.B. Soni and P. Devendra, “The transition to LED illumination: a case study on energy conservation,” Journal of Theoretical and Applied Information Technology, 2005, pp.1083-1087 R. Faranda, S. Guzzetti, C. LAZAROIOU, and S. Leva, “LEDs lighting: two case studies,” U.P.B. Sci. Bull., Series C, to be published http://www.autorita.energia.it/it/docs/04/052-04.htm http://www.leonardo-energy.org/node/3527 IEEE Trial use std definitions for measurement of electric power quantities. IEEE Std 1459-2000, 2000
VII. BIOGRAPHIES Alberto Dolara (St.M’09) (St.M’09) received the M.S. and Ph.D. degree in Electrical Engineering from the Politecnico di Milano, Milano, Italy, in 2005 and 2010, respectively. Now he is temporary researcher at the Department of Energy, Politecnico di Milano, Milano, Italy. His areas of research include traction systems, power quality, electromagnetic compatibility and renewable sources. Roberto Faranda (M’07) received the Ph.D. degree in Electrical Engineering from the Politecnico di Milano in 1998, and at the moment he is Assistant Professor in the Dipartimento di Elettrotecnica of the Politecnico di Milano. His areas of research include power electronics, power system harmonics, power quality, power system analysis and distributed generation. He is a member of Italian Standard Authority (C.E.I.), Italian Electrical Association (A.E.I.), IEEE, and Italian National Research Council (C.N.R.) group of Electrical Power System. Stefania Guzzetti received the M.S. degrees in industrial design from the Politecnico di Milano, Milan, Italy, in 2008. Now, she is collaborating at the Department of Energy of the Politecnico di Milano regarding the lighting sector and the energy saving. She is tutor at the lighting design course at the School of Industrial Design of the Politecnico. She works, as a freelancer, in the field of industrial product design. Sonia Leva (M’01) received the M.S. and Ph.D. degrees in electrical engineering from the Politecnico di Milano, Milan, Italy, in 1997 and 2001, respectively. Currently, she is Assistant Professor in Elettrotecnica in the Department of Energy, Politecnico di Milano. Her research interests include electromagnetic (EM) compatibility, power quality, the foundation of the EM theory of the electric network, and the renewable energy. She is member of the Italian Standard Authority (C.E.I.) and of the IEEE Working Group “Distributed Resources: Modelling & Analysis”.
