FLICKERMETROLOGY - Petteri Teikari · Flicker€metrology Petteri€Teikari...

HELSINKI UNIVERSITY OF TECHNOLOGYS18.3156 POWER SYSTEMS ENGINEERING, SPECIAL ASSIGNMENTESPOO, FINLAND, MAY 2006

FLICKER METROLOGY

PETTERI TEIKARI([email protected])

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Author:Name of the seminar:Date:Number of pages:

Petteri TeikariFlicker metrologyMay 30, 200632

Department:Professorship:

Department of Electrical and Communications EngineeringS18 Power Systems

Supervisor:Instructor:

Professor Matti Lehtonen

Flicker or rapid voltage fluctuations, is a phenomenon where supply voltagechanges very rapidly and often, which is most common perceived as dimming andbrightening of lamps (light flicker). Even fluctuation under a percent can cause lightflicker that is perceived annoying. Most common sources for flicker, are pulselike andintermittent loads like rolling mills, welding and electrical arc furnaces. In residentialenvironments and in especially in rural environments with old wiring, flicker canfollow from the use of big residential load as coffee maker or microwave oven.

In the past, severity of flicker was determined by using simple curves (IEEE 141),which had been established from human experiments. They were later replaced withdevices called flickermeter, which design was started in the 70s. First IEC standard wasIEC 868 (1986) which now has been replaced with IEC/EN 61000415 (1997). Butthese IEC flickermeters have serious deficiencies with measurement of discharge lampsand interharmonics.

In this special assignment, the basic characteristics of the phenomenon are firstexamined, followed by measurement methods. And after current methods and theirdeficiencies we are going to review couple of proposed methods and see their benefits.New proposed methods use new signal processing or digital algorithms to ensure bettermeasurement accuracy under all conditions.

Keywords: flicker, flickermeter, voltage fluctuations, metrology, measurements, IEC,IEEE, UIE, CRIEPI, incandescent, fluorescent, lamp, electric arc furnace, spectralanalysis, simulation, health effects, perception, brain

ABSTRACT

HELSINKI UNIVERSITY OF TECHNOLOGY Abstract of a special assignment

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Tekijä:Työn nimi:Päivämäärä:Sivumäärä:

Petteri TeikariFlickerin mittausmenetelmät30. toukokuuta, 200632

Osasto:Professuuri:

Sähkö ja tietoliikennetekniikkaS18 Sähköverkot

Työn valvoja:Työn ohjaaja:

Professori Matti Lehtonen

Jännitteen nopeilla vaihtelulla tai välkynnällä (flicker) tarkoitetaan käytännössäsyöttöjännitteen nopeita vaihteluita, joka näkyy käytännössä parhaiten valojenvälkkymisenä. Jopa alle prosentin muutokset syöttöjännitteessä voidaan havaitaärsyttävänä valojen vilkkumisena. Suurimpia lähteitä tälle häiriölle ovat pulssimaisetkuormat, jotka eivät ota vakiotehoa verkosta. Näitä ovat esimerkiksi valssaamot,hitsaamot ja valokaariuunit. Myös kotona, etenkin vanhoissa taloissa tai pitkänsyöttölinjan päässä, voivat valot himmetä suuren kuorman käynnistyksen johdosta,jollainen voi olla mikroaaltouuni tai kahvinkeitin.

Ennen jännitteen laadun tarkkailuun flickerin osalta käytettiin yksinkertaisiakäyrästöjä (IEEE 141), jotka oli saatu ihmisillä suoritetuilla kokeilla. Käyrästötmyöhemmin korvasi ”flickermeter”:it, joiden suunnittelutyö alkoi jo 70luvulla.Ensimmäinen standardi oli IEC 868 (1986), jonka on nyt korvannut standardi IEC/EN61000415 (1997). Näissä on kuitenkin havaittu olevan vielä puutteita, jotka johtavatepätarkkoihin mittaustuloksiin joissain erikoistilanteissa, kuten purkauslamppujen javäliharmonisten taajuuksien kanssa.

Tässä työssä on tarkoitus ensin esitellä flickerin perusominaisuuksia ja mitkä tekijätvaikuttavat flickerin amplitudiin. Sen jälkeen käydään läpi nykyisiä menetelmiä jaesitellään muutama uudempi tekniikka, jota on esitetty uudeksi standardiksi. Uudetesitetyt menetelmät käyttävät uusinta signaaliprosessointia, mutta mikään niistä ei olevielä huolimatta hyvistä parannuksistaan, saavuttanut standardin asemaa ja laajaahyväksyntää standardoivien tahojen osalta.

Avainsanat: flicker, flickermeter, välkyntä, äkilliset jännitemuutokset, metrologia,mittaukset, IEC, IEEE, UIE, CRIEPI, hehkulamppu, loistelamppu, valokaariuuni,spektrianalyysi, simulointi, terveysvaikutukset, havaitseminen, aivot

TIIVISTELMÄ

TEKNILLINEN KORKEAKOULU Erikoistyön tiivistelmä

TABLE OF CONTENTS

Abstract ........................................................................................................................................... 2

Tiivistelmä ....................................................................................................................................... 3

Table of contents ........................................................................................................................... 4

List of abbreviations ...................................................................................................................... 5

List of symbols ............................................................................................................................... 6

1. Introduction ........................................................................................................................... 7

2. Flicker ..................................................................................................................................... 82.1 Standards ................................................................................................................................................... 8

2.2 Sources and affected devices ........................................................................................................... 9

2.3 Light flicker .............................................................................................................................................. 10

2.3.1 Frequency .......................................................................................................................................... 11

2.3.2 Time constant of a lamp ............................................................................................................... 13

2.3.3 Gain factor of a lamp ..................................................................................................................... 15

2.3.4 Waveform of the voltage .............................................................................................................. 16

2.3.5 Duty cycle ........................................................................................................................................... 17

2.3.6 Flicker return time constant ........................................................................................................ 18

2.3.7 Dimming of lamps ........................................................................................................................... 19

2.3.8 Electric arc furnaces (EAF) ......................................................................................................... 19

2.3.9 Load management signals .......................................................................................................... 20

2.4 Health risks associated to flicker .................................................................................................... 20

3. Flicker metrology ............................................................................................................... 21

3.1 Current methods ................................................................................................................................... 21

3.1.1 IEC 868 flickermeter ...................................................................................................................... 22

3.1.2 IEC 61000415 flickermeter ...................................................................................................... 23

3.1.3 The CRIEPI Index ∆V10.............................................................................................................. 24

3.2 Proposed new methods ..................................................................................................................... 24

3.2.1 Eyebrain model............................................................................................................................... 25

3.2.2 Voltage spectral analysis ............................................................................................................. 27

3.2.3 Digital flicker measurement using continuous wavelet transform............................... 28

3.2.4 Genetic based algorithm for voltage flicker measurement ............................................ 28

4. Conclusion .......................................................................................................................... 29

5. Glossary (EnglishFinnish) ............................................................................................... 29

6. References........................................................................................................................... 30

Flicker metrology Petteri TeikariS18.3156 Power Systems Engineering, special assignment [email protected]

List of abbreviations 5

LIST OF ABBREVIATIONS

4FTE fourfoot fluorescent lamp with electronic ballastAC, ac alternating currentCFF Critical Fusion FrequencyCFL compact fluorescent lampCFLE compact fluorescent lamp with electronic ballastCFLM compact fluorescent lamp with magnetic ballastCRIEPI Central Research Institute of Electric Power Industry (Japan)DC, dc direct currentDFT Discrete Fourier TransformEAF electric arc furnaceEEG electroencephalogramEMI electromagnetic interferenceERG electroretinogramFFT Fast Fourier TransformGA genetic algorithmHF high frequencyIEC International Electrotechnical CommissionIEEE Institute of Electrical and Electronics EngineersIESNA lluminating Engineering Society of North AmericaipRGC intrinsically photosensitive retinal ganglion cellPFC power factor correctionRMS, rms rootmeansquare,UIE International Union for Electricity Applications

(l'Union Internationale Pour Applications de l’Electricité)UVLO undervoltage lockout

mailto:[email protected]

LIST OF SYMBOLS

γ duty cycle [%]τ time constant [ms]φ luminous flux [lm]λ luminous flux [lm]ϖ angular velocity [rad/s]a pupil area [m2]C capacitance [F]e illuminance [lx]G gain factori current, instantaneous [A]I current, rootmeansquare [A]K amplifying constantm mass [g]P power, rootmeansquare [W]p power, instantaneous [W]PF5 instantaneous flicker sensationPlt longterm flicker severity indexPst shortterm flicker severity indexPU instantaneous flicker sensationR resistance [Ω]s Laplace sT temperature [K]v voltage, instantaneous [V]V voltage, rootmeansquare [V]Vd voltage, dc [V]Vo voltage, dc average [V]


Introduction 7

1. INTRODUCTION

Flicker, a phenomenon characterized by rapid voltage fluctuations mainly showing as a light flicker.Light flicker basically being dimming and brightening of lamps. Many people may have noticed that ifthere’s a large load change (like operating a microwave oven) especially in houses with old electricalwiring. And most of the times, the flicker isn’t selfcaused and isn’t limited to one location. Most commonsources for flicker are intermittent loads like welding, electrical arc furnaces, rolling mills, which candisturb all consumers behind same 20kV/400V transformer for example. The problem have existed sincethe dawn of power networks.

Light flicker itself is a difficult phenomenon to measure as there’s human factors involved and personalexperience can differ greatly opposed to straightforward voltage fluctuation measurements. Traditionallyengineers have used flicker curves that are based on voltage changes per time unit to assess flickerseverity but they have proved to be a highly inadequate in modern networks with constantly increasingnumber of harmonic and interharmonic voltage components. Next step from curves have been the use offlickermeters (IEC), but they have been also deficient to measure accurately all type of situations in powersystems, especially interharmonics and different type of lamps. Now there’s a large interest towardsbetter ways to measure flicker more accurately and solving the shortcomings of old flickermeters. Sadly,no single method haven’t yet gained vast approval, and the search for better flicker measurement devicestill continues. In this paper we will look at current methods and see what could be improved, and whathave already been proposed as prototypes.

Figure 1 presents two different practical implementations of flicker measurements. They both are incompliance with IEC/EN standards, the other is small handheld power quality analyzer from Fluke,enabling mobile measurements from various points of distribution system. Other is then PCbased powerquality analyzer allows users to control the measurement system via a TCP/IP network, allowing them toimplement a distributed powerquality evaluation system via LAN or modem.

Figure 1. (left) PCbased Virtual Instrument (VI) power quality analyzer[1]. (right) Fluke 434[2], which is incompliance with IEC/EN 61000430 standard and being able to measure Pst, P lt and PF5.



Flicker 8Standards

2. FLICKER

Flicker is defined as fast voltage fluctuations, which can normally be seen most easily as a flicker oflighting. One possible effect on sinusoidal voltage can be seen in Figure 2, where we can notice thatamplitude of sine wave isn’t constant. Flicker has been a major concern for both industrial and residentialcustomers since the dawn of power systems. Flicker is a difficult problem to quantify and solve because ofit’s subjective nature. There’s always a human factor involved, in addition to possible technical problemscaused by flicker, there can be major differences in flicker perception by different observers.

Even minor voltage changes are sensed by eyes causing discomfort. On the basis of investigations, asmall voltage flicker of 0,3% to 0,5% at the frequencies of 7 to 10 Hz will cause annoyance[3]. This flickernot only depends on the robustness of the power system, but also upon the design of light fixture as wecan see later. The effects of light flicker can range from minor irritation to a health risk, especially forthose who are prone to epilepsy, which we later take a more detailed look.

Figure 2. Voltage flicker, simplified waveform.

2.1 STANDARDS

As flicker or voltage fluctuations have been a problem in power systems since from the very start itwould seem natural that there are some standards controlling the level of flicker induced by a givenappliance, it should have met the EN6100033 standard[4]. Normally these measurements have beenmade with a device called “flickermeter”, but like we will later see, there are some deficiencies whichneed to be solved. The flickermeter itself is based on EN/IEC 61000415 standard[35], which has replacedthe old IEC 868 standard[32].

EN/IEC 61000415 standard give the limits forflicker[5] seen in Table 1. The used flickermetersaccording to standard are capable of giving the Pst

out, which can then be used to determine theseverity of flicker.

Flicker severity is sometimes measured also usinginstantaneous flicker sensation (PU or PF5), but likewe see later from block diagram (Figure 35), PU isthe output from block 4 and the actual output offlickermeter is Pst and Plt. But in some cases it is usedto estimate flicker severity like seen in chapter 3.2.2.

Good quality: Pst,3max ≤ 1; Plt,max ≤ 0,74Normal quality: Plt,max ≤ 1Standard quality: 95% of measured Plt ≤ 0,74Measurement: ManuallyCalculation:

3

12

1i

3sti

lt 12P

P ∑=

=

Pst = Shortterm flickerseverity index, measured in10 minute intervals.

Plt = Longterm flickerseverity index, calculated onPstvalues over 12 hours.

Table 1. Flicker limits in EN61000415.



Flicker 9Sources and affected devices

2.2 SOURCES AND AFFECTED DEVICES

Figure 3. Internal and external flicker sources[6].

Variations in the load current of connected load may inducevoltage fluctuations in other loads that share a common couplingimpedance. Figure 3 presents one illustration of the flickersources, which are further divided into internal and externalsources. Internal sources are the equipment in residenciesthemselves, like air conditioners, washers, refrigerators, dryers,computers. The external sources, are the sources fromdistribution network like capacitor switching, electrical arcfurnaces (EAF), rolling mills, welders, etc. And what is common toall these sources, that the load current taken by these equipmentare far from constant and being very pulselike.

Flicker and harmonics have become recently a problem morefrequent with the development of power electronics andincreased number of switched mode power supplies. Switchingmode power supplies are probably most commonly found innormal homes from personal computers, which on every peak ofmain sine wave draws a pulse of current from the supply, asshown in Figure 5[7]. Whilst one of these computers loads makesno detectable difference to the supply, the proliferation of suchequipment, each drawing currents at the peak of the mains, leadsto a flattening of the mains waveform, as shown in Figure 4.Every time power supply draws that peak of current, currentthrough common coupling impedance causes the voltage drop.

Figure 5. Switched mode power supplycurrent.

Figure 4. Flattening of the mains voltagewaveform.

Figure 7. A.C. electric arc furnace witheccentric bottom tap hole.Figure 6. Power levels measured during a Furnace heat.



Flicker 10Light flicker

And when it comes to industrial sources, electric arc furnaces (EAF) have been the target for interestlately. Typical AC EAF can be seen in Figure 7[8]. Electric arc furnaces are used for example for steelmaking and melting of the ingredients. Power intake of electric arc furnaces are typically megawatts andEAF loads can cause serious electrical disturbances on a power system due it’s pulselike nature. We cansee in Figure 6, typical power levels of Furnace heat (the whole process of steel making, consisting boring,melting and refining) in an 8tons electric furnace of 2,5MW[9] in Buenos Aires, Argentina, connected inthe 13,2 kV voltage level.

Due to the random motion of the electric arc; and resulting changes in arc length, there are randomfluctuations in current which in turn cause voltage fluctuations upstream of the furnace in proportion tothe system impedance. In Figure 8[9], we can see effects of this fluctuating power intake (Figure 6) toflicker. The value of Pst95% = 2.21 is well above the IEC/EN standards of Pst95% < 1, and above theArgentinian Standard Res. 99/97[10] used as a reference in the publication[9].

Besides obvious effects to lighting, recent studies have underlined the consequences onasynchronous motor aging[11], referring the less discussed topic of the effect of subharmonics to inductionmotor life span. Namely it was observed that the presence of minute amounts of subharmonics in thevoltage frequency spectrum cause significant additional power loss in the stator winding, yielding anincreased hot spot temperature and accelerating the thermal aging of the insulation. More work on thistheme is however required and it might turn out that induction motors aren’t necessarily the mostsensitive group of equipment to subharmonics. Flicker also influences on TV sets, where the size of thescreen image size changes with the intensity of the flicker. Also it can create problems with electronicsthat use supply voltage, or it’s zero point more precisely, as an external clock to time it’s functions.

2.3 LIGHT FLICKER

Like already mentioned, the effect of voltage fluctuations are the most significant with lighting.However the amplitude of light flicker from voltage fluctuations depends on many things. First there’s abig difference on flicker characteristics between incandescent lamp and fluorescent lamp, as their way ofproduce light differ greatly. Also the frequency of the flicker (voltage fluctuations) have an impact onvisually perceived light flicker. Also certain type of the fast switching of power electronics producesquarewave modulated voltage which impact on flicker differ from normal sinusoidal voltage. Andrecently electric arc furnaces (EAF) have been the target of interest as they have been shown to produceunique voltage distortion and interharmonic voltage components mainly the disturbing component beingat 187 Hz. Now we take a closer look of the these different factors.

Figure 8. (left) Shortterm flicker severity index Pst measured in 1minute interval during a complete furnacecycle. (right) Pst measurements during a week as a normalized oneweek 10minute interval Pst.




2.3.1 Frequency

Flicker perceptibility depends quite heavily on the flicker frequency and it’s very different for thermalradiators like incandescent and halogen lamps and gas discharge lamps like fluorescent lamps. Simplifieddifferences between incandescent lamps and fluorescent lamps (worst case for fluorescent lamp takenfrom ) can be seen in Figure 9[33]. The perceptibility threshold remains lower for incandescent lamps from35Hz to 65Hz, and higher for fluorescent lamps from 0 to 35Hz and from 65 to 100Hz.

Figure 9. Flicker perceptibility thresholds for incandescent ( ___ ) and fluorescent lamps ( ….. ).

Current and old measurement methods of flicker have been based on characteristics of incandescentlamp and frequency response have been presented as seen in Figure 10[33]. This curve has been the basefor IEC flicker metrology aswe examine more closer later.We can see from it that flickerfrequency of 8,8 Hz is themost disturbing to the humaneye and incandescent looks“the worst” at this frequency.

And what comes evenmore evident later on thispaper, that components over100Hz have almostnonexistent influence onperceived flicker which is alsothe reason why IEC methodsfor flicker are deficient forflicker determination of gasdischarge lamps likefluorescent, metal halide andsodium lamps.

Figure 10. Normalized frequency response of a coiled coil filament gasfilledlamp (60W/230V) and human visual system G(f).




We can analyze fluorescent lamps more carefully when including various types of fluorescent lampswith different ballasts, results can be seen inFigure 11[33]. Should be noted that theperceptibility curves for traditional lamps dropoff quickly at higher frequencies and thatinterharmonics of the same amplitude atdifferent frequencies produce different effects interms of flicker. The electronic ballasts appearto be very sensitive between 30 and 70Hz, andto better filter the interharmonic frequenciesbetween 130 and 170Hz. They can even beconsidered to be insensitive to frequencieshigher than to 170Hz. Interesting is thatcompact electronic lamps remain sensitive tohigher frequencies.

Recently electronic ballast using high frequency to feed fluorescent lamps have replaced old magneticballasts totally in new luminaires, so it’s important to examine the flicker properties of these new high

frequency (HF) ballasts, block diagram can be seen inFigure 12[12]. Without any disturbance, the luminousflux is produced by a fluorescent lamp with externalelectronic ballast is composed of a direct andalternative part. The frequency of the ac coupling goesup to 40kHz, modulated by 100 Hz “ripple” voltage ofthe input rectifier/filter selection which is configuredas a fullwave bridge for 230V line operation. Theoutput waveform of an electronic high frequencyballast is slightly modulated by 100/120 Hz “ripple”,

but with decent filtering design this ripple won’t be visible or a problem to human eye. So, if the lamp isoperated at high frequency, it produces continuous light. This is because the time of the discharge is tooslow for the lamp to have a chance to extinguish during each cycle. This is the reason for better lightquality of electronic ballasts. Figure 13[13] show the oscillograms of the instantaneous light intensitywaveform of the lamp fed by the sinusoidal line voltage via HF ballast.

Figure 13. Measured waveforms at HF. Light intensity is the upper trace and lamp current the lower trace.(left) Time scale: 10µs/div, (right) time scale: 2,5ms/div with 100Hz “ripple” showing (every fourth vertical line).

However interharmonics between can causeflicker even to HF ballasts as seen in Figure 14[13]. A35Hz component with 10% amplitude in regard to50Hz component can be seen to distort both lightintensity and lamp current of HF ballast drivenfluorescent lamp. However it should be noticed thatthis effect is highly dependant on ballast design and canbe minimized with proper electronics design. Still HFelectronic ballasts are the choice in flicker pollutednetworks with best flicker bearing ability[3].

Figure 11. Flicker perceptibility thresholds versusinterharmonic frequencies.

Figure 12. Block diagram of HF ballast. PFCcorrects power factor. UVLO = undervoltagelockout.

Figure 14. Measured waveform at HF with 35Hzinterharmonic component. Light intensity (uppertrace) and lamp current (lower trace). Timescale: 100µs/div




2.3.2 Time constant of a lamp

The light flicker caused by any type of lampis strongly dependent on the inertialcharacteristics of the lamp. The mechanismsbehind thermal time constants are very

different to incandescent and fluorescent lamp because of their different mechanisms in producing light.We will first examine incandescent lamp which is based on thermal radiation.

The heat behavior of an incandescent lamp can be reasonablyestimated with the help of the equivalent circuit presented inFigure 15[20]. The filament is modeled by the thermal resistance R,("C/W) in parallel with the thermal capacitance Cθ (Ws/°C). Thefilament temperature raise above the ambient equals the voltageacross the resistance Rθ. The current source supplying the Rθ,Cθ

load equals the power dissipated by the filament, p = v2/R, wherev is the lamp's voltage and R is the filament resistance. In the firstapproximation R is assumed constant. Time constant of thefilament then is:

Thermal constant of an incandescent lamp (120V) can be also approximated with Equation 2[17]. The timeconstant of a 230V is equivalent to that of a 120V lamp having nearly half power due to the reduction inthe filament thickness in order to have the same rated power[34].

We see that with bigger nominal power the thermal time constant is longer thus making flicker lesssevere, this can be noticed in Figure 16[17].

Figure 16. Computed flicker curves (borderline of irritation), for square wave modulation. The effect oflamp time constant.

LAMP TYPETIMECONSTANT

120/230V incandescent lamp (45200W) 10200ms[14,20]

Fluorescent lamp (magnetic ballast) 15ms[15,17]

Figure 15. Incandescent filament lamp.Equivalent thermal circuit for heattransfer study.

θθθ =τ CREquation 1. Filament time constant.

( ) ;ms3P52,0 L −⋅≈τθ W200PL15 ≤≤Equation 2. Approximation for thermal time constant of 120V incandescent lamp.




The luminous flux produced by the incandescent lamp is a nonlinear function of the filamenttemperature, physical characteristics and geometry. In general it can be expressed by an exponentialfunction[20]:

The first term is the average luminous flux (λ0) and the second term represents a 120Hz fluctuation,which can not be directly detected by the human eye.However, fluctuations caused by flicker aren’t that bigand we can linearize the luminous flux around theoperating point (T0,λ0) as seen in Figure 17.

Most of the existing voltage fluctuation (or lightflicker) standards are based on incandescent lamps, butas they are coming more and more obsolete and beingreplaced by fluorescent lamps we need to examine thebasic different of these lamp types in the sense of flicker.Incandescent lamps use the Joule heating process asalready described, and their voltage/currentcharacteristic is linear (Figure 18, left). While fluorescentlamps belong to electric discharge lamp family, theyconvert the electric energy into light by transformingelectric energy to kinetic energy of moving electronsand ions, and it’s voltage/current characteristics isnonlinear (Figure 18, right).

Discharge lamps having virtually no energystorage respond instantly to changes in voltage givingfluorescent lamp time constant less than 5 ms[15],which is the arc time constant. Normal residentiallamps are seen in Figure 19.

( )[ ] [ ]lmt2cosTmVRRk 2

2 =β−ω∆−

⋅

⋅=λ α

αθ

Equation 3. Luminous flux λ.

Figure 17. Luminous flux λ/Filamenttemperature linearization.

Figure 18. Voltage/current characteristics of aincandescent lamp (left) and fluorescent lamp (right).

Figure 19. Normal residential lamps. (upperleft) Fluorescent tubes, (upperright) incandescent lamp, (lowerleft)halogen lamp, (lowerright) compact fluorescent lamp with integrated electronic ballast.




2.3.3 Gain factor of a lamp

Describing amplifying characteristics of a given lamp is defined normally by a gain factor. Gain factor isdefined and calculated by measuring relative changes in light level while inducing controlled voltagefluctuations. By controlling the magnitude and the frequency of voltage fluctuations, the lamp’s flickerresponse can be determined using a photometer to measure the lamp output. If the percentage of lightfluctuation is greater than the percentage of voltage fluctuation, the lamp is said to have an amplifyingeffect, or gain factor greater than unity. Table 2 shows some typical gain factors of typical lamps, it shouldbe noted that these gain factors are only indicative. Especially with gasdischarge lamp, electronic ballastdesign have a great impact on final flicker output and in an optimal case, changes in supply voltagewouldn’t have any impact on light output because of used rectifiers and filters. Gain factor depends alsoon flicker frequency, and there’s a big difference between fluorescent lamp and incandescent lamps as it’sseen in Figure 20[36].

LAMP TYPEGAINFACTOR

Incandescent lamp 13,5[36]

Fluorescent lamp 00,6[36]

Table 2. Typical gain factors.

Gain factor has been generally an effective wayto predict the variations in light output for a givenflicker waveform. More than 50 different lamptypes were evaluated by Halpin et al.[36] and somethe results are shown in Figure 21.

Figure 21. Flicker response test results

Figure 20. Gain factor variations for fluorescent andincandescent lamps.




2.3.4 Waveform of the voltage

There’s a difference in flicker depending on the waveform of flicker. In addition to normal nearsinusoidal supply voltage, squarewave modulation exists also in supply voltage caused by large loadsrecurrently being on/off (switched mode power supplies, welding etc.). Basic differences betweensinusoidal and squarewave modulation can be seen in Figure 22[20].

Rectangular squarewave modulation also causes slightly more significant flicker than sinusoidalmodulation, which can be seen in Figure 23[16].

Figure 22. Computer simulated oscillations for squarewave modulation (left) and for sinusoidal modulation (right).a) Voltage u, b) Filament power p, c) Temperature T, d) Illumination λ (actual variation), e) Eye perception of λ,f) Fourier spectrum λ.

Figure 23. (left) Gain factor of 60W incandescent lamp for 120V and 230V sinusoidal voltages. (right) Mathematicalsimulation of flicker response to squarewave modulation.




2.3.5 Duty cycle

With a periodical squarewave modulation, the light flicker depends on the duty cycle as well, meaningthe percentage of one period when voltage is up or on compared to total period time, as seen in Figure24. The definition of duty cycle γ is seen in Equation 4. We can see in Figure 25[17], that flicker is mostsevere when duty cycle is 50%, meaning that voltage is on the same time as it is off.

Figure 24. Squarewave modulation.s

on

Tt

%100 ⋅=γ

Equation 4. Duty cycle γ.

Figure 25. Computed flicker curves (borderline of irritation), for rectangular modulation. The effect of dutycycle. 30ms incandescent lamp time constant.




2.3.6 Flicker return time constant

When the voltage flicker is caused by a starting motor, a spot welding transformer, or a recurrentinrush current, the light flicker is characterized by a sudden drop and a nearly exponential recovery to itsinitial level, an example of that seen in Figure 26[18]. Such a recovery is governed by a sag time constant τs.The flicker curves presented in Figure 27[17] show that the threshold of irritation due to light flicker thatincorporates both voltage sag time constant and lamp time constant decreases as the voltage timeconstant increases.

Figure 26. Example of an voltage sag due to a short circuit. Voltage is given as relative value.

Figure 27. Computed flicker curves (borderline of irritation), for exponential recovery of the voltage flicker. Theeffect of recovery time constant. 30 ms incandescent lamp time constant.




2.3.7 Dimming of lamps

Lamp dimmers are also believed to play a role in the increased number of flickerrelated complaints.The use of incandescent dimmers in homes substantially increases lamp susceptibility to voltage changes.A typically electronic dimmer will nearly double the change in light output for a typical voltage changecompared to the same lamp with no dimmer. Figure 28[36] shows the test results for lamps withpercentages (0, 25, 50, 75%) of dimming.

Figure 28. Dimmer effects on lamp gain factor.

2.3.8 Electric arc furnaces (EAF)

One new topic in flicker study, has been the uniquevoltage distortion caused by electric arc furnaces. Recently,special cases of harmonic distortion and harmonic phaseshifting were found to be a direct cause of lamp flicker influorescent lamps[19]. To better understand how higherfrequency

harmonics can cause low frequency flicker, tests wereperformed using a 5%, 185 Hz interharmonic componentadded to the fundamental. This interharmonic alters thewaveshape and effects the voltage peaks much more thanthe rms value, which remains fairly constant on a cyclebycycle basis. The 185 Hz noninteger harmonic causes acyclical “beat” of 5 Hz and also cyclically changes the phaseangle of the voltage peaks by a few degrees. It was foundthat while incandescent lamps exhibited a slight amount offlicker, certain fluorescent lamps responded to theinterharmonic voltage by flickering at the “beat” frequencymuch more noticeably. Figure 29[36] shows the flicker testresults caused by interharmonic voltages.

Figure 29. Lamp response to a 5%, 185 Hzinterharmonic voltage and 5%, third harmonicvoltage with ±90° phase shift.



Flicker 20Health risks associated to flicker

It must be noted that a 180Hz voltage harmonic will not cause flicker since the voltage waveformremains the same every halfcycle. As a matter of fact all the integer harmonics will not cause flicker. Anoninteger harmonic, for example 187Hz, will cause the continuous change of voltage distortion fromone halfcycle to the next. Such a variation does not have any effect on incandescent lamp[20], as wealready noticed before. But this 187 Hz component can have a significant effect to the performance offluorescent lamp flicker with magnetic ballasts[21,22].

2.3.9 Load management signals

Study by Frater et al.[23] showed that load management signals used in electricity distribution networkscan cause flicker to fluorescent lamps with magnetic ballasts. Load management signals are audiofrequency signals between 110Hz and 1048Hz at about 1,1 to 3% of the fundamental voltage, used tomanage peak loads, space heating switching for night rates, control of street lighting, etc. Especially a175Hz carrier signal has been found to be problematic. For example, n New Zealand, company calledOrion uses at Christchurch urban network currently a Telenerg “telegram” via a 175Hz ripple carrierfrequency. The signal begins with a 1650ms start bit followed by 50 information bits 400ms long spaced at600ms intervals meaning that it takes a maximum of 52,25 seconds to transmit but this depends on thecontent of the information as well.

It was noted that the variation (0,52%) in peak voltage from the 175Hz signal is not the direct causeof the light flicker. As the supply power crosses zero the current through the tube also drops to zeroextinguishing the arc. The power increases the arc is reignited. It is speculated that the magnetic ballastsare very sensitive the angle of ignition and that the interharmonic ripple signals change the zero crossingangle. The 175Hz ripple signal interacts with the 50Hz fundamental creating a variation in ignition angle, at25Hz. This sensitivity of the ballasts would then cause the light produced to fluctuate at this 25Hz rate,which is visible to humans. A complication factor is the interaction between the capacitive components inthe light fitting and the inductance of the supply circuit and ballast. This may provide the conditions forresonance within the fittings.

2.4 HEALTH RISKS ASSOCIATED TO FLICKER

Health risks associated with flicker can range from minor asthenopic (weakness or fatigue of the eyes)symptoms, such as increased eyestrain, headache and migraine[24], into more serious health risks likeepileptic seizures to those who are prone to them[25].

Like already said, there can be large individual differences in flicker sensitivity, and normally personalflicker response is measured using the Critical Fusion Frequency (CFF). In CFF measurement, subjects arerequired to discriminate flicker from fusion, and vice versa, in a set of four light emitting diodes arrangedin a one centimeter square. The diodes are held in foveal fixation at a distance of one meter. Individualthresholds are determined by the psychophysical method of limits on four ascending (flicker to fusion)and four descending (fusion to flicker) scales. The mean of these four ascending and descendingpresentations gives the threshold frequency in hertz. And the CFF is then the lowest level of continuousflicker that is perceived as a steady source of light.

It has been found in studies[26,27] that lowfrequency flicker (on the order of 120150Hz) may add extranoise to neural activity even though that the flicker isn’t perceived visually. In a study by Küller et al.[26],this extra noise resulted more alphawaves in brain EEG (sign of fatigue) and more errors in a studiedwork task. This Similar mechanism could be thought to found at lower frequencies as study byHerrmann[28] suggests.

Flickering light can also affect saccadic eye movements, which are voluntary, conjugate movementsresulting in changes of fixation observed during visual search. This brings the retinal image being viewedonto the fovea. In a study by Wilkins[29] comparing the differences between low frequency flicker and highfrequency flicker, showed that eyes tended to overshoot of the target, causing asthenopic symptoms.Generally, it has been suggested to replace old magnetic ballasts with electronic ballasts to improveworking environments addressing the clear health risks involved in light flicker[26].



Flicker metrology 21Current methods

3. FLICKER METROLOGY

3.1 CURRENT METHODS

In the early days of the power system. Measurement and analysis tools were primitive and as flickerwas a common problem, engineers developed empirical guidelines as to what levels of flicker weretolerable and what levels would likely to lead complaints. Keeping mind the tools that were available atthe time, parameters were verysimplified. The guidelines were based onthe number of voltage changes perminute and the percentage voltagechange. Figure 31[30] shows the IEEE 141which was considered as the standard ofthe time. There were also other ruleofthumb flicker limit curves, different forexample to rural and urban areas as seenin Figure 30[31].

Obviously the system had numerousshortcomings, for example there’ssignificant in perception to step changesas opposed to gradual changes (squarewave vs. sinusoidal). And another big concern is how to combine different components, for example ifyou have large change every 10 seconds and a smaller change every second[31].There is also the questionof how to deal with episodic flicker, where you may have rapid changes for a few minutes once an hour,or once a day.

Figure 31. IEEE 141, historical flicker curve with UIE/IEC curve for 120V incandescent lamp.

Figure 30. Ruleofthumb flicker limit curve with IEEE 141 curve.




3.1.1 IEC 868 flickermeter

Figure 32. IEC/UIE 868 flickermeter.

Figure 32 shows a block diagram of the IEC 868flickermeter (presented in 1986). IEC 868 standard[32]

was drafted for an analog flicker meter designed duringthe 1970s. For the last 15 years however analog flickermeters have been replaced by new digital meters, whichhave been taken to account in IEC 61000415 standard(described later in more detail).

First there is an input transformer before Block 1,which function is the insulation and adaptation of theinstrument input circuit to the level of measured signal,allowing nominal input voltages from 55 and 415V at linefrequency.

The function of Block 1 is then to provide anormalized rms voltage to the input of the demodulatorin Block 2 which is achieved with an automatic gaincontrol ranging from 10% to 90%. Block 1 also consiststwo filters to eliminate dc components and doublefrequency ripple. This circuit emulates a wellknowncharacteristic of the human perception for whichmoderatelevel, constant stimuli to the senses graduallybecome imperceptible. Block 1 includes a calibrationgenerator also. Block 2 then specifies the use of asquaring multiplier as a demodulator. The purpose of this is to recover modulating signals and suppressthe mainfrequency carrier signals via filtering, as the modulating signal is the only desired output fromthis block.

Then Block 3 is the “heart” of this device containing the filters emulating lampeyebraincharacteristics. It consists of three filters, first being a firstorder highpass filter, with the cutofffrequency set to 0,05 Hz. The second one is a sixthorder Butterworth lowpass filter with a cornerfrequency of 35 Hz. These first two filters removethe DC component, and the 100 Hz doubledcarrier, with its associated sidebands from theoutput of Block 2. The last third filter then gives abandpass response centered at 8,8 Hz, providing avery specific weighting function within the frequencyband of interest (0,05 to 35 Hz), simulating theresponse of the lampeyebrain system for anaverage observer as seen in Figure 34[33].

Block 4 then implements the remainder of thelampeyebrain model. The squaring operatorsimulates nonlinear eye/brain responsecharacteristics, while the firstorder filter emulatesperceptual storage effects in the brain with the timeconstant of 300ms. And when the instrument gain is

Figure 34. Normalized frequency response versus themodulating frequencies of a coiled coil filament gasfilled lamp (60W/220V) and the human visual systemproposed by IEC/UIE.

Figure 33. Voltages at different blocks.




properly set, modulation levels corresponding to the mean human threshold for flicker sensation willgenerate values of 1 at the output of this block. The output of Block 4 is called instantaneous flickersensation, denoted by PF5 or PU.

The last Block 5 then emulates human irritability due to flicker stimulation; it is a sampling A/Dconverter followed by a statistical classifier. This classifier translates the output into shortterm flickerseverity index Pst and longterm flicker severity index Plt

[34].

3.1.2 IEC 61000415 flickermeter

Figure 35. IEC 61000415 flickermeter.

We can see the block diagram of IEC 61000415 flickermeterdescribed in IEC 61000415 standard[35] (1997) in Figure 35. Themajor portions of the flickermeter are 1) input processing (Block 1),2) “lampeyebrain” response (Blocks 24), and 3) output processing(Block 5). It should be noted that IEC 61000415 has replaced theold wellknown IEC 868 flickermeter standard with increased digitalsignal processing. Basically the block diagram is almost the same asin IEC 868.

The “lampeyebrain” characteristic is obtained from amathematical derivation of 1) the response of a lamp to a supply

voltage variation,2) the perceptionability of thehuman eye, and 3)the memorytendency of the human brain. This section of the IECflickermeter is where modifications can be made to fitparticular needs. The transfer function shown in isprovided as a reasonable model for the first two ofthese responses. Note that proper selection of thecoefficients in (Figure 35) provides the “UIE 120 V”frequency characteristics shown in Figure 31. Throughthese coefficients, the historical flicker curveinformation is incorporated in the flicker meter.

The coefficients are given by the IEC[35] for 230V,60W incandescent lamps. Response characteristics of Equation 6 can be modified with Equation 6 toinclude lamp characteristics and used for virtually any application.

ω

+

ω

+

ω+

⋅ω+λ+

ω=

43

22

12

1

s1

s1

s1

s2ssK

)s(H

Equation 6. "Lampeyebrain" transfer function

newbulbIECbulb,V230

IECnew )s(H

)s(H)s(H

)s(H ⋅=

Equation 6. "Lampeyebrain" transfer functionmodified to include lamp characteristics.

Figure 36. TTi HA1600. Example ofa harmonics and flicker analyzercompliance to EN6100032 andEN6100033 standards.



Flicker metrology 24Proposed new methods

The output processing of the flickermeter translates the output of Block 4, called the instantaneousflicker sensation (PU), into the statistical indices Pst and Plt. The shortterm flicker severity index Pst is thenormal statistical quantification used in flicker evaluation. A single Pst is calculated in 10 minute intervalsand Pst = 1 corresponds to the level of irritability for 50% of the persons subjected to the measuredflicker and when it’s greater than one it’s perceived even more annoying by average group of people.Longterm flicker severity index Plt is a combination of twelve Pst values.. Practical flicker limits aretypically developed from 95th and 99th percentiles of a series of Pst and Plt collected over time periodsperhaps as long as on week. More work is still required with this model on flicker sensitivity of variouslamps in spite of the possibilities brought by Equation 6. However this model automatically incorporatesdifferent flicker frequencies and nonstandard (i.e. not square or sine wave) modulating waveforms whichhave been lacking in previous models. IEC provides shape factors for many typical waveforms intranslating these into equivalent sine wave or square modulating waveforms so that flicker calculationscan be fitted to standard Pst = 1 curves[36].

3.1.3 The CRIEPI Index ∆V10

In addition to the IEC methods there’s an index,called equivalent 10Hz voltage fluctuations, ∆V10, usedin Oriental countries like China, Japan, Korea to assessflicker. The index, was achieved by CRIEPI (CentralResearch Institute of Electric Power Industry) inJapan[37] and is based on a visual sensitivity curve, seenin Figure 37[33], and it is based on experiments donewith 580 people. We can see that the peak frequencyis at 10 Hz as name implies compared to 8,8 Hz usedin IEC methods. And on experiments was found to bethe most uncomfortable to human eyes (in Japan), theweighing value for the 10 Hz component of a signal usunity, with other values lower than 1.

The amplitude of voltage modulation at frequencyfn, ∆vn, can be calculated as being twice the amplitude of the voltagespectral component at frequency 50Hz calculated with Fast FourierTransform (FFT). The equivalent effects of all voltage modulations withrespect to 10 Hz calculated as presented in Equation 7, where αn is theweighing value corresponding to flicker sensitivity at frequency fn (Figure37). Normally, frequencies are considered up to 30 Hz. On the basis of the CRIEPI experiments, the valueof ∆vn, at a bus should be limited within 0,45%. Meters are built to estimate flicker following thisapproach. In addition to these two methods (IEC, CRIEPI), there’s also IESNA (The IlluminatingEngineering Society of North America) flicker index[38], which is sometimes used to determine flicker offluorescent light but it isn’t nearly as popular as IEC or CRIEPI methods, so we won’t examine it furtheron this paper.

3.2 PROPOSED NEW METHODS

Major deficiencies of the most commonly used IEC flickermeter is it’s ability to measure flickerscaused by interharmonics whose frequencies are higher than 102Hz, and it should be noted thatinterharmonics between 100Hz and 400Hz aren’t that uncommon[39]. And as old IEC flickermeters havebeen based on incandescent lamps, gas discharge lamps have produced to measurement technology inspite of the corrections made to IEC flickermeter as shown in Equation 6. These problems have beentried to solve in following proposed new methods for flicker metrology, of which some I will review now.

Figure 37. Visual sensitivity curve measured byCRIEPI.

( )2M

1nnn10 vV ∑

=

∆⋅α=∆

Equation 7. ∆V10 calculation




3.2.1 Eyebrain model

Emanuel and Peretto[17] proposed a novel flicker measurement in 2004, which was based oncomputational model of flicker perception eliminating the need for large number of human subjects.Traditionally threshold of perception and the thresholdof objection to light flicker were determinedexperimentally using large number of human subjectsand incandescent lamps. However, there has been aclear need for a model that works despite the lamptype, but to obtain such results by using conventionalsurveys of large populations are time consuming andexpensive. An effective eyebrain simulator would be amuch better way to go according to the authors.

The proposed system is seen in Figure 38. The totalluminous flux φ produced by a lamp depends on theinput voltage magnitude, frequency and waveform andthe lamp type, size and condition. The light getting toretina λ, is proportional with the flux φ and the pupildiameter d. The neurodynamic phenomena that governthe pupil mechanics are very complex and depends atleast on intensity and spectrum[40,41,42,43]. Rough estimateof the intensity dependency is given in Figure 40[41]. Andevidence for the role of ipRGC in pupillary constrictionwas get in a study by Lucas et al.[42], giving an estimatefor human action spectra for pupillary constriction aswell seen in Figure 40. Action spectra for pupillaryconstriction in wildtype mice (cone/rodknockout),which is matching with melanopsin containing ipRGCsand the action spectra suggested for humans.

However, in this model interactions are simplified tothe point where only the basic functions are addressed,and using linearization around the working pointmeaning that small increment variation of φ causes smallvariations of the pupil aperture. And this problem was meant to be addressed in further development ofthis simplified model according to the authors.

Figure 38. Proposed eyebrain model:(a) Schematic. (b) Block diagram.

Figure 40. Pupil diameters were evaluated forthree subjects (square, triangles anddiamonds) under different constant light fluxillumination.Figure 40. Action spectra for pupillary constriction in wild

type mice (cone/rodknockout), which is matching withmelanopsin containing ipRGCs and the action spectrasuggested for humans.




Figure 41. Borderline of irritation flicker curves. Incandescent lamp with30ms time constant. Squarewave voltage modulation.

The retina is simulated by means of a photodiode D that generates a voltage v1 assumed proportionalwith the luminous flux determined by Equation 8, K1 being amplifying constant and a the aperture of thepupil [m2].

A first order lowpass filter with a time constant given by C1, R1 and R2 then attenuates the signal v1

and provides the voltage v2 that is compared with a reference level VREF determined by the backgroundillumination and the adaptation time The error signal vε (VREFv2) is transmitted from the visual center tothe iris muscles that are modeled by means of an actuator M, chosen to be a linear dc motor (accordingto the assumption of a linearization around the working point). Specific mathematic equations for thedifferent blocks and parts are presented in original publication[17].

The block diagram is presented in Figure 38b, where lamp is presented with a first order transferfunction with a time constant of τ0

[35] and a gain factor G. The supply voltage V is modulated asrecommended by the European standards for flickermeters’ calibrations[44], with both sinusoidal andsquarewave modulated voltage that yields a fluctuating luminous flux. Figure 42 shows the typicalwaveforms with incandescent lamp (k0G=1 and τ0=30ms) with squarewave modulated voltage adjustedto yield ∆emax=0,75 pu. We can see that pupil size (Figure 42c) follows voltage u, and when eye’sluminance increases voltage decreases, with decreasing pupil size accompanied by pulses of instantaneouspower developed by the iris muscles.

Then output of the model was compared to IEEE curve presentedin Figure 31, using a 120V/60W incandescent lamp with time constantτ0=30ms, to the test it’s accuracy. The simulated flicker curve isshown in Figure 41 together with the IEEE curve, which seems to be aclose match to the IEEE curve.

The proposed is very versatile, at least in theory, being suitable for any type of light that flickers. Oncethe correlation between the output luminous flux and the input modulated voltage is known and can bemodeled, then the described model can be used to compare the effects of different lamps. For examplethis model can easily incorporate temperature dependence of the filament resistance which is neglectedin the IEC flickermeter. However, authors themselves admit that the results aren’t prefect, and especiallythe action spectra should be incorporated for improved model as shown in Figure 40.

aeKKv 111 ≈λ=Equation 8. "Retina".

Figure 42. Typical waveforms forf=5Hz, 50% duty cycle, andτ0=30ms. (a) Normalizedluminance with ∆emax=0,75. (b)Actuator current i and velocity u.c) Pupil area a (arbitrary units). (d)Actuator instantaneous power p.




3.2.2 Voltage spectral analysis

Gallo et al.[35] take adifferent approach forrevisal of the old model,they base their newmodel on spectralanalysis. Basic idea beingto incorporate signalprocessing used in∆V10

[45] to standard IECflickermeter. The blockdiagram of thisproposed model ispresented in Figure 43.Signal processing thenconsists of spectral analysis, weighing spectral components basing on their impacts in terms of light flicker,combining the spectral components at different frequencies to account for interactions and finallycalculating the cumulative flicker index and giving instantaneous flicker sensation (PU) as output. Basicallyblocks 2, 3 and 4 of the standard flickermeter (Figure 35) are replaced, while blocks 1 and 5 remain thesame.

The proposed voltage spectral analysis model was tested using different situations by the authors, butfor the sake of brevity, we will only examine one test done with the deliberate injection of interharmoniccomponents with control signals. The case was reproduced by a power waveform generator and referredto in[46], in which the frequency ofthe ripple control was 175Hz andits amplitude was 1,35%. Thespectral analysis is then performedby means of a very high accuracyDFT on a time period of 3 secondsand utilizing the Hanningwindow[47].

Figure 44 shows quite clearlythe difference between new andold method in terms of flickerinstantaneous flicker perceptibility,PU. During the laboratory tests, itwas experienced that this kind ofvoltage, with a 175Hzinterharmonic component,produces an evident light flicker inelectronic compact fluorescentlamps. However measurementwith IEC flickermeter showed a PUof 0,32 (Pst=0,41), that is to saythere is no flicker. On the other hand, the result obtained by the weighted spectrum oscillates around 3,6PU (Pst=1,38), which means sensible light flicker and above the standardized limit of P st<1.

In conclusion, more comprehensive results could be obtained using this method compared to old IECmethod. Weighted spectral analysis seems to be particularly effective giving accurate results with differenttypes of lamps and with the existence of interharmonic components, which have been one of the greatestdeficiencies of the old IEC method. In general this new method offer great flexibility over old IECmethod and earns definitely further research.

Figure 43. New flicker evaluation approach.

Figure 44. Emulation of ripple control signal results with standard andnew flickermeter based on weighted spectral analysis.



Flicker metrology 28

3.2.3 Digital flicker measurement using continuous wavelet transform

Paper by Huang and Lu[48] in 2004, studies the possibility to use continuous wavelet transform inassessing flicker severity. Wavelet transform is a technology that has become more and more popular insignal processing applications. It has been used in image processing, acoustics[49], telecommunications, andas well in electrical power engineering to analyze power system transients[50], the protection of electricpower equipment[51], the detection of power quality disturbances[52], and the measurement of electricalpower[53].

Traditionally fast Fourier transform (FFT) is used in digital power quality analysis, but it has someshortcomings, as an improper choice of sampling frequency and sample number can produce totallymisleading results[54]. And generally, the Fouriertransform will become less efficient in tracking signaldynamics[55]. In contrast to Fourier transform, wherea window is used uniformly for spread frequencies,this new emerging wavelet technology uses shortwindows at high frequencies and long windows atlow frequencies. This way, transient behavior anddiscontinuities can be more closely monitored, inother words, focus has been put on points ofinterest and sort of neglecting the uninterestingpoints in signal.

According to authors, this waveletbasedmethod provides engineers more flexible way ofvisualizing the voltage flicker with the capability topresent frequency and time informationsimultaneously. This simultaneous presentationcould be further developed into didactic tool for students for better understanding of electric powersignals. Also the same method owns the potential to be extended to examine other disturbances as well.And according to test results presented in the publication, this method with wavelet transformationproduced more reliable and accurate than for example Fourierbased methods. Figure 45 shows anexample of the visualized flicker data produced by this digital method.

3.2.4 Genetic based algorithm for voltage flicker measurement

ALHasawi et al.[56] have chose genetic algorithms (GA) as an approachto measure flicker in power systems. Genetic algorithms are exploratorysearch procedures based on mechanics of selection and survival of thefittest, and as name implies. GAs have got their inspiration from nature.Simple flow diagram of GA is seen in Figure 46[57]. Genetic algorithms itselfare more of an optimization method, working on a coding of the problemparameters, not on the parameters themselves. GAs consist of three basicoperations, namely, reproduction, crossover and mutation. GA is a blindsearch using stochastic operation rules. No information is needed for theobjects, only random number generation (mutation), string copying(reproduction), and partial string exchanging (crossover).

In practice the genetic algorithms are done using a programmedalgorithm (in this, a GAs software package was written in FORTRAN, andis written by David L. Carrol from the University of Illinois, USA), whichthen uses digitized samples of the supply voltage signal. After testing withvarious different voltage waveforms, the authors found the method very accurate to be used as an onlineflicker voltage estimator. However, despite the study being as old as from 2002, it hadn’t produced manycitations implying that it wouldn’t be the most optimal solution for flicker measurement.

Figure 46. Simple GA flowdiagram.

Figure 45. Display of voltage flicker trend.



Conclusion 29

4. CONCLUSION

As we have noted, the current widely recognized methods ∆V10 and IEC flickermeter are inadequatein measuring flicker in special cases like with interharmonics and discharge lamps. And, like in almostevery field of electric technology, digital methods and devices are pushing analog flicker measurementdevices to museum shelves. First, Fourierbased digital signal processing devices were introduced toimprove flicker measurements and they also present the current state of flickermeters. But like wenoticed from the study of wavelet transform[48], Fourierbased flickermeters have some shortcomings,which will most likely rule them out from the technologies used in future devices. We also examined thepossibility to introduce novel algorithms to power quality analysis like genetic algorithms and proposedsimulated model of eyebrain response. As it seems quite clear that old flickermeters will be replacedwith a new standard soon, it can still take long time before big players like IEC and IEEE will reach aconsensus about the measurement standard.

In addition to examined new methods, there are some other proposed new methods like the oneproposed by Guan et al.[58] , which is based on the ∆V10model and it considers reactive power as well asactive power, and is especially targeted for problems caused by electric arc furnaces. Also a methodbased on virtual instrumentation is proposed by Caldara[59], similar to the one seen already in Figure 1.And in addition to improvements in measurements, there’s effort to mitigate flicker propagation[6], butthat would be worth of it’s own paper.

And what is really important thing to notice from current and proposed models of flickermeasurement, is the fact that they are all based on visual perception of flicker based more or less tohuman eye responses. However, it’s a wellknown fact that luminous modulation is sensed by the braineven though it wouldn’t be perceived visually[26]. In general, this means that even though you wouldn’tperceive the flicker it could still be measured for example from ERG (electroretinogram) or from EEG(electroencephalogram) and maybe needs to be accounted to models at the field of power systems aswell.

5. GLOSSARY (ENGLISHFINNISH)

ballast kuristin, liitäntäilaitebandpass filter kaistanpäästösuodatincarrier frequency kantotaajuuscoefficient kerroinconstriction supistuminencorner frequency kulmapistetaajuuscoupling kytkentäcutoff frequency rajataajuusdischarge lamp purkauslamppuelectric arc furnace valokaariuunifilament hehkulankaflicker välkyntä, jännitteen nopea

vaihtelu, ”flicker”fluctuation heilahtelu, vaihtelufluorescent lamp loistelamppuhighpass filter ylipäästösuodatinilluminance valaistusvoimakkuusimperceptible huomaamatonincandescent lamp hehkulamppuinduction motor epätahtimoottoriinstantaneous hetkellineninteger harmonic ”kokonaisluvulla kerrannainen

harmoninen”interharmonics harmonisten välissä oleva

taajuus (=noninteger)load kuorma (sähkötekn.)longterm flickerseverity index

pitkäaikainenhäiritsevyysindeksi (välkynnälle)

lowpass filter alipäästösuodatinluminous flux valovirtametal halide lamp monimetallilamppumitigation pehmennys, vaimennusnoninteger harmonic ”eikokonaisluvulla

kerrannainen harmoninen”novel uusipeak load huippukuormapercentile prosenttipiste (tilastot.)power electronics tehoelektroniikkaproliferation [räjähtävä] lisääntyminenpropagation eteneminenripple sykkeisyys, ”rippeli”robustness robustisuus, jäykkyysrolling mill valssaamoshortterm flickerseverity index

lyhytaikainenhäiritsevyysindeksi (välkynnälle)

sodium lamp natriumlamppusquarewave kanttiaaltosubharmonics 50 Hz:n alle jäävät taajuudetsusceptibility herkkyysswitched mode powersupply

hakkuriteholähde

time constant aikavakiowelding hitsaaminenwinding käämiminen (esim. muuntajan

tai sähkömoottorin)



References 30

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