Cahier technique no. 205 - Schneider Electric

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Cahier technique no. 205

Power supply of lighting circuits

J. SchonekM. Vernay

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no. 205Power supply of lighting circuits

CT 205 first issue, April 2002

Jacques SCHONEK

Graduate engineer from ENSEEIHT (Ecole Nationale Supérieured’Electrotechnique, d’Electronique, d’Informatique, d’Hydraulique etdes Télécommunications) with a doctorate in Engineering from theUniversity of Toulouse, he was involved in designing variable speeddrives for the Telemecanique brand from 1980 to 1995.He then became manager of the Harmonic Filtering group.He is currently responsible for Electrotechnical Applications andNetworks in the Advanced Design Office of Schneider Electric’selectrical distribution division.

Marc VERNAY

Graduate engineer from CNAM (Conservatoire National des Arts etMétiers) in Grenoble, he worked for Merlin Gerin from 1991 to 1996and was responsible for the “lighting dimmer control” project, afterwhich he provided technical support for lighting applications.He is currently responsible for the Electronic Roadmap for LowVoltage applications in Schneider Electric’s electrical distributiondivision.

Cahier Technique Schneider Electric no. 205 / p.2

Lexicon

Color rendering index - CRI -Number designated by CRI or Ra whichcharacterizes the capacity of a light source toaccurately restore the various colors in thevisible spectrum of a lit object, without loss orcoloration.The International Commission on Illumination(C.I.E., Commission Internationale de l’Eclairage)has defined a general color rendering index Ra,where the maximum value is 100.

ConverterDevice designed to modify at least onecharacteristic of the electrical energy (voltage,magnitude, frequency).

Dimmer switchConverter designed to vary the magnitude of anAC voltage via an electronic switch whoseconduction time is limited to a fraction of theperiod of this voltage.

“Electric arc” and “Luminescent discharge”An electric arc is a gas conduction in which thecharge carriers are electrons produced by aprimary emission (released by the cathode).A luminescent discharge is a gas conduction inwhich the load carriers are electrons producedby a secondary emission (released by the atomsof gas in which the discharge occurs).

“Fluorescent” tube and “neon” tubeA “fluorescent” tube is a lamp consisting of abulb coated on the inside with a layer of aluminescent substance containing a gas(mercury vapor); the light it diffuses is emitted bythe luminescent layer sensitized by the UVradiation from an electrical discharge.

A “neon tube” is a lamp consisting of a bulb inwhich the light is produced by an electricaldischarge passing through the gas (neon argonmixture: 75/25) it contains.The different colors of these tubes, used forilluminated signs, are obtained by powderdeposits inside the bulbs or by using tinted glassthroughout.

Interference-suppressing capacitorLow-value capacitor (several nF) placed on thepower supply circuit terminals of electronicdevices, designed to protect them from high-frequency disturbance carried by the line supply.

K (Kelvin unit)Unit of color temperature, this characterizes theapparent color of a light. This value is notrepresentative of the actual temperature of thesource of this light.

LuminaireDevice which distributes, filters or transforms thelight from one or more lamps. Excluding lamps, itcontains the fixings, the auxiliary circuits (starterand ballast) and the connection elements to thepower supply circuit.

Luminous efficiency (lm/W)Quotient of the luminous flux by the powerconsumed for its emission.

Smoothing capacitorCapacitor usually placed at the output of arectifier circuit and designed to reduce the DCvoltage ripple.


Power supply of lighting circuits

A source of comfort and productivity, lighting represents 15% of thequantity of electricity consumed in industry and 40% in buildings. Thequality of the lighting (light stability and continuity of service) depends onthe quality of the electrical energy thus consumed. The supply of electricalpower to lighting networks has therefore assumed great importance.

To help with their design and simplify the selection of appropriateprotection devices, the authors present in this document an analysis of thedifferent lamp technologies and the main technological developments inprogress. After summarizing the distinguishing features of lighting circuitsand their impact on control and protection devices, they discuss the optionsconcerning which equipment to use.

Contents

1 The different lamp technologies 1.1 Artificial light p. 41.2 Incandescent lamps p. 4

1.3 Fluorescent lamps p. 5

1.4 Discharge lamps p. 6

1.5 LEDs (Light Emitting Diodes) p. 6

1.6 Lamps for special applications p. 7

2 Power supply of incandescent lamps 2.1 Lamps with direct power supply p. 8

2.2 Extra low voltage halogen lamps p. 9

3 Power supply of luminaires 3.1 The magnetic ballast p. 10with magnetic ballasts 3.2 The starter p. 10

3.3 Compensation p. 10

3.4 A technological development p. 12

4 Power supply of luminaires 4.1 Principle and characteristics p. 13with electronic ballasts 4.2 Layout p. 13

4.3 Constraints p. 14

5 Technical characteristics and usage 5.1 Main technical characteristics p. 16of lighting devices 5.2 Fields of application, advantages and disadvantages p. 16

5.3 The different power supply modes p. 17

6 Difficulties and recommendations 6.1 Constraints related to lighting devices and recommendations p. 18

6.2 Sensitivity of lighting devices to line voltage disturbances p. 20

6.3 Choice of light dimmers p. 21

7 Conclusions: technological developments 7.1 Developments in luminaires p. 22and professional requirements 7.2 Developments in control and protection equipment p. 22

7.3 The necessity for suitable equipment p. 22

Bibliography p. 23


1 The different lamp technologies

1.1 Artificial light

Artificial luminous radiation can be produced fromelectrical energy according to two principles:incandescence and electroluminescence.

Incandescence

This is the production of light via temperatureelevation. The energy levels are plentiful, and inconsequence, the emitted radiation spectrum iscontinuous. The most common example is afilament heated to white state by the circulationof an electrical current. The energy supplied istransformed into the Joule effect and intoluminous flux.

Luminescence

This is the phenomenon of emission by amaterial of visible or almost visible luminousradiation.

c Electroluminescence of gasesA gas (or vapors) subjected to an electricaldischarge emits luminous radiation.

Since this gas does not conduct at ordinarytemperature and pressure, the discharge isproduced by generating charged particles whichpermit ionization of the gas. The spectrum, in theform of stripes, depends on the energy levelsspecific to the gas or vapor used. The pressureand temperature of the gas determine the lengthof the emitted rays and the nature of thespectrum.

c PhotoluminescenceThis is the luminescence of a material exposedto visible or almost visible radiation (ultraviolet,infrared).When the substance absorbs ultraviolet radiationand emits visible radiation which stops a shorttime after energization, this is fluorescence. Notall the photons received are transformed intoemitted photons. The best efficiency rating forexisting fluorescent materials is 0.9.When the light emission persists afterenergization has stopped, it is phosphorescence.

1.2 Incandescent lamps

Incandescent lamps are historically the oldest(patented by Thomas Edison in 1879) and themost commonly found in common use.They are based on the principle of a filamentrendered incandescent in a vacuum or neutralatmosphere which prevents combustion.

A distinction is made between:c Standard bulbsThese contain a tungsten filament and are filledwith an inert gas (nitrogen and argon or krypton).c Halogen bulbsThese also contain a tungsten filament, but arefilled with a halogen compound (iodine, bromineor fluorine) and an inert gas (krypton or xenon).This halogen compound is responsible for the

phenomenon of filament regeneration, whichincreases the service life of the lamps andavoids them blackening. It also enables a higherfilament temperature and therefore greaterluminosity in smaller-size bulbs.

The main disadvantage of incandescent lamps istheir significant heat dissipation, resulting in poorlight output, But, they have the advantage of agood Color Rendering Index (CRI) due to thefact that their emission spectrum is fairly similarto the eye’s reception spectrum (see fig. 1 ).

Their service life is approximately 1,000 hoursfor standard bulbs, 2,000 to 4,000 for halogenbulbs. Note that the service life is reduced by50% when the supply voltage is increased by 5%.


1.3 Fluorescent lamps

Fig. 1 : eye response curve and emission spectra from different sources of visible light.Note: the spectrum of fluorescent sources differs according to the lamp model.

Sun

Tungsten

Fluorescent

Eye

300 350 400 450 500 550Wavelength (nm)

600 650 700 750 800

This family covers fluorescent tubes andcompact fluorescent lamps. Their technology isusually known as “low-pressure mercury”.

Fluorescent tubes

These were first introduced in 1938.In these tubes, an electrical discharge causeselectrons to collide with ions of mercury vapor,resulting in ultraviolet radiation due toenergization of the mercury atoms. Thefluorescent material, which covers the inside ofthe tubes, then transforms this radiation intovisible light.

This technology has the disadvantage of amediocre CRI due to the fact that the emissionspectrum is discontinuous. However, nowadaysthere are different product families which meet

the many needs of CRI, for example so-called“daylight” tubes.

Fluorescent tubes dissipate less heat and have alonger service life than incandescent lamps, butthey do need an ignition device called a “starter”and a device to limit the current in the arc afterignition. This last device called “ballast” is usuallya choke placed in series with the arc. Theconstraints affecting this ballast are detailed inthe rest of the document.

Compact fluorescent lampsThese are based on the same principle as afluorescent tube. The starter and ballastfunctions are provided by an electronic circuit(integrated in the lamp) which enables the use ofsmaller tubes folded back on themselves.


Compact fluorescent lamps were developed toreplace incandescent lamps: they offersignificant energy savings (15 W against 75 Wfor the same level of brightness) and anincreased service life (8,000 hrs on average andup to 20,000 hrs for some).

Standard compact fluorescent lamps take a littlelonger to ignite and their service life is reducedaccording to the number of times they areswitched on. So, if the ignition frequency ismultiplied by 3, the service life is reduced by aratio of 2.

Lamps known as “induction” type or “withoutelectrodes” (see fig. 2 ) start instantaneouslyand the number of switching operations does notaffect their service life. They operate on theprinciple of ionization of the gas present in the

Fig. 2 : compact fluorescent lamps:a] standard; b] induction.

a] b]

1.4 Discharge lamps

The light is produced by an electrical dischargecreated between two electrodes within a gas in aquartz bulb. All these lamps (see fig. 3 ) thereforerequire a ballast to limit the current in the arc.

The emission spectrum and the CRI depend onthe composition of the gas and improve as thepressure increases. A number of technologieshave therefore been developed for differentapplications.

Low-pressure sodium vapor lamps

These have the best light output, however thecolor rendering is very poor since they only havemonochromatic radiation, which is orange in color.Applications: tunnel, motorway lighting.

High-pressure sodium vapor lampsThese produce a white light with an orange tinge.Applications: street lighting, monuments.

High-pressure mercury vapor lampsThe discharge is produced in a quartz or ceramicbulb at pressures of more than 100 kPa. Theselamps are called “fluorescent mercury discharge

Fig. 3 : discharge lamps.

lamps”. They produce a characteristically bluishwhite light.Applications: car parks, hypermarkets,warehouses.

Metal halide lamps

The latest technology. They produce a color witha broad spectrum.The use of a ceramic tube offers better luminousefficiency and better color stability.Applications: stadia, retail premises, projectors.

1.5 LEDs (Light Emitting Diodes)

The principle of light emitting diodes is theemission of light by a semi-conductor as anelectrical current passes through it. LEDs arecommonly found in numerous applications, butthe recent development of white or blue diodeswith a high light output opens new perspectives,especially for signaling (traffic lights, exit signs oremergency lighting).

The average current in a LED is 20 mA, thevoltage drop being between 1.7 and 4.6 Vdepending on the color. These characteristicsare therefore suitable for an extra low voltage

power supply, especially using batteries.A converter is required for a line power supply.

The advantage of LEDs is their low energyconsumption. As a result, they operate at a verylow temperature, giving them a very long servicelife. Conversely, a simple diode has a weak lightintensity. A high-power lighting installationtherefore requires connection of a large numberof units in series.

These diodes are used particularly where thereis little power available.

tube by a very high frequency electromagneticfield (up to 1 GHz). Their service life can be aslong as 100,000 hrs.


1.6 Lamps for special applications

The types of lamp mentioned in this sub-sectiononly have, with the exception of the last two, asingle application. Their electrical power supplyshould always be designed according to thespecial technical information provided by theirmanufacturers.

Special incandescent lamps for 3-color trafficlights.

Their service life is increased and their specialmounting helps them resist vibrations.

Special mercury vapor lamps

These produce a uniform beam of blue-whitelight designed for reproduction graphics, screen-printing or jewelers’ decorative lighting.

Lamps producing white light with a radiationaround 655 nm

These are designed to acceleratephotosynthesis in plants. Applications includeflorists’ shops, entrance halls, industrialgreenhouses.

Germicidal lamps

These produce ultraviolet in the 253.7 nm wavelength. Applications include purification,sterilization of air, water and instruments in thepharmaceutical industry, hospitals, treatmentplants or laboratories. These lamps produceradiation that is dangerous to the eyes and skin.

UVA lamps

These are used for tanning and light therapy.

Black light lamps

These generate ultraviolet emission in the longwavelengths which has the effect of activatingfluorescent pigments. Applications includefinding defects in industry or counterfeit items(notes, pictures, etc) as well as use in showbusiness.

Special halogen lamps

Used for projection of images (slide viewer,overhead projection, microfiche reading), theirheat radiation onto the film is reduced by 60%compared to a conventional lamp.

Lamps adapted to projection in film studiosand theatersTheir color temperature is 3200° K. Their powerrating can be as high as 5000 W.These lamps have better luminous efficiency andmore luminous flux but a reduced service life(12 hrs, 100 hrs, 500 hrs).

Heating lamps

These generate a short infrared heat energybeam. Certain types are designed for farming,others for drying and curing paintings, heating inindustrial processes or zone heating byradiation.


2 Power supply of incandescent lamps

2.1 Lamps with direct power supply

ConstraintsDue to the very high temperature of the filamentduring operation (up to 2500° C), its resistancevaries greatly depending on whether the lamp ison or off. As the cold resistance is low, a currentpeak occurs on ignition that can reach 10 to15 times the nominal current for a fewmilliseconds or even several milliseconds.

This constraint affects both ordinary lamps andhalogen lamps: it imposes a reduction in themaximum number of lamps that can be poweredby a device such as remote-control switch,modular contactor or relay for busbar trunking.

Varying the brightnessThis can be obtained by varying the voltageapplied to the lamp.

This voltage variation is usually performed by adevice such as a triac dimmer switch, by varyingits firing angle in the line voltage period. Thewave form of the voltage applied to the lamp isillustrated in figure 4a . This technique known as“cut-on control” is suitable for supplying powerto resistive or inductive circuits. Anothertechnique suitable for supplying power tocapacitive circuits has been developed with

MOS or IGBT electronic components. Thistechnique varies the voltage by blocking thecurrent before the end of the half-period (seefig. 4b ) and is known as “cut-off control”.

The latest devices use both these techniqueswhile adapting automatically to the nature oftheir load.

Switching on the lamp gradually can also reduce,or even eliminate, the current peak on ignition.

Note that light dimming:

c is accompanied by a modification in the colortemperature;

c has an adverse effect on the service life ofhalogen lamps when a low voltage is maintainedfor a long time. Indeed, the filament regenerationphenomenon is less effective with a lowerfilament temperature.

Another technique is used for timer switch-offwarnings. These devices warn that the lightingwill shortly be switched off by reducing theluminous intensity by 50% for a several seconds.This reduced brightness is obtained by applyinga voltage half-wave, positive or negative, to thelamps at intervals of one second, using a triacdevice.

Fig. 4 : shape of the voltage supplied by a light dimmer at 50% of maximum voltage with the following techniques:a] “cut-on control”,b] “cut-off control”.

300

200

100

0

0

t

(s)

0.01 0.02

-100

-200

-300

300

a] b]

200

100

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t

(s)

0.01 0.02

-100

-200

-300


2.2 Extra low voltage halogen lamps

Constraints

Some low-power halogen lamps are suppliedwith ELV 12 or 24 V, via a transformer or anelectronic converter.c With a transformer, the magnetizationphenomenon combines with the filamentresistance variation phenomenon at switch-on.The inrush current can reach 50 to 75 times thenominal current for a few milliseconds.The use of dimmer switches placed upstreamsignificantly reduces this constraint.c Electronic converters, with the same powerrating, are more expensive than solutions with atransformer. This commercial handicap iscompensated by a greater ease of installationsince their low heat dissipation means they canbe fixed on a flammable support. Moreover, theyusually have built-in thermal protection.These devices can therefore be marked(IEC 60417 – 1st October 2000):

Varying the brightness

There are a variety of possible technicalsolutions:c dimmer switch and transformer,c electronic converter controlled by a 0-10 Vexternal signal,c dimmer switch and converter; this solution isused to control the brightness of several lampswith a single dimmer switch, but it is important tocheck carefully that the dimmer switch andconverters are compatible.

Developments

New ELV halogen lamps are now available witha transformer integrated in their base. They canbe supplied directly from the LV line supply andcan replace normal incandescent lamps withoutany special adaptation.

F

75

non-flammable

resistant to 75° C


3 Power supply of luminaires with magnetic ballasts

3.1 The magnetic ballast

Fluorescent tubes and discharge lamps requirethe intensity of the arc to be limited, and thisfunction is fulfilled by a choke (or magneticballast) placed in series with the bulb itself(see fig. 5 ).

This arrangement is most commonly used indomestic applications with a limited number oftubes. No particular constraint applies to theswitches.

Dimmer switches are not compatible withmagnetic ballasts: the cancellation of the voltagefor a fraction of the period interrupts thedischarge and totally extinguishes the lamp.

Fig. 5 : magnetic ballasts.

3.2 The starter

The starter has a dual function: preheating thetube electrodes, and then generating anovervoltage to ignite the tube. This overvoltageis generated by the opening of a contact(controlled by a thermal switch) which interrupts

the current circulating in the magnetic ballast.During operation of the starter (approx. 1 s), thecurrent drawn by the luminaire is approximatelytwice the nominal current.

3.3 Compensation

Since the current drawn by the tube and ballastassembly is essentially inductive, the powerfactor is very low (on average between 0.4 and0.5). In installations consisting of a large numberof tubes, it is necessary to provide compensationto improve the power factor.

Possible layouts

For large lighting installations, centralizedcompensation with capacitor banks is a possiblesolution, but more often this compensation isincluded at the level of each luminaire in avariety of different layouts (see fig. 6 ).

The compensation capacitors are therefore sizedso that the global power factor is greater than 0.85.In the most common case, that of parallelcompensation, its capacity is on average 1 µFfor 10 W of active power, for any type of lamp.However, this compensation is incompatible withdimmer switches.

Constraints affecting compensationThe layout for parallel compensation createsconstraints on ignition of the lamp. Since the

capacitor is initially discharged, switch-onproduces an overcurrent. An overvoltage alsoappears, due to the oscillations in the circuitmade up of the capacitor and the power supplyinductance.The following example can be used to determinethe orders of magnitude.c Assuming an assembly of 50 fluorescent tubesof 36 W each:v total active power: 1800 W,v apparent power: 2 kVA,v total rms current: 9 A,v peak current: 13 A.c With:v a total capacity: C = 175 µF,v a line inductance (corresponding to a short-circuit current of 5 kA): L = 150 µH.The maximum peak current at switch-on equals:

I.

.c max

-6

-6V A= = =CL

230 2175 10

150 10350

The theoretical peak current at switch-on cantherefore reach 27 times the peak current duringnormal operation.


The shape of the voltage and current at ignitionis given in figure 7 for switch closing at the linesupply voltage peak.There is therefore a risk of contact welding inelectromechanical control devices (remote-

control switch, contactor, circuit-breaker) ordestruction of solid state switches with semi-conductors.In reality, the constraints are usually less severe,due to the impedance of the cables.

a

a] b] c]C

Ballast Lamp

Ballast Lamp

Ca

Ballast

LampC a

Ballast

Lamp

Fig. 6 : the various compensation layouts: a] parallel; b] series; c] dual series also called “duo” and their fields ofapplication.

Fig. 7 : power supply voltage at switch-on and inrush current.

600

400

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0

-200

-400

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0

(V)

t (s)

0.02 0.04 0.06

300

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(A)

t (s)

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Compensation layout Application CommentsWithout compensation Domestic Single connectionParallel [a] Offices, workshops, Risk of overcurrents for control

superstores devicesSeries [b] Choose capacitors with high

operating voltage (450 to 480 V)Duo [c] Avoids flicker


Standard IEC 60669–1 (switches for householdand similar fixed-electrical installations, generalrequirements) specifies the capacities to betaken into account when designing switches (fora prospective short-circuit current Isc of 3 kA):c rating < 6 A: 70 µF,c rating u 6 A: 140 µF.

Specific constraint to ignite several groups offluorescent tubes

When a group of tubes is already switched on,the compensation capacitors in these tubeswhich are already energized participate in theinrush current at the moment of ignition of a

Fig. 8 : magnitude of the current peak in the control switch of the moment of ignition of a second group of tubes.

second group of tubes: they “amplify” the currentpeak in the control switch at the moment ofignition of the second group.The table in figure 8 , resulting frommeasurements, specifies the magnitude of thefirst current peak, for different values ofprospective short-circuit current Isc. It is seenthat the current peak can be multiplied by 2 or 3,depending on the number of tubes already inuse at the moment of connection of the lastgroup of tubes.Nonetheless, we recommend sequential ignitionof each group of tubes so as to reduce thecurrent peak in the main switch.

Number of tubes Number of tubes Inrush current peak (A)already in use connected

(second group) Isc = 1500 A Isc = 3000 A Isc = 6000 A

0 14 233 250 320

14 14 558 556 575

28 14 608 607 624

42 14 618 616 632

3.4 A technological development

The most recent magnetic ballasts are known as“low-loss”. Their magnetic circuit has beenoptimized, but the operating principle remainsthe same. This new generation of ballasts iscoming into widespread use, under the influenceof new regulations (European Directive, EnergyPolicy Act - USA).


4 Power supply of luminaires with electronic ballasts

Electronic ballasts are used as a replacement formagnetic ballasts to supply power to fluorescenttubes (including compact fluorescent lamps) anddischarge lamps. They also provide the “starter”

function and do not need any compensationcapacitor. They were first introduced in themiddle of the 1980s.

4.1 Principle and characteristics

The principle of the electronic ballast (see fig. 9 )consists of supplying the lamp arc via anelectronic device that generates a rectangularform AC voltage.A distinction is made between low-frequency orhybrid devices, with a frequency between 50 and500 Hz, and high-frequency devices with afrequency between 20 and 60 kHz.Supplying the arc with a high-frequency voltagecan totally eliminate the flicker phenomenon andstrobe effects. The electronic ballast is totallysilent.During the preheating period of a dischargelamp, this ballast supplies the lamp withincreasing voltage, imposing an almost constantcurrent. In steady state, it regulates the voltageapplied to the lamp independently of anyfluctuations in the line voltage.Since the arc is supplied in optimum voltageconditions, this results in energy savings of 5 to10% and increased lamp service life. Moreover,

Fig. 9 : electronic ballast.

the efficiency of the electronic ballast canexceed 93%, whereas the average efficiency ofa magnetic device is only 85%. The power factoris high (> 0.9).The electronic ballast is also used to provide thelight dimming function. Varying the frequency infact varies the current magnitude in the arc andhence the luminous intensity.

4.2 Layout

An electronic ballast essentially consists of arectifier stage (with Power Factor Correction -PFC - if necessary), a smoothing capacitor for

Fig. 10 : simplified schematic of a lamp supplied by an electronic ballast.

the rectified voltage, and a half-bridge inverterstage (see fig. 10 ). It can also be supplied withdirect current.

a Lamp

ou

ou

or

or

+

-


4.3 Constraints

Inrush current

The main constraint that electronic ballasts bringto line supplies is the high inrush current onswitch-on linked to the initial load of thesmoothing capacitors (see fig. 11 ).

Fig. 11 : orders of magnitude of the inrush currentmaximum values, depending on the technologies used.

Technology Max. inrush Durationcurrent

Rectifier with PFC 30 to 100 In i 1 ms

Rectifier with choke 10 to 30 In i 5 ms

Magnetic ballast i 13 In 5 to 10 ms

supply equals 1.8 times the currentcorresponding to the lamp active power, whichcorresponds to a power factor of 0.55.

In order to balance the load between thedifferent phases, lighting circuits are usuallyconnected between phases and neutral in abalanced way. In these conditions, the high levelof third harmonic and harmonics that aremultiples of 3 can cause an overload of theneutral conductor. The least favorable situationleads to a neutral current which may reache times the current in each phase. For moreinformation, read Cahier Technique no. 202“The singularities of the third harmonic”.

Harmonic emission limits for lighting systems areset by standard IEC 61000-3-2. For example, forpower devices above 25 W, the percentage ofthird harmonic should be less than 30% of thefundamental current.

Leakage currentsElectronic ballasts usually have capacitorsplaced between the power supply conductorsand the earth. These interference-suppressingcapacitors are responsible for the circulation of apermanent leakage current in the order of 0.5 to1 mA per ballast. This therefore results in a limitbeing placed on the number of ballasts that canbe supplied by a Residual Current DifferentialSafety Device (RCD) (See Cahier Techniqueno. 114).

At switch-on, the initial load of these capacitorscan also cause the circulation of a current peakwhose magnitude can reach several amps for10 µs. This current peak may cause unwantedtripping of unsuitable devices.

In reality, due to the wiring impedances, theinrush current for an assembly of lamps is muchlower than these values, in the order of 5 to 10 Infor less than 5 ms.Unlike magnetic ballasts, this inrush current isnot accompanied by an overvoltage.

Harmonic currents

For ballasts associated with high-powerdischarge lamps, the current drawn from the linesupply has a low total harmonic distortion(< 20% in general and < 10% for the mostsophisticated devices). Conversely, devicesassociated with low-power lamps, in particularcompact fluorescent lamps, draw a very distortedcurrent (see fig. 12 ). The total harmonicdistortion can be as high as 150%. In theseconditions, the rms current drawn from the line

Fig. 12 : shape of the current drawn by a compact fluorescent lamp.

0.6

0.4

0.2

0

-0.2

-0.4

-0.6

0

(A)

t

(s)

0.02


High-frequency emissions

Electronic ballasts are responsible for high-frequency conducted and radiated emissions.

The very steep rising edges applied to theballast output conductors cause current pulsescirculating in the stray capacities to earth (seefig. 13 ). As a result, stray currents circulate inthe earth conductor and the power supplyconductors. Due to the high frequency of thesecurrents, there is also electromagnetic radiation.To limit these HF emissions, the lamp should beplaced in the immediate proximity of the ballast,thus reducing the length of the most stronglyradiating conductors.

c Ballast controlled by a 0 to 10 V externalsignal. The ballast then supplies the tube with avariable-frequency voltage which can vary thecurrent and hence the level of brightnessproduced. This is the most commonly usedsolution (see fig. 14 ).

c Ballast controlled by a digital control signal.

The use of dimmers can also save energy byreducing the amount of light at certain times,depending on occupation of the premises.Electronic ballasts are incompatible with timerswith a switch-off warning.

Comment: If the electronic ballast is powered byan electronic switch, there is a risk of intermittentignition of the fluorescent tubes. In fact, acapacitor (0.1 to 0.2 µF) is usually placed inparallel on the switch to protect it from transientovervoltages. As a result, a leakage currentoccurs which can trigger ignition unintentionally.The use of a pre-charging circuit, which can shiftthe leakage current, is compulsory.

Fig. 13 : high-frequency emission loops linked to anelectronic ballast.

Fig. 14 : remote dimmer for electronic ballast(Merlin Gerin brand).

a Electronicballast Lamp

To avoid these conducted and radiatedemissions disturbing certain sensitive systems(power line or radio wave communicationdevices), interference-suppressing filters areincorporated in the ballasts.

Conformity with standard EN55015 requiresemission limits in the 9 kHz - 30 MHz band.

Light dimmers for electronic ballasts

The use of electronic ballasts makes it possibleto vary the brightness of fluorescent tubes.There are a number of possibilities, dependingon the ballast technology:

c Ballast powered by a dimmer switch that variesthe voltage by phase angle. The current suppliedto the tube is a function of the voltage applied tothe ballast entry point.


5 Technical characteristics and usage of lighting devices

5.1 Main technical characteristics

In all cases, the service life of lamps is reducedby frequent ignition, except for inductioncompact fluorescent lamps and LEDs.

5.2 Fields of application, advantages and disadvantages

Technology Application Advantages DisadvantagesStandard - Domestic use - Direct connection without - Low luminous efficiency andincandescent - Localized decorative intermediate switchgear high electricity consumption

lighting - Reasonable purchase price - Significant heat dissipation- Compact size - Short service life- Instantaneous lighting- Good color rendering

Halogen - Spot lighting - Direct connection - Average luminous efficiencyincandescent - Intense lighting - Instantaneous efficiency

- Excellent color renderingFluorescent tube - Shops, offices, - High luminous efficiency - Low light intensity of single

workshops - Average color rendering unit- Outdoors - Sensitive to extreme

temperaturesCompact - Domestic use - Good luminous efficiency - High initial investmentfluorescent lamp - Offices - Good color rendering compared to incandescent

- Replacement of lampsincandescent lamps

HP mercury vapor - Workshops, halls, - Good luminous efficiency - Lighting and relighting timehangars - Acceptable color rendering of a few minutes- Factory floors - Compact size

- Long service lifeHigh-pressure - Outdoors - Very good luminous efficiency - Lighting and relighting timesodium - Large halls of a few minutesLow-pressure - Outdoors - Good visibility in foggy weather - Long lighting time (5 min.)sodium - Emergency lighting - Economical to use - Mediocre color renderingMetal halide - Large areas - Good luminous efficiency - Lighting and relighting time

- Halls with high ceilings - Good color rendering of a few minutes- Long service life

LED - Signaling (3-color - Insensitive to the number of - Limited number of colorstraffic lights, “exit” signs switching operations - Low brightness of single unitand emergency lighting) - Low energy consumption

- Low temperature

Technology Power Efficiency Service life(watt) (lumen/watt) (hours)

Standard incandescent 3 – 1,000 10 – 15 1,000 – 2,000Halogen incandescent 5 – 500 15 – 25 2,000 – 4,000Fluorescent tube 4 – 56 50 – 100 7,500 – 24,000Compact fluorescent lamp 5 – 40 50 – 80 10,000 – 20,000HP mercury vapor 40 – 1,000 25 – 55 16,000 – 24,000High-pressure sodium 35 – 1,000 40 – 140 16,000 – 24,000Low-pressure sodium 35 – 180 100 – 185 14,000 – 18,000Metal halide 30 – 2,000 50 – 115 6,000 – 20,000LED 0.05 – 0.1 10 – 30 40,000 – 100,000


5.3 The different power supply modes

Technology Power supply mode Other device

Standard incandescent Direct power supply Dimmer switch

Halogen incandescent

ELV halogen incandescent Transformer Electronic converter

Fluorescent tube Magnetic ballast and starter Electronic ballastElectronic dimmer + ballast

Compact fluorescent lamp Built-in electronic ballast

Mercury vapor Magnetic ballast Electronic ballast

High-pressure sodium

Low-pressure sodium

Metal halide


6 Difficulties and recommendations

6.1 Constraints related to lighting devices and recommendations

The current actually drawn by luminairesc The riskThis characteristic is the first one that should bedefined when creating an installation, otherwiseit is highly probable that overload protectiondevices will trip and users will often findthemselves in the dark.It is evident that their determination should takeinto account the consumption of all components,especially for fluorescent lighting installations,since the power consumed by the ballasts has tobe added to that of the tubes and bulbs.

c The solutionFor fluorescent lighting, remember that unlessotherwise specified, the power of the magneticballasts can be assessed at 25% of that of thebulbs. For electronic ballasts, this power is lower,in the order of 5 to 10%.For incandescent lighting, it should beremembered that the line voltage can be morethan 10% of its nominal value, which would thencause an increase in the current drawn.The thresholds for the overcurrent protectiondevices should therefore be calculated as afunction of the total power and the power factor,calculated for each circuit.

Overcurrents at switch-on

c The riskThe devices used for control and protection oflighting circuits are those such as relays, triac,remote-control switches, contactors or circuit-breakers.

The main constraint applied to these devices isthe current peak on energization, described insections 3 and 4.This current peak depends on the technology ofthe lamps used, but also on the installationcharacteristics (supply transformer power, lengthof cables, number of lamps) and the moment ofenergization in the line voltage period. A highcurrent peak, however fleeting, can cause thecontacts on an electromechanical control deviceto weld together or the destruction of a solidstate device with semi-conductors.

c Two solutionsBecause of the inrush current, the majority ofordinary relays are incompatible with lightingdevice power supply. The followingrecommendations are therefore usually made:v Limit the number of lamps to be connected to asingle device so that their total power is lessthan the maximum permissible power for thedevice.v Check with the manufacturers what operatinglimits they suggest for the devices. Thisprecaution is particularly important whenreplacing incandescent lamps with compactfluorescent lamps.

By way of example, the table in figure 15indicates the maximum number of compensatedfluorescent tubes that can be controlled bydifferent devices with 16 A rating. Note that thenumber of controlled tubes is well below thenumber corresponding to the maximum powerfor the devices.

Fig. 15 : the number of controlled tubes is well below the number corresponding to the maximum power for thedevices.

Tube unit power Number of tubes Maximum number of tubes that can berequirement corresponding controlled by(W) to the power Contactors Remote Circuit-

16 A x 230 V GC16 A control breakersCT16 A switches C60-16 A

TL16 A18 204 15 50 11236 102 15 25 5658 63 10 16 34


These operating limits must be adhered to whenan existing installation is being worked on.But a technique exists to limit the current peakon energization of circuits with capacitivebehavior (magnetic ballasts with parallelcompensation and electronic ballasts). Itconsists of ensuring that activation occurs at themoment when the line voltage passes throughzero. Only solid state devices with semi-conductors offer this possibility. This techniquehas proved to be particularly useful whendesigning new lighting circuits.More recently, hybrid technology devices havebeen developed that combine a solid stateswitch (activation on voltage passage throughzero) and an electromechanical contactor short-circuiting the solid state switch (reduction oflosses in the semi-conductors) (see fig. 16 ).

As far as overcurrent protection devices areconcerned, it is necessary to provide 4-polecircuit-breakers with protected neutral (exceptwith the TN-C system for which the PEN, acombined neutral and protection conductor,should not be cut).

This type of device can also be used for thebreaking of all poles necessary to supplyluminaires at the phase-to-phase voltage in theevent of a fault. Indeed, as shown in the examplein figure 17 , this cut-off could cause certainsingle-phase loads to be supplied at a voltagedistinctly higher than their nominal voltage andcause their destruction due to thermal stress orbreakdown relating to the overvoltage.

A breaking device should therefore interrupt thephase and Neutral circuit simultaneously.

Fig. 16 : “standard” CT+ contactor [a], CT+ contactorwith manual override, pushbutton for selection ofoperating mode and indicator lamp showing the activeoperating mode [b], and TL+ remote-control switch [c](Merlin Gerin brand).

a b c

Overload of the neutral conductorc The riskIn an installation including, for example, numerousfluorescent tubes with electronic ballasts suppliedbetween phases and neutral, the number of thirdorder harmonic and harmonics that are multiples of3 can cause an overload of the neutral conductor.

c The solutionFirstly, the use of a neutral conductor with asmall cross-section (half) should be prohibited.Installation standards IEC 60364, section 523-5-3,is clear on this point:“If the neutral conductor carries current without areduction factor corresponding to the load of thephase conductors, the neutral conductor shouldbe taken into account for the rated circuitcurrent. Such currents may be due to significantharmonic currents in the 3-phase circuits. If thevalue of the harmonics exceeds 10%, the neutralconductor should not have a cross-section lessthan that of the phase conductors.”

Fig. 17 : consequences of disconnecting the Neutralconductor only in an installation when the single-phaseloads are unevenly balanced.

5.3 kW

Z1 = 10 Ω

1

2

3

0

N

1 2 3 N

N

2.65 kW

Z2 = 20 Ω

0.53 kW

Z3 = 100 Ω

V1→

V3→

V2→

Voltages (V) between phases and Neutral:in normal use after disconnecting the Neutral

V1 230 150V2 230 275V3 230 375


Leakage currents to earth

c The riskAt switch-on, the earth capacitances of theelectronic ballasts are responsible for residualcurrent peaks that are likely to causeunintentional tripping of protection devices.

c Two solutionsThe use of Residual Current Devices immuneagainst this type of impulse current isrecommended, even essential, when equippingan existing installation (see fig. 18 ).For a new installation, it is sensible to providesolid state or hybrid control devices (contactorsand remote-control switches) that reduce these

impulse currents (activation on voltage passagethrough zero).

HF disturbances

c The riskHF emissions, conducted and radiated, candisturb certain sensitive systems (power line orradio wave communication devices).

c The solutionIt is also possible to reduce HF emissions at thetime of installation: this requires the lamp to beplaced in the immediate proximity of the ballast,so as to limit the length of the conductors subjectto voltage gradients.

Overvoltages

c The riskAs we illustrated in earlier sections, switching ona lighting circuit causes a transient state which ismanifested by a significant overcurrent. Thisovercurrent is accompanied by a strong voltagefluctuation applied to the load terminalsconnected to the same circuit.

These voltage fluctuations can be detrimental tocorrect operation of sensitive loads (micro-computers, temperature controllers, etc).

c The solutionIt is advisable to separate the power supply forthese sensitive loads from the lighting circuitpower supply.

Fig. 18 : s.i. residual current devices with immunityagainst impulse currents (Merlin Gerin brand).

6.2 Sensitivity of lighting devices to line voltage disturbances

Short interruptions

c The riskDischarge lamps require a relighting time of afew minutes after their power supply has beenswitched off.

c The solutionPartial lighting with instantaneous relighting(incandescent lamps or fluorescent tubes)should be provided if safety requirements sodictate. Its power supply circuit is, depending oncurrent regulations, usually distinct from the mainlighting circuit.

Voltage fluctuations

c The riskThe majority of lighting devices (with theexception of lamps supplied by electronicballasts) are sensitive to rapid fluctuations in thesupply voltage. These fluctuations cause aflicker phenomenon which is unpleasant forusers and may even cause significant problems.

These problems depend on both the frequencyof variations and their magnitude.Standard IEC 61000-2-2 (“compatibility levels forlow-frequency conducted disturbances”)specifies the maximum permissible magnitude ofvoltage variations as a function of the number ofvariations per second or per minute.These voltage fluctuations can be caused byhigh-power fluctuating loads (arc furnaces,welding machines, starting motors) or remotecontrol signals (ie: Pulsadis, at 175 or 188 Hzused by EDF -Electricité de France-).

c The solutionSpecial methods can be used to reduce voltagefluctuations. Nonetheless, it is advisable,wherever possible, to supply lighting circuits viaa separate line supply.

The use of electronic ballasts that can becontrolled at 1-10 V is recommended fordemanding applications (hospitals, clean rooms,inspection rooms, computer rooms, etc).


High line voltage

c The riskA high line voltage is responsible for reducing theservice life of incandescent lamps. This difficulty isencountered in areas where the voltage regulationprovided by the energy distributor is inadequate.

c The solutionDimmers can be used, but are not a commonsolution. The use of compact fluorescent lampsis recommended if the installation allows.

6.3 Choice of light dimmers

Light dimmer technology should be adapted tothe lamp and luminaire technology:c incandescent lamps: dimmer switches withtriac, voltage variation by varying the firing angle,c electronic ballasts with variable voltage: dimmerswitches with triac, voltage variation by varyingthe firing angle (this technology is on the way out),c electronic ballasts that can be controlled by a1-10 V signal,c dimmer switches with automatic matching toELV transformers or electronic converters.

Light dimmers supply the lamps gradually atswitch-on, and thus reduce high inrush currents.Their use therefore avoids any derating of controland protection devices and oversizing ofconductors.

Precautions should still be taken to ensure thereliability of installations and it is especiallynecessary to check that no overload is imposedon electronic devices, for example by using theinformation provided by switchgearmanufacturers (see fig. 19 ).

Fig. 19 : manufacturer data for the selection of light dimmers (Merlin Gerin brand).

Type of lamp Auxiliary switchgear Remote dimmer Variation Maximum Pre-required or dimmer range unit power charging

-Merlin Gerin- (W) deviceLV incandescent TV700 5 to 95% 700or halogen TVe700 500230 V TVo1000 1000

Vo1000 1000ELV halogen Ferromagnetic TVe700 550 PTV112/24 V transformer TVo1000 800

Vo1000 800“Universal” TVe700 650 PTV1electronic transformer TVo1000 800

Vo1000 800“Standard” TVe700 650 PTV1electronic transformer

Standard Ferromagnetic Dimming not possiblefluorescent tube ballast and starter(18, 36 or 58 W) Standard

electronic ballastRemote control TVBo Depend on 1500electronic ballast ballast1-10 V specifications

Compact Electronic ballast Dimming not possiblefluorescent integrated in the lamp

Note:In addition to the limits indicated in this table, a 30% reduction in the permissible power must be allowedfor in the following cases:c switchgear placed in small non-ventilated cabinets or enclosures with a high density of power switchgear(circuit-breakers, contactors, solid state contactors, remote control dimmers, etc)c ambient temperature of the premises likely to exceed 30° C.To reduce the thermal stress on modular electronic devices, we recommend that neighboring equipmentwith significant dissipation kept separate by ventilation modules.


7 Conclusions: technological developments andprofessional requirements

7.1 Developments in luminaires

The main technological developments envisagedare related to energy saving, encouraged bystatutory regulations (European Directive andEnergy Policy Act in the USA). For this reason,new installations are equipped with lamps with astrong light output, whereas old installations areoften subjected to retrofit work.

In these conditions, the use of electronic ballastsis likely to increase, to the detriment of magnetic

ballasts. The major preoccupation ofmanufacturers of luminaires is now to reduceconstraints on energization such as harmoniccurrents, especially for compact fluorescentlamps.

A trend towards reduction or even totalelimination of mercury in lamps can also beobserved.

7.2 Developments in control and protection equipment

The use of light dimmers is more and morecommon. The constraints on ignition aretherefore reduced and derating of control andprotection equipment is less important.New protection devices adapted to the constraintson lighting circuits are being introduced, forexample Merlin Gerin brand circuit-breakers and

modular residual current circuit-breakers withspecial immunity, such as ID switches and s.i.type Vigi circuit-breakers. As control andprotection equipment evolves, some now offerremote control, 24-hour management, lightingcontrol, reduced consumption, etc.

7.3 The necessity for suitable equipment

Manufacturers are subjected to ongoingdevelopments in equipment standards which arenecessary to satisfy all users of electrical lighting.But the quality and continuity of service of a lightinginstallation depends to a large extent on whetherthe right lamp is used with the right switchgear.

This is why certain manufacturers, aware of thedifficulties that all electrical contractors

encounter in choosing luminaires and control andprotection equipment, offer a variety of purpose-designed tools, for example Schneider Electricpublishes selection guides in association withtheir catalogues and this Cahier Technique.

Designers and installers are thus provided withthe means to create lighting circuits which areboth safe during operation and pleasant to use.


Bibliography

“ Product” standards with particularrelevance to lighting equipment

The extensive list of standards below, althoughnot exhaustive, demonstrates the importance ofthis field for the standards authorities.

c IEC 60570: Electrical supply track systems forluminaires.

c IEC 60598: Luminaires.Part 1: General requirements and tests.Part 2: Particular requirements including, forexample, among the 25 sections published or inprogress:Section 1: Fixed general purpose luminaires,Section 2: Recessed luminaires,Section 10: Portable child-appealing luminaires.

c IEC 60669: Switches for household and similarfixed-electrical installations.Part 1: General requirements.Part 2: Particular requirements including:Section 1: Electronic switches,Section 2: Electromagnetic remote-controlswitches (R.C.S.),Section 3: Particular requirements - Time-delayswitches (TDS).

c IEC 60730: Automatic electrical controls forhousehold and similar use.Part 2-3: Particular requirements for thermalprotectors for ballasts for tubular fluorescentlamps.Part 2-7: Particular requirements for timers andtime switches.Part 2-11: Particular requirements for energyregulators.

c IEC 60742: Isolating transformers and safetyisolating transformers. Requirements.

c IEC 60921: Ballasts for tubular fluorescentlamps. Performance requirements.

c IEC 60927: Auxiliaries for lamps - Startingdevices (other than glow starters) - Performancerequirements.

c IEC 60929: A.C. supplied electronic ballastsfor tubular fluorescent lamps - Performancerequirements.

c IEC 60968: Self-ballasted lamps for generallighting services - Safety requirements.

c IEC 60969: Self-ballasted lamps for generallighting services - Performance requirements.

c IEC 61000: Electromagnetic compatibility(EMC).Part 2-2: Environment - Compatibility levels forlow-frequency conducted disturbances andsignaling in public low-voltage power supplysystems.

Part 3-2: Limits - Limits for harmonic currentemissions (equipment input current i 16 A perphase).

c IEC 61347: Lamp controlgearPart 1: General and safety requirements.Part 2: sections 1 to 11: Particular requirementsfor starting devices and the various types ofballast.

“ Product” standards applicable to the mostcommonly used protection devices forlighting circuits

c IEC 61009: Residual current operated circuit-breakers with integral overcurrent protection forhousehold and similar uses (RCBOs).

“ Installation” standards

c IEC 60364: Electrical installations of buildings.

Schneider Electric Cahiers Techniques

c Residual current devices in LV.R. CALVAS, Cahier Technique no. 114.

c Earthing systems in LV.B. LACROIX et R. CALVAS,Cahier Technique no. 172.

c The singularities of the third harmonic.J. SCHONEK, Cahier Technique no. 202.

Internet (http://www.)

c sdv.fr/aimt67/dossier/eclairage.htmlWorkplace lighting: basic concepts. Site for theIntercompany Association of WorkplaceMedecine in the Lower Rhine –AIMT 67-.

c feder-eclairage.frLighting Syndicate site.

c inrs.fr/indexnosdoss.htmlDocuments for designing workplaces.Site for the National Research and SafetyInstitute (INRS).

c For standards:AFNOR http://www.afnor.fr/IEC http://www.iec.ch/home-f.htmCENELEC http://www.cenelec.org/ISO http://www.iso.ch/indexf.htmlUTE http://www.ute-fr.com/

Schneider Electric Direction Scientifique et Technique,Service Communication TechniqueF-38050 Grenoble cedex 9Télécopie : 33 (0)4 76 57 98 60E-mail : [email protected]

DTP: AXESS - Valence (26).Edition : Schneider Electric.- 20 € -

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