Philips Electromagnetic Lamp User manual

Main ballast functions
In chapter 2.1 of this Guide:General aspects,section 2.1:Main ballast
functions,the main functions of ballasts have been described.The term
‘ballasts’ is generally reserved for current limiting devices,including
resistors,choke coils and (autoleak) transformers.Other pieces of
auxiliary equipment are compensating capacitors,filter coils and
starters or ignitors.Some systems use an additional series capacitor
for stabilisation.
With the components summed up,all control functions which are
necessary to operate standard fluorescent lamps can be carried out.
Special arrangements,including sequence start,constant wattage or
dimming circuits will not be described in this Guide,as such circuits
are more and more being replaced by the modern high-frequency
(HF)systems.
Stabilisation
In section 3.2:Stabilisation,the need for current stabilisation in
fluorescent lamps has been described,resulting in the following two
formulae:
Ilamp = (Vmains -Vlamp)
/
Zballast
and: Plamp =Vlamp .Ilamp .αlamp
where Ilamp = the current through the lamp
Vmains = the mains voltage
Vlamp = the voltage across the lamp
Zballast = the impedance of the ballast
Plamp = the power of the lamp
αlamp = a constant called lamp factor
From these formulae it can be concluded that the power of the lamp
(and therefore the light output) is influenced by:
- the lamp voltageVlamp,which in turn is highly dependent on
the operating temperature (see section 5.3.12:Ambient and operating
temperatures) and on the lamp current,according to the negative
lamp characteristic (see section 3.2:Stabilisation).
- the lamp current Ilamp,which is dependent on the mains voltage (see
section 5.3.13:Effects of mains voltage fluctuations),the lamp voltage
and the linearity of the ballast impedance.
In order to avoid undesirable variations in light output as a consequence
of mains voltage fluctuations,the lamp voltage must be not more
than approx.half the value of the mains voltage (100 to 130V) and the
impedance should be as linear as possible.
Ignition and re-ignition
In chapter 3:Lamps,section 3.3:Ignition,the need for ignition of a
fluorescent lamp has been described.
ELECTROMAGNETIC LAMP
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51
13
BALLASTS
12
107
CONTROL GEAR

In the case of electromagnetic control gear,a combination of preheating
and a high ignition peak is obtained by using a normal choke ballast
and a preheat starter or an electronic ignitor.
Energy is supplied to the discharge in the form of electrons.The lamp
current,just like the mains voltage,is sinusoidal,with a frequency of
50 or 60 Hz.If the energy flow is zero (at lamp current reversal) the
lamp stops burning and in theory would have to be re-ignited.
This could be done by supplying additional energy to the electrodes
via a higher lamp voltage,the way it is done when initially starting the
lamp.But from the moment the lamp has reached its stationary
condition,the lamp voltage is constant.
And yet,in practice the lamp does not extinguish at current reversal.
Why not?
The phase shift introduced by the inductive element of the ballast
ensures that the mains voltage is not zero at that moment.Because of
the inductive properties of choke coil ballasts a phase shift ϕoccurs
between the mains voltage and the lamp current (see Fig.102).So,at
the moment of current reversal the lamp voltage would be equal to the
mains voltage,since the voltage over the ballast is nil.The difference
(gap) between the mains voltage and the average lamp voltage as a
consequence of the phase shift ensures proper re-ignition of the lamp
at the moment the current passes the point of reversal (zero-pointA
in figure).
Types of ballasts
1 Resistor ballasts
Current limitation by means of resistor ballasts is a very uneconomic
form of current limitation,because in the resistor electrical energy is
dissipated in the form of heat.Nevertheless,until the advent of
electronic circuitry,use of a series resistor was the only way of stabilising
fluorescent lamps operated on DC,for example the‘TL’R lamp (see
Fig.103).For stable operation on a resistor ballast,it is necessary that
the supply voltage be at least twice the lamp voltage under operating
conditions.This means that 50 per cent of the power will be
dissipated by the ballast.A considerable improvement in efficiency
can,however,be achieved by using a resistor with a very pronounced
positive temperature characteristic (an ordinary or specially
constructed incandescent lamp serves well for this purpose).
A temperature-dependent resistor compensates for variations in the
lamp current resulting from variations in the mains voltage,which means
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5
108
Fig. 102. Phase shift between supply voltage
and lamp current (and lamp voltage) in a
discharge lamp with an inductive ballast. In
the case shown, the supply voltage is
sufficiently high for re-igniting the lamp after
every current reversal.
1.3 Ignition and re-ignition
V, A
t
A
VmIlVl
gap
ϕ

that the no-load voltage need be no more than 25 to 30 per cent
higher than the lamp voltage.This is also the proportion of the power
dissipated by the ballast compared to the total circuit power.
2 Capacitor ballasts
A capacitor used as a ballast causes only very little losses,but cannot
be used by itself,as this would give rise to very high peaks in the lamp
current wave form at each half cycle.Only at very high frequencies
can a capacitor serve satisfactorily as a ballast.
3 Inductive ballasts or chokes
Choke coils are frequently used as current limiting devices in
gas-discharge lamp circuits (see Fig.104).They cause somewhat higher
losses than a capacitor,but produce far less distortion in the lamp
current at 50 Hz.Moreover,in combination with a switch starter,they
can be made to produce the high voltage pulse needed to ignite the
lamp.
In practice,a choke ballast consists of a large number of windings of
copper wire on a laminated iron core.It operates on the self-inductance
principle.The impedance of such a ballast must be chosen in
accordance with the mains supply voltage and frequency,the lamp type
and the voltage of the lamp,to ensure that the lamp current is at the
correct value.In other words:each type of lamp requires for each supply
voltage its own choke as a ballast with a specific impedance setting.
Heat losses,occurring through the ohmic resistance of the windings
and hysteresis in the core,much depend upon the mechanical
construction of the ballast and the diameter of the copper wire.
The right ballast for a given lamp and supply voltage should be chosen
by consulting documentation and/or ballast markings.
The Philips standard range of ballasts is for supply voltages of
220/230/240V and for frequencies of 50/60 Hz.
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109
Fig. 103. Schematic diagram of a
fluorescent lamp operated on a resistor
ballast in a DC circuit.
Fig. 104. Schematic diagram of a
fluorescent lamp operated on a choke
ballast in an AC starter circuit.
1.4 Types of ballasts
+
-
‘TL’ R
I b
Il
La
BVl
Vm
+
-
+-+-
0
S

The most important value for stabilisation is the ballast impedance.It
is expressed as voltage/current ratio in ohm (Ω) and defined for a
certain mains voltage,mains frequency and calibration current (normally
the nominal lamp current).
Chokes can be used for virtually all discharge lamps,provided that
one condition is fulfilled:the mains voltage should be about twice the
arc voltage of the lamp.If the mains voltage is too low,another type
of circuit should be used,like the autoleak or constant-wattage circuits.
The advantages of a choke coil are:
- the wattage losses are low in comparison to those of a resistor,
- it is a simple circuit:the ballast is connected in series with the lamp.
Disadvantages of a choke coil are:
- the current in a lamp with choke circuit exhibits a phase shift with
respect to the applied voltage,the current lagging behind the voltage
(see also section 5.3.4:Power factor correction).
- a high starting current:in inductive circuits the starting current is
about 1.5 times the rated current.
- sensitivity to mains voltage fluctuations:variations in the mains
voltage cause variations in the current through the lamp.
Ballast specification and marking
There are two ways of selecting the right ballast for a certain lamp
and/or to compare various ballasts:
1) the ballast marking,
2) the manufacturer’s documentation.
As all ballasts have to comply with the norm IEC 920/921 some data
has to be marked on the ballast and other data can be mentioned in
the documentation.
On the ballast can be found:
- marks of origin,such as the manufacturer’s name or trade mark,
model or reference number,country of origin,production date code,
- rated supply voltage and frequency,nominal ballast current(s),
- type(s) of lamp with rated wattage,
- type(s) of ignitor with wiring diagram and peak voltage if this
exceeds 1500V,
- twand ∆t (see section 5.1.6),
- max.cross-section of mains or lamp cable;e.g.4 means 4 mm2,
- symbols of the officially recognised certification institutes,such as
VDE,SEMKO,SEV,KEMA,if applicable;CE marking for safety,
- in case of an independent ballast:the symbol ;an independent
ballast is a ballast which is intended to be mounted separately outside
a luminaire and without any additional enclosure,
- a symbol like top if there are mounting restrictions,
- F-marking if the ballast fulfils the IEC F-requirements;that means
it is suitable to be mounted directly on normally flammable surfaces,
-TS,P-marking or if the ballast is thermally protected
(* = thermo-switch temperature in degrees Celsius),
- indication of terminals:L for single phase,N for neutral, for
protective earth (PE), for functional earth,
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110
1.4 Types of ballasts

- rated voltage,capacitance and tolerance of separate series capacitor.
In the documentation can be found:
- weight,
- overall and mounting dimensions,
- power factor (λ,P.F.or cos ϕ),
- compensating capacitor value and voltage for λ= 0.85 or 0.9,
- mains current nominal and during running-up,both with and
without power factor correction,
- watt losses (normally in cold condition),
- description of version,e.g.open impregnated,‘plastic’ encapsulated,
potted or compound filled.
This information suffices to find the right ballast for a certain
application.Additional information can be obtained on request or can
be found in special application notes.Philips ballasts are designed for
use with IEC standardised fluorescent lamps.
Maximum coil temperature twand ∆T
A ballast,like most electrical components,generates heat due to its
ohmic resistance and magnetic losses.Each component has a
maximum temperature which may not be exceeded.For ballasts it is
the temperature of the choke coil during operation that is important.
The maximum permissible coil temperature twis marked on the
ballast.Coil insulating material,in combination with lacquer,
encapsulation material etc.,is so chosen that below that temperature
the life specified for the ballast is achieved.A twvalue of 130 ºC is usual
nowadays with a coil insulating class F (150 ºC) or class H (180 ºC).
Under standard conditions,an average ballast life of ten years may be
expected in the case of continuous operation at a coil temperature of
twºC.As a rule of thumb,a 10 ºC temperature rise above the twvalue
will halve its expected life (see Fig.105).If,for instance,the operating
temperature is 20 ºC above the twvalue,one may expect a ballast life
of 2.5 years of continuous operation.If no twvalue is marked on the
ballast,a maximum of 105 ºC is assumed for the coil temperature.
As the ballast normally does not function continuously,the actual life
of the ballast can be very long.It also takes some hours before the
thermal equilibrium is reached in the ballast,which again increases the
practical ballast lifetime.
To verify the twmarking,accelerated lifetime tests are done at ballast
temperatures above 200 ºC for 30 or 60 days.
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111
Fig. 105.The nominal life of choke coils
in relation to the permitted rated
maximum operating temperature of a
ballast winding tw, dependent on
insulation material:
a) class A: tw105 ºC,
b) class E: tw120 ºC,
c) class F or H: tw130 ºC.
1.5 Ballast specification and marking
250
200
150
100
0,1
1,0
10
temp. (°C)
t (years)
(c)
(b)
(a)
16

Another value marked on the ballast is the coil temperature rise ∆t.
This is the difference between the absolute coil temperature and the
ambient temperature in standard conditions and is measured by a
method specified in IEC Publ.920 (EN 60920).Common values for ∆t
are from 50 to 70 degrees in steps of 5 degrees.
The coil temperature rise is measured by measuring the ohmic
resistance of the cold and warm copper coil and using the formula:
∆t = {(R2- R1)/R1} .(234.5 + t1) - (t2- t1)
or: tc= R2/R1 .(t1+ 234.5) - 234.5 (IEC 598-1Appendix E)
where R1= initial cold coil resistance in ohm
R2= warm coil resistance in ohm
t2= ambient temperature at measuring R2in Celsius
t1= initial ambient temperature at measuring R1in Celsius
tc= calculated warm coil temperature in Celsius
∆t=t
c
- t2in Kelvin
The value 234.5 applies to copper wire;in case of aluminium
wire,the value 229 should be used.
So a ballast marked with tw130 and ∆t 70,will have the specified 10
years average life in continuous operation at standard conditions at an
ambient temperature of 130 - 70 = 60 ºC.When the ambient
temperature around the ballast is higher,a shorter ballast life has to
be accepted or sufficient air circulation or cooling has to be applied.
The so-called ambient temperature mentioned in this chapter is not
the room or outside temperature,but the temperature of the micro-
environment of the ballast.Built into a luminaire or ballast box the air
temperature around the ballast is higher than the outside ambient
temperature.This higher temperature has to be added to the coil
temperature rise ∆t to find the absolute coil temperature:tc= t2+ ∆t.
Additionally,a third temperature figure can be mentioned on the ballast:
the ballast temperature rise in abnormal conditions,again measured
according to specifications like EN 60920.In short:it is the winding
temperature rise at 110 per cent mains voltage when the glow-switch
starter,belonging to the system,is short-circuited.
The marking of the three temperature markings should be :
∆t ** / *** / tw*** with * = figure
Example:∆t 70 / 140 / tw130.
Watt losses
Ballast losses normally are published as‘cold’ values,meaning that the
ballast is not energised or only very shortly before and the ballast
winding is at ambient temperature (25 ºC).In practice the ballast will
reach more or less the marked ∆t value and then the copper resistance
is approx.25 per cent higher than in the‘cold’ situation.Therefore the
‘warm’ losses in practice will be 10 - 30 per cent higher than the
published values.
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1.6 Maximum coil temperature twand ∆T

As in some applications the power consumption is of prime importance,
there are low-loss ballasts for the major lamp types‘TL’D 18,36 and
58W ( BTA**L31LW).The 18 and 36W LW ballasts are bigger than the
standard types,resulting in lower ballast temperatures and 25 to
30 per cent less ballast watt losses.Due to practical restrictions the
BTA 58L31LW type could not be made bigger.The 15 per cent lower
ballast losses are the result of a better iron lamination quality,while
the ballast temperatures are only slightly lower than those of the
standard types.
Main starter function
Fluorescent lamps do not ignite at mains voltage.To ignite the lamps,a
starter is applied to preheat the lamp electrodes and to give a peak
voltage high enough to initiate the discharge.
So in fact there is only one basic function for a starter:to deliver the
ignition voltage to start the discharge in a fluorescent lamp in a proper
way.After ignition the starter has to stop producing ignition peaks.This
can be obtained by sensing the lamp voltage or lamp current and/or
by a timer function.
Starter types
There are two types of fluorescent lamp starters:
1 Glow-switch starters
The glow-switch starter consists of one or two bimetallic electrodes
enclosed in a glass container filled with noble gas.The starter is
connected parallel across the lamp in such a way that the preheat
current can run through the lamp electrodes when the starter is closed
(Fig.106).At the moment of switching on the mains voltage, the total
mains voltage is across the open glow-switch starter.This results in a
glow discharge starting between the bimetallic electrodes of the
starter.The glow discharge causes a temperature increase in these
bimetallic electrodes,resulting in the closure of the electrodes of the
starter.During this closure the lamp electrodes are preheated by the
short-circuit current of the ballast.After closure the temperature of
the starter electrodes decreases and the starter re-opens.At the
moment of re-opening,the current through the ballast is interrupted,
causing a peak voltage over the lamp electrodes high enough for lamp
ignition.This peak voltage depends on the inductance of the choke,
the level of the short- circuit current and the speed of the opening of
the glow-switch electrodes.In formula:
Peak voltage:Vpeak = L dI/dt
The minimum specified peak voltage depends on the type and is between
800 and 900V.
If the lamp electrodes are not yet hot enough or the peak voltage is
not high enough,the glow-switch starter will resume the whole
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STARTERS
22
113
1.7 Watt losses

starting process again until the lamp ignites.If the lamp will not ignite
(end of life) the starter will continue producing peaks (flickering) until
the mains voltage is switched off or until the electrodes of the glow-
switch starter stick together.In the latter case the short-circuit
current is continuously running through the lamp electrodes,which
can be seen at the glowing lamp ends.
Once the lamp is properly ignited,the lamp voltage is too low for a
glow discharge between the starter electrodes.So these electrodes
stay‘cool’ and in open position.
A capacitor across the starter electrodes prevents radio-interference
of the lamp.
There are five types of glow-switch starters,specified for a certain mains
voltage and/or lamp wattage ( S2-10-11-12-16).There are also resettable
glow-switch starters:SiS2,Si S3 and SiS10.These starters switch off
after a certaintime in case the lamps do not ignite and have to be
reset manually by a push button.Switching the mains supply does not
reactivate a switched-off resettable starter.
5
114
Fig. 106.Working principle of a glow-
discharge starter circuit.
1.The heat from the discharge in the
starter bulb causes the bimetallic
electrodes to bend together.
2.When the bimetallic electrodes make
contact, a current starts to flow through
the circuit, sufficient for preheating the
electrodes of the fluorescent lamp.
3.The bimetallic electrodes cool down
and open again, causing a voltage peak,
which ignites the fluorescent lamp.
2.2 Starter types
0
0
0

2 Electronic starters
In principle the electronic starter or ignitor is working in the same
manner as the glow-switch starter.But now the switching does not
come from bi-metallic electrodes,but from a triac.
The electronic circuit in the starter gives a well-defined preheat time
(1.7 sec) for the lamp electrodes and,after the preheat,a well-defined
peak voltage,which ensures optimum lamp ignition.The heart of the
electronic starter is a customized integrated circuit,containing the
intelligence of the product.It makes the starter switch off after seven
unsuccessful ignition attempts,so it is called‘flicker free’.
The electronic starter also contains an over-heating detection by
means of a PTC resistor,to switch off in case the starter becomes
too hot (e.g.with a short-circuited ballast).This second stop function
resets after approx.4 minutes.
The electronic starter extends the lamp lifetime up to 25 per cent on
account of the well-defined preheat time.The exact digital timing makes
the electronic starter independent of mains voltage fluctuations.
In the Philips programme there are two types of electronic starters:
one in the canister of the glow-switch starters (two-pin types S2-E and
S10-E Perform version),and one in a plastic housing (four-pin type ES08).
Lifetime
The lifetime of fluorescent lamp starters is expressed in the number
of switches.
At present the glow-switch starters have a lifetime of 10 000 switches
or more,while the electronic starters have a lifetime of 100 000 switches
or more.
Components
A customer primarily needs a solution to his lighting requirements.
Basically,he needs two things to obtain an installation which completely
fulfils his specifications:a design and components.To make sure that
the installation works properly under all circumstances,the right
components must be chosen and selected in combination with each
other.
In principle the following components are required in a lighting
installation:
- lamps,
- lampholders,
- luminaires,
- gear (ballasts,starters),
- compensating capacitors,
- cabling,
- fusing and switching devices,
- filter coils (if necessary),
- dimming equipment (if possible and required).
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53
SYSTEMS
115
2.2 Starter types

Information about lamps can be found in the lamp documentation,
where also the type of lampholder or lamp cap is mentioned.Be sure
to use the appropriate lampholder,as there are many different types.
Lamp types with different wattage are in principle not interchangeable
in a certain circuit,even though they may have the same lamp cap and
do fit in the same lampholder.
In some lamp types the glow-switch starter is incorporated in the
lamp base (2-pin version PL).In the SL family the total electric circuit
is incorporated with the lamp in the outer shell (see Fig.107).
In the luminaire documentation,information can be found on which
lamp types can be used.When installing other than specified types,
electrical,thermal or lighting problems will arise.In the luminaire
documentation it can also be found if the gear is incorporated in the
luminaire and what the cable entries and connections are.
In the gear documentation,information can be found about the
electrical terminals and the electrical diagrams.Also the value and the
voltage range of capacitors is mentioned here.
The remaining system-related components and subjects mentioned
above will be described in the following sections.
Capacitors
Two types of capacitors are possible in fluorescent lamp circuits.One
type is the parallel compensating capacitor for power factor
improvement,connected across the mains.The second type is the series
capacitor which also determines the lamp current.
Series capacitors are used in capacitive or duo circuits.
In installations with fluorescent lamps of more than 25W,capacitors
are necessary for power factor correction,as the power factor of an
inductively stabilised circuit is only approx.0.5.Power factor
compensating capacitors are connected across the mains supply voltage
(parallel compensation) between phase and neutral (220/240V).
In the relevant ballast documentation figures can be found for the
capacitor value in microfarad (µF) for a certain combination of lamp
and supply voltage to achieve a power factor of ≥0.9.
Every user can in fact create his own solution for obtaining the necessary
capacitance.
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Fig. 107.The circuit of an SL lamp
consists of the following components:
1. Discharge tube,
2. Starter,
3. Capacitor,
4. Ballast,
5.Thermal protector.
3.1 Components
L
N
mains 
supply
1
3
2
4
5

To do things well,some aspects have to be considered:
- First of all,capacitors for discharge lamp circuits have to fulfil the
requirements as specified in IEC publications 1048 and 1049.The use
of PCB (chlorinated biphenyl) is forbidden.
- It is recommended that capacitors which have some approval marks,
such asVDE,KEMA,DEMKO or ENEC be used.
- Normally every lamp circuit is compensated by its own capacitance.
Only in some special cases group or central compensation for more
lamp circuits can be a better solution.
- In case of failure of the parallel capacitor (open or short-circuited)
the lamp behaviour is not affected.Regular control of the mains
currents and/or power factor (λor cos ϕ) is advisable.
- In case of failure of the series capacitor the lamp behaviour is
immediately affected.This type of capacitor must create an open circuit
in case of failure,so that the lamp will be extinguished.
-The lifetime of capacitors depends on the capacitor voltage and
capacitor case temperature.Therefore capacitors with the correct
voltage marking (parallel 250V with a maximum capacitance
tolerance of +/- 10% or series 450V with a maximum capacitance
tolerance of +/- 4 %) and within the specified temperature range
(normally - 25 ºC to + 85 or 100 ºC) should be used.
Used within the specifications,capacitors with theVDE marking will
have a lifetime equal to that of ballasts:30 000 hours or 10 years.
- If a specified parallel capacitance value occasionally is not available,
the next higher value can be used,provided that the value is not more
than 20 per cent above specification.
Two general types of capacitors are currently in use:the wet and the
dry type.
Wet capacitors available today contain a non-PCB oil and are equipped
with internal interrupters to prevent can rupture and resultant oil
leakage in the event of failure.So a clearance of at least 15 mm above
the terminals has to be provided to allow for expansion of the capacitor.
In case of failure,these capacitors will result in an apparent open circuit,
which means the mains current drawn by the circuit approximately
doubles in case of a parallel capacitor.This can cause a fuse to blow,a
circuit breaker to open,but will have no further detrimental effect.
Used as a series capacitor,the open circuit of the failing capacitor will
extinguish the lamp.
Dry,metallised-film capacitors are relatively new to the lighting industry
and are not yet available in all ratings for all applications.However,
they are rapidly gaining popularity because of their compact size and
extreme ease of installation and are,therefore,widely used nowadays.
During its lifetime this type of capacitor gradually loses its capacitance,
resulting in a gradually increasing mains current when used as a
parallel capacitor.In the end the capacitor acts like an open circuit.
For the series capacitor a capacitance loss of only 5% during its
lifetime can be accepted,so the dry capacitor is not recommended
for series applications.
Dry capacitors are more sensitive to voltage peaks than wet capacitors.
In critical applications (mains supply containing peaks,frequent
switching,high level of humidity or condensation) the wet capacitor is
advisable.
5
117
3.2 Capacitors

Capacitors for lighting applications must have a discharge resistor
connected across the terminals to ensure that the capacitor voltage is
less than 50V within 1 minute after switching off the mains power.In
special cases the voltage level must be 35V within 1 second,see
IEC 598-8.2.7.
Filter coils
In some countries,including Belgium,the Netherlands and France,the
electric distribution network is used for transmitting messages under
responsibility of the local energy supply authority.
Signals are sent over the electricity supply network for a number of
purposes:to switch road lighting,to call up fire brigades and the
police,to switch night-tariff kWh-meters,and so on.It is important,
therefore,that this signalling system is not disturbed,which may occur
when parallel power factor correction capacitors for lamp circuits are
employed.Capacitors present a low reactance to the 200-1600 Hz
signals employed for signalling,with the result that these are in danger
of being short-circuited in a capacitive circuit.To avoid this,a coil must
be connected in series with the capacitor connected parallel to the
mains.This filter coil,as it is termed,presents a reactance that
increases with rising signal frequency.The coil reactance is therefore
chosen such as to balance out the reactance of the capacitor at 200 Hz
(the resonance frequency,see Fig.108).
For currents with a frequency of 50 Hz the circuit is predominantly
capacitive,which is necessary for power factor correction.Above 200 Hz
the circuit becomes predominantly inductive,which is necessary for
the blocking of audio-frequency signals.At 200 Hz the impedance is
only formed by the ohmic resistance,mainly of the filter coil.
As can be seen from the graph,the filter coil is effective for audio signals
of 300 Hz and higher,because then the impedance of the coil/capacitor
combination is higher than the impedance of the sole capacitor.Filter
coils should not be used when the audio signals are 300 HZ or lower.
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Fig. 108. Impedance of a filter coil, a
capacitor and a coil/capacitor
combination as a function of frequency.
3.2 Capacitors
impedance (Z)
frequency(Hz)
capacitive inductive
2
468102
2
468103
101
2
468
102
2
468
103
2
4
68
104
101
impedance of filtercoil
Z = ωL
impedance of coil
and capacitor
Z =
|
ωL -1
|
impedance of capacitor
Z = 1
___
ωC
___
ωC


There are other advantages to be gained from employing filter coils.
The parallel capacitor can cause troublesome switching phenomena
to occur,which can give rise to very large current surges.Although
these surges are of only very short duration (a few milliseconds),they
are nevertheless sufficient to cause switching relays to stick or circuit
breakers to switch off.The filter coil serves to prevent this problem
by damping the very short,high amplitude pulses in the current.
The type of filter coil needed depends on the capacitance of the
capacitor employed.So,in fact every capacitor needs its own filter coil.
But in some cases it is possible to group the capacitors and match
them with the corresponding filter coil.For example:two capacitors
of 4 µF parallel can be connected in series with one filter coil for 8 µF
(see Fig.109).
Also central filter coil systems exist where a filter system in the supply
system is blocking the applied signalling frequencies.
Although the voltage across the filter coils is rather low (approx.14 to
20V),the filter coils have to be regarded as ballasts,as they are directly
connected to the mains.They also cause some additional watt losses.
The amount of third and fifth harmonics in the mains current will rise
in cases where the mains supply voltage is disturbed with third or fifth
harmonics,when applying a filter coil.The total impedance for the
combination of capacitor and filter coil is lower than the impedance
of the sole capacitor for these frequencies (see section 5.3.9:Harmonic
distortion and Fig.108).
Power factor correction
Circuits with gas-discharge lamps are stabilised with inductive ballasts
and compensated for a good power factor with a parallel compensating
capacitor (mono-compensation,Fig.110).
Without the capacitor the inductive ballast causes a phase shift of the
current,which is lagging behind the applied voltage.
34
5
119
Fig. 109. Different ways of grouping
capacitors to match them with the
corresponding filter coil.
Fig. 110. Power factor correction with a
parallel compensating capacitor.
3.3 Filter coils
L
N
L
N
2 x 4 µF 
coils
2 x 4 µF 
capacitors =1 x 8 µF 
filter coil
4 x 4 µF 
capacitors
B
CLa
L
N

This can be seen in Fig.111,which is showing the lamp current Il,the
lamp voltageVl(both in phase with each other) and the sinus form of
the mains voltageVm.
The power factor of the circuit can be calculated by dividing the total
wattage by the product of mains voltage and current.In formula:
P.F. = (W l+Wb)/(Vm.Im) (1)
Without the parallel compensating capacitor the power factor of a
gas-discharge circuit is approx.0.5.
For the fundamentals of the voltages and current a so-called vector
diagram can be made (see Fig.112).Lamp voltage and lamp current
are in phase and the voltage across the ballast is leading 90 electrical
degrees to the current.The vectorial sum of lamp voltage and ballast
voltage gives the mains voltage.Now we see that cos ϕ=Vl/Vm,which
is less accurate than (1).
In any case the energy supply authority has to deliver an apparent
power ofVm.Ilto the system on which the distribution network must
be based (cabling,transformers).
The energy meter only records the in-phase componentVm.Ilcos ϕ,
so the supply authority does not get paid for the so-called‘blind’ part:
Ilsin ϕ.Vm(Fig.113).
For this reason,the supply authority demands compensation of the
phase shift.
Where in general the‘unadjusted’ power factor is about 0.50,it has to
be compensated to a minimum of 0.85 or even 0.90.This is achieved
by adding a capacitor across the mains.In contrast to an inductive
5
120
Fig. 111. Lamp current (Il), lamp voltage (Vl)
and mains voltage (Vm).
Fig. 112. Example of a vector diagram
showing lamp voltage and lamp current in
phase.
Fig. 113. Uncompensated circuit with lamp
current and mains voltage out of phase.
3.4 Power factor correction
Vm
Vl
I
ϕ
Vb
1.1 Vm
Vm
0.9 Vm
Vl Il
ϕ
VbVm
Vl Il
I
l
sin j
Il cos ϕ
ϕ

ballast,the capacitor current is leading 90 electrical degrees to the
capacitor voltage (which is the mains voltage).So the capacitor
current has the opposite direction of Ilsin ϕ(see Fig.114).
Maximum compensation is achieved when the current through the
capacitor Ic= Ilsin ϕ;then the power factor is 1.This is purely
theoretical,as the vector diagram is only valid for the fundamentals of
the currents.Due to distortion in the lamp current (see section 5.3.9:
Harmonic distortion),the maximum practical power factor is
between 0.95 and 0.98.This explains the difference between power
factor and cos ϕ.
The power factor is the result of the quotient of the actual wattage
and the product of mains voltage and mains current,including the
harmonics,and can be calculated as follows:
Power factor (P.F.) = total wattage/mains voltage .mains current
The angle ϕis the phase shift angle between mains voltage and mains
current and can be found and calculated by means of the vector
diagram.This is only valid for the fundamentals and does not take into
account the harmonics.
The same analogy is valid for the lamp:there is practically no phase
shift between lamp voltage and lamp current:both are zero at the
same time.So the phase angle αis zero and cos α= 1.
The product of lamp voltage and lamp current does not equal the
lamp wattage;the difference is called lamp factor:
Lamp factor = lamp wattage / lamp voltage .lamp current
and has a value between 0.8 and 0.9.For the same lamp type the lamp
factor is higher for higher wattages,identical to the lamp efficacy.
Typical capacitor values for this parallel compensation (also sometimes
called mono-compensation) for a 50 Hz mains are 4.5 µF for a 36 or
40W fluorescent lamp and 6.5 µF for a 58 or 65W lamp.
A second method for compensation is the so-called duo-circuit.This is
employed for pairs of lamps,as for example in two-lamp luminaires.Here
the capacitor is placed in series with one of the ballasts (see Fig.115).
5
121
Fig. 114. Compensated circuit.
3.4 Power factor correction
VbVm
Vl Il
I
l
sin ϕ
I
cap
Il cos ϕ
ϕ

The series capacitor has an impedance which is twice the normal
ballast impedance,resulting in a power factor of approx.0.5 capacitive
for one branch.Together with the power factor of 0.5 inductive for the
other branch,the total power factor of the two branches is approx.0.95.
With a normal 230V supply,the voltage across the capacitor is about
400V.To fulfil all relevant requirements,the tolerance on the capacitor
capacitance value has to be within +/- 4 %.The nominal value of the
capacitance is depending on the mains supply voltage,the applied
ballast impedance and the lamp wattage.Typical values are 3.4 µF for a
36W and 5.3 µF for a 58W lamp.
Compared with the mono-compensation the advantages of this way
of compensation are:
- only one capacitor is required for two lamps,instead of two,
- the capacitive branch is less sensitive to supply voltage deviations,as
it has a constant current characteristic,
- in case of actadis signals (see section 5.3.3:Filter coils) these signals
are not influenced,so no filter coil is needed.
Disadvantages of duo-compensation are:
- series capacitors are more expensive than parallel capacitors,
- the lamp power and so the light output from the capacitive branch
is slightly higher than that from the inductive branch.
In some countries,practically all multi-lamp luminaires have built-in
duo-circuits for each pair of lamps (also called a‘dual-lamp’ or‘lead-lag’
circuit).Mono-compensation,on the other hand,is generally left to
the installer,although there are also single-lamp luminaires available
with the compensation built in.
The capacitive circuit has a so-called‘constant current characteristic’.
This can be explained by the non-linearity of the inductive ballast.
Suppose that the impedance of the ballast is 400 Ω,which varies,say
10 per cent when the ballast voltage changes 10 per cent (see Fig.116).
With the inductive ballast the resulting (lamp) current at 90 per cent
mains voltage will be lower:
A:as result of the lower mains voltage,
B:as result of the higher impedance.
With the capacitive ballast combination,the resulting impedance of
inductive ballast and capacitor is reacting in just the opposite way:at
lower mains voltage the total impedance is also lower.This results in
a nearly constant current.
5
122
Fig. 115. Duo-circuit with the capacitor
placed in series with one of the ballasts.
3.4 Power factor correction
0
‘TL’
1‘TL’ 2
SS
L2
L1
C

Mains voltage 90 % 100 % 110 %
Circuit Ind. Cap. Ind. Cap. Ind. Cap.
Z ballast (Ω) 440 440 400 400 360 360
Z capacitor (Ω) 800 800 800
Z result (Ω) 440 360 400 400 360 440
Therefore the behaviour of the inductive and capacitive branch of a
duo-circuit is different at mains voltage deviations and deviations of the
ambient temperature.This can be seen rather well in a duo-luminaire.
Series connection of lamps
Under certain conditions it is possible to operate two lamps in series
on a common ballast (see Fig.117).A prerequisite for such operation
is that the sum of the operating voltages of the lamps is not higher
than approximately 60 per cent of the supply voltage.This means that
two lamps,each with an arc voltage of no more than 65 volt,can be
connected in series via a common ballast to the 220/240V mains.This
restricts the maximum lamp length to 600 mm (2 ft),or the lamp
power to 18/20W (26 or 38 mm diameter lamps only).
The series circuit can be compensated in the normal way by using a
parallel or series capacitor.
35
5
123
Fig. 116.Voltage/current characteristic
of an inductive ballast (example).
Fig. 117.Tandem circuit with two lamps
in series on a common ballast.
3.4 Power factor correction
180 180 180 180 180 180 180 180 180 180
180
160
140
120
100
80
60
40
20
100
200 300
400
500 600 700 800 900
1000
Z1= 165 = 360 Ω
Z1= 150 = 400 Ω
Z1= 135 = 440 Ω
____
0,458
____
0,375
____
0,307
1
2
3
V ballast (V)
I ballast (mA)
0


‘TL’1
‘TL’2
S
S

Parallel connection of two lamps on a common ballast is impossible
because of the negative characteristic of the fluorescent lamp.All the
current would flow through the lamp with the lower arc voltage.
Moreover,once the first lamp is ignited the lamp voltage is too low for
the ignitor of the second lamp to ignite this lamp.
Neutral interruption and resonance
Normally each lamp circuit has its own compensating capacitor.In this
way every luminaire can be switched separately without influencing the
power factor.For the same reason lamp circuits based on phase-neutral
(230V),are compensated with capacitors connected between each of
the phases and neutral.
In the phase-neutral network failure of one phase has no other effect
than to switch off the circuits on that phase.But if the neutral is not
connected,resonance will occur.For example,the current from phase
L1 via ballast and lamp 3 (see Fig.118) can pass via capacitor C1 to
phase L3.So lamp 3 is energised by 400V and stabilised by a ballast
with a capacitor in series.This will surely destroy components.
A good neutral is essential.
Moreover,when the neutral is interrupted and the loads on the phases
are not completely balanced ( i.e.the same wattage),then the voltage
across the smallest load will increase and much more power will be
consumed by that load.This will surely damage lamps and/or ballasts
(see Fig.119).
Suppose there are five loads of 1000 Ω,one connected between L1
and neutral and four connected between L2 and neutral.The current
from L1 will be 230/1000 = 0.23A and the power in the load will be
230 .0.23 = 53W.
The current from L2 will be four times higher (0.92A) and the power
too:212W.
If the neutral is interrupted,the phase-phase voltage of 400V will result
in a current which can be calculated from the resistances:1000 Ωin
series with 4 times 1000 Ωparallel.
36
5
124
Fig. 118. Compensation in a
phase/neutral network.
3.5 Series connection of lamps
La
LaLa
B
B
B
N
123
C3 C2 C1
L1
L2
L3

This makes 1000 + 250 = 1250 Ω.So the current will be 400 / 1250 =
0.32A.
The voltage across R1 will be 0.32 .1000 = 320V (V = I .R),so the
power in R1 will be 320 .0.32 = 102W.
The voltage across the four parallel resistors is 0.32 .250 = 80V,so the
power in each resistor is 80 .0.08 = 6.4W.
Now it is seen that the smaller load (R1) is overloaded by a higher
voltage (320 instead of 230V) and a higher current (0.32A instead of
0.23A).The higher load (R2 to R5) is greatly underloaded.
In practice the circuits are not that simple,but the essential aspect is
that in case of a floating neutral the smallest load will receive a higher
voltage and a higher current and so will be overloaded.
A second possibility of resonance has to do with the employment of
inductive and capacitive circuits in the same installation.In the capacitive
circuit,the impedance of the capacitor is twice the impedance of the
inductive ballast.So when an inductive and a capacitive circuit get in
series,the total impedance will be zero,resulting in an unlimited current
(resonance).This can happen in a delta-network when one phase is
interrupted (Fig.120) or in a star-network with common neutral when
the neutral is interrupted (Fig.121).
Resonance problems can be prevented with special switch gear.If the
neutral in a star-network or a phase in the delta-network fails,such
special gear switches off the overall supply for the lighting installation.
5
125
Fig. 119.The consequences of
interrupted neutral in a phase/neutral
network.
Fig. 120. Resonance in a delta-network.
3.6 Neutral interruption and resonance
L1
L2
Itotal
1000 
250 

400V
V1
V2
L1
N
L2
IR
IR
4 IR
IR
1000 

1000 

each
230V
230V
R1
R2R3R4R5
B
B
‘TL’D
‘TL’D
C
S
S

N
S
S
B
B
‘TL’D
‘TL’D
C
B
C
L
N
La V
B
C
L
NLa
La
V
V
B
CLa
L
N
37
5
126
3.6 Neutral interruption and resonance
Electrical diagrams
Fig. 121. Resonance in a star-network.
1) One lamp, inductive or compensated
with electronic or glow-switch starter
‘TL’,‘TL’D,‘TL’E,‘TL’U, PL-L, PL-T,
PL-T(S)(C) 4-pins
2)Two lamps, inductive or compensated
with electronic or glow-switch starter
‘TL’,‘TL’D, PL-L
3) One lamp, inductive or compensated
without starter
PL-S, PL-C, PL-T (starter incorporated)