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ELECTROMAGNETIC LAMP
5
CONTROL GEAR
BALLASTS
51
11 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 s
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1.3 Ignition and re-ignition 5 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. Th
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1.4 Types of ballasts 5 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. ‘TL’ R + Fig. 103. Schematic diagram of a - fluorescent lamp operated on a resistor ballast in a DC circuit. 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 c
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1.4 Types of ballasts 5 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
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1.5 Ballast specification and marking 5 - rated voltage, capacitance and tolerance of separate series capacitor. In the documentation can be found: - weight, - overall and mounting dimensions, - power factor (l , P.F. or cos j ), - compensating capacitor value and voltage for l = 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’ encapsula
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1.6 Maximum coil temperature t and ΔT 5 w Another value marked on the ballast is the coil temperature rise Δt. 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 Δt 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: Δt = {(R -
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1.7 Watt losses 5 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 58 W ( BTA**L31LW).The 18 and 36 W 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, whil
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2.2 Starter types 5 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. Fig. 106. Working principle of a glow- discharge starter circuit. 1. The heat from th
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2.2 Starter types 5 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, co
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3.1 Components 5 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 fa
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3.2 Capacitors 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 as VDE, 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 m
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3.2 Capacitors 5 Capacitors for lighting applications must have a discharge resistor connected across the terminals to ensure that the capacitor voltage is less than 50 V within 1 minute after switching off the mains power. In special cases the voltage level must be 35 V within 1 second, see IEC 598-8.2.7. Filter coils 33 In some countries, including Belgium, the Netherlands and France, the electric distribution network is used for transmitting messages under responsibility of the local energy
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3.3 Filter coils 5 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 curren
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I sin j l 3.4 Power factor correction 5 V m I V l φ Fig. 111. Lamp current (I ), lamp voltage (V ) l l and mains voltage (V ). m This can be seen in Fig. 111, which is showing the lamp current I , the l lamp voltage V (both in phase with each other) and the sinus form of l the mains voltage V . m 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 + W )/(V .I ) (1) l b m m Without the para
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I cap I sin φ l 3.4 Power factor correction 5 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 I sin j (see Fig. 114). l V V b m I cos φ l φ Fig. 114. Compensated circuit. I V l l Maximum compensation is achieved when the current through the capacitor I = I sin j ; then the power factor is 1.This is purely c l theoretical, as the vector diagram is only valid for the fun
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3.4 Power factor correction 5 L2 C L1 ‘TL’
‘TL’
SS 1 2 Fig. 115. Duo-circuit with the capacitor 0 placed in series with one of the ballasts. 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 230 V supply, the voltage across the capacitor is about 400
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3.4 Power factor correction 5 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. V (V) ballast 1 Z = 165 = 360 Ω ____
1 0,458 2 Z = 150 = 400 Ω ____
1 0,375 3
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3.5 Series connection of lamps 5 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. 36 Neutral interruption and resonance Normally each lamp circuit has its own compensating capacitor. In this way every luminaire can be sw
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3.6 Neutral interruption and resonance 5 I R L L 1 1 I I total R R 1 V 230V 1000
1 1000
N 400V I
R R R R R 2 3 4 5 1000
Fig. 119. The consequences of V 230V 2 250
interrupted neutral in a phase/neutral
each network. L L 2 2 4 I R This makes 1000 + 250 = 1250 Ω. So the current will be 400 / 1250 = 0.32 A. The voltage across R1 will be 0.32 . 1000 = 320 V (V = I . R), so the power in R1 will be 320 . 0.32 = 102 W. The voltage across the four parallel resistors is 0.32 . 250 = 8
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3.6 Neutral interruption and resonance 5 B ‘TL’D S B C ‘TL’D S Fig. 121. Resonance in a star-network. N 37 Electrical diagrams B L V C La 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 N B L V C La V 2) Two lamps, inductive or compensated with electronic or glow-switch starter La ‘TL’, ‘TL’D, PL-L N B L C La 3) One lamp, inductive or compensated without starter PL-S, PL-C, PL-T (starter incorporated) N 126
