4.1.3 Superimposed ignitor. Osram HQI-E 150 W/NDL CL
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4.1.3 Superimposed ignitor choke
Superimposed ignition unit
U
S
Capacitor for
PFC
Luminaire
Lamp
Fig. 21: Simplified circuit diagram for conventional operation of high intensity discharge lamps with a superimposed ignition unit with symmetrical and asymmetrical ignition pulses. In the asymmetrical units, care must be paid to correct polarity of the lamp connections!
At present, hot re-ignition is permitted for doubleended quartz lamps (with a few exceptions). As far as ceramic lamps are concerned, the single-ended
HCI ® -TM series with GY22 socket are approved for hot re-ignition. Approval of other double-ended ceramic lamps is in preparation.
4.4 Ignition at low ignition voltage (Penning effect)
In a superimposed ignition unit, the high voltage is only present at the lamp outputs of the unit. Depending on cable and structure, ignition units of this type can normally take loads of 100 pF, corresponding to a lead length of about 1.5 m.
4.2 Warm re-ignition
Normal ignition voltages in the range up to 5 kV do not permit immediate re-ignition of a lamp which is still hot. The high operating pressures demand ignition voltages of e.g. 25 kV. If a lamp goes out for instance because of a brief interruption in the supply voltage, it must cool down for a few minutes (for lamp wattages
< 150 W) until the falling pressure in the arc tube permits re-ignition for normal ignition units in the 5kV range. Higher wattage levels require considerably longer cooling down periods because of the higher thermal capacity. The cooling down process depends also on the ambient temperature and the luminaire. A narrow, hot luminaire prolongs the cooling down procedure, delaying re-ignition of the lamp.
Various methods can be used to reduce the voltage necessary to ignite the lamp. One such method uses the so-called Penning effect. When the energy stored in a meta-stable excitation level of the basic gas is larger than the ionization energy of the admixture, volume ionization begins at lower field strengths, resulting in a larger number of charge carriers at the same voltage than in pure gas. Examples for the Penning effect include mercury in argon for metal halide lamps and argon in neon for some discharge lamps.
4.5 Ignition at low ambient temperatures
Most metal halide lamps with wattages < 400 W can be operated at ambient temperatures of – 50 °C.
The usually evacuated outer bulb and the luminaire ensure that the arc tube is thermally decoupled from the surroundings, so that the normal operating parameters are achieved as far as possible. For
HQI ® 2000 W NI and 2000 W DI, ignition is only permitted to – 20 °C.
This cool down time must be considered for ignition units with a timer cut-out which are designed to shut off after a certain period of time with failed ignition.
The design intent assumes that the lamp is defective or not inserted. The selected timer period must be sufficient to allow the lamp enough time to cool down following a power interruption so that lamp re-ignition is again possible. The warm re-ignition times of the
POWERBALL ® are under 10 minutes, far shorter than those of the cylindrical version.
The timer period for ignition units with warm re-ignition must be appropriately long enough.
In the ignition units, the ferrite core is sensitive to temperature, that is, the rated ignition voltage is lower at lower temperatures. Some ignition unit manufacturers recommend the use of ignition units without cut-out, as the ferrite core in this case is heated up by the losses during failed ignition attempts so that the specified ignition pulse levels are reached again. There are also ignition units with an additional integrated resistor for heating the ignition unit so that these are approved for temperatures down to – 50 °C. Here again, it takes a while after switching the ignition unit on until it has heated up enough to reach the specified ignition pulse levels.
4.3 Hot re-ignition
For specific applications such as in cold storage houses, semi-parallel ignition units can be used (which permit longer lead lengths) that are fitted in warmer zones outside the luminaires.
High ignition voltages of 16 to 60 kV are necessary for immediate re-ignition of hot metal halide lamps (hot re-ignition) on account of the high vapor pressures.
The lamp, sockets and luminaire must be designed for these high voltages, and suitable ignition units must be used. There are two versions of hot re-ignition units
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