6.3.3 Broken lead or broken weld. Osram HQI-E 150 W/NDL CL
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This is one of the advantages of the rectangular electronic ballast. As the zero crossing for current is very steep, the events of limited current availability are very short and the plasma has little chance to cool down.
Lamp voltage Supply voltage Lamp current
Re-ignition peak
Supply voltage Lamp voltage Lamp current
28
Fig. 31: A lamp goes out because the re-ignition peak is too high
Fig. 30: Re-ignition peak, supply voltage and lamp current
A decline in the supply voltage can also cause the lamp to go out. It is only when the lamp has cooled down sufficiently that re-ignition is possible with the normal ignition units. After “cycling” for a long time, it is possible that the lamp will not ignite at all.
The lamp voltage and the re-ignition peak increase with progressing lamp age; in addition, this parameter also depends on the ambient temperature and increases while the lamp is heating up. This results in what is known as cycling, where the lamp periodically goes off and on again. The re-ignition voltage increases while the lamp is heating up and continues to increase until the luminaire is completely heated through. This is why it can happen that the lamp does not go off until after several or even many minutes of burning time.
This fault is not critical if the ignition unit does not suffer from the frequent ignition attempts.
6.3.3 Broken lead or broken weld
This can be caused by material fatigue or extreme mechanical load. Normally this is a non-critical fault; in very rare cases, a loose contact can cause high induced voltages.
Fig. 31 shows a lamp with high re-ignition peak. After the zero crossing, the current barely starts to flow. This is why the voltage loss across the choke is low and nearly the entire voltage supply falls across the lamp, with lamp voltage following supply voltage. The current flow decreases even further from period to period, so that conductivity continues to fall; in the end, the voltage required to re-ignite the plasma is higher than the supply voltage → the lamp stays off after the zero crossing.
Lamps with gas-filled outer bulb for supply voltages of
400 V can form an arc when a lead is broken or a weld comes loose. Due to the current-limiting choke, this arc can persist for a longer period of time and cause the lamp to burst. Such arcing occurs both in lamps with an ignition unit and lamps with auxiliary starter electrode (lamps for ignition at supply voltage with a wattage of 2000 W).
6.3.4 Leaking outer bulb
Mechanical impacts can cause the outer bulb to leak so that air penetrates. Given the high temperatures, leads oxidize when oxygen is present, causing an open in the circuit. This is a non-critical fault; the lamp no longer ignites. Ignition units without cut-out can, however, fail prematurely due to permanently generating ignition pulses.
6.3.5 Lamps that do not ignite
This can result from open electrical connections within the lamp or extreme aging and is actually a non-critical fault. Ignition units without cut-out can, however, fail prematurely due to permanently generating ignition pulses.
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