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depends on several factors, including lamp position, supply voltage,
temperature, age of the lamp (electrode) and also of the lamp current
wave form (peak factor).
4. Striations are noticeable as a pattern of more or less bright regions
in the long discharge tube of fluorescent lamps.The pattern can
move through the discharge tube. It can appear when the lamp is
cold or when the lamp is dimmed down to too low a level.
Circuit breakers, fusing and earth leakage
1 Standard conditions
Under normal conditions the highest current which can occur is the
current during the starting phase.When the starter is closed,
practically the entire supply voltage is across the ballast, resulting in a
high current and a low power factor.The fuses must be capable of
handling this high initial current for several minutes. For most of the
fluorescent lamps stabilised with copper/iron ballasts, this starting
current is about 1.5 times the normal operating current.
During switching on, a few other processes are going on as well:
- the (empty) parallel compensating capacitor will be charged with a
high inrush current,
- depending on the magnetic saturation of the ballast a voltage induction
will take place in the ballast,
- gas-discharge lamps can have some rectification or DC component
in the lamp current.
These phenomena occur in the very first 3 to 5 milliseconds and can
result in a peak current of 15 to 25 times the nominal current.This
surge current will depend on the lamp and ballast type and the number
of lamps per circuit as well as, of course, on the resistance and
impedance of the lamp and supply cables and the impedance of the
mains supply network.This latter part varies greatly in practice. It is
recommended that a surge current of 20 to 25 times the nominal
current during the first 3 milliseconds be used and 7 times the nominal
current for the first 2 seconds for parallel compensated circuits as a
guide for selecting fuse ratings.
In the duo-circuit the capacitor is connected in series with the coil, so
the very high surge currents cannot appear in this case.
Devices for switching and fusing must be capable of handling these
currents correctly.This means that for fuses slow-acting gI types (normal
general purpose type for cable fusing) have to be used (German name: gL).
The main purpose of the fuse is to protect the cable and the distribution
part of the lighting installation from damage in case of a failure in the
installation. So the fuse rating is primarily related to the cable core used
in the installation.
As the various national electrical safety rules differ slightly, the
recommended fuse ratings for lighting equipment published by the various
lamp, gear and fuse suppliers are not always the same. Moreover,there
are differences in the various brands of fuses.
As a guide, it is recommended to load gl-fuses to not more than
50 - 70 per cent of their rating.
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3.17 Stroboscopic effect and striations