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DISCUSSION:
Electronic ballasts cost more than the standard
iron core ballasts used in the past for fluorescent lighting.
However they are being installed in most new installations and
being retrofitted to many older installations. Why?
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Energy Savings:
the lower power costs justify the higher initial cost and
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Reduced System Harmonic Distortion:
electronic ballasts exhibit lower current harmonic levels than
standard iron core ballasts. 1 This can have a
beneficial effect on building current harmonics.
However, as with almost every up side, there is a
downside.
The standard iron core ballast is a comparatively
rugged induction device with a small capacitive element (L-C). But
most electronic ballasts incorporate an inexpensive switch mode
power supply (SMPS) - an integrated circuit (IC) which supplies a
small high frequency transformer.
The IC chip is much more vulnerable to transient
voltage/current surges. The surges degrade the IC components over
time and will eventually cause ballast failure.
Electronic ballasts generate transient
voltage/current impulses when their SMPS fire. Levels generated by
individual ballasts are not of sufficient magnitude to affect
other electronic ballasts on that circuit. But every so often,
several fire simultaneously. Like any wave, the amplitude is
additive and the result is a sufficiently large spike to degrade
ballasts on that panel.
Transients also enter the panel via the feed to its
bus or from other non-lighting loads on the panel. In most
commercial and industrial lighting applications, rooftop air
conditioners, elevators and other heavy loads will blast
transients back down their own feeder circuits and onto the
347/600v lighting circuits.
As
loads on the panels increase, it becomes necessary to protect
electronic ballasts from the ravages of transient voltage/current
surges. |
