4 Possible disturbances with magnetic ballasts

As mentioned before, magnetic ballasts provide a mature and long-proven technique unlikely to cause any trouble or damages to other power consumers or the supplying voltage. One possible source of disturbance, which is more likely today to cause damage or malfunction to modern sensitive equipment than was the case in the past, is the voltage peak generated by self-induction in its high inductance at the instance of turn-off. Normally this will not be a problem, since lamps are hardly ever operated in parallel with such equipment on the same circuit with a common switch, but in one case it did happen. This rather uncommon damage could only occur on account of this exotic constellation (Fig. 4.1) but it should be mentioned that it may be a bit less exotic to parallel magnetic ballast fluorescent lamps with electronic halogen lamp transformers. Cases have been reported where the latter have repeatedly been destroyed by the turn-off self-induction surges of the former, and a special surge protector has been developed. Yet the problem could as well have been avoided by paralleling the two lamp-ballast-units with a capacitor. An appropriately dimensioned compensation capacitor will form a resonance frequency equal to the mains frequency, and the AC will therefore softly sway out after the supply voltage is turned off. With a smaller capacitor the resonance frequency is higher, and the turn-off voltage peak is »only« substantially attenuated, not entirely avoided, but the height of peak is not as crucial for the likelihood of disturbances as the rise time edge, which is attenuated very much through even a small capacitance.

Fig. 4.1: Unhealthy parallel connection of an electronic load and a highly inductive load on one common power switch

In another case an old Commodore computer locked up every second time the 18 W fluorescent lamp in the bathroom of an old residential building was turned on. The home was TN-C wired, without a dedicated earth / protective conductor but only two cores in all single-phase supply lines and an interconnection between the neutral and protective earth connectors inside each single socket. This alone may have been the cause for the trouble or at least may have contributed to it [2], but anyway a capacitor connected in parallel with the ballast and lamp solved the problem.

Comment

Print

Share / Save

Your name *

E-mail *

The content of this field is kept private and will not be shown publicly.

Homepage

Subject

Comment *

Switch to plain text editor

More information about text formats

Text format Filtered HTMLPlain text

Filtered HTML

• Lines and paragraphs break automatically.
• Web page addresses and e-mail addresses turn into links automatically.

Plain text

• No HTML tags allowed.
• Web page addresses and e-mail addresses turn into links automatically.
• Lines and paragraphs break automatically.

CAPTCHA

This question is for testing whether you are a human visitor and to prevent automated spam submissions.

What code is in the image? *

Enter the characters shown in the image.