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"The flow of electrons through ionised space" This is probably the most common fact of life; With there being electricity, there are sparks. The problem is sometimes we want them to fly, other times not. Tuning on a medium wave radio to a quiet spot and listening will show just how much arcing there is all around us. Most of it is harmless to day-to-day living. It is when it's not, the fun truly begins! The reason arcing is such a major issue within the realms of power quality is arcing is the primary cause of the most destructive element within power being impulses (the collective term for 'spikes' and 'transients'). Impulses are short duration pulses of high frequency noise. When one hears of 'transients', one is most likely to associate this with lightning strikes and badly performed network switching. This is as a result of very lob-sided marketing raising the awareness of the targeted audience to the instantaneous and usually disastrous damage such high-energy impulses can inflict. It will probably, therefore, be quite alarming to learn that up to 80% of impulses emanate from within a site with the power feed only carrying the other 20%. The classiclassic noise emitters are inductive based circuits fed from a non sparked-quenched switch e.g. fluorescent fittings (ballast), motors, etc. If allowed to proceed unhindered in to a sensitive electronic device, then there is no telling what will occur with the electronics accepting an impulse as a valid signal when it shouldn't. If of sufficient intensity, then such impulses can lead to damaged or destroyed components. Even rudimentary items such as circuit breakers can suffer if the impulse causes insulation breakdown and there is sufficient ride-through current available. Before I move on to noise emitted from electrical devices, I want to first concentrate on static. Although walking past a door frame wearing clothes that were not treated against static usually produces nothing more than a little jump, I'm going to scale things up and deal with the mother of all static discharges - Lightning! With lightning out of the way, I will then deal with the most common form of arcing which is contacts operation e.g. a light switch turned on and off. Accidental Arcing deals with the situation when two contacts are just too close for comfort (nothing like producing a little man-made lightning!). Spurious Arcing is the exact opposite, this being when the contacts are not close enough! Finally, as we humans are not satisfied with the above, there are times we actually want sparks to fly - but we usually turn this into a useful resource and so give it a fancy name - Welding!
© 27.07.04 |
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