Heavy Rain and 500-KV HT Tower Line

for short circuiting there are certain conditions which are to be fullfild first first as you know the basic requirement for short circut of current flow it need a continious path or potential difference regarding potential difference as b/w tow line there is phase difference which can cause flow of current but as for continious path is concern raining do not provide a continious path b/w two lines..

during rain water drop fall only on one line so no contect take place between two line .it is same as a bird sitting on one line did not get any shock due to uncompletion of ckt

Dear Bluestone

Thank you very much of your good answer

Regards

Dear sb Guru,

Thank you very much for your very good answer.

Regards

Good answer Mr. Bluestone and excellent picture Mr. sb.

To add to bluestone's comment on environmental contamination, the insulators must be periodically maintained to remove the dirt film that does build up over time. If too much film builds up, the water does not shed properly and can cause a short when the insulator gets dirty and wet enough. I learned this during a plant electrical shutdown when the utility was replacing the main service transformer. They were amazed at how dirty the 34.5KV insulators were from cooling tower overspray, and surprised we had not previously shorted out during rain. In this case, we were lucky, but it does occasionally happen.

Cleaning of insulators was an annual requirement at an industry where I used to work.We maintained all equipment from 13.2KV. down to 120 vac outlets in the plant.Switchgear,insulators,bus bars,transfomers,etc. all require periodic maintenence to ensure reliability.I have seen the results of CATASTROPHIC arcing, where 1/2 inch thick steel girders were turned into molten puddles.According to witnesses, it looked and sounded like a bomb.

Hi aikhh,

Pure water is not a conductor of electricity. It takes some contamination such as salt to make it conductive. If there is enough air pollution, it may pick up enough to have some measurable conductivity. There is no such thing as a stupid question, but you may get some stupid answers. Hope this is not considered one!

S

Thank you very much StandardsGuy , I like your sentence :

"There is no such thing as a stupid question "

Regards

Contamination flashover of insulators is interesting and I've spent a good share of my life designing, developing, testing and applying insulators of all types. Your comment about pure water is correct; but more correctly, deionized water is non-conductive. In fact, deionized water can be used as an insulator. (I've used it with inline deionizers in closed cycle cooling loops between energized thyrister valves and refrigeration units on the ground). Clean atmospheric rain water is ionic but not usually highly conductive.

Contamination flashover will not generally occur during heavy rain. Heavy rain tends to wash and remove water-soluble contaminants from exposed insulation surfaces.

Power frequency contamination flashover generally occurs when contaminated insulator surfaces are lightly wetted by mist, light rain, heavy fog, wet snow, etc. Water soluble contaminants become conductive and leakage currents begin to flow over the insulator surface. Those currents do not flow through the contamination layer but rather along the interface between the insulator surface and the contamination. The worst type of contaminant is hard, crusty contamination such as dust from nearby cement plants, gypsum, fertilizer, and similar materials because it usually cannot be removed by natural rainfall washing. Removal requires high pressure water washing or removal by abrasive blasting with walnut shells or other media.

Anyway, the leakage currents can generate very high temperatures in the interface that may craze the glaze on porcelain insulators, etch glass insulators and track some types of polymer or non-ceramic insulators. The evidence is usually dendritic or tree like patterns on those surfaces. A similar condition can occur on ice-covered insulators. Usually not a problem until the ice begins to melt and leakage currents begin to flow in the liquid interface between the insulator and the ice.

One cardinal rule with insulators and that is they only fail in interfaces.

The clearence is suitably designed on tower lines between conductors taking the possibility of the swing of conductors under certain conditions like wind etc so that phase to phase short is not likely.As regards insulators the clearence is very high and in towers nearing the substation u will see horn gaps in addition which ensures the flash over is in the gap and it does not travel to the substation.In addition hot line washing of insulators is adopted which ensures contamination and hence breakdown doe not take place.The only thing on a rainy day is coronna losses increase