Formula About Minimum Phase-Earth Distance

What if that were the last evidence of a large seagull that got a bit too close?

Why one insulator and not the other?

And why in different places instead of the whole insulator?

And what sort of numpty would install insulators on a 170kV line that were not up to the job?

Could have been a lightening strike or some knothead released a mylar party balloon!

Seems like in 2 years, you would have worked this out.

yes, you are right but I couldn't find its answer. They always tease

The local code in my country says that you should know what you are doing before working with anything over 120 V.

That disqualifies you.

do u know everything?

at least I could have learned that I don't know. What about you!!!!

Lyn;

Why 120V won't cause any accident? I have seen one engineer shorted 6V and wire sleeve melted in his hand and he had to go to hospital finally.

I think, few million electrons one may swallow but be careful with lots of charge anywhere. Remember that post in which the entire house was burnt due to spark in the wiring.

I think it might have happened in some kind of acid rain when conductive water simply zipped the heavy arc. Water will simply drip over and there may be some dust accumulated over the insulator. They are supposed to be cleaned. This looks more reasonable. Some bird or bat getting hit is also possible.

I think there must some life also for these insulators after which they are to be replaced.

That black thing looks from safety arc electrodes through some dust in the air or perhaps something in ir due to local fire or chemical release. That is why it is on one side where over voltage protection arc electrodes are.

It is not possible to tell whether the equation works for free air or for a particular composition of insulator. Where did it come from, please?

hi RAMConsult,

Thanks for your noble answer. I am also wondering that value creep distance for 170 kV should be. Could you calculate it for me?

You don't look like PWSlack.

Thanks again..

I am sure if you ask nicely RAMConsult will direct you to the relevant American HV insulator standard where the values can be obtained.

You want the values applicable for American insulators right?

et tu brutus ?

yes please. assume that I asked nicely.

sorry for english barrier.

but try to say a hi, just hi in my language...

You probably should buy this Insulator and clearance requirements in overhead line transmission systems without shield wires It is from the IEEE.

RAMConsult;

Dirt or contamination estimation and maintenance by cleaning supposed to be an integrated part of cost effective plan. There is nothing like a design totally fool proof protected forever.

Most interesting event was when lightning stuck the base of the Moscow Tower leaving all top electrode purposeless for the event. Corona path is also statistical and there is a probability that all calculations that were buried in under estimation may actually happen as some nasty surprise. These are risk factors known to all designers and are somehow accepted as rare "sudden death" events / hazards.

I think micro corona currents can be easily measured in zones and then cleaning procedure can be initiated at times earlier than scheduled under regular plan as some kind of emergency procedure as catastrophe preventing.

Firstly what were the conditions at time of the failure? 2nd. Looking at the polymeric shed, this did not happen over night. This was a long term condition and the first thing that pops to mind if that the polymeric were very dirty from deposits of dust, salt or another conductive dust.

What does the surrounding area comprise of, industry wise? Where is this tower located? Open space, near a cement factory, heavy industry etc. Do the corona rings have carbonising on the surfaces? Look closer and I think you may discover that they failed due to poor maintenance, (cleaning), and damp air, (fog, humidity, rain). If the insulators were clean the flash over would have flashed over the arcing horns rather than a leap over the rain shed. Least path of resistance was down the polymeric and this can only be caused by dirt on the shed.

The left hand side top poly looks grimy and dirty where the right side one is slightly cleaner looking.

Just an educated guess without all the details and it is a good place to start looking. What do the other line insulators look like?

englis;

They look pretty dirty.

Thanks for the pictorial feedback! Obviously the wrong choice of insulator type for the environmental conditions. The flat undersurface and lack of deep skirts/sheds allows for an easy path through any material that collects on those surfaces. I'll bet removing those insulator strings from service cost a few bucks.

My fellow man, thanks for your serious replies.

I would guess that the budget is now set for insulator cleaning on this line?

In my opinion what do you need it is the recommended creepage path. See IEC 60071-2 Table 1 - Recommended creepage distances

I don't have that is why if you have that as pdf, can u send me ?

engilis, I am sorry, I cannot send you the standard-first of all in my Microsoft Office it is not Acrobat software and second this will be against the forum rules. So I check the creepage path for 170/sqrt(3) kV, for very polluted atmosphere =31*170/sqrt(3)=3042 mm.

Most of composite [silicon+] for this voltage present more than 4000 mm. So I don't know what could be your problem. You have to consult the insulator Manufacturer, I guess.