Overhead Line Testing

Words fail me sometimes, what the heck are people being taught now days that simple analysis and fault finding techniques are beyond some people and have to be outsourced.

...to anonymous strangers who cannot see the installation, have no financial interest in it, and, at the time of writing, have no idea where on the planet the problem is located.

It is absolutely astonishing.

Your electric utility company may benefit from using a DayCor camera. If you've any arcing, excessive corona in your system this camera will find it. (I am not connected with DayCor's mfr in any way)

I like the Rail system they have, but may not be sensitive enough to detect hipot discharge, with generally limited current available. I tend towards IQ Post 24, where you just put the boots to it, and back-check with your DayCor, if the insulator string doesn't flash over. The Preventive Maintenance possible with that, combined with thermographic data, would make you both efficient and reliable.

What else could it be but your insulators?

Check your insulators.

There is a LOT of air to be checked.

I think I found his problem

He said overhead line testing, right?

I too would post this question as an "AP"! Common sense would tell you are not qualified to work with HV, but stupidity tells you to continue on and go to an anonymous forum and seek answers!

Hopefully, you live to tell about it!

I am starting to wonder if this is partially a cultural thing where some people are just too afraid to lose face (or something similar) by asking a more senior engineer on site a question and so resort to asking on online forum instead.

We are not talking toys and games here. The MW level power generation and high kV transmission-level power line selection and fault finding questions like these asked on CR4 recently should NOT be this common.

What's going on out in the industry that could be causing this? Is this common and CR4 is just becoming more popular and attracting more of these questions.

This is becoming too common here on CR4. But if you think about how some countries string their lines, it's amazing that the magic smoke hasn't appeared sooner, taking the continent's power grid out of service

I tend to agree - it may be a cultural thing. Could also be they work for a harsh superior who's unapproachable and so feel safer asking elsewhere anonymously.

There are also areas in the world where professional training isn't accessible for any number of reasons, and so people are trained by being thrown to the wolves. I suspect this is the case more often than not.

I don't think it'll hurt us too much to help these folks out. There was a time when I knew diddly squat about my field (and about many, many subjects I still do), and so being able to ask someone was a huge help. Sometimes all I needed was just one tiny little key piece of information and the rest of it all fell into place.

The way I look at it, I give them credit for asking. The ones who don't ask, who think they know what they're doing (but don't really, and don't know that they don't know), are the really dangerous ones. Those and the ones who come here repeatedly with questions but don't learn anything. We've a few of those, yes.

Well, maybe this?

Do you have any power factor compensation capacitor on the line?

You didn't specify if your test was conducted with AC or DC.

it is DC

On a (test isolated) section of 132kV overhead transmission line? Are you sure? Can you provide a link of an example.

AC or DC Hi-Pot? There may be more than "the next section" in the test circuit unless it is isolated or sectionalized in some manner. You are likely seeing the effect of charging current over a much longer section of the transmission line than you realize.

The answer to the three questions is "It doesn't matter". The test failed. End Of.

So the only thing to do is to investigate why the test failed, carry out an appropriate remedy, and repeat, until the installation passes the test. It could be anything.

As the installation and the test equipment cannot be seen from here, the investigation, and the remedy/ies, are all in the domain of Anonymous Poster #1.

Test is not failed, its just not upto the mark ., as leakage current in 40mA at 80kv or some times leqkage current is more then 40mA but voltage only 1 or 2kv and equipment get tripped, and this is also happening specially in night .

Then what's different at night do you think? Increased moisture in the air perhaps causing a path to ground through a faulty insulator? <hint> <hint>

Why bother testing at all? Why not just energise and be done with it?

<...its just not upto the mark...> So which side of the pass/fail boundary is it, then?

Too bad "they" (he/she) posted as an "AP", we have no clue about where in this world they reside in and what climate they're dealing with, moisture, dust, bird droppings- the list goes on ...... Sounds like a homework question to me

Hmm...I dunno. Homework questions are usually a bit too 'tidy' and clear-cut. I tend to suspect this is a real, in-the-field situation.

thanks for the reply

Is it in all phases?In both circuits?Try Isolating the sections,I mean disconnect the jumpers at angle towers and take only a section at a time.Weather makes a difference but values are very low even otherwise

i did this , now line only 2km in length and insulators also cleaned but leakage current is too much and at night no voltage applied ? not more the 1kv

So above 1kV DC power, you exceed the current output rating of your hipot set (?).

As asked before, do all 3 phases show the same behavior?

I've never hipot tested an open line. Insulated HV cable, yes, to prevent excessive and perhaps un-repairable damage to insulation/stress cone, or prevent a fire in the middle of a cable tray, in the case of pulling/install or manufacture defect.

Risk of excessive or consequential damage beyond blowing apart or flashing an insulator string you should be able to confirm & evaluate, and decide whether to energize at full voltage,

Isolate to smaller section, one that you know you can charge successfully,

Or get a bigger hipot.

Just try charging the line with rated voltage.See whether it stands.At best Breaker will trip and may be the bad insulator show up.By the way Is it a Tee Off Line?

Seems elementary but...

Your 80 kV tester may have enough current to test one insulator or transformer but not miles of line - the first line section you tested may be short and the next long.

Tell us the line length and test set current capacity @ 80 kV and maybe a line guru will appear.