Different methods of measuring OH conductor temp

[jdagenhart]

What methods do you use? What instruments? Do you make measurments energized? What is the accuracy?

 

[marks1080]

infrared comes to mind first. As far as I know these devices are very accurate.

 

[jdagenhart]

So, I take it, you've used them to do this? Have you compared them to any other devices? Compared the results to calculations like IEEE Std 738?

We have an instrument that was made by Exergen (made to put on a hot stick and measure a line energized), but is no longer produced. It was only about $1200. At the time, that was a bargain, compared to the IR cameras. I'm trying to see if there is anything else out there like what we had at that kind of price.

 

[marks1080]

Nope I've never used one, I am a P&C guy. I've worked with maintenance and line fellows who have used them. I've never heard of Exergen, but I think I recall that Meggar makes a unit. I'm not the best person to ask on the details, I just know that our guys use them and with a good degree of accuracy. Sorry I couldn't be of more help.

 

[marks1080]

I just did a quick search on the Megger (sorry not Meggar) site and found nothing. Some promising results on the Fluke website. No idea who the industry leader is for IR temp sensing.

 

[Marmite]

It would be helpful to know the purpose of the temperature measurement. eg are you looking at real time dynamic rating, or trying to spot faulty joints? Or some other purpose.
Both examples would use completely different instruments and techniques.
Regards
Marmite

 

[jdagenhart]

If you are trying to determine where an existing line "will" be at a certain temperature or mechanical loading (i.e., ice), then you need to know the conductor temperature when you measure existing sag and clearance. If you assume ambient, and the temperature is higher, you're going to be wrong. If your temperature measuring device is not accurate, you're going to be wrong.

This can be important on a dynamic rating, since the same factors would apply. You want to make sure you don't allow the line to sag below a certain level at maximum load, whether from expected load or emergency load.

 

[marks1080]

Are these existing lines or a new project? If it is a new project you want math, noth a temp sensor, as the MVA through the line at any given time will be a major influence.

 

[jdagenhart]

I think it would more applicable to an exising line. But I could see applying this to a new line to make sure you are stringing it at the right temperature.

 

[marks1080]

I'm just trying to understand what you are doing. If the line is already existing does it not already have this engineering work done? Or do you want to build next to an existing line and you are trying to really push your limits of approach. I'm a little confused. Your question is more applicable to a new build situation. You don't build a line and then figure out the sag characteristics. You do the math first then build the line.

 

[jdagenhart]

I think this is getting off the original purpose of my thread. I think I've made it clear in previous responses.

But, yes, there are times you try to determine sag characteristics of an existing line. There are many reasons why this might be necessary.

 

[jghrist]

One way to estimate the temperature is to measure the sag. If you know the current and the ambient temperature, you can back calculate the conductor temperature by trial and error.

 

[jdagenhart]

I know. IEEE Std. 738 gives the guidelines for this and Southwire has a neat program for doing so. I use this method as a back-check on the direct reading, just in case something looks odd. But there's nothing like a direct reading at the time you're measuring sag.