Transmission line voltage estimation Rule of Thumb

[Billgas]

Is ther a reliable method of estimating the voltage on transmission line by direct observation?

I had heard something about the number of grooves of an insulator, with each groove equivelant to so many kV....

 

[davidbeach]

There may be ways of estimating the maximum operating voltage of a transmission line, but there is no way of estimating the actual operating voltage as lines may be built to one voltage and operated at a lower voltage.

I don't know about grooves in an insulator, but counting the number of bells used can give some estimation, but there are many variables that would determine the number of bells used in a given area. In areas with little air borne contamination you can get away with fewer bells than in an area with much air borne contamination; coastal areas always require more bells than clean inland areas.

For one class on line construction, for one type of insulator bell, in one location, I've worked out that it must be about 1 bell per 25kV plus 1 bell. The best approach would be to know the voltage of some lines in your area and work out a similar formula.

 

[dpc]

As David indicates the length of the insulator can give a rough guide to the nominal voltage. But there are a lot of variables. And sometimes lines are overinsulated in anticipation of increasing the operating voltage at some point in the future.

 

[Zogzog]

My last job required quite a bit of travel so to fight off boredom I traied to self teach my self by learning about a utillities operating voltage in my travel area and trying to ID different lines. I was always visiting a HV user so I found the answer to that line when I arrived inthier switchyard.

It is harder than you can imagine, every area has thier own voltages and design requirements, I got pretty good at Detroit Edison, Consumers power, 1st energy, NSP, and reliants systems.

I like the 25kV/Bell +1 bell idea, I will give that a try.

I also have made some interesting observations on birds on powerlines, but dont get me started on that.

Here is a good song to listen too while you are drivin the lines.

 

[tlr7616]

I once had to do this for a project. I gathered a fair amount of sample data and let Excel curve fit an equation that tells you how many ceramic bells (i.e. weather sheds) are required at a given voltage level, see below:

Empirically derived equation (curve fit)where:
kV is voltage (line to line)
N is number of insulators

kV=(0.0248*N^2)+(17.859*N)-18.316

For what its worth this equation holds true most of the time--as others have mentioned there are other factors that might cause it to vary. It WILL get you close...

 

[davidbeach]

tlr7616, your area must have far more contamination than around here. Per your formula I get 53.5kV and 89.7kV for 4 and 6 insulators while I know that 4 are used on 57kV lines and 6 are used on 115kV lines.

 

[Zogzog]

OK, here is the song, I must have missed something the 1st time.

 

[busbar]

Great tune, ‘zog. [Maybe a verse on overtime to pay for the new boat?]

 

[PUNGLU]

In some places you may be mislead by the insulators. I have to ares where insulators for 36 kV are used for 15 kV lines! You may have to get the exact voltages rather than judge by the no. of bells....

 

[oldfieldguy]

Down here on the US Gulf Coast, one 'bell' of an insulator equals approximately 8 kV to ground. 13.8 system (8 kV to ground) has one bell. 69 kV system (40 kV) to ground) has five bells. Of course, this is all going out the window as the utilities slowly move from the ceramic bells to the new moulded polymers, but it's still good for now...

old field guy

 

[stevenal]

See

http://www.usda.gov/rus/electric/pubs/1724e-200.pdf

page 82. Need to find an angle structure to see the difference between 34.5 and 46.

 

[oldfieldguy]

Apparently the local utilities add a bell to those numbers for fog and contamination...


old field guy

 

[apowerengr]

In my experience a "standard" 10 inch diameter porcelain bell in the US was rated 20kV. 69kV used 4 bells, 115kV used 6 bells. Small diameter bells were rated less, typically 7.5 or 15kV. Now days with poly deadend insulators the skirt diameter drives the number of skirts to arrive at the required leakage distance/BIL rating. You see the same thing with cable terminators - for 25kV class the termiator could have two large diameter skirts (Raychem for example) or multiple small diameter skirts (like 3m). Hope this helps.

 

[Zogzog]

See? Like I said, it is different everywhere you go, you just need to learn the system in your area.

 

[lansford]

Also note that if a transmission line is dead ended or on steel, it will likely have at least one more bell than on a wooden suspension structure.
JIM