Sticky

#### what is the voltage?

can one just by looking at the design of the power lines figure out what voltage they carry?

Longer answer: the one in the picture you have is a long distance transmission line, likely around 33,000 - 110,000 volts.

The wires on poles are distribution lines and can range from 220 V for the line into your house to 33,000 V for a rural distribution line, though 2400 V is more common for urban distribution in North America and 3300 V in Europe.

My information is coming from Wikipedia (en.wikipedia.org/wiki/Electric_power_transmission and en.wikipedia.org/wiki/Electricity_distribution) but it matches up with discussions i've had in the past.

I'd also note that some of the local lines have their voltages marked on transformers that hang on the poles. And if you follow the one you have in your picture to a substation you might find the voltage on the transformers there, though it could be a long and hard to follow trip.
For example, this one:

You can see a 37.5 on it which makes me think it's 37.5 kV. Somewhat more than what i said above for a rural distribution, but still close...
thanks for the info!

@johansegen:
in your picture i see a 150-220 KV (1 KV = 1000 V) power line...

@mdmarkus66#1:
in Italy the voltage of the power lines is:
extra high voltage: 220 - 380 KV
high voltage: 60 - 150 KV
middle voltage: 8.4 - 20 KV
low voltage: 0.240 - 0.400 KV :-)

@mdmarkus66#2:
Uhm... 37.5 is the power of the MV/LV Transformer, 37.5 KW...
IMHO, its a 20KV (or less) power line ...

Bye
A few months ago I posted this shot:

Kinsler33, responding to my question for more info on the shot, said:

"With 18 insulators rated for perhaps 18,000 volts, this is probably about a 300,000 volt power line." So, assuming he's right, you can tell the voltage of a substation's line from the number of insulators. As for the lines running to that transformer, I have no idea.

Hope this helps.
To mdmarkus66. Sorry, 37.5 is the KVA rating, or size of the transformer. That number refers to the load it can sustain. For instance, my area is serviced with 7,200 volt overhead service. Years ago the OH transformer for my section of houses was a 25 KVA. As more people added A/C units, that transformer became too light for the job. They moved up to a 37.5 and then finally to a 50 KVA. That number you see would be the amp rating of the transformer, not the voltage.

The number just above the KVA rating is the transformer number. That is the "serial number" given the transformer by the power company. Below the KVA rating is a blue sticker saying NON PCB. In other words they transformer has been tested or certified that the oil contained in the pot is not PCB contaminated. Mainly it's just a pure form of vegitable oil.

That pole has a whole host of other interesting features on it also.
Typical voltages in this area for that structure is 345,000 volts or 135,000 volts.
That wood pole structure won't carry that load. The insulators are way too small. Cutouts that small would arc over if you tried to break the load.

If you're talking about the 10' insulator picture taken through a chain link fence, I agree absolutely. Those lines and insulators are designed for that load.
I would say 160 000 volts by looking, in Canada we have planty of 735 000 V lines !
my guess for the photo postes is 220Kv to 260Kv. possibly 344Kv.

good rule of thumb, the bigger the strs, the higher the Kv.

the only way to know for sure, is ask someone at the power line company!

what Rickd248 says above about the transformers is correct.
johansegen,

it could support from 200 kV to about 400 kV. Depending on the insulators, distance between phases and ground, number of conductors per phase, etc.

Best regards.
My brother received a rough-and-ready answer to this question when being trained as a forest fire fighter. For the large tower transmission lines, count the number of glass rings on each insulator -and multiply by 20,000 to get the voltage.
there are different ways in how you can tell the voltage of the line. You can usually tell what the kilovoltage is by the size of vertacle suspension insulators. Supsension insulators contain a chain of severial disks each rated about 20kv. By multiplyting 20 by the number of disks you can get a good estimatation of the voltage. However it is not exact though because some utilities use more insulors sacrificing costs while others sacrifice safty and reliabilty for the cost of less.

Here's a chart of generall voltages with the numer of insulators per chain while hung vertical on a pylon.

metal pylons:

4 disks - 34.5kv
5 disks - 46kv
6 disks - 69
8 disks - 115kv
10 disks - 138kv
13 disks - 230kv
17 disks - 138kv
25 disks - 500kv

wood pylons:
3disks- 34.5- 46kv
4disks-69kv
7- 115-138kv
12- 230kv
15-345kv
20-500kv

Lower voltage lines are often harder to tell by looking at the insulor sizes. The disk insulators are a smaller size. Generally 1 disk is 0-8.32kv, 2 disks is 8.32-13.8kv, 3 disks 21-34.5kv. Sometimes some utitlies use more disks. Metal poles will often use more disks too. With regarded to pin and cap type insulators you can generally familiarize yourself with the different sizes and what voltages they generally fall into.

Some utilities list their voltages in substations or on pole transformers make sure you don't confuse the number with KVA or serial numbers like in the previous posting. Some pole transformers have double voltage settings. A switch on the side of the transformer sets the voltage and often has the voltages labeled by it. When looking for a voltage on a transformer look for a number with the letters "kv" labeled after it.

Also look for switch poles. Voltages are often labeled on the the machanical levers on the bottom of the pole. Make sure it's not the rating for the switch though. Also look for padmounted transfomers too (the transformers inside the metal boxes by buildings). Voltages are often labeled on those too.

Another way I find is helpful is to do a google search by typing in the name of the power utility fallowed by the letters "kv". There you can find the list of voltages from that utility.

Ohter ways you can find out the voltage:
1) size lightning arresters
2) familiarizing your self with the size of pin and cap insulators
3) size of insulation on cut out fuses
4) the size of the transformer insulation (bushing).
If you want to look through a PowerPoint presentation put out by
Baltimore Gas and Electric,check out BGE and Power Delivery

The presentation indicates that the standard voltage for most distribution lines carried by those wooden poles is 13.8 KV

Distribution transformers on these poles reduce the voltage from 13.8 KV to 240 V
Rickd248 gives the first good answer. The biggest mistake people make about voltage is calling 120 volts "110" and calling 240 volts "220".
Thomas Edison is probably the last person to produce and use 110 and 220. The problem is motors and other devices are rated with the lower numbers which are an industry standard for such. The lowest utility voltage, 120 v, has killed more people than all other combine.
wow, there is a lot of good information here!
You can tell fairly accurately by the number of discs-roughly 10-12kv for each one if the discs are 10" diameter. Most accurate way is to read the nameplate on the transformer(s) connected to the line. If you can see the nameplate well enough to read it on a substation transformer, you can find out the voltages in the sub. Most difficult is by simply looking at the poles, especially the new ones, even with the transformers, because they put up the same insulators for 13kv and 4kv, for example. Many newer transformers can be selected to run on 2 or more voltages.If you follow the lines far enough ,you'll get a better idea of the voltage-some older stuff may still be used: 4kv and other lower voltages have small insulators, single discs, box cutouts, and transformers with small side bushings.
looks like 115kv a very common transmission voltage.
mdmarkus66:

No- that 37.5 in the power-handling capacity of the transformer.
It stands for KiloVolt-Amperes- which is the same as kilowatts if there is no reactance in the line. Standard transformers sizes for residential service is 10, 15, 25, 37.5 and 50-KVA.
nafana:

agreed that tell the KVA that number.
johansegen:

i would just say since the location on the photo and tower size i would just guess 115kv (115,000 volts).
Transmission voltages can not be determined by sight alone. Public records, intranet or the utility can be contacted to request basic information. Signage may or may not be present. The towers, span lengths and conductors are designed for a specific circuit but have capacity for fluctuations. Subtransmission circuits route from substation to substation to feed distribution grids in-which primary voltage is stepped down to service levels. Insulators are rated and ranged. Each utility does it's own thing based on load and demographics. In California information on voltage ranges can be obtained by review the minimum standards embodied within GO 95, www.cpuc.ca.gov/puc or referring to the NESE. This is meant to be a non-technical overview.
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