Tuesday, October 6, 2009
Tutorial 7: Identifying The Wires, Part II
Welcome back. I have some old material that I wrote a ways back for another cause that I am bringing in here to recycle, in order to expand on the cause of identifying stuff on power poles. I took all of these pictures myself, so am more familiar with what's in them than the generic reference pics I used in the last tutorial.
This is going to be a VERY long post. Go refill your coffee now, get your potty break in, and then come back when you're ready to sit a spell. I am confident that, despite the length of this post, you'll be pleased with the information you pick up from it.
I think it is high time to put in a disclaimer, however.
I am a power dispatcher, but I have never been a lineman. I know enough about this subject to sound like I know what I am talking about, but any lineman knows enough to make me look clueless. If you are dealing with someone on site who should know what they are talking about (power company field employee), don't rate my info better than theirs.
Click on these pictures in order to open them up in a larger window to see better. If you 'right-click' the picture, you should be able to choose to open it in a new window, so you can have the picture up full size while also reading the text.
In this picture, three conductors of this 14kv feeder are coming in from the upper left, and traveling towards the lower right, they are the wires at the very top of the front pole.
Under the top crossarm of the front pole there is a three-phase tap (all three conductors are tapped), and these travel downward in the photo to the pole across the street where they are then on the very top as they go off the left side of the photo. Also, on the right side of the lower crossarm is a single phase tap that travels off the right side of the photo.
So far, all of what has been described is 14kV, bare cable (not insulated).
Now, across the street you see the streetlight on the back pole. Just above where the light attaches is a triplex cable. Off the left side of the photo and out of view is a poletop transformer that steps down the 14kV to something the street light can handle, and the 120v insulated cable coming back from that transformer is wrapped around the neutral to form the triplex. The triplex then extends to the front pole and terminates. You can see on the right side of the front pole that the triplex at one time continued towards the right, but it is no longer in use, as the right side has been disconnected and is bundled back towards itself. The triplex on the left is hot, the triplex on the right is not (I only say this because I know what happens to the triplex off the right side of the photo, it dead-ends at nothing). Also, at the same point on the front pole, you can see the lone neutral wire coming in from the upper left and following the single phase tap off the right side.
Below the neutral is telecom stuff (cable TV and/or telephone) on both poles.
Remember that ANY wire can be hot: Neutral, cable TV, phone. Say for example a power pole is broken as a result of a traffic accident. The innocuous neutral or cable TV line may have whipped backwards and draped over a high voltage line before landing on the ground. Always visually trace the path of wires on the ground to their source regardless of the kind of line that is on the ground! Check for things contacting the guy wires, too!
This is a different section of the same feeder. The 14kV uninsulated conductors are on the top crossarm.
Just below the crossarm is the poletop transformer, stepping the 14kV down to 120V. If you look very closely you can see that only the back of the three phases is tapped by the transformer. A solid rule is that a lone poletop transformer will only be connected to one phase of high voltage. As you go down a feeder you will see how transformers are tapped off of the different phases more or less sequentially (A B C A B C etc) to equalize loading on the three high voltage phases. That little gadget in the tap between the conductor and the transformer is the fused cutout, the fuse is a cylinder not quite 12" long in a spring clip or hinged apparatus. It can be opened/removed to de-energize the transformer and its taps.
Under the transformer the customer taps fan out. These transformers frequently may have only one tap, but there is no reason they can't have several, like this one. Starting with the first one that points almost straight left and going counter-clockwise, the first one goes to a house, the second one goes to the next pole (and thus is on the main neutral) to serve a street light, the third and fourth go to houses. The wire heading sharply down towards the right is just a guy wire. Heading from the transformer off the right are two more lines. One goes to another street light across the street, and then above that you can see the bare neutral going off the right but staying on this side of the street. Remember, all of these insulated cables are at the same potential as household current, so although a hazard exists it's not big time stuff.
Under all of that is telecom.
This is a fused poletop switching point. Each of the three phases has an inline fuse (basically like the poletop fuse in the last post but with a higher rating). The fuses will pop as needed so that the entire feeder doesn't have to go dark for a fault on the far side of the fuses. Since it is a switch, the three fuses are attached to hinges so they can be collectively opened for work clearances on the far side of the switch.
This one is a little more complicated.
You see the familiar three phases on the crossarm on top. On this pole, all three phases are tapped to inline fuses on the right side of the lower crossarm (at a right angle to the upper crossarm), then onto small insulators on the left crossarm and then into individual transformers. This is a large customer requiring three-phase service. The three phases and the neutral are individually tied to the pole instead of them being wrapped together, so you see four wires leading to the customer, but often they will be wrapped together and referred to as quadplex. You can also see that one of the low side lines is tapped for something else since it is running wrapped around the neutral to the far pole for something else.
There is some increased danger here. The three phases are tapped into inline fuses before the lower crossarm, and then converted into insulated cable before heading into the riser tubing and going down the pole underground. Note that there are no transformers in sight on this pole. This means that the cables running down the pole behind a little flimsy sheet metal are a full 14kV. Smack a car into this pole hard enough and/or in the right place and you'll get a dandy light and sound effect show for a second or two until the fuses blow. Long enough to kill you for sure. Tread carefully here.
I think everyone can identify the neutral and cable TV/phone here, right?
Another poletop switch, this one with bladed disconnects on the top of the crossarms, is on the right pole. A three phase customer is tapped off of the pole on the left. Linemen like this kind of switch a little more because it can be opened without a bucket truck. If you look close at the pole on the right you'll see a control rod going down the pole. This can be operated by hand with a hotstick while standing on the ground. Some control handles go all the way to the street level, and in these cases the control is locked in position with a power company padlock.
You might conclude that in an EXTREME emergency, you could theoretically open the switch, but this is a bad idea in every way. Linemen wear linemen's gloves for this kind of switching (for all switching, actually), because you never know when the switch is going to fall apart and something energized falls into the switchgear. Plus, you'd have to know without a doubt that there was no potential from the other side of the switch for it to be worth your trouble. And don't forget some dope might have an incorrectly installed generator on auto start on the dead side which would heat you up a few seconds later. Or... there might be an "auto flop" configuration installed by the power company to automatically energize from somewhere else down the dead line in an attempt to restore some customers after an equipment failure. You can see why there are far more chances of failure than success, plus major personal safety hazards in attempting it. Just put it out of your mind.
The picture on the left is a better angle on the this switch and control rod - that you won't be touching.
Here we have the point that three phases are split into different directions, but they are still elevated distribution voltage.
The three phases come in from the upper right. The left phase can be seen as tapped to the upper wire going off the left. The middle phase dead-ends here. The right phase taps off to the upper wire going off the right. You have to look close to see it, but the second wire that looks like it is right next to the right phase is actually the neutral and goes to a point on the pole about 3' below the crossarm, and it also splits so a neutral is continued with each of the tapped single phases.
The three wires going downward on the left are guy wires. Since this pole is a dead end, there is a lot of tension pulling in one direction, the guy wires make up the difference so the pole is not yanked over.
What you have here is some 34kV subtransmission on the right side tapped to underground. While it is underground and out of sight, it goes off the picture frame about 200' to a large pad-mount transformer where the voltage is reduced to (I think) 8kV. That's still 8,000 volts even on the 'low' side. Then it comes back through the underground and back up the pole on the left before being distributed by feeder to local customers. On both poles you have three phases of either 34kV or 8kV behind a relatively flimsy shield of sheet metal.
Even though there are not major differences in the size of the insulator bells on either the 34kV or 8kV to help you figure out which is which, the different sizes of the cutout fuses ('C'-clamp looking things) mounted below the crossarms gives the difference away. High side, low side, doesn't really matter, it'll all blow your arm off.
This is next to a two-lane 60 MPH highway. Can you imagine what would happen if a vehicle took out one (or both) of these poles and also careened into those propane tanks? Big Fun!
Over here on the left, doesn't look like much, but this is 115kV, about 8 times higher voltage than most of what we've been looking at so far. Note the two shield wires above the three conductors.
This is outside a power plant. The other wires crossing by are a distribution underbuild (meaning it runs under something larger), of the 14kV variety we've already been learning about .
Over on the right, this is twice as much voltage as above, 230kV. Again, note the shield wires.
On the left, this should keep some people honest... this angle shows that the wires some people are afraid of (because they are on lattice steel structures) can also be found on wooden pole structures that aren't as visually menacing. The voltage is the same on all of these, all 230kV stuff from the same substation. Note the quantity of insulators instead of judging by the structure. Better yet, stay away no matter what.
This is 34kV subtransmission coming in from the upper right and being stepped down to (I think) 8kV distribution. This is a cheap way to get around building a proper substation behind a fence. The box on the second set of poles is a field recloser, the device which will open for a fault farther along the low side and then may attempt to reclose the line one or more times. If the fault self-clears, the customers see an outage of a second or two. If it doesn't clear, the recloser will give up and stay open.
This tower on the left is one of the big dogs, a 500kV line, over twice again as big as the last big line picture earlier in the psot. If this is laying on your structure you better be a long, long way away from it.
As mentioned in the last tutorial, one clue to extremely high voltages is the presence of multiple conductors per phase. In this case, each phase is made up of three cables. You can see little triangular brackets holding them in place along the line. Then there's those really long insulator strings to clue you in.
Once again you can barely make out the shield wires way up on top.
On the right is a close up of the triple conductors on the 500kV line.
The parting shot illustrates another exception to the rules. I kept going on about high voltage transmission lines always being present in threes, and here you can see there are only two conductors on what in every other way looks like high voltage.
This is one of the small handful of high voltage DC transmission lines in North America. Six DC lines tie the Eastern and Western electrical interconnections across the Rockies, two DC lines tie Texas to the rest of the U.S., two DC lines tie Quebec to the world, and there are probably no more than 10 or so major DC lines anywhere else in North America. Other than the interconnection tie points, they always go a long long way (many hundreds of miles) when they are built.
All major AC lines, the stuff that makes up 99.9% of the grid, are three phase and require three conductors to be in service. DC lines are singular, thus you can run either one of these individually, but normally both are in service. So, despite the 'rule of threes', here is a way you can get one or two cables of high voltage, and these run at around 250kV. The long insulator strings should give away the high voltage present, anyway.
What we learned: (1) You can now impress your friends and coworkers by identifying the clutter on poles. Impress them further by showing that you know enough to stay away from all of it no matter what. (2) The Grumpy Dispatcher's posts are waaay too long, except for those nifty FAIL pics he puts up once in a while.
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