Electrical transmission line upgrade

This is one of a series of presentations of photographs of an ongoing upgrade to a 345 kV electrical transmission line that passes near my home. The upgrade consists of the addition of a second circuit to increase the overall capacity of the line.




Here we see a 120' tall transmission tower being moved to an extended base in order to raise its overall height by about 25'. As I understand it, this is required to meet current standards for conductor clearance over urban structures. (The line was originally built in 1979.)

These tower relocations were made after the addition of the new second circuit (on the far side of the tower in this view). Otherwise, the unbalance in weight of the original circuit conductors would have made it impossible to move the tower with a single crane.

In fact, to minimize imbalance caused by small weight and tension differences in the two sides, the outermost conductor pair on each side was removed from the tower and temporarily supported by a crane (seen on the right, with the other one seen behind the tower).

The "original circuit" conductors remaining on the tower had to be removed from their suspensions and temporarily put into pulley-like stringing blocks ("dollies") so that the tower could shift while the conductors retained their location. On the new side, the conductors were still in the dollies through which they had been placed just last week.

The foreman said that his crew can usually do three of these relocations in a day.

Here we see the tower crew guiding the tower into place on its new base section.



The crew members were mostly from El Salvador, and were very skilled.

As soon as the tower was aligned and temporarily secured by drift pins though the holes, and the first few bolts put in place, a two-man crew ascended in a boom crane to begin making the permanent attachments of the conductors to the tower (actually now on both circuits).

If I were to prepare this image for display, I'd remove the crane seen behind the tower, but here I wanted to be scrupulous about "photographic honesty!

Best regards,

Doug

Doug,

I found these two photos fascinating. They're both beautifully composed images of crucial moments of infrastructure construction. Did your being on location involve luck, or some degree of foreknowledge?

If you have more to share, please do so.

Tom

Hi, Tom,

Tom Robbins said:

Doug,

I found these two photos fascinating. They're both beautifully composed images of crucial moments of infrastructure construction. Did your being on location involve luck, or some degree of foreknowledge?

Click to expand...

No, I'd been following the preparations for this job for some while (I had first noticed some premliminary work), and as it has gotten underway I have frequently visited some of the sites. Some time I will arrive at one site and the foreman will say, "you need to go down to Route 180, they will probably be moving that tower in an hour or so."

I takes lots of shots of the workers and distribute prints for them to take home. They seem to really enjoy that.

I have a lot more shots, and plan to do an extended essay, with a lot of technical discussion. I've been delayed by some family medical adventures.

Here is another one, posted earlier in another thread to pull somebody's leg:

http://www.openphotographyforums.com/forums/showthread.php?t=10037&p=82922

Thanks for your support.

Best regards,

Doug

Here we see a conductor of the "old" 345 kV circuit being detached from its insulator in preparation for the moving of the tower to its new, taller base.



On the right we see the two small stringing sheaves ("dollies") on a crane used to take the weight of the conductors while the workers detach them from the supporting insulator.

The spiral strands we see "sprung out", known as armor rods, were earlier tightly gripping the conductor. They are made of spring steel, "preformed" into that spiral shape, and gripped the conductor by virtue of that without benefit of any clamps.

At the center, they have an offset, where they pass by a split neoprene "spool" surrounding the conductor. Around them on the outside is a split metal "spool" (dark gray), around which passes a clamping band, by which this suspension unit and its mate on the other conductor are attached to a triangular plate (not clearly visible) suspended from the insulator string.

In the case of the two inboard conductor pairs, similar dollies were placed on the insulator and the conductors put into them, to be supported by the tower during the move. But for the "outboard" conductors we see here, they remained supported by the crane during the move. Because of their distance from the centerline, any difference in the weight or tension of the outboard pairs on the two sides of the tower would make it difficult to keep the tower upright as it was moved.

Nevertheless, after the workers removed these outboard conductors from the insulator, two small dollies were hung on the insulator. After the move, these conductors were put into those dollies, so that the "sag" of the conductors could be equalized on both sides of the relocated tower by shifting them appropriately through the dollies.

Only then were the conductors (all six pairs) permanently (re)attached to the insulators (using new, but identical, preformed armor-rod suspension units), a process known as "clipping in" ("clip" referring to a simpler, earlier type of attachment used on simpler traansmission lines).

This ingenious arrangement of preformed spiral armor rods was developed (for a slightly different application) in 1947 by Thomas F. Peterson of Cleveland, and became the springboard for his company, Preformed Line Products, which makes these (and numerous other products, many of them following the same concept) today.

Peterson's son, Thomas Jr., graduated from MIT in 1957, and joined his father's firm (which he later headed). Several of my college buddies (Case Institute of Technology, also class of 1957) somehow knew the younger Peterson. Notwithstanding the family business, his real passion was motion picture sound recording, a field in which I was also interested at the time.

One evening my buddies and I visited Peterson in his recording and editing studio in the basement of his parents' home in an eastern suburb of Cleveland. In fact, I negotiated with him to buy an antique Western Electric microphone mixer from his collection, but thought better of it before the deal closed.

(Instead, I used the money to buy a diamond ring for a young lady - not an engagement ring, just a Christmas present. But we later married, and remained married for 38 years until her untimely death from complications following a heart attack at the age of 58.)

Watching these skilled workers quickly remove (and later replace) the PLP Armor-Grip suspension units brought me quite a wave of nostalgia about that visit about 50 years ago.

Best regards,

Doug

One of the most interesting steps in the transmission line upgrade, and just about the last, is the installation of the spacers used to keep the two conductors of each pair at a consistent spacing. The work is done from "buggies" that travel along the conductors.

Here we see one as it crosses Meadowview Road near my home:


The buggy is powered by a small gasoline engine we see just forward of the worker's feet, driving the front wheels through the vertical shafts (brown) we can see here. We see several "dog-bone" spacers hung from hooks, ready for use. The rest are in a traditional lineman's canvas bucket at the rear of the buggy.

The hank of rope is for the worker to descend on if he should have an engine failure!

For perspective, here we see first-arriving buggy, earlier, as it approaches from two towers away:


Look at where the lower inner conductor pair on the right side is suspended from the tower (on the V-shaped insulator configuration). The small bundle of what looks like open-end wrenches dangling from the point of attachment is the set of spacers to be used in the next span. They were earlier staged at each of the towers (from bucket trucks) so the buggy riders would not have to carry a heavy load of spacers all the way.

Visually adjacent to the attachment point of the lower, outer conductor on the right side we see one of the spacers already applied between the two conductors in the prior span.

The buggies on the two lower conductors come along later to avoid any risk from objects dropped from the upper one:


They have just passed by the suspensions for their conductor pairs in a fascinating maneuver we will see in detail in the next part of this series.

[continued]

The buggies can't just drive past the points of suspension of their conductor "rails". A fascinating maneuver is used to get them past.

Here we see the worker having climbed out of his buggy onto the conductors to get ready for the maneuver. His safety strap, whose hook slides over one of the conductors while the buggy is traveling, has been snapped onto the suspension hardware.


He will then take the front wheel supports of the buggy and swing them outwards, clear of the suspension. He then pulls the buggy forward (supporting its front end with one hand) until the front wheel supports are past the conductor suspension, and he swings those wheels back onto the conductors.

Then he swings the rear wheels outward, pulls the buggy further forward until they are on the near side of the suspension, and swings them back onto the conductors.

Here we see this just before the rear wheel supports are swung back into place:


He then climbs back into the buggy and heads out onto the span. Total time: about three minutes.

Here we see one of the spacers being applied.


The two halves of the unit slide longitudinally, opening the ends so they can be placed around the conductors. Then the unit is slid closed as far as possible, bringing the neoprene liners against the conductor. We see it here almost fully closed.

Then a tapered-end "bolt" (we see it, bronze colored, at the center top of the unit) is screwed down from one half into the other. The taper forces the "sliding closed" to complete (slightly compressing the neoprene liners against the conductors), and then the bolt is "run home" to retain the assembly in the closed configuration.

In this shot, we get a better view of the vertical shafts (brown) that drive the front wheels through two 90° gearboxes (light aluminum color). Just above the lower gearboxes are universal joints, allowing the shafts to swing when the wheel supports are swung out when passing a suspension point.

This was the last major step in completing the transmission line upgrade. The two circuits were scheduled to be re-energized tonight.

I was fortunate to be able to follow the many stages of this process. The workers and foremen were very accommodating in helping me complete this project. And each morning, I filled them in on some background I acquired through study of Internet articles the night before.

Best regards,

Doug

Thank you for sharing these photos and for providinf the write-up.

Doug_Kerr said:

I was fortunate to be able to follow the many stages of this process. The workers and foremen were very accommodating in helping me complete this project. And each morning, I filled them in on some background I acquired through study of Internet articles the night before.

Click to expand...

Hi Doug,

Thanks for documenting it, it's interesting.
I'm sure some of the workers would love a print of them in action.

Cheers,
Bart

Hi, Bart,

Bart_van_der_Wolf said:

I'm sure some of the workers would love a print of them in action.

Click to expand...

Yes, I have distributed quite a few. In some cases, it's been hard to "catch up with them" to make the delivery!

Thanks.

Best regards,

Doug

Other onlookers

I wasn't the only onlooker during the transmission line upgrade.

Here we see some local residents across the road from the "pull feeding" site near my home:



We might ponder if they are wondering whether their headaches will get worse now.

Best regards,

Doug

Doug, are you a teacher by any chance? The pictures as good as they are, your narration gives tells me
the enormity of the task that these guys as a matter of course. The effort to bring to us, what is now accepted as common, is a little clearer. Concurrently, I can appreciate the monies, know-how, labor that goes into such an infrastructure undertaking. And the reason why many many people across the globe
are still without electric power.

Yes the bovine on-lookers must be having the same thoughts, too.

Thank you for enlightening me.

Hi, Fahim,

fahim mohammed said:

Doug, are you a teacher by any chance?

Click to expand...

Yes, although not always by title!

I have in fact taught in such contexts as a university continuing engineering education program, as well as in seminars presented to technical firms, government agencies, and the like.

But as an engineer, I am always a "teacher" at heart.

The pictures as good as they are, your narration gives tells me the enormity of the task that these guys as a matter of course. The effort to bring to us, what is now accepted as common, is a little clearer. Concurrently, I can appreciate the monies, know-how, labor that goes into such an infrastructure undertaking. And the reason why many many people across the globe are still without electric power.

Click to expand...

Thanks so much. In fact, I plan (perhaps later today) to pick up the story with a description of some more of the various processes involved.

Although I have a lot of background in the area, a large fraction of the information in this series was just acquired lately, by a combination of observation, asking questions, and then long trails of research over the Internet to find out what was really going on.

This has been my habit over the years. It can be dangerous.

About 40 years ago I had engaged a small "air taxi" service to take me from one of the New York City airports (where I had landed on a trip from Los Angeles) to central New Jersey, where I lived and worked at the time. I had flown with them several times.

Evidently, my seeming familiarity with the procedures, terminology, radio communication, and the like made this pilot think I was also a pilot, and after we had taken off, he said, "Boy, am I beat! It was a tough day. Do you mind taking her down to Red Bank"?

I gulped and said I would.

As we approached the little airport, and I was on the downwind leg of the approach, I said to the pilot, "I guess you know by now that I'm not a pilot".

He said, "Well, yeah. But you did really well. But would you rather that I made the landing?"

I told him that would be nice.

Sadly enough, the next year, a plane he was flying crashed into Raritan Bay, killing him and the passenger, a co-worker of mine.

Then there was the time, when I was just out of college, when at the invitation of the hostler, I took the last steam locomotive based in Cleveland on its last trip, from the roundhouse out over the turntable to be towed to the breaker's yard. But that's another story.

Best regards,

Doug

The actual placement of the conductor "bundles" (in this case, a bundle of two) is done in a multi-stage fashion.

The first step is to hang from each place a conductor bundle will be attached (usually at the bottom of an insulator string) a stringing block (sometimes known as a stringing sheave, a threading block, or just a wheel, but most often called, even in formal documents, a dolly).

Here Wes, a rope winch operator, shows off the type of dolly most commonly used in this project:


We can see the arrangement of the dolly sheave (wheel) here:


The center groove will carry, in the technique used here, in order, three pulling lines of successively larger size and greater strength.

When the actual conductor bundle is being pulled through, the two conductors ride in the two outer grooves. (We'll see in the next part of this how they get started into the grooves).

In territory such as this, with the right of way between towers easily accessible, the next step (actually done when the dollies are being placed) is to thread a small rope, called a pilot line, though each of the dollies. This is typically in pieces, each long enough to pass through the dollies on two or three adjacent towers. The pilot line is not under tension, and droops to the ground immediately on each side of each dolly.

Next the pilot line sections are connected together and a winch at the "pull" end of the pull section hauls on the pilot line, first pulling out all the slack in it, and then drawing a larger rope, called a sock line, through the dollies from the "feed" end. The name comes from the use of such a rope line in a different scheme, and doesn't actually fit what is done here.

The sock line is fed from a large drum on a rope winch. In this phase, this does not pull the sock line (which is heading out from this station), but rather (by means of brakes on the drum) places tension on it. The object is to prevent the sock line from sagging to the ground between towers.

Her we see the triple rope winch used on this pull, with Wes at the controls:


After the sock line reaches the pull station (in this case 19,000 feet away; 15,000 feet is the common limit), it is connected to a steel cable, often called the hard line. The rope winch at this end now hauls on the sock line, bringing the hard line through the dollies. At the "pull" end, the hard line is fed through a tensioner so that it will be under enough tension that it does not sag and touch the ground (it is fairly heavy).

The hard line will be used to actually pull the conductor bundle from its supply reels (at the "feed" end, here) to the "pull" end. We'll see that in the next section of this series.

All these pulls take place at a fairly high speed (up to 7 mph); at that speed, the transit of any of these ropes and cables through the 19,000 foot section takes about 30 minutes.

Now we are ready to actually emplace the conductors - actually, "conductor bundles", two cables about 15" apart actually making up each of the three conductors of the transmission line.

There are several reasons why the conductor is made of two cables, rather than perhaps one larger one. The main reason has to do with corona discharge. At these operating voltages (this line operates at a nominal voltage of 345 kV "phase-to-phase", which means a voltage to ground on each conductor of about 300 kV) the electric field surrounding the conductors is so concentrated that it "ionizes" the air molecules, such that the surrounding air may actually glow. This represents a loss of energy, generates radio-frequency interference, releases ozone into the atmosphere, and looks scary to nearby residents, so it is not an acceptable phenomenon.

Using a larger-diameter conductor decreases the concentration of the electric field and can prevent this phenomenon. But a conductor of sufficient diameter would be gigantically heavy and costly.

Instead, we "trick nature" into thinking (with respect to the electric field) that we have a larger conductor by using two conductors spaced some distance apart. (In fact, for extremely high voltage operation, three-conductor "bundles" are used, sometimes even six-conductor bundles - the emplacement of which is really tricky!.)

The conductors used are of the aluminum conductor, steel reinforced (ACSR) type, in this case with an effective cross-sectional area of about 1.6 MCM (million circular mils).

We see a sample of the conductor here, held by Carla (so as to show the scale):


A circular mil is the area of a circular conductor 1/1000 inch in diameter. This peculiar unit (which is actually pi/4 millionths of a square inch) is used so that calculations of area from diameter are simplified and do not involve the constant pi (we just square the diameter in thousandths of an inch). A solid conductor 1" in diameter (hardly practical) would have an area of one million circular mils (1 MCM).

The actual overall diameter of this cable is 1.56" (not all of the cross-section is conductor, and the area of the steel core is discounted to reflect its higher resistivity). It comprises 54 aluminum stands and 19 steel strands. Both serve to carry the tension in the cable. (There is another type of cable in which the aluminum strands are "soft and slack", so that the steel core carries all the tension. The theory of this is beyond this article.)

The conductor cable is fed from the reels on which it is shipped, mounted on trunnions on this feed trailer:


Two or three trailers are used in rotation on a pull involving a greater length of cable than can be shipped on one reel (perhaps 9000 ft.). The trailers are loaded with the reels with a crane at a nearby staging site, where the reels are stored after delivery.

The reel spindles are equipped with simple vacuum-operated mechanical brakes to apply enough tension that the cable does not unreel itself from the reels.

At the right, we see another view of the rope winch. The large truck tractor in front is not needed to haul it (it is not that heavy) but rather serves to anchor it so it does not pull itself along the ground. (This tractor, Marine Corps surplus, is actually one of the first pieces of equipment the founder of the construction company acquired, many years ago.)

The two red ropes we see passing through the scene to the rope winch are the sock lines that will be used to pull the hard line back to this end to pull the second, and later yet and third, conductor bundles.

The two conductor strands, as they come off the supply reels, pass through a tensioner, seen here:


There, they are each wrapped several times (five in this case) around a pair of grooved bull wheels. (There is an independent set for each of the two conductors.) The bull wheels are connected to hydraulic pumps/motors.

As the cable pays out, these act as pumps, with the hydraulic fluid flowing through restricting orifices, so that the back pressure retards the rotation of the bull bull wheels, placing tension on the cable strands. This is needed so the cables do not sag to the ground between towers.

The energy absorbed appears as heating of the hydraulic fluid, which is then removed by fan-blown radiators seen at the left end of the tensioner.

The tensioner can also pull the cable back a short distance, as is sometimes needed to deal with "snags" in the pull. To do this, an engine-driven pump on the tensioner feeds the bull wheel hydraulic motors/pumps as motors.

The D6R XL Caterpillar bulldozer on the left serves as part of the "anchor" for the tensioner (the total tension on the two strands can approach 20,000 pounds). The "dug-in" siting of the tensioner is also partly in the interest of resisting the reaction to the tension, but ismainly to assure clearance for the departing cables (since the next tower is some distance away, across a road , and on slightly lower ground).

The two clamp-like devices seen on the cables to the left of the tensioner are "traveling grounds". Their purpose it to prevent any possibility that a voltage could appear on the cable, either as a result of inadvertent contact with another energized power wire along the route (although elaborate precautions against that are taken) or as a result of "pre-lightning" atmospheric conditions. On each one, one of the two dangling "cables" seen is the actual electrical ground cable, and the other is a tether rope which prevents the tensioner from traveling away along with the moving cable.

All equipment grounds and the grounds for the traveling grounds are made to a heavy copper cable strung along the ground between the towers on each side of this site (the towers are grounded to elaborate buried ground fields).

Best regards,

Doug

The hard line (final steel pulling cable) attaches to the two conductor stands via a leader board, seen here in mid flight (about to cross Meadowview Road, near my home):


Curiously enough, this crew referred to the leader board as a "diving board" (a term that, in this industry, usually colloquially refers to a temporary rectangular work platform cantilevered out from a tower, sometimes called a "Baker board").

The leader board always reminds me of a manta ray.

The hard line connects to the apex of the board, and each of the rear corners connects to one of the conductor strands. The attachment is made with a woven steel mesh gripper (similar in concept to the famous "Chinese finger puller), called a sock. The open end is clamped with a steel strap to prevent any possibility that it might retreat, and both ends are taped to prevent snagging on the dollies. (We'll see that better illustrated in a later picture.)

We are now ready to explain why the pulling rope is often called a "sock rope". When there is only a single conductor to be emplaced (not a bundle), and the conductor is of more modest size and weight than we have here, the pulling rope is used to pull the conductor itself, not to pull a steel cable used for the actual pull. The rope then connects to the sock used to grip the end of the cable, hence the name. The name is often used, by inertia, even in the mode we have here (although this crew had never heard of it!).

The jointed "tail" of the leader board is sort of a keel, used to keep the board horizontal (especially when approaching a dolly). As the board passes through the dolly, the tail lifts up as needed to pass accross the sheave.

Here we see the leader board just having passed through a dolly, with the two socks (that's my daughter-in-law's horse's name) just about to enter the outside grooves of the sheave. (This sheave has an extra groove just left of center, probably used in some other situation. Most of the dollies in this job did not have such.)


Here we see the end of one reel of cable being attached to the beginning of the next (once for each conductor). You can see the socks in place.


Here we see all three conductor bundles in place after the pull to the South. The rope winch has already been moved to its position for the pull to the North (the last pull of this particular transmission line section).

The H-shaped wood structures are "guards" intended to prevent pull ropes or conductors from contacting the road (which passes just this side of the nearest tower) in case of some inadvertence in the process.

These had been erected every place the pull route crossed a road or another power line.


That just about completes the story of the transmission line upgrade (the final step, placing of the conductor spacers from little overhead buggies, was covered in an earlier episode).

Best regards,

Doug