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Erection of Kincardine River Crossing Pylons

Flash Bristow was lucky enough to watch a film showing how the Kincardine River Crossing pylons were erected in the 1960s. Here she gives a step by step explanation of the process.

As with other river crossings, the Forth crossing at Kincardine required a tall crossing tower (pylon) on each side of the river, and some way back from each of those was a solid and squat looking anchor tower, also known as strainers (they take the strain between the regular towers and the elevated river crossing towers).

Thames crossing pylons

To demonstrate what the arrangement looks like, here are the anchor tower and crossing tower from one side of the Thames crossing at Thurrock. You can see that the wires run from tension insulators on the anchor tower up to suspension insulators on the crossing tower. From here the wires pass over the river to the opposite crossing tower, and run back down to the anchor tower behind it.

Below are stills from the film, with explanation of each stage. You should read them row by row, from left to right, i.e.
1 - 2
3 - 4
5 - etc.

We start with the construction of a crossing tower. Bolt assemblies are fixed at each corner (to form the bottom of each leg).

Parts are assembled on the ground and lifted with a 125 foot derrick (crane).

Slowly the tower takes shape.

Once the main body is done, a centre column 15ft square is built. Because the tower has such a wide base, it's easier to get a straight lift inside the tower.

Bolts are tightened by hand.

The cross arms are lifted up the tower, one at a time. Each weighs 2.5 tons and will support a 3 ton insulator set.

In the lab, the insulators are given a flashover test at more than 1,000,000 volts. Once on site, they are winched up the tower, completing the pylon's construction.

The conductors (wires) must be strung through the pylons without touching land or water at any point, to avoid damage from abrasion.

In order to keep the conductors off the ground, they will be pulled across using ropes. These ropes are laid on the river bed and then pulled taut by winches.

The conductors arrive in reels, ready to be connected to the ropes and hauled up onto the pylons.

A pulling plate is attached to the end of the conductor...

...then it is attached to the haulage rope and begins rising towards the first anchor tower.

As the conductor approaches the tower it goes over rollers...

...through a cradle attached to the side of the tower.

As the conductor passes through the anchor tower, every 80 feet of the track rope a trolley is put on, which is clamped to the haulage rope.

To each trolley a boom is attached, with a bobbin...

...which supports the conductor as it continues towards the crossing tower.

The conductor passes through the crossing tower's cradle and is now pulled across the river.

As each suspender reaches the crossing tower, it is removed and reattached on the other side.

Once the conductor has reached the opposite tower, an engineer checks the ropes and wires.

As planned, the conductor now crosses the Forth, hanging from the ropes on suspenders.

Back at the start point, the end of the conductor passes into the first anchor tower, where it is attached to a quadrant plate.

This way, the trailing end of the conductor is supported clear of the tower.

Now both ends of the conductors are attached to winches, which start turning.

As the winches pull the conductor tight, it lifts up, pulling itself free from the suspenders. Above, you can also see the cradle on the side of the tower.

Now the cradle is lowered until the conductor it supports is at the right height for attaching to the insulator set.

The ends of each conductor are attached to the tension insulator sets on each anchor tower.

On the crossing towers, where the conductor will be connected to suspension insulators, a layer of armour rods are attached.

This will prevent damage to the surface of the conductor, which is then attached to the bottom of the insulator set.

Dampers are added to the conductor to prevent the wind causing dangerous oscillations.

Finally, arcing rings are fitted to the insulator sets.

That's it! All six conductors, plus the earth wire at the top, are strung by the same method. Finally the track and haulage ropes are removed.

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