Building a Line

Step 1: Land clearing

The power line right-of-way is cleared of vegetation to allow operation of a 735-kV line according to the established standards. The work can be done by the landowner or by a logging contractor appointed by Hydro-Québec after an agreement is reached with the landowner. Depending on the terms of the agreement, the cut wood is either left with the landowner or recovered by Hydro-Québec.

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In order to properly locate the centreline of the right-of-way, or ROW, surveyors must clear a strip approximately two metres wide.

The ROW is cleared of vegetation for reasons of safety and reliability. In fact, its width is mainly determined by two factors: the intensity of the electric field at the edge, and the height of the surrounding vegetation, since any trees or branches falling on conductors constitute a potential danger for the power system.

The wood is then gathered: merchantable timber is recovered when necessary, and branches and plant debris are generally burned.

Recovered logs are generally left at the edge of the right-of-way.

Step 2: Temporary access

Temporary access roads are used to build the line. A crew sets up the equipment and structures necessary to protect rivers and streams, cultivated lands and other sensitive components.

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The temporary access roads used throughout the project are carefully studied and, after agreements are reached with the landowners concerned, clearly identified.

Sensitive components such as rivers and streams are protected. Here, a crawler carrier transports a temporary bridge.

Here, a stream is crossed by means of a temporary bridge over ten metres long.

Step 3: Stockpiling

The various tower parts are manufactured and delivered by type. The stockpile managers take care to organize the hundreds of parts in the order in which they'll be used to assemble each tower. In fact, each tower has different characteristics based on angle, topography and soil capacity.

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Parts are manufactured and delivered by type to a stockpile site. To construct a tower, hundreds of parts must be gathered, each with specific dimensions and in precise quantities.

Towers from the same line are not all identical. The type of tower used (suspension, angle, anti-cascading, etc.) depends on the angle of the line route, and each tower is adapted in height according to the obstacles encountered (rivers, roads, etc.).

Step 4: Delivery of steel

The steel parts needed for the placement of the foundations are delivered by semi-trailer at the edge of the right-of-way and are usually transported to the jobsites by crawler carrier. Then the steel tower parts and hardware are delivered to their sites by the same method.

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After careful planning, the steel parts are generally delivered by a crawler carrier.

All the necessary parts are piled up in the location where the tower is to be erected.

As soon as the foundation is assembled, the crew is ready to move on to the next step.

Step 5: Establishing the foundations

A work crew excavates the foundations using bulldozers and hydraulic shovels. Depending on the nature of the soil, the foundation may be made of fill delivered by truck or crawler carrier, or of concrete, which may be delivered or prepared on-site. Once the foundation is in place, the excavation is backfilled.

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Here, excavation work is done with a hydraulic shovel.

In sites with low bearing capacity, piles are driven into the ground.

Preparatory work is required before the concrete can be poured.

This formwork will hold the concrete in place at the pile head, to which one of the tower legs will be attached.

Step 6: Tower assembly and erection

A crew assembles the towers using cranes and bulldozers. The 800 or so parts of a 735-kV double-circuit tower contain some 10,000 bolt perforations ... Definitely a job best left to the professionals.

The tower is then erected by means of a telescopic crane.

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Assembling the tower on the ground might seem simple, but it's actually a huge three-dimensional jigsaw puzzle ... a job reserved for professionals!

A lattice tower such as this one includes some 800 parts and 10,000 holes in which thousands of bolts are inserted.

This suspension tower, which will weigh some 30 tonnes, is slowly erected by a telescopic crane.

Depending on the project, lineworkers erect extra-high-voltage towers as much as 40 to 60 metres in height.

Clamps, insulators and other line hardware are installed.

Step 7: Conductor stringing

The conductor stringing is done segment by segment. The conductor is paid out from a cable drum at one end of the segment and run through stringing blocks at the tops of the towers. At the other end of the segment are a puller and a take-up reel. Line crews are on hand to ensure that the operation runs smoothly.

Finally, for tower grounding and protection from lightning, "counterpoises" or anchor rods are installed in the ground.

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The cable reels, also called drums, need to be transported by bulldozer, because each drum contains some 2,000 m of 735-kV conductors and weighs some 5 tonnes.

A tension site (a cable let-off reel and a bull-wheel tensioner) is installed at one end of the line segment and a pull site equipped with a winch at the other.

The conductor is strung over segments of 2 to 6 km. For example, with this 735-kV line, it is being strung over 7 or 8 towers at a time, which is about 4 km. Because each drum contains approximately 2 km of conductor, compression joints are applied.

This 735-kV conductor, made up of a 7-wire steel core and 47 strands of aluminum, must be prepared for connection to the next length of conductor.

A conductor joint is placed on the two ends and pressure is applied, thus forming a solid connection between the two lengths.

Conductor sagging requires detailed calculations. The distance between the ground and the lowest point between two towers is called the "sag." Using sag measurements, a predetermined strain is applied to the conductor. The conductor will then stretch in a predictable way depending on its temperature as well as other factors.

Clipping-in consists in securing the conductors in suspension clamps, then with spacers to maintain the distance between the conductors.

The anchors ensure that the towers remain grounded.

Step 8: Inspection

A compliance monitoring plan is prepared for each project according to the specific requirements of the engineering team. Hydro-Québec inspectors ensure that ISO 9001 (quality management system) and ISO 14001 standards (environmental management system) are met throughout the project; their inspections include sampling of steel, foundations, conductors and other components.

At the end of the work, before the crews are authorized to leave the site, Hydro-Québec conducts a final inspection to ensure that all aspects of the project meet the current standards.

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To inspect the thousands of bolts in the tower, inspectors must venture 40 or even 60 metres above the ground!

Placed end to end, the 800 parts of one tower would stretch over 2.1 km.

Steel, bolts, insulators, ground wire ... everything must be methodically inspected and approved.

Step 9: Site restoration

At the end of the project, work begins on restoring the right-of-way and dismantling temporary access roads. A tour of the site with the landowner ensures that the restoration work meets his expectations. Compensation is also provided for any losses incurred.

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After the work is completed, the temporary equipment is removed.

The earth is leveled, drainage restored and the soil decompacted where needed.

Hydro-Québec then inspects the site together with the landowner.

Step 10: Preparing land for cultivation

When a new right-of-way is located in a wooded area and is adjacent to a field where there are farming or silviculture operations, Hydro-Québec will, at the landowner's request, evaluate the possibility of cultivating the land. If the land has adequate potential, Hydro-Québec will carry out the necessary preparations such as grubbing, destoning, draining, etc.

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If the right-of-way is adjacent to cultivated land, it can be put to agricultural use. Here we see a right-of-way before cultivation.

The same right-of-way after planting.

In the case of the 735-kV Saint-Césaire–Hertel line, the area of cultivated land is 60 times greater than the area occupied by the 125 towers (36 hectares cultivated versus 0.6 hectares occupied by the towers).