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Operational transmission lines running at a power station

Withstanding the heat

When changing circumstances create the need to transfer more power through an existing transmission network the simplest solution is to “turn up the juice”.

But the scope to do so is very limited. Increasing the power raises the operating temperature of the conductors, the thick wires between the pylons. This causes them to sag and could infringe clearances – the statutory regulations that dictate the distances from live cables to physical things below, such as motorways, woodlands and moorland. Turn up the power too much and the conductor will anneal and weaken, and corrode at a faster rate. Eventually it will fail.

Increasing capacity

In most circumstances, capacity cannot be increased by simply adding more cables because that will overload the pylons. However, high-temperature conductors that expand less and can run at double the operating temperature of conventional ones without compromising electrical clearances are now available. They transmit about twice the amount of power.

Jason Rowan, manager of Mott MacDonald’s South Africa-based power group, says that, although there are many different types of high-temperature conductors, they basically all use a material that deals better with heat.

Early conductors were made of copper, which is hugely expensive. Aluminum replaced copper in the mid-20th century, with alloy blends coming in during the 1970s and 1980s. Some relied on a steel core for strength. The technology remained reasonably static until the early 2000s when carbon fibre core cables were developed and improved the business case for renewing overhead power transmission lines.

Fraction of the cost

The basic process, which is a common activity for many Mott MacDonald transmission and distribution teams around the world, is to undertake a full condition survey of the existing assets. This involves inspecting the condition of structures to identify corroded or missing members. Pylons are then refurbished, electrical clearances checked and new conductors installed, increasing the transmission capacity for a fraction of the cost of installing a new line.

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