Although only one Tesmec machine will work on a job, up to 100 or so portable diesel-powered winches are at work raising operators and equipment up the power line towers. They help raise the workers’ aerial work platforms, the 2,000 kg insulators from which hang the cables, tools and other supplies.

Five years ago, the company bought a consignment of NIMS hydraulic winches from the UK’s Lifting Gear Hire to replace aging mechanical winches fitted with a five-speed truck gearbox. The risk of electrocution prevents the use of electric equipment, and air compressors tend to be loud and can be problematic in cold weather, he said.

What Power Networks found was that even with a maximum speed of 30m/min the hydraulic winches could not match the speeds of the mechanical gearboxes – particularly when it came to finishing the job and spooling the wire rope back up.

“There is a lot of wire rope standing 60m up the tower, and down, doing nothing,” said mechanical plant manager Rob Sonnex. “When you put the mechanical winches into fourth gear, they went like the clappers,” he said. “They were favoured by the staff because they were fast, but now they are very old.”

Instead, Sonnex headed up a team that worked to design a 3t hydraulic winch with the power to reel in unloaded rope at high speed. The winch, which was first used in summer 2005 jobs, can lift 3,000kg at 30m/min, 2,000kg at 65m/min and up to 750kg at 95m/min.

The winch has three hydraulic pumps: one 42L/min, one 84L/min and a third low-pressure circuit. It uses the small pump for heavy loads, the big pump for medium loads, and both together for the lightest loads and fastest speeds. The low-pressure circuit powers the operator switch and the three hydraulically-extended legs.

The winch uses a Brevini TNE3000 rope drum, Yanmar TNE 82 engine and produces a maximum 270 bar of pressure and a peak pressure of 324 bar. The team also helped develop an automatic safe load indicator that monitors hydraulic working pressure and drum diameter and emits a warning sound when the winch is working at 90% of capacity and cuts the engine at 100%.

This year, the company built a prototype and then built another 21. Sonnex said that the winch has been accepted for use by the UK’s power distribution organisation the National Grid, but has not been CE marked.