North Shore cable upgrade project: AusGrid


In June, Ausgrid made headway with its major cable upgrade project in Sydney’s North Shore; an investment that will replace the area’s 40-year-old cables and keep the backbone of Sydney’s electricity supply running reliably.

Crews have begun trenching for Ausgrid’s North Shore Cable Project, designed to replace fluid-filled cables that are about 40 years old.

The 132kV cable circuits were installed in 1971 and 1978 and help form part of the backbone of Ausgrid’s electricity supply to Sydney, running between a switching station at East Lindfield and substations at Castle Cove and Artarmon.

Ausgrid general manager network development Brett Hooper said the route for these cables follows the existing cable routes in most places.

“The existing cables have served the area well, but the time has come for them to be replaced,” Mr Hooper said.

“These replacement cables will also support new and upgraded substations at North Sydney and Crows Nest.”

Ausgrid considered a number of factors in deciding the route for these replacement cables including environmental impact, construction risks, traffic impact, route length and the cost efficiency of the project.

“Ausgrid has been working very closely with the community on finalising the location of the cables,” Mr Hooper said.

Initially, the Artarmon end of the route was designed around a section of local bushland. Following concerns raised by a local bushcare group, the planned route was altered to continue along the road and minimise any impact on nearby trees.

Heating effects from existing cables in the street had to be considered to ensure the capacity of the cables would not be affected before this route change could be confirmed.

A planned joint bay in Roseville has also been relocated from a residential street to a section of land at the end of a cul-de-sac. This relocation followed consultation with the local community and achieved a cost saving by reducing the length of cable needed by more than 200m. It also means construction impacts on homes is minimised.

Electric and Magnetic Fields (EMF) were raised as a concern by some residents. EMF is produced by everything that uses electricity including cables, electrical appliances, televisions, fridges and computers.

Safety is Ausgrid’s highest priority and the network is planned and operated to keep the community and workers safe. Based on independent magnetic field modelling, the cables will operate well within Australian and international health guidelines.

In considering magnetic field limits, Ausgrid is guided by the Commonwealth Government agency, the Australian Radiation Protection and Nuclear Safety Agency (ARPANSA). The current interim guidelines for exposure to magnetic fields recommend a safe public 24-hour exposure limit of 1000mG.

Ausgrid held a number of meetings with the community and individuals to discuss the project and measure existing levels of EMF in the streets and at their homes.

In line with the concept of prudent avoidance, Ausgrid has developed a new technical solution to reduce the predicted impact by rearranging the way the new cables will be installed.

Known as inverted trefoil, this arrangement involves optimising the phasing while physically orienting the cables with one circuit in a conventional trefoil arrangement and the adjacent circuit in an inverted or upside down trefoil.

This innovation has been tested at Ausgrid’s testing laboratory in Lane Cove and has been proven to reduce EMF levels by more than 50 per cent at a distance of 5m from the cables.

For this project, the cables will also be installed in the roadway, rather than the footpath, which will further reduce the fields experienced at properties. Additional network measures both upstream and downstream of the cables will also be implemented to better balance loads on adjacent feeders. This will reduce EMF levels further by increasing the level of EMF cancellation.

Conservative and independent modelling of this project shows average magnetic fields to be less than 1 per cent of the recommended exposure level when 5m away from the cables.

At property boundaries it is expected to be less than 2mG – that’s less than 0.2 per cent of the recommended level and consistent with typical background levels.

“We build our network to be safe,” Mr Hooper said.

“The innovative solution of the inverted trefoil shows our commitment to continuous improvement.”

Construction work on the North Shore Cable project is expected to continue until mid-2015, with crews safely excavating trenches, installing conduits, pulling the cables, jointing and connecting them to the substations.

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