From the magazine, Microtunnelling, Tunnelling

Sparking Sydney’s CBD

The Sydney CityGrid project is Ausgrid’s plan for the Sydney CBD electricity network over the next decade and beyond. It involves constructing up to four new substations, replacing and upgrading the high voltage cables and constructing a new tunnel.

Ausgrid plans are also designed to meet new licence requirements to build extra backup capacity into the CBD network, further enhancing the high reliability of power supplies to businesses and residents in and around the CBD.

City East Cable Tunnel

A key part of the plan is a new cable tunnel running from Ausgrid’s property on the corner of Ann, Riley and Albion Streets to join the two existing CBD cable tunnels.

The first stage of the new City East Cable Tunnel (CECT) involves a 150 m extension to the existing City South Cable Tunnel (CSCT) from the Riley Street site to Wade place where the existing tunnel ends.

This extension would be constructed using roadheader technology and work is scheduled to begin in the first half of 2011, subject to the planning approval process.

The second stage of the CECT will be a 3.2 km tunnel from Riley Street into the new City North zone substation on the corner of Sussex and Erskine streets in Sydney.

This main section of the tunnel would be constructed using a tunnel boring machine (TBM), which was also utilised for the construction of the recently completed City West Cable Tunnel (CWCT).

The cable tunnel will be approximately 4 m diameter and between 10 and 55 m below ground level.

The use of the cable tunnel for the 132,000 and 33,000 volt cables is designed to minimise major disruption to the community and widespread relocation of other utility services. The alternative would be the traditional “÷pit and duct’ method of cable installation. This would involve the excavation of trenches – often in busy city streets – laying of conduits in the trenches, pulling cables through the conduits and finally jointing the cables from pits or vaults along the cable route.

The CECT will be the third dedicated transmission cable tunnel in the CBD and will link into the CSCT and the CWCT to form an electricity supply ring around the CBD.

The key elements of the proposed CECT project are:

  • Constructing a 3.2 km fully lined electricity transmission cable tunnel, using predominantly TBM technology
  • Constructing a connection point into the 33,000 volt network in the domain
  • Installing 132,000 and 33,000 volt electricity transmission cables, and
  • Constructing a permanent tunnel entrance and ventilation intake at the Riley Street site that would be housed within the proposed new Riley Street substation.

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