Work is well underway on the manufacture of extra high voltage underground cable to be supplied by Olex for the Victorian Desalination Project being built at Wonthaggi, 138 kilometres south-east of the Melbourne CBD.
Olex has taken delivery of eight drums of 220kV 500mm2 cable from Nexans’ Charleroi plant in Belgium as part of the $43M contract. Meanwhile, at Tottenham, 84 drums of 400m2 cable have been manufactured as at the end of May, which equates to about 105 kilometres of cable being manufactured for the project.
Operations Manager HV Projects, Naveed Rahman, described the project as one of the most significant in Olex’s history.
“Historically this length of circuit would be built as an overhead transmission line,” Mr Rahman said.
“An underground link was the preferred option for the project because it has the least impact on landowners, farmers and other people living and working in the area.”
The 87 kilometre cable route length will be installed in three sections:
· Section 1- Cranbourne Terminal Station to the Northern Compensation Station (NCS). This 12km section of the job uses 220kV 500mm2 cable supplied by Charleroi.
· Section 2 - NRS to the Southern Compensation Station (SRS), a distance of 37 kilometres, using 220kV 400mm2 cable supplied by Tottenham.
· Section 3 - SRS to the Desalination Plant Terminal Station (DPTS), a 38 kilometre length of 220kV, 400mm2 cable supplied by Tottenham.
Mr Rahman said Olex’s part of the project was currently running ahead of schedule, with manufacture of the cable at Tottenham expected to be complete by November 2010. The cable will be progressively installed throughout 2010 and 2011.
The $3.5 billion Victorian Desalination Project will deliver up to 150 billion litres of water a year to Melbourne and regional communities. The project includes an 84 kilometre underground pipeline to connect the desalination plant to Melbourne’s existing water network at Berwick and regional towns in South Gippsland and Westernport.
The electric power required by the new plant and booster pump station will be supplied by the underground cables, which will be co-located with the pipeline. This will be fully offset by the purchase of Renewable Energy Certificates by AquaSure
The cable being produced at Tottenham for the project is being made on equipment recently installed as part of a $20M factory upgrade. The new manufacturing equipment enables the plant to produce XLPE (cross-linked polyethylene) cables up to 500kV.
Technical Viewpoint
Olex is supplying approximately 260 kilometres of 220kV cables as part of the Victorian Desalination Project. This purpose-built 220kV cable system comprises many layers around the copper conducting core to provide electrical insultation, protection from external impacts (ie water, physical damage, termite attack) and the effects of induced sheath currents and voltages.
When transferring power using AC transmission (overhead or underground), the capacitance of the transmission line becomes a key design issue. Compensating devices installed at appropriate locations along the cable route – at the Booster Pump Station in Cardinia and Southern Compensation Site, near the Holden Proving Ground – will address this matter.
The transmission voltage of 220kV and cable conductor sizes were selected to minimise losses.
Olex has worked closely with AquaSure’s construction contractor, Thiess Degrémont Nacap, to finalise the cable system design including:
· optimum trench size and cable configuration to carry the required loads;
· consideration of local geotechnical conditions, including thermal resistivity;
· consideration of design life and durability requirements;
· induced sheath voltages mitigated by cross bonding; and
· finalising the location of cable jointing bays.
To get the best results, Olex has designed the system by implementing an earth bonding system known as ‘cross bonding’, which involves cross linking the metal sheaths in a link box to minimise the circulating currents / heat losses, thereby optimising cable circuit ratings. The link boxes are installed adjacent to every second joint bay location.
Olex, and its parent company Nexans, are global leaders in the design, manufacture, supply and installation of high voltage cables. The Victoria Desalination Project is drawing on this broad base of expertise to deliver a critical piece of infrastructure for the Victorian community.
*Image courtesy of Thiess Degremont