State-owned power utility Eskom’s 765 kV transmission projects’ activities, which fall under its Power Delivery Projects (PDP) division, are currently concentrated on the Hydra-Sterrekus transmission line scheme, in the Western Cape, with completion for the Sterrekus line estimated to be in March 2016, says project manager Ravi Naidoo.

The 765 kV team is constructing the transmission line on the remaining section of the scheme from Ceres to Cape Town, which will service the province.

Naidoo notes that the completion of this section in the Western Cape presents several challenges for the team. “Construction of this project is extremely difficult, owing to restricted access in the mountains, where it is difficult for construction vehicles, heavy cranes and concrete trucks to reach tower positions.

The 765 kV Portfolio
“The PDP division has, to date, construct about 1 400 km of line for the Hydra-Sterrekus scheme and has yet to construct about 200 km to complete the entire scheme,” he says.

The 765 kV portfolio of build projects consists of transmission lines and substations across four provinces – Mpumalanga, Free State, the Northern Cape and the Western Cape. The portfolio comprises two main schemes, the projects north of the Hydra substation near De Aar, in the Northern Cape and projects south of the substation.

Although the 765 kV transmission line expansions were discontinued in the 1980s when Eskom had surplus electricity, the 765 kV lines expansions were re-introduced when the country’s electricity needs increased in 2006.

Advantages of the 765 kV line infrastucture include the capacity to transfer power at 400 kV and 765 kV, but should increased capacity be required, infrastructure would be in place to accommodate the increased capacity and provide better transfer capability of bulk power over long distances, such as to centres in KwaZulu-Natal and the Western Cape, Naidoo says.  

However, he notes that the 765 kV lines will not replace the existing 400 kV lines, but will enhance the network’s transfer capacity.

Transmission Expansion
Eskom notes that, by 2016, the 765 kV network will stretch from the power stations in Mpumalanga to those in the Western Cape, while the projects – once completed – will introduce a transformational capacity of 10 000 MVA and 1 600 km of 765 kV transmission lines.

Further, the expansion plans for the transmission grid infrastructure will continue until 2021, while the total estimated cost of the projects is R171-billion. About R4-billion is allocated to customer-related projects, R27-billion to integration projects and an estimated R140-billion to reliability projects.

Engineering News reported last year that Eskom noted that 6 000 MVA of the planned 10 000 MVA had been commissioned and was in commercial operation, while 1 243 km of 1 600 km of line had been built, with 501 km energised at 765 kV and a further 300 km energised at 400 kV.

Energisation of the southern portion of the portfolio would introduce 2 000 MVA and 1 100 km of 765 kV transmission lines to the national grid, with the strategic benefit of a strengthened feed to the Western Cape, while the remaining 2000 MVA transformer would be energised in 2015/2016, Eskom reported.

Meanwhile, the Hydra 765 kV substation was commissioned in July last year, and the 2000 MVA 765/400 kV transformer was put on load in August last year.

Further, electrical installation and testing is currently ongoing at the Kappa and Sterrekus substations in the Western Cape.

However, Naidoo says the integration of the new Medupi power station, outside Lephalale, in Limpopo, is mainly through the 400 kV network to Rustenburg, in the North West, and Polokwane, in Limpopo. While one of the lines is built at 765 kV, it will be operated at 400 kV in the interim, enabling Eskom to have the option of upgrading the line to 765 kV in the future, he adds.

In addition, Kusile power station, in Mpumalanga, and the Ingula pumped- storage scheme, in the Drakensberg of KwaZulu-Natal, will mainly be linked to the grid through existing 400 kV networks, as both are close to established networks and load centres, Eskom says.