Fire retardant cabling has been a critical factor in the overall safety requirements for Eskom’s two new OCGT (open cycle gas turbine) power stations, called Gourikwa and Ankerlig at Mossel Bay and Atlantis in the Western Cape.
Power cable manufacturer Aberdare Cables, a Powertech company, was approached by main contractor and project co-ordinator Siemens to provide all of the cabling for both OCGT power stations, which are part of Eskom’s R150-billion newly-revised five-year capacity building programme.
“It was agreed that the control, LV and MV cabling would be manufactured by Aberdare Cables to SANS 1507 and SANS 1339 specifications which are attuned to local engineering, phase colour requirements as well as physical and climatic conditions,” said Aberdare technology development manager Antony Falconer.
“The cables are not armoured but had to meet very stringent fire performance criteria including IEC 60332 Part 3 Category C, which demands that the cables withstand a flame propagation test at a density equating to 1½ litres of combustible material per linear metre.”
Falconer added that the major challenge was to meet the SANS specifications and the flame retardant requirements with unarmoured cable insulated with XLPE (cross-linked polyethylene), ensuring minimal damage would be caused if the cables were exposed to fire.
“We were able to overcome this challenge by applying a special tape over the laid-up XLPE insulated control and LV cable cores while the MV cabling, which incorporates a screening copper tape as standard, met the fire-retardant requirements without modification. A major advantage of the XLPE insulation is that it has a higher temperature rating and is safer than cables sheathed with PVC (polyvinyl chloride) which, when burnt, release halogen gases.”
The issue of power cables in fires is both complex and multi-faceted. Falconer said it is difficult to predict with any accuracy or certainty how cables will behave when a fire breaks out because so many variables can apply.
“This is why tests, conducted in a specific and scaled manner, and the detailed comparison of cable performance across different designs and materials, are essential to arrive at the right cable design for a specific application.”
Aberdare Cables also had a parallel enquiry from a marketplace in Europe for the manufacture of similar fire-retardant cabling that is tape-free and precludes use of PVC. This cabling has subsequently been developed by Aberdare and approved in Europe. Falconer believes that local applications for this cabling will soon materialise.
The Gourikwa and Ankerlig OCGT power stations at Mossel Bay and Atlantis will bring an additional 1050MW of electricity to supplement the national power grid. They are expected to come on line in time to provide Eskom with a capacity buffer to meet peak demands during winter this year.
The 450MW Gourikwa plant is located next to the PetroSA fuel manufacturing facility in Mossel Bay, which provides diesel fuel for the turbine. The 600MW Atlantis plant receives diesel fuel by road. Eskom has plans in place for the OCGTs to deliver an additional 1 050 MW in the future, which will double the total output of the two gas-fired power plants to 2 100 MW.
The open cycle gas turbines are fired by liquid fuel mixed with compressed air in a combustion chamber which ignites to form hot, high velocity gas. The gas passes through turbine blades that turn generator rotors to produce electricity. Gas turbine generating sets inherently have high operational flexibility and their rapid run-up capability makes them ideal for meeting relatively short peaks in load demand.