IN its first order for generator power transformers, ACTOM Power Transformers has been awarded a R40m contract to produce four customised 60 MVA 12/132 kV units that are to replace old transformers at Cape Town’s 180 MW Steenbras pumped-storage.

The contract is also among the first orders the company has received for higher rated power units since upgrading and expanding its plant to enable design and manufacture of power transformers up to and including 160 MVA. The company’s highest rated units were 45 MVA prior to the R30 million expansion, which was completed in late-2007.

The transformers for Steenbras were ordered in early-April this year by Consolidated Power Projects, the electrical project management company contracted by the City of Cape Town’s Electricity Services Department to procure, install and commission the new power transformers in place of the existing 55 MVA units, which were supplied by GEC Alsthom when the power station was built more than 30 years ago.

The new transformers will incorporate oil-forced and air-forced equipment for cooling. “The design of these transformers is based on the most advanced technology available from our Europe-based consulting engineer, who is a leader in this field and who we are working closely with in the design and manufacture of the higher rated units we have begun producing since the expansion of our plant,” says Ronnie Russell, ACTOM Power Transformers’ general manager.

The first of the transformers is due to be delivered in February next year, with two more scheduled for delivery towards the end of 2010 and the fourth at the beginning of 2011.

Steenbras, located 50 km from Cape Town near Gordon’s Bay, was the first hydroelectric pumped-storage scheme in Africa. Primarily intended to generate during peak loads, it is used as the regulating station on the city’s electricity distribution network.

“It provides the city with very cost-effective generation,” says John Davidson, head of generation for the Electricity Services Department.

“Its generation output is automatically regulated to keep the Eskom power in-feed to the system within a predetermined monthly target demand, which ensures optimum utilisation of the plant and minimum overall cost of electricity supply.”

Each of the station’s four 45 000 kW generator units acts as a pump-motor in one mode and a turbine-generator in the other. Surplus national generating capacity is employed to utilise relatively low cost off-peak electricity available at night to pump water from a lower to an upper storage reservoir. During periods of peak demand in the day the water is released back to the lower reservoir, thereby generating electricity as in a conventional hydroelectric power station.