Gearbox designer and manufacturer Hansen Transmissions South Africa has completed the supply of 384 Hansen M4 air-cooled condenser (ACC) drives each to State-owned power utility Eskom’s coal-fired Medupi power station, in Limpopo, and the Kusile power station, in Mpumalanga, last month.

While the company, a subsidiary of Japan-based Sumitomo group of companies, has been supplying drives to Eskom’s new builds for the past three years, the Medupi order received in 2008 was the single biggest order received by the group worldwide, Hansen MD Fritz Fourie tells Engineering News.

“Projects of this size are, therefore, regarded as flagship projects and become a material reference project for the Sumitomo group and for Hansen Transmissions South Africa,” he stresses.

The Hansen M4 ACC drive is a purpose-designed gearbox, comprising a mono-block housing, ensuring a rigid casting with relatively low deflection. Other features include high thermal efficiency from a finned housing casting dissipating heat efficiently and an axial fan mounted in the motor lantern specially designed for efficient air distribution over critical parts of the gearbox.

The design also lends itself to long-service intervals and low operational cost through the use of low volumes of long life synthetic oil alleviating the difficult access conditions at the power stations to conduct maintenance, Fourie notes. To eliminate the risk of oil leaks, all lubrication piping is enclosed in the housing and each housing has an integral drywell. The gearboxes are also equipped with integral backstop assemblies to prevent windmilling.

According to Hansen Transmissions’ website, the M4 ACC drive is also available in six sizes, with an output torque range from 20 kNm to 70 kNm, and a range of reduction ratios, designed to comply with the standard Cooling Technology Institute specifications for gearboxes. The website further states that the drive’s helical gears are designed and rated in accordance with the American Gear Manufacturers Association for maximum load capacity, minimum losses and quiet operation.

The company also completed delivery of 65 P4 conveyor-drive gearboxes for materials handling operations at the coal stockyards and feeding terrace of the Kusile power station last month, says Hansen Transmissions South Africa project manager Chris Lubbe. He adds that 32 drives will be delivered this month.

The P4 conveyor-drive range is available in 19 different sizes, with a torque capacity ranging from 6 kNm to 1 100 kNm, and power rating of up to 7 500 kW. It is available in two, three or four-gear stages, with reduction ratios of between 6.3 and 630. There is also the option of a solid or hollow low-speed shaft arrangement, and a parallel or right-angle shaft arrangement to cater for specific industrial requirements. A single-stage version for applications, such as pumps, is also available.

Lubbe says orders for projects, such as Medupi and Kusile, prove that the company can manage three substantial projects successfully and simultaneously, as the delivery times of the Medupi and Kusile ACC drive orders, as well as the orders for the Kusile stockyard conveyor drives, overlapped.

The three orders involved material intricacies – particularly the stockyards and the different specification levels that the products had to meet to apply, Lubbe emphasises, noting that this challenged Hansen Transmissions South Africa to maximise company performance. He suggests that this performance created a material selling point for the company’s capabilities as a supplier and after-sales service provider for megaprojects.

Protection and Preservation
Hansen Transmissions sales and marketing manager David Main adds that, since several of the gearboxes remain in storage, as a result of project delays and complications at the new builds, the company introduced a corrosion-protection and preservation programme for the drives and gearboxes.

The programme entails the company inspecting the gearboxes every three months, as well as adding a corrosion inhibitor to them. The regular inspections also aim to ensure and monitor corrosion protection, as well as monitor any tampering, which might disturb the hermetically sealed environment of the gearboxes, he explains.

“As the gearboxes are stored on site – often under fairly arduous conditions and exposed to the natural elements – we need to ensure that we safeguard against any damage or wear prior to installation,” Main emphasises.

Planning Increase
While the new build project orders amount to almost R200-million, Fourie adds that a sizeable amount of the company’s yearly business is generated from direct and indirect contracts, new installations, as well as general, daily work on repairs and maintenance on Eskom’s existing coal-fired fleet, with work conducted at Majuba, Matimba, Kendal and the Lethabo power stations across South Africa.

However, Fourie notes a definite increased awareness in the importance of regular service and repairs, as well as planned maintenance, from Eskom in the past six months.

Lubbe adds that, in the past year, the power utility increased its efforts to monitor its ordered products in storage and inspect the condition of the equipment.

This forms part of understanding product and maintenance risks, Main points out, reiterating that, in the gearbox industry, product lead and delivery times might vary from 16 to 22 weeks, with even longer times for larger drive units.

“These lead times, therefore, necessitate careful planning in terms of understanding the risk on existing equipment in the field,” Main concludes.