Electricity and Control December 2021-January 2022

DRIVES, MOTORS + SWITCHGEAR : PRODUCTS + SERVICES

Complex stator rewind at Eskom pumped storage power station

Marthinusen & Coutts (M&C) performed a significant rewind in 2020 when it was contracted by leading international hydro power generation OEM – Voith Hydro of Germany – to wind the stator of Unit 1 at Eskom’s Drakensberg hydro pumped storage power station near Bergville in KwaZulu-Natal. The massive stator winding contract, undertaken by a winding team from M&C under the supervision of Voith, was the final stage in the refurbishment of three of the station’s four motor-generator units. Eskom engaged Voith to refurbish Unit 1. Richard Botton, M&C’s Divisional CEO, who project- managed the winding of the stator of the 281.5 MVA reversible motor-generator, said: “We have worked with Voith over several years, during which time we have performed similar projects, such as a stator rewind at Eskom’s Ingula pumped storage scheme and others. These projects have stood us in good stead and almost certainly played a role in Voith’s decision to award us the contract for Unit 1.” Work was due to have started early in 2020 but got under way only in late August as a result of Covid-19 and the ensuing strict lockdowns. “This left us with only three months to complete the rewind – half the period originally allocated. We introduced two shifts per day with a 10-man team on each shift to ensure the work was completed on time,” Botton said. After removal of the rotor, the 6.5 m diameter stator was wound in situ. Deploying a Voith-supplied winding kit, the winding teams were required to install 720 heavy- duty stator bars that had to be connected in an extremely complex bus arrangement. “Our teams had to undergo special training by Voith technicians before starting their work,” Botton pointed out. The contract was completed on schedule in mid- November 2020. A further demonstration of the depth and range of expertise M&C offers in its field followed when Engineering & Technical Executive Rob Melaia recommissioned the unit.

After the rotor was removed, M&C technicians set to work inside the stator to install several hundred stator bars as part

of the stator winding contract. Recommissioning Unit 1

When international travel restrictions prevented Voith from flying in one of its own senior engineers from Germany to recommission the unit, the company asked Botton if M&C could assist. He recommended Rob Melaia to perform the recommissioning, as Melaia has previously commissioned other power plants as part of repair and refurbishment contracts M&C has undertaken. These have included the N’zilo hydro station in Katanga province, DRC, in 2013 and the SA Bureau of Standards’ National Electrical Test Facility’s High Power test laboratory in Gauteng last year. After checking and approving Melaia’s credentials, Voith assigned the recommissioning to M&C. Hours of conference calls followed between Melaia in his office at M&C’s main repair facility in Cleveland, Johannesburg, and senior technicians at Voith’s head office in Heidenheim, Germany, who provided detailed instructions on the required procedures. He performed the recommissioning successfully over a period of five days in March 2021. Commenting on it, Melaia said: “By the time I got to the site I was thoroughly briefed on what I was required to do. The process was challenging and I had to give it all my attention. The single thing that gave me the greatest confidence was knowing that M&C had done the winding of the stator; I wouldn’t have felt so confident if anyone else had done it.” Mike Chamberlain, M&C’s Marketing & Commercial Executive, commented: “In this contract M&C has again demonstrated its ability to rewind complex large machines, including complying with the OEM’s stringent specifications. M&C also demonstrated its flexibility in adapting to the delays caused by circumstances outside its control – the team ensured that the project was delivered on time.” For more information contact Marthinusen & Coutts. Tel: +27 (0)11 607 1700 Email: support@mandc.co.za, visit: www.mandc.co.za

[Image courtesy of Eskom]

The turbine hall at Eskom’s Drakensberg pumped storage power station.

14 Electricity + Control DECEMBER 2021-JANUARY 2022