Sulzer engineers rebuild Australian generator from other side of the globe

After more than 25 years of continuous dedicated service, the trusty generator at Darwin power station, in Australia, was in need of a serious refurbishment. Cue a logistical triumph from Sulzer, as their engineers worked in tandem, from both sides of the globe, to hand build the generator's 108 new high voltage bars and rewind the stator for another quarter of a century of performance.

Darwin power station requires overhaul of 25-year-old generator

The power station in Darwin, Australia started life as a 200MW gas fired installation with three gas turbine generators that started full production in 1987. Having provided the population of Darwin with electricity for 25 years, it was important to ensure the generators continued to provide reliable service.

This led to the owners calling on the services of Sulzer to carry out an overhaul of the generator including a rewind of the stator. The 42kVA generator, operating at 11.5kV, was originally built in 1986, but after more than 25 years in service, the time had come for an overhaul.

Sulzer engineers, on opposite sides of the world, oversee the refurbishment

Using the OEM drawings, combined with the latest CAD, the engineers at Sulzer were able to start on the initial design stages and plan the logistics that would allow the contract to be completed on time. Once the project was underway, two teams of Sulzer engineers, on opposite sides of the world, set about the wide range of tasks required to complete the refurbishment.

The service engineers on site in Darwin began with dismantling the generator, while in Birmingham, UK, the coil shop worked on the design of the new high voltage bars and the dummy stator that would be used to check the dimensions of every one of the 108 bars as well as the support blocks for the windings.

'Reassembled and returned to service, ready for another 25 years'

The generator design consists of 54 bottom bars and 54 top bars, all of which have to be manufactured to tight tolerances in order to ensure they fit exactly into the stator slot. Each bar has to be formed and shaped by hand, using the CAD-designed, wooden formers that allow every bar to be produced with exactly the right shape and dimensions. The final shape is then checked again in the wooden dummy stator that was constructed earlier.

Every bar is tested in the dedicated test cell with the results recorded and kept in the engineering archives. Testing includes tan δ, which relates to the power factor of the bars as well as strand-to-strand short circuit testing and the outer corona protection (OCP) surface resistance measurement.

At this point the logistics team at Birmingham take over, having already constructed the shipping crates for the bars. Carefully packaging the bars to ensure they arrive undamaged is crucial to ensuring a trouble-free installation in Darwin. The shipment is timed to coincide with the disassembly of the stator on site, so as to avoid any unnecessary delays.

Once all 108 bars have been installed and secured to the end winding brackets, with wedges in place, each bar is subjected to a final high voltage test to be certain that none of the insulation has been damaged during the installation process. With the test results recorded in the project file, the next step is to braze the bar end windings together in order to create the final coils, before taping, sealing and applying the class "H" top glass tape.

With the stator nearly complete, the high voltage terminals were cleaned and tested at 25kV to prove their insulation resistance before they, too, were installed. Having completed the checks and minor work to the rotor, the generator was reassembled and returned to service, ready for another 25 years.

For more information please visit www.sulzer.com.