Delivering the assessmentThe proposal for inspection from Sulzer was accepted and the contract to assess the generator was awarded. The engineering team removed the rotor and shipped it to Sulzer’s service center in Birmingham, UK, before starting the full assessment of the stator on site.
An inspection report was issued to the customer highlighting the findings with the recommended levels of work required to get the unit back to a safe operating condition. Sulzer accepted the customer’s request to use the report as the backbone for their tender document. This was issued to all suitably qualified repair specialists including original equipment manufacturers (OEMs) and maintenance providers.
Aneil Hanafiah, Mechanical Design Manager at the Birmingham Service Center, explains: “Sulzer offered a very competitive tender that was accepted as a result of the extensive technical expertise, the overall price and the speed with which the repair would be completed. A range of solutions for the repair of the generator was provided, and in this case speed and cost led the customer to choose a partial insulation as opposed to a complete overhaul or total re-insulation.”
Recreating partsThe rotor had also suffered damage to the composite bronze coil wedges, which had melted, distorted and fragmented due to the fault incident, causing molten particles to contaminate the stator due to the internal circulating air. Using a similar process to the retaining rings, the rotor wedges were reverse engineered and those that could be reused were tested and refurbished as per the customer’s instructions.
While the new components were being manufactured the rotor coils were inspected and the slot liners were replaced without having to remove the copper coils, which reduced the time for the overall repair. Throughout the repair, the customer received regular, weekly reports and visited the Birmingham Service Center twice during the repair.
Meanwhile, in Cyprus, the field service engineers worked to thoroughly clean and repair the stator, which had been damaged and contaminated by the rotor wedges. Once all the foreign materials had been removed, the stator was tested for core imperfections before reassembly with the rotor.
Before the rotor could be shipped back to the power station, it was balanced using Sulzer’s in-house high-speed balance facility. This is able to balance the rotor at its rated speed (3’000 rpm) and for this rotor in particular, an overspeed exercise was performed for two minutes at 115% (3’450 rpm), as requested by the customer. As a result of the precision processes involved, there was no need to carry out any additional trim balancing after the rotor was reassembled with the stator.
Aneil concludes: “Of course, in projects such as this, speed is important and the ability to deliver such projects on time requires considerable expertise and flexible facilities. Especially when a project is under competitive tender, the repairs need to be completed on time and to budget, even when major components need to be replaced. We have managed to repair a major asset that will ensure tens of thousands of local residents can rely on their power company to continue delivering a vital resource.”
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