Rapid repair saves refinery downtime

Paul Boughton

Rapid repairs to high voltage generator rotor were carried out in just eight weeks.

In the power generation business, speed is of the essence, especially for maintenance work that can result in generating capacity downtime. When it is the generator’s rotor itself that needs repairing, the timing of the steps toward resuming normal output is crucial.

When regular maintenance checks on a high voltage 60MW generator at a large oil refinery signalled a potential earth fault in the rotor, engineers were keen to have a repair completed as soon as possible.

Sulzer specialises in delivering rapid repairs to high voltage equipment and was able to offer an efficient, bespoke service to repair the rotor in just eight weeks.

Sulzer operates manufacturing and testing facilities located throughout the world, so is able to provide a global turnkey service to keep power plant generation capacity in operation.

Inspection report

Sulzer worked in partnership with the client to quickly identify a solution and formulate a plan of action for the repair of the rotor. Sulzer provided a comprehensive inspection report and quote to overhaul the rotor within the constricted deadline.

With lost production costs looming, the plan was put into action. The rotor was shipped from Italy to the Birmingham Service Centre site, where work began on the initial strip down. In a project such as this it is frequently possible to reuse the rotor’s retaining rings, provided they are in satisfactory condition. However, detailed inspection following the strip down revealed that in this case they would have to be replaced.

To provide a fast track solution for the client, minimising site downtime costs, Sulzer was able to produce a set of replacements for the vented 800mm diameter stainless steel rings utilising its established materials supply network and in-house large precision machining facility.

In many cases rotor windings can also be reused, having first cleaned them and reapplied the insulation. However, in this instance, reuse was not possible and so new windings had to be manufactured and tested before the rebuild could begin.

Upon further inspection by the Sulzer team, it was found that the rotor body wedges would also have to be replaced; a further task for the designers and the machine shop. With all of the new components remanufactured and tested, the team could begin to rebuild the rotor.

Having completed the rebuild and the electrical, static and mechanical tests, the rotor was then checked for rotational balance, using the company’s own purpose-built large capacity overspeed balancing pit. During the process the rotor is first accelerated to its normal operating speed of 3,000rpm, any balance corrections are made, then the rotor is subsequently tested in an overspeed condition, in this case specified by the client at 3,600rpm.

"The balancing facility in Birmingham can accommodate rotors up to 12 metres in length and weighing up to 40 tonnes, with the ability to test at speeds up to 5,200 rpm. High-speed balance relieves residual stresses introduced during the repair process and allows the rotor components to settle into place. Following a high-speed balance at the Birmingham Service Centre, engineers review the results to ensure that any imbalances have been corrected and will not affect the future performance of the rotor. This forms the final step in a truly unique in-house, turnkey offering for the power generation industry,” said Keith Barbier, Head of International Contracts and Projects at Sulzer Birmingham Service Centre.

Keith Barbier concludes: "Fortunately the client employed excellent proactive maintenance procedures which were able to highlight a potential issue before it developed into a fault. Fortunately we were able to manage the project in-house. This meant we could control costs and meet very short deadlines – even as the task escalated in complexity and resource requirements, while keeping the client informed throughout the repair process."

Repairs completed in the past have proven the effectiveness of Sulzer technology for rotor rejuvenation. Rotors that would have been considered as scrap a few years ago can now be successfully re-engineered using sound engineering repair solutions. An extensive repair of this nature can normally be completed significantly quicker than a new rotor can be manufactured.

Additionally, the cost of a repair of this nature is approximately a third of the cost of a new rotor. This cost control and time effectiveness of the process have benefited the client, which as a result, experienced minimal disruption and downtime costs.

Sulzer Rotating Equipment Services, Birmingham, UK.

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