Rapid HV rotor repair saves Italian refinery downtime 11 November 2014

When recent maintenance checks on a high voltage 60MW generator at a large unnamed Italian oil refinery signalled a potential rotor earth fault, Sulzer prioritised repairs and had the plant back up within eight weeks.

Keith Barbier, head of international contracts and projects at Sulzer Birmingham Service Centre, says the firm worked with the company to quickly identify a solution and provide a quote to overhaul the rotor.

The rotor was shipped from Italy to the Birmingham Service Centre site, where work began on the initial strip down, and Barbier reports that the rotor's retaining rings were too far gone to be reused.

To provide a fast track solution, Sulzer produced a set of replacements for the vented 800mm diameter stainless steel rings using its existing materials supply chain and in-house large precision machining facility.

It was a similar story with the rotor windings, he says, with new windings having to be manufactured and tested before rebuild could begin. And Barbier says the same applied to the rotor body wedges.

"Having worked in this industry for over 30 years I have seen many rotors being repaired, and it is rare for all three components to be in need of replacement at one time," comments Barbier.

Having completed the rebuild and the electrical, static and mechanical tests, the rotor was then checked for rotational balance, using the company's overspeed balancing pit.

During the process the rotor is first accelerated to normal operating speed of 3,000 rpm and balance corrections made, explains Barbier , and the rotor is then tested in an overspeed condition, in this case 3,600 rpm.

"The balancing facility in Birmingham can accommodate rotors up to 12 meters in length and weighing up to 40 tonnes, with the ability to test at speeds up to 5,200 rpm," states Barbier.

"High-speed balance relieves residual stresses introduced during the repair process and allows the rotor components to settle into place," he continues.

"Fortunately, the client employed excellent proactive maintenance procedures which were able to highlight a potential issue before it developed into a fault," he adds.

Brian Tinham

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Sulzer Dowding & Mills plc

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