CUSTOMER: First Hydro Dinorwig Power Station North Wales

PROBLEM: To repair a 5.5 metre diameter pump-turbine regulating ring bearing and top cover journal face, in-situ, in one of Europe’s largest pumped storage power stations while avoiding the need for a several week shutdown and lost generating time.

The bespoke circular self-levelling milling machine was developed and operated by specialty services company Furmanite for Dinorwig power station in North Wales, operated by First Hydro company and owned by Edison Mission Energy, to repair a damaged bearing track and to replace the grease lubricated bronze with a self lubricating bearing. First Hydro Company was keen to move away from grease for environmental reasons and to improve working conditions.

The phosphor bronze regulating ring bearing was found to be worn, and there was damage caused to the top cover vertical and horizontal journal faces by the bearing’s retainer screws having worked loose.  The damage had to be repaired before replacing the bearing, but stripping down the turbine and removing the top cover (5.5 metres diameter, weighing 100 tons) to a workshop, would have entailed several weeks’ shutdown, and transportation of the sizeable cover.

SOLUTION:  The operator First Hydro approached Furmanite to find an in-situ solution.  Based on its previous experience with similar types of repair, Furmanite developed its circular self levelling milling technology to re-machine the top cover journal faces, and fit stainless steel liners as a counter face for the self lubricating bearing.

To guide the milling machine, which rotates around the main drive shaft, a special split bearing sleeve on the shaft was designed.  This was set concentric to the top cover outside diameter using a clocking arm.  The flatness of the top cover horizontal bearing was maintained by the machine’s novel self-levelling technology, which controls the milling cutter height via an electro-hydraulic interface from the pre-set datum ring.  A special split datum ring was manufactured for the purpose, to go around the drive shaft and mount on the top cover.  The datum ring flatness was set using Furmanite’s precision scanning laser system, for maximum accuracy

OUTCOME: The set-up, machining, and fitting of the stainless steel liners and the replacement of the bearing took nine days working in 24 hour shifts to complete.  The work continued on the power station’s six turbine units.