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Along with using straps, we first make sure we use an engineered locking pin and ensure the winds are low before servicing the blades.
Below is an example found in news article about another site, which may help
Best Practices – Higgins
New, safer method of rigging halves time for ACC gearbox change-out
Best Practices Award
Challenge. Walter M Higgins Generation Station has a 40-cell Hamon air-cooled condenser (ACC) with 34-ft-diam Howden fans. The Flender gear reducers are driven by Teco-Westinghouse two-speed, 200-hp motors.
When changing an ACC gear reducer, the hub and blade assembly usually is disconnected as a unit and held in position by rigging and come-alongs or chain falls. Such rigging work can be a challenging process with safety implications. Fact: Rigging to the fan blades/hub assembly is never straight, in-line, or perpendicular to anything because of the nature of the equipment and structure.
During the installation of the new or replacement gear reducer, aligning the fan hub assembly to the gear reducer hub is difficult at best (Figs 1, 2). Since the rigging and come-alongs/chain falls are not directly supporting the assembly, adjusting any of them results in the assembly moving in strange ways.
Solution. After much discussion and several gear-reducer changes, the mechanical maintenance crew determined there had to be a better way to hold the hub and blade assembly to facilitate replacement (Fig 3). A basic design was drawn up and presented to NV Energy’s corporate engineering staff for review. After the design was finalized and engineered for safety and load, the project was handed out for fabrication.
The plant’s concept was simple and direct. Two cross members fit into the structural elements of the fan bridge and lock down with high-strength “C” clamps. Four 1¼-in. B-7 alloy high-tensile-strength all-thread rods drop down into the cross beams to hang over the hub plate (Fig 4). Four custom-designed clamps fit onto the hub plate and clamp securely to the plate, while the all-thread rods are through-bolted to the clamps and tensioned (Fig 5). The nuts on the top cross beam are then tensioned as well, locking the whole blade assembly in one position.
The gear reducer is then unbolted and removed. The fixture is now holding the entire blade assembly securely and stable (Fig 6). Once the new or replacement gear reducer is dropped into position it is a simple matter of turning the input shaft to align the bolt holes on the fan hub assembly.
Note the center eye bolt in Fig 7. It is for the chain fall that actually removes the gear reducer from operating position and takes it outside for transfer to ground. The arrangement of eye bolts gives a clear and safe way to change from one hoist to another, without binding, confusion, or risk of rigging failure. Since the fan assembly has not moved at all during the gear-reducer change, it becomes a very quick, safe, and easy job.
Results. The fixture saved approximately two hours the first time it was used to change a reducer. There was a strong up-draft through the ACC cell during the change out and the fixture held firm and didn’t wobble or twist at all. In fact, in adjoining cells the fans were being turned by the wind to equivalent high rpm.
In conjunction with the gear-reducer fixture the entire gear-reducer change-out time has been reduced from a two-day event (working day shifts only) or about 20 hours, to a single 10-hr day job. The gear-reducer fixture increased safety and improved rigging height issues for removal of reducer from the fan deck of the ACC as well.