Lydenburg Hydro Runner repair

Since 2007, MBB has been under contract to operate and maintain the 2.3 MW water permitted Lydenburg Hydro facility.

The turbine was shut down for examination on March 12th after a significant vibration was detected. As it happened, a prior blade failure worsened and one of the runner blades broke off entirely.

Fortunately, the broken blade was discovered in the tail race.

The runner needed to be removed, which proved to be a difficult task in and of itself, before it could be repaired. Using a size 55 spanner, the runner was freed from the shaft. Since the overhead crane could only be used in the turbine position, it was carefully moved out of the turbine house and raised eight meters to the cable car. It was likely in place since 1982. It was moved to the top landing using the cable car system after it reached the cable car level, where it was placed into a vehicle for transportation.

After the material was metallurgically tested, we located a specialized welding contractor in Johannesburg who took on the task of welding the fractured blade back together. The runner material and the small gap between the blades presented difficulties, but the weld was completed satisfactorily, and the entire runner was heat treated to eliminate any remaining tension.

Since the one blade (with the missing pieces) could not be restored, the runner was then taken to a dynamic balancing shop to be balanced.

It was gathered and reinstalled when it was balanced. The end product is a perfectly balanced turbine, but because of the remaining broken blade, its output is still subpar.

Using specialized epoxy filler, the labyrinth on the shaft and some cavitation damage to the deflector plate system were repaired during the disassembly of the turbine. Along with cleaning the canal, a new inlet screen was built.
The missing sections of the blade could not be fixed, therefore after removing the runner, it was partially surveyed to build a three-dimensional file of the missing pieces. This was done by deducting the shape of the broken blade from the shape of the full blade.

After that, a 5-axis CNC machine will be utilized to cut the missing portion out of a virgin material piece. The produced piece will be welded in once it is finished. All of the aforementioned steps—removal, welding, stress relief, dynamic balancing, and reinstallation—will need to be repeated in order to accomplish this. This will happen as soon as the machined component is finished.

Successfully removed after a days’ hard work.
Removed runner with the completely missing blade (at the lifting chains), and the partially broken blade to the left clearly visible.
Dynamic Balancing in progress.
3D Scanning in progress.
Screenshot of 3D model clearly showing the missing blade. Also note the weight bar bolted on during balancing.
Repaired runner ready for re-installation. Note the deflector stickers used during the scanning process.
Cavitation damage on the deflector plate structure.
Repaired Deflector plate structure.
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