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C. Neumeyer 2/15/01

Status of OH Repair. C. Neumeyer 2/15/01. Coil was successfully removed and lifted over south wall of NTC on Monday 2/12. Fault was apparent from visual inspection, about 30% down as predicted by measurements. Close-up view upon first discovery.

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C. Neumeyer 2/15/01

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  1. Status of OH Repair C. Neumeyer 2/15/01

  2. Coil was successfully removed and lifted over south wall of NTC on Monday 2/12

  3. Fault was apparent from visual inspection, about 30% down as predicted by measurements

  4. Close-up view upon first discovery

  5. After removing ground plane from area around fault, 1000V Megger reads OK

  6. Some other problems were noticed, namely pitting under ground plane clamps and evidence of contact with PF1a coil holders

  7. Repair Plan (Procedure now under development) • Identify, as accurately as possible, the location of the boundaries of the turns in the area of the fault, using eddy current probe • Area around the fault will be sanded and cleaned in preparation for application of repair • Excavation will be performed by experienced technician. The area to be excavated will be marked in advance. Excavation will aim to remove all evidence of carbonization, all the way down to the copper, while minimizing the amount of material removed, and avoiding the turn-turn boundary if possible. During the process of excavation any evidence of the cause of the fault will be noted, and photos will be taken.

  8. During excavation, the turn-turn boundary is to be avoided if possible. If the fault appears to involve the region between turns, then it will be necessary to excavate between turns to remove all carbonization. • Assuming that the problem does not involve the region between turns, the repair will consist of: • the area will be cleaned and slightly heated to drive out any remnant moisture; • a suitable low viscosity dielectric sealer/primer will be applied which will fill and flow into voids and microfissures • layers of epoxy/glass/kapton will be applied in wet lay-up fashion. A generous build and overlap of existing insulation shall be achieved; • a primer sealer will be applied over the repair area, followed by the ground plane paint.

  9. Diagnostic wiring will be re-routed around the repaired area. • In parallel with the fault repair, the areas under the ground plane grounding straps will be carefully sanded/cleaned to determine the depth of the observed arcing damage. If it is entirely superficial to the scotchply groundwall, then the area can be simply repainted.

  10. Testing will be at the full 13kV to ensure that all weaknesses are identified while the coil is out of the center stack casing. • A new design will be developed for the ground plane grounding strap and clamping, to ensure that it does not loosen and maintains good contact. • Improvements will be made to other areas of known weakness, including the possible use of additional sleeving over the water tubes, and encapsulation of the water tube lead-out areas. • A goal is to cover all copper, leaving no exposed areas, to enhance reliability.

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