may be made from a portable boat floating in the draft tube while water level is
maintained below the bottom of the draft tube access door. Most areas of the
runner which are susceptible to cavitation damage can be seen from the draft
tube side. The leading edge of the blades, however, can best be inspected from
the wicket gate area. On small units where access to the runner from the wicket
gate area is poor, a polished metal mirror can be used for observing the leading
edge area from the draft tube side.
maintained below the bottom of the draft tube access door. Most areas of the
runner which are susceptible to cavitation damage can be seen from the draft
tube side. The leading edge of the blades, however, can best be inspected from
the wicket gate area. On small units where access to the runner from the wicket
gate area is poor, a polished metal mirror can be used for observing the leading
edge area from the draft tube side.
"Adequate lighting is necessary for a thorough inspection--the stronger the light
source the better. When the runner erection platform is in place, photographic-
type lighting is optimum. For the wicket gate area, large portable battery
powered lights are usually sufficient. A drop-cord-type light is also suitable for
difficult areas. For safety, ground fault detectors are necessary in the power
supply to the turbine water passages. Alternately, a low voltage direct current
power source should be used.
source the better. When the runner erection platform is in place, photographic-
type lighting is optimum. For the wicket gate area, large portable battery
powered lights are usually sufficient. A drop-cord-type light is also suitable for
difficult areas. For safety, ground fault detectors are necessary in the power
supply to the turbine water passages. Alternately, a low voltage direct current
power source should be used.
"The inspection should be thorough, covering not only the runner, but the draft
tube liner, discharge ring, wicket gates, bottom ring, and headcover. The runner
blades should be permanently numbered. The wicket gates may be identified by
referencing them to the baffle vane.
tube liner, discharge ring, wicket gates, bottom ring, and headcover. The runner
blades should be permanently numbered. The wicket gates may be identified by
referencing them to the baffle vane.
"It is recommended that a checklist be prepared to ensure that all parts of the
turbine are inspected, and that all areas of cavitation damage be recorded on
sketches or in tabular form. The records should include the following:
turbine are inspected, and that all areas of cavitation damage be recorded on
sketches or in tabular form. The records should include the following:
Date of inspection
Number of hours of operation and the generation (kWH) since the
previous repairs and/or inspection
previous repairs and/or inspection
Operation limits (i.e., net head, tail-water level, low flows, and any
incidence and duration beyond these limits
incidence and duration beyond these limits
Overall area of each area of pitting, as well as the average depth and
maximum depth
maximum depth
Dimensions of damaged areas from the leading and trailing edge of the
blades
blades
Photographs of the damaged areas and of subsequent repairs
"When taking photographs, the blade number, the date of the inspection, and
dimensions of the pitted area should be clearly marked on the blade for
reference.
dimensions of the pitted area should be clearly marked on the blade for
reference.
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