MECHANICAL OVERHAUL PROCEDURES FOR
HYDROELECTRIC UNITS
I.
INTRODUCTION
Periodically, all hydroelectric generators require a major overhaul. The extent of the work
required during an overhaul will depend a great deal on operating conditions such as water
quality and how the unit was loaded. In order for the overhaul to proceed smoothly and to
accomplish all the work required, planning should start well before the overhaul starts.
required during an overhaul will depend a great deal on operating conditions such as water
quality and how the unit was loaded. In order for the overhaul to proceed smoothly and to
accomplish all the work required, planning should start well before the overhaul starts.
II
PREPARATION
2.1
Maintenance records
One of the best sources of information in planning a major overhaul should be the
maintenance records for the unit or units involved. These records should provide
details on the history, present condition, and any unusual maintenance problems of
the unit. This can help identify specific items that may need attention during the
overhaul. Reports of previous overhauls can prevent the same mistake from being
made twice and may provide tips that can expedite the overhaul procedure. The
maintenance files may also provide names of sources for parts and materials.
maintenance records for the unit or units involved. These records should provide
details on the history, present condition, and any unusual maintenance problems of
the unit. This can help identify specific items that may need attention during the
overhaul. Reports of previous overhauls can prevent the same mistake from being
made twice and may provide tips that can expedite the overhaul procedure. The
maintenance files may also provide names of sources for parts and materials.
2.2
Inspection
At least 6 months, but preferably a year before the planned overhaul, a thorough
inspection of the unit should be made to determine the condition of the equipment.
Any items that will require maintenance or replacement should be documented.
Many times, due to power or water delivery constraints, the amount of time allowed
for the unit inspection may be very limited. Because of this, any item that can be
inspected or checked without a full clearance should be taken care of prior to, or
following, the outage for the main inspection. This will allow more time for a
thorough inspection of the other items.
inspection of the unit should be made to determine the condition of the equipment.
Any items that will require maintenance or replacement should be documented.
Many times, due to power or water delivery constraints, the amount of time allowed
for the unit inspection may be very limited. Because of this, any item that can be
inspected or checked without a full clearance should be taken care of prior to, or
following, the outage for the main inspection. This will allow more time for a
thorough inspection of the other items.
The inspection should include, but not be limited, to the following items:
Turbine runner.
Unwater the unit and install draft tube scaffolding to allow
the inspection of the underside of the runner. Check each bucket carefully for
cavitation damage and cracks. If possible, use die penetrant or other
nondestructive test to check for cracks. Compare seal ring clearance readings
with design 'clearances. Open wicket gates to full open to allow inspection of
inlet area of runner. Again look for cavitation damage and cracks.
cavitation damage and cracks. If possible, use die penetrant or other
nondestructive test to check for cracks. Compare seal ring clearance readings
with design 'clearances. Open wicket gates to full open to allow inspection of
inlet area of runner. Again look for cavitation damage and cracks.