MECHANICAL OVERHAUL PROCEDURESFOR HYDROELECTRIC UNITS

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.
Contents
I. Introduction
II. Preparation
2.1 Maintenance records
2.2 Inspection
2.3 Drawings
2.4 Lifting devices and rigging
2.5 Scheduling
2.6 Hydraulic transient study
2.7 Procurement of equipment and supplies
III. Disassembly
3.1 Preshutdown and preteardown readings
3.2 Labeling and match marking
3.3 Disassembly
IV. Inspection and repair of unit components
4.1 Bearings
4.2 Turbine runner
4.3 Wicket gates
4.4 Facing plates and wicket gate bushings
4.5 Packing box and shaft sleeve
4.6 Servomotors
4.7 Cooling coils and generator air coolers
4.8 Exciter
4.9 Generator structure
4.10 Generator brakes
V. Field machining procedures
5.1 Seal rings
5.2 Facing plates
5.3 Wicket gate bushing line boring
5.4 Redoweling
5.5 Coupling boltholes
VI. Reassembly
6.1 Torque or stretch of bolts
6.2 Unit alignment
6.3 Wicket gate adjustment
6.4 Gaskets and packing
6.5 Governor
VII. Startup
7.1 Final inspection
7.2 Initial startup
7.3 Operational readings
APPENDICES
Appendix A-Seal ring design and specifications
Appendix B-Sample calculation for seal ring installation
Appendix C-Tolerances for hydrounit assembly
Appendix D-Wicket gate adjustment procedures
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