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GENERATORS MAINTENANCE

GENERATORS MAINTENANCE . Typical Generator Maintenance . Generators . System controls . FOREIGN OBJECT DAMAGE Problem: Objects can come from external sources or failure of internal components, they can pick up energy from the spinning rotor and do extensive damage

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GENERATORS MAINTENANCE

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  1. GENERATORS MAINTENANCE

  2. Typical Generator Maintenance

  3. Generators

  4. System controls

  5. FOREIGN OBJECT DAMAGE Problem: Objects can come from external sources or failure of internal components, they can pick up energy from the spinning rotor and do extensive damage Prevention: Inspect on a regular basis all internal parts that are prone to failure or can be dislodged. Inspection tests can be a combination of visual inspection along with ultrasonic or magnetic particle tests on rotating components REASONS WHY GENERATORS FAIL

  6. Problem: Primarily a design related problem that affects large (>300Mw) generators which have insufficient end winding bracing to limit the movement of end turns. Prevention: Proper bracing of the end winding is required to limit motion caused by steady state and transient electromagnetic forces. STATOR WINDING VIBRATION

  7. Problem: Rotor winding distortion caused by poor end turn blocking support design or by foreshortening of the rotor coils. Foreshortening is caused by thermal forces which compress rotor coils. Prevention: Proper design of rotor coils and bracing to support the coils under axial load is essential. Rotors should be tested for turn to turn shorts at operating speed. ROTOR WINDING DISTORTION

  8. Problem: Primarily a design related problem that affects large (>300Mw) generators which have insufficient end winding bracing to limit the movement of end turns. Prevention: Proper bracing of the end winding is required to limit motion caused by steady state and transient electromagnetic forces. STATOR WINDING VIBRATION

  9. Problem: Overheating of the rotor or stator can lead to insulation failure, shorting of turns and ground faults. Overheating can result from blocked ventilation passages caused by shifting insulation components or slot wedges. Prevention: Inspect on a regular basis to ensure all rotor wedges are "locked" in place preventing migration and thus blocking of cooling passages. OVERHEATING

  10. Problem: For air cooled machines, dirt and dust cause tracking which can lead to electrical ground faults. Prevention: Inspect air filterson a regular basis , the filters must be checked and cleaned regularly. Polarization index (PI) tests give a good indication of overall cleanliness of the rotor winding. CONTAMINATION

  11. Problem: There are many causes, turn-to-turn shorts, rotor coil foreshortening, electrical grounds, mechanical imbalances, overheating, etc. Prevention: Comprehensive vibration measuring is effective combined with a regular maintenance program. ROTOR VIBRATION

  12. Problem: When stator wedges become loose, coils can vibrate causing insulation wear leading to ground faults or turn-to-turn shorts. Prevention: Inspect on a regular basis tightness of wedge blocks. STATOR WEDGE LOOSENESS

  13. Problem: Stator core looseness can occur over time as pre-tensioned through bolts relax. A loose core results in insulation wear to coils and laminations resulting in hot spots and core-to-coil failures. Prevention: Inspect bolt tightness on a regular basis. STATOR CORE DAMAGE

  14. The following tests which should be carried out annually in addition to vendor recommended maintenance. GENERATOR MAINTENANCE

  15. • “Megger” rotor winding • “Megger” exciter armature winding • “Megger” exciter field winding • Complete polarization index (pi) on main stator • Check bearing insulation A) INITIAL GENERATOR TEST

  16. • Remove exciter end cover • Examine condition of diode carrier • Examine exciter armature/stator for contamination • Examine exciter armature/stator for winding wear • Check pmg magnets for contamination B) INSPECTION ON STATIC EXCITER

  17. • Visually inspect external surfaces of panel • Complete insulation resistance checks of panel wiring • Check function of all relays • Check all fuses • Check all lamps • Check operation of all switches • Check operation of panel heaters • Run generator; recalibrate avr • Secondary inject all protective relays C) ELECTRICAL CONTROL/PROTECTION PANEL

  18. • Carry out static checks to confirm operation of detector • Carry out functional check to confirm operation of detector E) ROTOR EARTH FAULT PROTECTOR

  19. • Check all brushes for grade and length • Check condition of brush holders/mountings • Check that spring tensions are correct • Check conditions of slip-rings • Check mechanical run-out of slip-rings • Check cooler and leakage alarms F) SLIP-RINGS AND BRUSH-GEAR (IF FITTED)

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