GENERATOR OPERATIONAL CHECKS (SURVEILLANCE AND MONITORING)
Regular monitoring of the following parameters is required:
1. Temperature of stator windings.
2. Core temperature.
3. Temperature of slip rings.
4. Vibration levels at the bearings.
5. Brush gear inspection (monthly or bimonthly). Remove the brush holder. Clean the car- bon brushes by compressed air. Inspect the brushes for uneven wear (do not touch the brushes with bare hands). Replace worn brushes. Use a stroboscope to inspect the slip rings. Vary the frequency of the stroboscope to check for uneven wear of the slip rings. The temperature of the slip rings should be measured using an infrared detector. If the slip ring temperature is high, the brushes will overheat and wear quickly. Generator derating is required if the slip ring temperature is high.
6. On-line partial discharge activity.
Major Overhaul (Every 8 to 10 Years)
The electrical and mechanical tests required are described in Appendixes A and B, respec- tively. In summary, the work includes the following:
1. Perform insulation resistance and polarization index tests.
2. Investigate the causes of partial discharge.
3. Check the tightness of the stator wedges by tapping them with a hammer. The wedges must be tight to minimize the movement of the stator conductor bars during operation. Rewedging and adding packing may be required.
4. Perform the EL-CID test to determine if there is any loosening in the core laminations or deterioration in the core insulation. Apply penetrating epoxy if insulation is degrading.
5. Perform casing pressure and stator pressure and vacuum decay tests.
6. Refurbish the rotor including inspection of radial pins and end caps (including ultrasonic and dye penetrant testing), vacuum test, slip ring refurbishment, and check for copper
dusting. Note: Copper dusting occurs due to fretting of the rotor copper windings as they move in the slots when the machine is on turning gear. This problem does not occur during normal operation because centrifugal forces push the windings against the wedges. Copper dusting can cause shorts in the machine.
7. Calibrate protection equipment.