Generator Aging Factors

TURBINE GENERATOR MAINTENANCE, INC.

CONSTRUCTION: The Critical Components TURBINE GENERATOR MAINTENANCE, INC.

Generator Stator Finger Plates & Compression Ring

Stator Windings Stator Core Iron

Circuit Ring Assembly

Building Bolts & Through Bolts

End Winding Support System

Finger Plates & Compression Ring

Circumferential Ribbing

CONSTRUCTION: The Critical Components TURBINE GENERATOR MAINTENANCE, INC.

Generator Rotor Collector Rings / Rectifier Wheel

Retaining Ring Main Field Coil

Bore Copper Insulation

Slot Cell

Centering Ring Snap Ring

Fan Blades

Bore Copper & Radial Leads

Rotor Body Wedges

Rotor Body Forging Coupling Coupling Pins Retaining Ring Insulation

End Winding Blocking

Generator Aging Factors TURBINE GENERATOR MAINTENANCE, INC.

Generator Stator-Specific Aging Factors TURBINE GENERATOR MAINTENANCE, INC.


15

s d n i w10 e R f o r e b m 5 u N

0 6 10 12 15 17 19 21 25 27 29 31 35 37 39 41 Air-Cooled Age at Rewind (Years)


15

s d n i w10 e R f o r e b m 5 u N

0 5

10

15

20

25

30

35

40

45

Hydrogen-Cooled Age at Rewind (Years)

50


Other 9%

Stator Core 12%

Insulation Fault 8%

Loose End Windings 34%

Stator Winding 79%

Loose Slot Wedges 24%

Windings, Other 13%


Circuit Rings: Mechanical dusting is the term used to describe the act of two generator stator components fretting against one another (within an oil-free environment). The associate dust is actually winding material abraded away by the frictional process.


Stator Wedges: The stator windings are locked radially into the stator core slots by rows of wedges. Old style wedges were fabricated of such materials as hard woods or phenolic. More modern wedges are fabricated of epoxy/glass laminates. Wedges have a tendency to shrink over time, facilitating looseness, fretting, and axial migration.


Moisture and Contaminates: The combination of moisture (i.e. heat exchanger leaks, condensation, inclement weather) and contaminates (dirt, dust, carbon, fly ash) can become the catalyst for phase-tophase and phase-toground flashovers and faults.


Moisture and Contaminates: Water, surface moisture, and condensation will evaporate. However However,, evidence of their presence typically remains; this in the form of familiar-shaped runs, streamers, and deposits.

Generator Stator-Specific Safety Alert TURBINE GENERATOR MAINTENANCE, INC.

Lead Carbonate: Lead carbonate contamination of generators is most prevalent in hydrogencooled machines with coolers typically (but not always) made before 1968. Lead carbonate typically appears as a grayishwhite or orangish-red powdery substance; generally first seen covering the generator stator end windings, bore, and rotor.

Generator Stator-Specific Safety Alert TURBINE GENERATOR MAINTENANCE, INC.

Asbestos: Vintage generator, particularly those with asphaltic-mica (thermoplastic) insulation system should be suspect of having Asbestos Containing Materials (ACM). Stator coils might be wrapped with an outer binder of ferrous asbestos tape, which was used to help control destructive slot electrical discharges.

Generator Rotor-Specific Aging Factors TURBINE GENERATOR MAINTENANCE, INC.


25 s d n20 i w e R r 15 o t o R f o 10 r e b m u 5 N

0 2 4 6 8 10 12 14 16 18

20 22 24 26 28 30 32 34 36 38 40 Generator Age (Years)


Winding Distortion 11%

Other 9% Turn Shorts 13%

Retaining Rings 8% Insulation 34%

Winding Cracks 8%

Exciter 3%

Damper / Wedges 15%

Ground Short 3% Collector Rings 7%

Other 18%


Rotor Turn Insulation: Rotor turn-to-turn insulation can migrate axially within the slots of a rotor body forging. With respect to radiallyvented rotors, gas passage ways can be blocked-off. Asymmetrical heating of the rotor then leads to thermal sensitivity and excessive vibration at higher loads.


Rotor Turn Insulation: Certain General Electric rotors were wound with a specific type of turn-to-turn insulation, which has a tendency to migrate out from between the conductors of the main field winding. Without this insulating material properly in place, turnto-turn shorting will eventually occur.


Rotor Windings: Thermal cycling can cause significant main field winding deformation (generally most pronounced with regard to the outer most turns). This conductor displacement can then lead to turnto-turn, coil-to-coil, and even pole-to-pole shorting.


Rotor Wedges: Unbalanced load, system oscillations, and other types of abnormal operation can induce alternating currents into the rotor body forging, flowing along teeth, wedges, and within the retaining rings. Pitting, arcing, and burning can develop across high resistance contact areas (i.e. wedge-toretaining ring).


Retaining Rings: Subjected to their own hoop stresses as well as centrifugal loading of the main field end windings, retaining rings are the most highly stressed components within a generator. Visually inspected and nondestructively tested for evidence of impact damage, stress risers, and other such deficiencies is critical.

Generator Rotor-Specific Safety Alert TURBINE GENERATOR MAINTENANCE, INC.

Lead Carbonate: Lead carbonate contamination of generators is most prevalent in hydrogencooled machines with coolers typically (but not always) made before 1968. Lead carbonate typically appears as a grayishwhite or orangish-red powdery substance; generally first seen covering the generator stator end windings, bore, and rotor.

Generator Rotor-Specific Safety Alert TURBINE GENERATOR MAINTENANCE, INC.

Asbestos: Vintage generator rotor may also have Asbestos Containing Materials (ACM). Blocking, end winding armor, retaining ring insulation, and slot armor should all be suspect of being ACM until proven otherwise through appropriate testing.

Key Take-Aways TURBINE GENERATOR MAINTENANCE, INC.

Generator Aging Factors

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