Cycling can cause accelerated deterioration in generator rotors. EPRI (Electric Power Research Institute) states that “Cyclic operation can result in an increase in forced outage rates, higher operation and maintenance (O&M) costs, and further wear and tear on components…” Most industry references do not differentiate between speed cycling and load cycling. Speed cycling is the worst kind of cycling, leading to cracking and fatigue failure of many generator rotor components.

The outline of the paper will include the following major topics:

• Definition of Cycling

• Focus on Speed Cycling versus Load Cycling/Load Following

• Low Cycle versus High Cycle Fatigue -

• Fatigue progresses to cracking; cracking to failure, failure to forced outages, schedule delays, additional costs

• Key Generator Rotor Components Affected by Low Cycle Fatigue

• Rotor Forging Shaft including the rotor bore, tooth tops, snap ring groove cracking

• Rotor Field Winding including pole crossovers, J-straps/terminal studs, bore copper, conductor end turns

• Support Components including slot wedges, retaining rings

• Preventative Action by Investigation and NDE/DE

• Conclusions and Recommendations.

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