Inspection, repair and rewind experience on large, air-cooled, high voltage generators

摘要

From the early 1950's up through the 1980's, original equipment manufacturers continued to produce new generators with increasingly higher output. Large, hydrogen-cooled units, sometimes with water-cooled coils, went into large-scale production. Smaller air-cooled machines were not the primary emphasis. In the late 1980's and into the 1990's, smaller, more cost-competitive units became the focus. Units that could be built quickly, with a smaller footprint, at the lowest cost, were the new trend. Naturally, air cooling was cheaper than hydrogen, and with the advancement of new insulation materials, and more aggressive design approaches, the desired ratings could be achieved. The smaller air-cooled machines increased in popularity, and power output pushed upward. Air-cooled generators can now produce up to 400 MW. As with the hydrogen units that were pushed to the limit in the 1970's and 1980's, the larger air-cooled machines have begun to show their own set of unique problems. Although initially thought of as requiring less maintenance, the low-cost, simplified air-cooled generator put into service in the last ten years is requiring significantly more maintenance than expected. More frequent inspections and repairs are necessary, along with rewinds due to premature failure. The primary failure modes on these newer, large air-cooled generators are: 1. spark erosion, sometimes referred to as vibration sparking 2. partial discharge 3. phase lead and end winding vibration 4. pole to pole crossover fatigue cracking. Each particular failure mechanism is thoroughly described. Inspection, Repair and Rewind considerations for each failure mode are discussed in detail.