When gearboxes are used in applications in which the connectedload has high inertia, the starting torque transmitted by thegearbox can be much higher than the rated load of the prime mover.Power plants often require several evaporative cooling towers orlarge banks of air cooled condensers (ACC) to discharge waste heat.Because of the very large size of the fans used in theseapplications, they fall into this category of high inertia startingload devices. When started from zero speed, a very high torque isrequired to accelerate the fan to normal operating speed. If thefan is started infrequently and run continuously for long periodsof time, this high starting torque is of minimal significance.However, when the fan is started and stopped frequently, the numberof cycles at the high starting torque can accumulate to a pointwhere they can cause extensive fatigue damage, even if the gearsystem is adequately rated. Where the gear unit is marginallyrated, very early, catastrophic gear failure is often the result.As part of the overall investigation of several failures in suchgearboxes, we measured starting torque on a typical installation,examined many failed gears, and calculated the load capacityratings for the gearboxes under actual operating conditions. Thispaper describes the failures observed, the testing conducted, thedata analyses and the effect of the high measured starting torqueon the life and performance of the gear systems. The test resultsrevealed surprising results, especially during starts where the fanwas already wind-milling due to natural air flow in the ACCbank.
- Edition:
- 07
- Published:
- 10/01/2007
- Number of Pages:
- 13
- File Size:
- 1 file , 750 KB
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