Analysis of a Large-Scale Cooling System Fan Gearbox Loads

Abstract

South Africa’s coal-fired power stations use super heated steam to drive generator turbines. In arid regions, air-cooled condensers (ACCs) are used to condense the process steam. These ACCs consists of an array of over 200 axial flow fans, each driven by a motor via a reduction gearbox. Distorted fan inlet air flow conditions cause transient blade loading, which results in variations in output shaft bending and torque. A measurement project was conducted where the input and output shaft of such a gearbox were instrumented with strain gauges and wireless bridge amplifiers. Gearbox shaft speed and vibration were also measured. Torsional and bending strains were measured for a variety of operational conditions, where correlations were seen between gearbox loading and wind conditions. The input side experienced no unexpected loads from the motor or changing wind conditions, whereas output shaft loading was influenced by the latter. Digital filters were applied to identify specific bending components, such as the influence of fan hub misalignment and dynamic blade loading. Reverse loading of the gearbox was measured during the fan stop period, and vibration analysis revealed torsional and gearbox vibrations. This investigation documented reliable full scale ACC gearbox loads.

Experimental Testing on an Air-Cooled Condenser Motor, Gearbox and Fan

“…The average calculated absolute bending moment for power station I is ∼2.52 kN•m. This coincides well with that measured by [1] at ∼2.8 kN•m at the same power station. This confirms that the experimental setup used and calibration of the sensors were correctly done.…”

“…The most common areas of gearbox failure are found to be the bearings and gear tooth fatigue damage [4]. Measurements on both shafts of the gearbox was taken by [1] to relate the input torsion and bending strain to the output side of the gearbox.…”