Research on Fatigue Damage of Hydrogenerator Unit Head Cover Connecting Bolts Based on Time-Frequency Analysis

Aiming at the problem of fatigue damage caused by long-term alternating loads on the connecting bolts of hydrogenerator unit head cover, the concept of power density is introduced in the paper. Combined with the short-time Fourier transform, a method for calculating the fatigue damage of the head cover bolts based on the combination of power density theory and time-frequency analysis is proposed to study the influence of the coupling effect of loading frequency and variable amplitude load on the fatigue damage of roof connecting bolts. Based on the raw data collected by the monitoring system for the head cover bolts of a hydrogenerator unit in an actual operating hydropower station, the proposed method is used to calculate the bolt fatigue damage. Timefrequency analysis method based on power density can effectively calculate bolt fatigue damage. For the stress data of the measured power station within 300s, the fatigue damage is calculated is 2.8208×10-7, this study method and result can provide a reference for fatigue damage calculation of hydraulic turbine head cover bolts.

I. Introduction

The head cover connecting bolts of the hydrogenerator unit is the main component that supports the water guiding mechanism, guide bearing and other parts, and it is also one of the main flow-passing parts of the unit. It is connected to the seat ring of the turbine through the head cover connecting bolts [1]. In the actual operation process, the head cover bolt bears the long-term effect of random alternating load, which is easy to cause cracks and defects inside the bolt. The accumulation of time and the huge impact of changes in working conditions will cause fatigue damage to the bolts and cause accidents in flooded workshops [2]. Therefore, it is necessary to analyze and study the fatigue of the head cover connecting bolts of the hydrogenerator unit.