[128] Usage of shaft vibration signals for turbine blade monitoring

Electricity production is increasingly influenced by renewable energy sources. It raises demands for increased flexibility of conventional coal-fired power stations. Turbine operation under operational conditions other than those for which the turbine was designed may lead to increased vibration of rotating blades, mainly of last-stage blades (L0) of low pressure (LP) turbines. Excessive, unmonitored blade vibration may lead to the origination of cracks and, in the worst cases, to blade rupture. The safety, reliability and efficiency of turbines is conditioned by online monitoring of blade vibration, but online monitoring systems are still not standardised in LP turbines. The previous research showed that relative shaft vibration signals contain components related to blade vibration modes, except for 0ND (nodal diameter) bladed disc modes. However, the latest results confirmed the possibility of monitoring 0ND modes through the addition of relative shaft axial shift signals into the measurement chain. The results of a detailed comparison of blade vibration analysed using the blade-tip time (BTT) system and signal processing of shaft vibrations and the axial shift are described in this paper.