Shaft Ground Monitoring can work in tandem with EMI Monitoring to determine early detection of a developing failure mode. Analytic capabilities and waveforms together with a continuous – based monitoring approach give the insights necessary to forecast potential failures such as poor shaft contact, bearing or stator core issues. With this technology plants are able to better plan outages and maintenance allowing better optimization of capital and manpower.
Analysis of Waveforms:
Shaft Ground Monitoring was on a pilot server when the analysts began seeing shaft voltage increases (Figure 1). Correspondingly, the M&D Center saw similar spikes in the Electromagnetic Signature Analysis (Figure 2).
Two Monitoring Systems Working Together:
When comparing the SGM and EMSA waveforms they overlaid and were closely correlating to one another (Figure 3). The red waveform on the graph is EMI trending overtime, the blue is peak shaft voltage, and the yellow waveform is current. As the generator load increased, so did the voltage and EMI, but not current. Personnel were able to determine that as a result of voltage increasing on the shaft, bearing electrolysis is occurring due to arcing, while lacking good grounding due to low current flow.
Using both monitoring systems helped to quickly determine the ground lead had become detached from initial installation (Figure 4). Immediately upon reconnecting the lead, the voltages and EMI came down. The issue was able to be resolved without having to shut down the unit, thus saving the plant a costly forced outage.
With automated failure detection, plant personnel can easily interpret waveform patterns and determine potential failures. This allows plants to have better predictability, while reducing risk of failures and operating costs, and having fewer surprise outages.