Introduction
Electro – Magnetic Interference (EMI) Monitoring is a non – intrusive, on – line surveillance technique to detect and identify electrical defects in motors, generators, IsoPhase Bus, Transformers, and other electrical systems:
- Arcing
- Partial Discharge
- Gap Discharge
- Corona
- Random Noise
- Micro – Sparking (Rapid Gap Discharge)
emi assessment algorithm
The EMI Assessment Algorithm allows plants to move away from costly third-party technicians coming onsite to take periodic readings. Plants are able to continuously trend values using thousands of data points and 25 trend parameters.
The upper graph in figure 1 trends these parameters. Selecting the excursions in this graph allow plant personnel to highlight and analyze the peak waveforms within the Power Spectrum (lower left graph) and evaluate the data in the Assessment Table (lower right data table). Even when events occur outside regular hours, personnel can go back and look at the data to determine what caused the peaks.
With the Time Domain Classification table, troubleshooting efforts can focus the investigation on components based on the type of signals, i.e., Arcing, Corona, Discharge, Noise, Tone.
Case study
The following is a recent case study of an east coast plant that was able to use EMI Monitoring to detect failures.
Power Spectrum
The Power Spectrums show waveforms before and after the event. Plant personnel noticed a change in the circled areas, and knew to focus on the time domain waveforms frequencies near the peaks.
Assessment Table
The Assessment Table below showing before and after the event, is a powerful addition to the enhanced application. This data set confidently drives plant personnel to the right location in which to find the failure mode using these rules of thumb:
- 30k – 500k: exciter
- 500k – 5M: Stator core and slots
- 5M – 30M: end windings
- 30M – 100M: isophase bus
An increase in the Corona and Discharge categories narrowed the potential sources within the asset, resulting in a more efficient investigation. The source was discovered of cracked insulators (Figure 4) were replaced, which reduced the EMI levels.
Financial impacts
Converting one Major Outage to Minor Outage over Five Years:
* Note: The results are illustrative only. Specific risks, costs, and prices will vary. This is not a guarantee of savings nor a guarantee of eliminating risk. Proper maintenance must be performed
conclusion
The industry is heading toward continuous monitoring systems for cost effective solutions to analyze and prevent failure modes. EMI Monitoring is the best tool to decipher the most significant failures over a broad array of equipment, specifically with generators.
For information on Electro-Magnetic Interference Monitoring click on the image below to view the webinar.
