Using Initial Scan Readings

When the first EMSA scans are taken, look at the frequency scan for humps or spikes of higher-level frequencies. Record the higher readings for future comparison.

For the permanently installed units, the Power Spectrum of the frequency bands are captured and trended in InsightCM. The overall EMSA spectrum is saved on a company/IT determined frequency for comparison.

For periodic monitoring, capture the peak values and frequencies for comparison as more data is captured for trending purposes.

Currently, neither method automatically captures the demodulated time-domain waveforms. However, you should capture the demodulated time-domain waveforms for all the areas of interest to compare with similar data in the future.

NI-9770 card trends and periodic measurements have different levels of concern. The NI-9770 card uses the Power Spectrum, which is more sensitive to developing problems and can more easily detect issues that have not developed signals stronger than the local radio stations. The periodic measurement process uses the peak scan voltage.

The NI-9770 card has the following levels of concern for the areas of interest:

Recently, a generator was above 10,000 uV for about five years. A step change in level from 13,000 uV to 16,000 uV (Power Spectrum: 30 MHz – 100 MHz) was noted approximately three months before the unit tripped on stator ground. The issue was found in the Isolated Phase Bus: some cracked insulators and significant dirt contamination on other insulators.

For the periodic Instrument (Agilent E-7402), peak values of the spectrum are:

In the demodulated data from the areas of interest, sometimes the same patterns are seen at different frequencies. However, there may be some changes to the patterns that may be of interest:

These indications may help indicate to which frequencies the defect is mostly attributed.