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EGMA-401, EGSA-310, EGSA-320, EGSK-404, EGSK-405, EXMC-001, EXMC-002

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grounding current, zero-to-peak, readings


This document provides strategies for advanced troubleshooting.

Advanced Troubleshooting

Possible Grounding Fault Indicators

Every generator has its own distinct set of normal operating conditions. Normal conditions on one generator may be alarming on another, even if the two units are of the same type. Plant personnel responsible for monitoring the systems should be familiar with normal average and peak levels for each unit.

It is also advantageous to periodically view the waveforms on the Premium Monitoring System for each generator and watch for signatures that are markedly different from what has been viewed in the past.

A change in a unit’s waveform output can be a powerful indicator that something requires attention within the generator or the grounding system.  

The conditions listed in this topic may be fault indications. This is not a comprehensive list, but rather it is intended to draw attention to scenarios that can warrant further investigation.


Grounding Current Steps Down and Shaft Voltage Steps Up

If a significant step down in grounding current takes place in conjunction with an increase in shaft voltage this could indicate a potential loss of grounding and should be investigated immediately. Inspect the grounding assembly, grounding rope, and shaft surface for potential deterioration of the grounding rope-to-shaft connection.


Average and/or Zero-to-Peak Grounding Current and Shaft Voltage both Step Down

If you notice an unusual step down in grounding current and shaft voltage occurs, it may be a significant event:

  • Has something else contacted the shaft, or has a bearing lost insulation allowing alternate paths to ground?

  • Is the rope-to-shaft contact of good integrity to allow current to flow freely when voltage is present?  

When grounding current and voltage are markedly lower than what is normally seen on the generator and no correlating operating condition exists to explain it, the grounding hardware should be evaluated to ensure that the generator shaft is grounded.

Baseline measurements are crucial for identifying events of concern. Baseline readings should be known for generator online status, turning gear status, offline status, and at differing load levels for comparisons when questions arise.


Average or Zero-to-Peak Shaft Voltages or Grounding Currents Step Up

Typically, shaft voltages and grounding currents on the generator increase or decrease in amplitude along with generator output levels and other operating conditions. Soon after installing, you should capture what normal readings are for your generator at different loads. Knowing the difference between your generator's grounding system's readings at lowest and highest generator outputs helps you to fine tune your monitoring system's thresholds so that you are not triggering snapshots and alarms at levels that are potentially just normal periods of greater demand.

If taking the above into consideration, shaft cleaning does not resolve the higher levels. Share the waveforms you are seeing with Cutsforth so we can compare against our library of waveforms which may indicate other possible problems occurring in the generator that are being detected by the grounding monitoring waveforms.


Average and/or Zero-to-Peak Shaft Voltages or Currents Trending Up or Down Over Time

Trending values on the generator can be a powerful diagnostic tool. If your challenge is poor rope-to-shaft contact tracking, the trend will help to know if steps at remediation are effective or not before alarming takes place. If your waveforms are showing, for example, that there are shorts in the stator winding insulation, trending the amplitude and frequency of the problem signature over time and at various unit loads can help give insight as to whether the condition is getting worse and at what load does the condition first appear now vs time past when the condition was first identified.


Questionable Readings

If you have questions concerning the integrity of shaft voltage or current measurements:

  1. Clean the shaft surface, and inspect the shaft grounding hardware.

  2. Collect another set of waveforms to compare.

If you have concerns:

  • Record a snapshot or set threshold levels so they capture the events in question in a waveform view.

  • Record the date and time along with generator load and vibration trends along with known generator problems that exist.

Cutsforth can then help you connect with professionals experienced in shaft diagnostic and root cause analysis.


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