Shaft Voltage Testing

Every rotating machine has the potential to be damaged by stray shaft currents, whether mechanical or electrical.  Determining the severity of these currents and the proper solutions for each rotating machine, is the focus of the Shaft Voltage Tests performed by the MPS 'gaussbusters'.  MPS engineers will measure shaft voltages and grounding currents to determine if there may be circular or stray currents.   The MPS 'gaussbusters' will determine if discharging and sparking are currently present, and classify shaft current and voltage sources as either electromagnetic or electrostatic in nature.   Without implementing proper solutions any type of rotating machinery may be in danger. In addition, MPS engineers perform complete and comprehensive site surveys looking for areas which may cause problems in the future.  If appropriate, MPS ' gaussbusters'  may recommend the utilization of one or more MPS Shaft Condition Monitoring or Shaft Earthing/Grounding Products to control and/or eliminate shaft currents and voltages in the future.




The most common signs of shaft current damage (sometimes referred to as electromagnetic discharge) are frosting, pitting, or spark tracks on bearings, collars, journals and even shafts. This type of damage is often passed off as mechanical wear.   The typical solution is to incur the cost and replace the damaged parts, or  if these parts are  sent for machining, more residual magnetism may be introduced, causing more damage visible only at the next shutdown. 

In some machines with shaft current problems, the loss of material can be significant enough that radial or axial movement of the shaft occurs. Proximity probes may register high peaks caused by the presence of high magnetic fields, incorrectly identified as electrical runout or as vibration harmonics. One machine vendor, after trying typical solutions, such as replacing oil, balancing, adding probes with monitoring, finally described the machine as having "mysterious mechanical damage." During MPS's many years of investigating shaft currents, no two machines have shown identical symptoms and signs. If a machine has continued problems of varying nature, shaft currents may be a factor. Shaft currents should only be ruled out after a thorough magnetic survey, and shaft voltage and current analysis have been completed.




Want to Learn More?

Download Understanding Shaft Voltage and Grounding Currents of Turbine Generators




 Contact MPS and ask for an available engineer to answer your questions.