Technical Frequently Asked Questions (FAQs)

  • A permanent flux probe is a magnetic sensor installed on a stator wedge that accurately measures the magnetic field variations close to the rotor surface.

    The orientation of the sensor produces either a radial flux probe or a tangential flux probe. Generatortech investigated both types of probes and determined that radial flux probes are a much better option.

    The probe-to-rotor distance is extremely important since invalid data is produced when the distance is either too close or too far away from the optimum distance.

    A turn short bypasses a complete turn in a coil, reducing the strength of the field above the slots used by that coil. A measurement of the field above the rotor can determine how many turns are shorted out of each coil.

  • Shorted-turns are the result of failed insulation between individual windings in generator rotors. The impact of operating with shorted turns can result in higher vibration, elevated field excitation requirements, load limits, higher operating temperatures and forced outages.

    The amount of magnetic flux produced by a coil is the product of the field current and number of active turns in the coil as measured in amp-turns or magnetomotive force (MMF). If a shorted turn is present, the number of active turns in a coil is reduced and the resulting decrease in magnetic flux produced by the coil can be determined by analysis of the flux probe waveform. 

    In order to get the best sensitivity for detecting shorted turns in all rotor coils, Generatortech records a series of data points as the load on the unit is varied.

  • Testing at stand-still will miss both speed-dependent and temperature-dependent turn shorts. Speed-dependent shorts need the high centrifugal force to compress the turns to produce a short. Temperature-dependent shorts require the thermal expansion of the turns to produce a short.

    Flux probe testing while on-line has the rotor at rated speed and temperature and shows turn shorts with high sensitivity. A single short can be detected in any coil when a wide range of loads recorded.

  • Although isolated shorted turns are undesirable, their existence in a rotor winding does not necessarily indicate a call to action. Generatortech estimates 33% of the rotors in operation today may have one or more shorted turns. In fact, rotor windings on new generators may have one or more shorted turns after a few stop-start cycles. If the shorted turns are not significantly affecting satisfactory operating performance, no corrective actions need be taken.

    Periodically monitoring for shorted turns will help establish whether new turn shorts are developing and when corrective action should be taken. If turn shorts are increasing over time, this trend will likely accelerate.

  • Partial turn shorts cannot exist for long. The very high temperatures generated at the initial small contact point will melt copper and cause a low resistance spot weld. The low resistance short will completely bypass one turn in the coil.

    The calculated turn short indications reflect differing detection sensitivities as load changes the FDZC position. The changing indications are not reflecting changes in the resistance of the short.

  • As long as the flux probe was designed correctly to have a adequate probe-to-rotor distance (neither too small or too large) and is sensitive to radial magnetic flux, the Generatortech software will analyze the waveforms correctly.

  • Yes! Generatortech will be happy to answer your questions about testing, installation or to advise regarding data analysis. Contact Us via phone or email.

  • We have two options for our customers who have not purchased a Generatortech Analysis Package:

    1. You can rent a Generatortech Portable Analysis system, record data files according to our testing protocol, return the equipment and we will analyze your data and prepare a formal report.

    2. Generatortech personnel can travel to your site, record test data and provide you with a formal report. 

  • Yes, Generatortech can be contracted for data analysis and reports. We also provide brief email discussions of data for customer’s who purchased one of our analysis systems.

  • Shorted-turns are the result of failed insulation between individual windings in generator rotors. Undesired turn-to-turn movement as the winding heats up and cools off causes shear forces on the insulation between the turns. The shear forces can cause tears or insulation movement that allow turn shorts to develop. Stop-Start cycles, over-speed incidents, line disturbances, contamination, moisture, manufacturer errors, and damage during retaining ring installation are some of the reasons insulation fails. 

  • The impact of operating with shorted turns ranges from no-problem to abnormal vibration, load limits, higher operating temperatures and forced outages. 

    The location and number of shorted turns in a rotor determines the magnitude of the effects of running a rotor with shorted-turns.

    As generator units age, shorted-turn problems are more likely to be experienced. The stresses involved in each Stop-Start cycle play an especially important role. Occasionally, newly rewound fields will have shorted-turns. 

    Shorted-turns in the field winding can cause operating conditions which may limit unit loads. If conditions are extreme, forced outages may occur.

    The amount of magnetic flux produced by a coil is the product of the current and number of active turns in the coil as measured in amp-turns or magnetomotive force (MMF). If a shorted turn is present, the number of active turns in a coil is reduced and the resulting decrease in magnetic flux produced by the coil can be determined by analysis of the flux probe waveform. 

    In order to get the best sensitivity for detecting shorted turns in all rotor coils, Generatortech records a series of data points as the load on the unit is varied.Description text goes here

  • With the G50 your generator’s flux probe is permanently connected to a server which can be accessed via Internet or your company intranet using a secure VPN connection. The G50 allows test data to be acquired automatically and/or manually. So, you no longer need to travel to distant power stations for testing. Also, Generatortech can be contracted to be responsible for your regularly scheduled testing and analysis via the secure VPN connection.

  • When planning the installation of permanent probes, critical machine dimensions such as rotor outer diameter (O.D.), retaining ring O.D., and stator core inner diameter (I.D.) need to be supplied to Generatortech so the flux probe can be custom manufactured before assembly. Generatortech will provide a drawing showing which dimensions must be supplied. If desired, Generatortech personnel will take the dimensions.

    If plans are being made to assemble an air-gap probe we recommend contacting Generatortech as early as possible.

  • Generatortech provides a Windows-based program that combines data acquisition with the display and analysis of waveforms for rotor winding shorted turns.

    The system uses high-speed data acquisition hardware to record the flux probe waveforms. The program provides an oscilloscope-like display while recording the data. The signal is continuous analyzed to determine when to record waveforms that optimize detection sensitivity for each rotor coil.

    The program automatically identifies and labels the waveform features and measures the appropriate values to provide estimates of turn shorts.

    Waveforms that optimize detection sensitivity in each rotor coil are automatically recorded as load on the unit changes, making testing hands-off.

    Generatortech's Acquisition and Analysis Program has been designed to quickly and easily acquire and save data from flux probes.

  • Power generating utilities and co-generation industries worldwide including turbine and hydro generators. 

    Refineries, paper plants and other plants that run their own generators make use of Generatortech equipment and testing services.

    Service companies who provide retrofit installations and use our probes & analysis software for high-speed balance pit (spin pit) flux probe testing. 

    Original Equipment Manufacturers (OEM) who install Generatortech equipment in new generators and as retrofit applications during major outages.