Inventing a Novel Sensor for Online Motor Monitoring

Researchers in the Electrical Machines Lab here at the Global Research Center in Niskayuna, NY are developing future generation asset management tools for industrial motors, generators, and other electrical power & driven equipment. Recently, we invented a novel High Sensitivity differential Current Transformer (HSCT) that can measure key health indicators of stator insulation on electrical motors online.

Novel High Sensitivity differential Current Transformer (HSCT)
Novel High Sensitivity differential Current Transformer (HSCT)

Initial feasibility of online monitoring of capacitance and dissipation factor on small motors was shown in 2003. Later on in 2008 onwards efforts were made to apply this technology on large motors. The GE Measurement and Control business supported this effort through a four-year development project to introduce a novel online motor health monitoring product named Motor Stator Insulation Monitor based on the new sensor HSCT.

This novel sensor is a parts per million (PPM) sensitivity sensor that can measure very small currents (in the order of mA) present in the overwhelming background of large motor currents (kA). This new sensing technology enables online measurement of motor insulation leakage current that helps monitoring of key insulation health indicators of industrial motors: capacitance and dissipation factor of stator windings.

No such online health monitor exists today.

Inside of a 3000HP, 4160 V induction motor terminal box during validation of the new HSCT sensors.
Inside of a 3000HP, 4160 V induction motor terminal box during validation of the new HSCT sensors.

With presently available off-line technology this requires a costly two-day process shutdown and test equipment rental. The novel sensor is validated on a few 4160V, 5000 HP industrial motors. This validation stage confirmed the break-through sensitivity of better than one part per million. This unique monitoring technology enables the on-line health assessment of stator insulation of all industrial motors from a few HP to over 75,000 HP. Today the world population of large industrial motors and generators is estimated to be over 135,000 motors and 35,000 generators. The new online monitoring technology that uses HSCT can be applied to a large population of motors today.

Our team continues to develop advanced diagnostic and prognostic rules for this novel sensor by leveraging both lab and field reliability data. We look forward to updating you further with even more exciting news in the near future. Please stay tuned!

- Prabhakar

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