Analyzing the motor current for transient In-Rush peak and Start-Up time is a standard approach to troubleshooting a tripped motor. An instantaneous trip might indicate a stator or trip set point anomaly. An overload/time delay trip would indicate more of a mechanical load/rotor driven anomaly. If at all possible, before the next start an off-line MCE® test should be performed to identify any damage that exists to the stator windings and insulation that may result from a high current event or that may have been responsible for the unexpected trip. And, the very next re-start of the tripped motor should be monitored with your EMAX technology to record exactly how the three phase voltage and current respond to the re-application of power following the trip. Monitoring all phases of voltage and current throughout the In-Rush/Start-Up in an RMS enveloped and time domain format allow you to see exactly what the peak In-Rush current on each phase is and don’t be surprised if the highest value of the three phases is on the negative side of the sinewave. Additionally, the RMS envelope is the ideal tool to trend and compare the Start-Up times from start to steady state.
To see a case study on a tripping motor view PdMA Finds Fault in Stator of Re-Wound Motor on our PdMA YouTube Channel.