After installing a new motor you are experiencing what some call nuisance trips. Are they nuisance trips or is the motor trying to tell you something is really wrong? New doesn’t always mean good. The first thing to do is look for a NEMA Code Letter on the nameplate. This letter will help you calculate the design locked rotor or In-Rush current the motor is supposed to see. Then use the MCEMAX^® 6-channel In-Rush/Start-Up test to see the actual In-Rush current. If the actual current is not exceeding the design current, then you would want to focus your troubleshooting on the trip relay settings.

For details on calculating the locked rotor current from the NEMA Code letter, visit the PdMA website at:

http://www.pdma.com/pdfs/tips/2011/2_21_11.pdf

Leading indicators are those that occur early in the P-F curve while lagging indicators occur later in the failure cycle. Both are key indicators, but it is important to know which one you are dealing with to better diagnose the severity of the situation.

Phase resistance, like infrared thermography, is a leading indicator of power circuit anomalies. Performed at proper intervals you would expect the resistance imbalance to identify early stages of a power circuit high resistance connection. At early stages the effect of a high resistance connection on the motor is minimal and only localized heating occurs. At later stages the current through the affected phase changes resulting in circulating currents in the motor. These circulating currents cause elevated temperatures that may reduce the life expectancy of the insulation system.

Finally, both indicators being on the P-F curve doesn’t mean you have to wait to get to the lagging indicators to make a decision. The general rule of thumb is that the earlier you can correct these issues, without affecting production, the less expensive the repair.

To see a video on the Power Circuit Fault Zone visit the website below at:
http://www.pdma.com/webinars/Power_Circuit_Fault_Zone/powercircuit.html
Thanks to our friends at PdmA for this tip.

The Rotor Influence Check (RIC) is performed by rotating the rotor in specific increments (determined by the number of poles) over a single pole group, and recording the change in inductance measurements for each phase of the motor. Have you ever seen a Rotor Influence Check (RIC) that showed no sinusoidal activity and changes in rotor position resulted in only minor variations in inductance? If so, you may be looking at test results from a low influence rotor. Click here to learn more about low influence rotors.

This tip of the week from Decatur Industrial brought to you by our friends at PdMA.

In the electric motor maintenance business, motor reliability is paramount. When a motor fails unexpectedly, it means downtime, less of productivity, expensive maintenance fees, and a major pain in the neck! Wouldn’t it be great if you could predict motor failure before it happened?  Watch this short video from PDMA and talk to Decatur Industrial about a preventative and proactive maintenance program!