Tip of the Week

Test Your Knowledge - Part 3

For the remainder of 2018, our Tip of the Week will consist of a true/false question presented to the Tip of the Week recipients.

After pushing the start button on an AC induction squirrel cage motor, the motor begins rotating but trips after 20 seconds failing to reach full load speed. After a visual inspection and resetting of the overloads a second attempt fails in the same way. The most likely cause of the motor tripping is a turn-turn short in the stator windings. True or False.

Answer: False

A motor tripping overloads on a delay trip is likely a rotor or machine train issue. Broken rotor bars will increase the reflected impedance on the stator windings, reducing startup torque and extending the startup time. If enough bars are broken the motor will trip as described. Heavier than normal loading on startup due to machine train resistance to rotation does not change the impedance on the stator but does lengthen the startup and if bad enough will trip the overloads.

If you answered incorrectly and feel you need additional training or if you answered correctly and still feel like you need additional training, we can help. CLICK HERE to go to our training page or contact PdMA at pdma@pdma.com or phone (813) 621-6463.


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