Deenergized stator inductance is a valuable tool in identifying the internal magnetic condition of your electric motor. It is important to know that inductance measurements can be influenced by the running characteristics and power supply of the motor before it was shutdown. A three-phase balanced power supply on a healthy motor is generally expected to produce a balanced three-phase inductance measurement. However, an unbalanced three phase power supply like a single-phase incident will often result in a large inductance imbalance when measured after the incident. The same is true for popular post repair tests that are often performed on a motor at the motor repair facility. Quarter voltage, growler, magnetic particle, and core loss testing are examples of shop tests that will have a residual effect on the stator inductance and could mislead an analyst into thinking there is a stator or rotor anomaly. It is highly recommended to run a motor on a balanced three phase power supply following a repair or refurbishment before performing acceptance testing. If you are requiring inductance testing as a new motor or post repair acceptance criteria, make sure you are working with your motor shop to make them aware of the correct test sequence when performing inductance testing.
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