NETA ETT Certified Assistant Level 3 Certification Practice Test

A PI (Polarity Index) value of 1.5 during the acceptance test of a 300HP 5kV AC induction motor indicates that the readings are unacceptable and warrant further investigation. The Polarity Index is a measure used to evaluate the insulation condition of electrical motors, and it represents the ratio of the insulation resistance at 10 minutes to the insulation resistance at 1 minute. A value of 1.5 suggests that the insulation is potentially degrading, as it falls below the generally accepted thresholds for healthy motor insulation, which typically require a PI value of at least 2.0.

In this context, a PI value of 1.5 signifies that there may be moisture, contamination, or physical damage present in the motor's insulation system, which could lead to failure if not addressed. It is essential to conduct further investigation to determine the cause of the low PI value and to take appropriate action, such as performing maintenance or repairs, to ensure the reliability and longevity of the motor.