Phase imbalance

What does 37 mean?

There is a significant current imbalance detected between the power units within the frequency converter. This can indicate issues with the motor, motor cabling, or an internal problem within the drive's power stage. Sustained phase imbalance can cause overheating in the motor or drive components and lead to premature failure.

• Unbalanced incoming AC supply voltages (e.g., >2% phase voltage deviation) supplied to the drive's input.
• Loose or high-resistance connections in one or more motor phases (U, V, W) in the motor cabling or at the motor terminal box.
• Internal fault within the motor windings, such as shorted turns or a partial ground fault in one phase.
• Failure of an internal power unit component within the drive (e.g., faulty IGBT, degraded DC bus capacitor for one leg).
• Significant difference in cable length or impedance between the three motor phases for very long cable runs.

Click steps to track your progress.

1. 1

   1. Measure incoming AC line voltages (L1-L2, L2-L3, L3-L1) at the drive input terminals (e.g., U_in, V_in, W_in) and confirm they are balanced within 2% of the average.

2. 2

   2. Monitor the drive's output current (P0-01, Motor Current) for each phase (U, V, W) at full load, looking for an imbalance exceeding 5%.

3. 3

   3. De-energize the drive and measure the resistance across motor windings (U-V, V-W, W-U) at the motor terminals; confirm balanced resistance values (e.g., within 2% of each other).

4. 4

   4. Tighten all motor cable connections at the drive output terminals (T1, T2, T3) and at the motor terminal box to eliminate loose connections.

5. 5

   5. Perform an insulation resistance test (Megger test) on the motor windings to ground and between phases (e.g., 500VDC, >100M Ohm) to detect winding degradation.