Motor phase U missing

What does ALARM 30 mean?

Motor phase U between the frequency converter and the motor is missing. This indicates a loss of one of the three phases supplying the motor, which can lead to motor damage or failure if operated in this state.

• Loose electrical connection at the motor terminal block (U phase) or frequency converter output terminal (U phase).
• Open circuit in the motor cable conductor for phase U, often due to mechanical stress or insulation breakdown.
• Internal open circuit in the motor winding for phase U, measured from the motor terminal box.
• Failure of an IGBT (Insulated Gate Bipolar Transistor) or its gate driver circuit for the U-phase output in the frequency converter.
• Faulty motor output contactor (if present) where one pole (U-phase) has failed to close or has high resistance.

Click steps to track your progress.

1. 1

   1. Disconnect main power, then verify terminal tightness for phase U at the frequency converter output and the motor terminal box.

2. 2

   2. Measure resistance between motor phases U-V, V-W, and W-U (motor disconnected from converter) to detect an open winding on phase U.

3. 3

   3. Perform a continuity test on the motor cable conductor for phase U from the frequency converter output to the motor terminal.

4. 4

   4. Use an insulation resistance tester (megohmmeter) to check for breakdown on the U-phase motor cable (e.g., 500V DC test).

5. 5

   5. If an output contactor is used, measure voltage across its coil and check continuity of its main contacts for phase U when energized.

6. 6

   6. Visually inspect the frequency converter's U-phase output stage for signs of damage or discoloration (if safe and accessible).