A: Causes:
1. The input voltage—especially during startup and when reaching 19 Hz—is below 340 V (for a three-phase 380 V inverter). This could be due to worn-out contactor contacts or poor contact in the upstream circuit breaker/fuse;
2. The internal electrolytic capacitors in the inverter may degrade over time or in high-temperature environments, resulting in reduced energy storage capacity;
3. There may be insulation issues with the motor or cables.
Troubleshooting Steps:
1. First, use a multimeter to measure the input voltage and check if it drops significantly when the motor reaches 19 Hz. If so, address the external wiring.
2. If the input voltage remains stable, the issue is most likely due to aging capacitors inside the inverter or a problem with the rectifier circuit’s contactor. Replace the contactor or capacitors.