Cause : Power Supply Frequency Pre-Alarm comes when the input power supply frequency fluctuates more than ±15 Hz. The regenerative unit enters the baseblock state during pre-alarm. When the input supply frequency returns to normal conditions, the regenerative unit will release the base block and continue to operate.

1. Momentary power loss has occurred.
2. Activate the momentary power loss ride-thru.
3. Voltage distortion is large.
4. Increase the power supply capacity.
5. Voltage detection failure .
6. Phase loss has occurred.
7. Confirm the power supply and regenerative unit is correctly connected.