AI Under Frequency

What does F26 mean?

This fault indicates an under-frequency condition detected by the anti-islanding protection. This mechanism ensures the inverter disconnects from the grid if grid power is unstable or absent, preventing dangerous backfeeding and potential damage to equipment.

• Grid supply frequency dropping below the inverter's configured lower threshold (e.g., 49.5 Hz or 59.5 Hz) for the anti-islanding protection.
• Grid instability, excessive demand, or localized power generation issues causing a sustained frequency dip.
• Inverter's internal frequency measurement circuit experiencing drift or failure, leading to an erroneous under-frequency detection.
• Anti-islanding parameter P_AI_Freq_Low set too close to the nominal grid frequency, making the system overly sensitive.

Click steps to track your progress.

1. 1

   Using a true RMS multimeter with frequency measurement, monitor the incoming grid frequency at the inverter's AC input terminals (e.g., L1-L2) over a 15-minute period.

2. 2

   Compare the recorded frequency against the inverter's configured anti-islanding low-frequency trip point (e.g., Parameter P_AI_Freq_Min).

3. 3

   Inspect the integrity of the AC voltage sensing connections on the inverter's input terminals for any signs of corrosion or looseness.

4. 4

   If measured grid frequency is stable and within limits, consider decreasing the anti-islanding under-frequency threshold (e.g., Parameter P_AI_Freq_Min by 0.2 Hz) only if compliant with local grid codes.

5. 5

   If the fault persists despite stable grid and parameter adjustments, initiate an inverter self-diagnostic routine to assess the internal frequency measurement hardware.