Cause: Mains Freq Out Of Range comes when the input power supply frequency deviates from the acceptable range specified for the drive. The frequency of the power supply might be lower than the specified range.

"MFF" fault in Schneider ATV950 drive indicate "Mains Freq Out Of Range" issue.  This means the frequency of the incoming mains power supply is outside the acceptable range for the drive. This can lead to improper operation or even damage to the drive if not addressed. 

Here’s a structured approach to troubleshoot and resolve this issue:

1. Verify Mains Frequency:

• Check Supply Frequency: Use a reliable frequency meter to measure the frequency of the incoming power supply. Ensure it matches the specified range for the drive (typically 50 Hz or 60 Hz, depending on the region and drive settings).
• Frequency Stability: Verify that the mains frequency is stable and not fluctuating beyond the acceptable limits.

2. Review Drive Settings:

• Frequency Range Settings: Check the drive’s configuration settings to ensure that the allowable mains frequency range is set correctly. Adjust if necessary.
• Parameter Configuration: Verify parameters related to mains supply and frequency settings in the drive’s configuration menu.

3. Inspect Power Supply:

• Power Quality: Ensure the quality of the mains power supply. Poor power quality, including fluctuations or harmonic distortions, can cause frequency issues.
• Power Source: If using a generator or UPS, verify that it is providing a stable and correct frequency output.

4. Check for External Interference:

• Electrical Interference: Ensure that the drive and its power supply are not subject to electrical interference from nearby equipment or installations.
• Isolation: If possible, isolate the drive’s power supply to determine if external factors are causing frequency variations.

5. Test Under Different Conditions:

• Load Variations: Test the drive with different load conditions to see if the mains frequency out of range fault occurs under specific circumstances.
• Environmental Factors: Consider environmental factors such as temperature and humidity, which can affect power supply stability.

6. Consult Power Supply Provider:

• Utility Provider: If the mains supply frequency is consistently out of range, contact your utility provider to report the issue and seek resolution.
• Power Quality Analysis: Request a power quality analysis from the utility provider if frequent fluctuations are detected.

7. Use of Filters or Regulators:

• Frequency Filters: Consider installing frequency filters or regulators to stabilize the incoming power supply frequency.
• Power Conditioning Equipment: Use power conditioning equipment to ensure a stable and clean power supply to the drive.