An OBF fault on an Altivar Process ATV900 (also ATV600 and ATV340) variable speed drive from Schneider Electric indicates the drive is measuring high voltage on the DC Bus capacitors.

This occurs when the drive's DC bus voltage exceeds the permitted threshold while the drive is running the motor.

This can happen if the drive is attempting to slow down the motor/load.

It can also occur if there are voltage surges or spikes on the incoming voltage.

Possible solutions

• Adjust the DEC ramp time: If the load can be stopped more gradually, try increasing the DEC ramp time to give the drive more time to ramp down.
• Check the line voltage: Make sure the line voltage is within specifications.
• Monitor the DC bus voltage: If the OBF fault occurs when the drive powers up, check that the display isn't set to show the last fault on power up.
• Use a dynamic brake resistor: If the load is overhauling, a dynamic brake resistor may be needed (NOTE, it is not possible to connect a DB resistor to an ATV600 drive).

If the error occurs shortly after a run command is given, check the motor and cables for signs of a short or bad connection phase to phase or phase to ground.   At low speeds it may be possible to trip on the OBF error instead of a motor short circuit or ground short circuit error.

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Released for:Schneider Electric Canada