Cause : DC link voltage overvoltage comes when the power unit has detected an overvoltage condition in the DC link. If you're encountering a DC link voltage overvoltage fault with a Siemens SINAMICS G120 drive, it means that the voltage level in the DC link has exceeded the allowable limit. 

- motor regenerates too much energy.
- line supply voltage too high.
- line phase interrupted.
- DC-link voltage control switched off.
- dynamic response of DC-link voltage controller excessive or insufficient.

Fault value (r0949, interpret decimal): DC link voltage at the time of trip [0.1 V].

Remedy:

-increase the ramp-down time (p1121).
- set the rounding times (p1130, p1136). This is particularly recommended in U/f operation to relieve the DC link voltage controller with rapid ramp-down times of the ramp-function generator.
- Activate the DC link voltage controller (p1240, p1280).
- adapt the dynamic response of the DC-link voltage controller (p1243, p1247, p1283, p1287).
- check the line supply voltage and setting in p0210.

Here's how you can address this issue:

1. Stop Operation: Immediately stop the operation of the drive to prevent further damage to the equipment and ensure safety.

2. Identify the Cause: Determine the reason for the DC link voltage overvoltage fault. Common causes include:

   • Regenerative energy from the motor during deceleration or braking, which exceeds the capacity of the DC link capacitors.
   • Power supply fluctuations or disturbances.
   • Issues with the braking resistor or its connection.
   • Incorrect configuration settings or parameterization of the drive.

3. Inspect Braking System: Check the braking resistor and its connection to the drive. Ensure that the resistor is functioning correctly and that its capacity matches the requirements of the application. Inspect the wiring and connections for any signs of damage, overheating, or loose connections.

4. Review Drive Parameters: Verify the configuration settings and parameterization of the SINAMICS G120 drive. Pay particular attention to parameters related to braking and regenerative energy handling. Adjust these parameters as necessary to optimize the performance and prevent overvoltage conditions.

5. Monitor DC Link Voltage: Utilize the diagnostic tools provided by the drive to monitor the DC link voltage during operation. Analyze the voltage waveform and trends to identify any irregularities or spikes that could indicate an overvoltage condition.

6. Implement Protective Measures: Consider implementing additional protective measures such as dynamic braking modules, external braking resistors, or voltage clamping devices to mitigate the risk of DC link voltage overvoltage faults.

7. Perform Test Runs: Conduct test runs with the drive and motor system under different operating conditions to verify that the overvoltage issue has been resolved. Monitor the DC link voltage closely and observe the performance of the drive system.