Cause : Overvoltage comes when the DC link voltage exceeds its allowed limits. If you're encountering a DC link voltage overvoltage fault with a Allen Bradley drive, it means that the voltage level in the DC link has exceeded the allowable limit. 

"overvoltage" fault in "Allen Bradley drive" indicate the DC bus voltage has exceeded the permissible limit. This means the DC link voltage has exceeded its allowable threshold.

Key Reasons for "Overvoltage in Allen Bradley Drive":

1. Regenerative Energy: During deceleration or stopping, the motor generates regenerative energy, which feeds back into the drive. If the drive cannot dissipate this energy, it results in an overvoltage condition in the DC link.
2. Incorrect Deceleration Settings: If the deceleration ramp is set too short, the motor slows down too quickly, creating excessive regenerative energy.
3. Faulty or Missing Braking Resistor: Braking resistors help to dissipate excess energy. If they are not installed or are faulty, the drive will experience overvoltage.
4. Mains Power Surges or Fluctuations: Sudden increases in the incoming power supply voltage can cause the DC link voltage to rise beyond safe limits.
5. High-Inertia Loads: Large inertia in the mechanical system may create high amounts of regenerative energy when decelerating, which leads to overvoltage.

Steps to Diagnose and Resolve Overvoltage Fault:

1. Monitor DC Link Voltage:

   • Use the drive's diagnostic tools to monitor the DC link voltage during operation.
   • If the voltage exceeds the limits, especially during deceleration, it indicates that the drive is not managing regenerative energy effectively.

2. Check and Adjust Deceleration Ramp Time:

   • Extend the deceleration time to give the drive more time to handle regenerative energy.

3. Check or Install a Braking Resistor:

   • Verify if a braking resistor is installed and functioning correctly. If none is installed and your application involves frequent braking, consider adding one.
   • Test the resistor’s continuity with a multimeter or check its correct sizing.

4. Enable Overvoltage Control:

   • Activate the overvoltage protection feature, which helps limit the DC link voltage by managing deceleration.

5. Check the Power Supply:

   • Measure the mains voltage to ensure there are no spikes or fluctuations. If external power surges are causing the issue, installing surge protectors or stabilizers may help.

6. Review Mechanical Load:

   • If the load has high inertia, consider increasing the deceleration time or using dynamic braking to handle the regenerative energy effectively.