ovd Over-Voltage during Deceleration fault in delta drive

ovd Over-Voltage during Deceleration fault in delta drive troubleshooting

Description

The ovd fault is the classic "Regeneration" fault. It occurs when the DC bus voltage rises too high while the motor is slowing down. This is the most common over-voltage fault and is directly related to the physics of kinetic energy.

Causes

When an AC motor is mechanically driven faster than the synchronous frequency set by the VFD (which happens when you lower the frequency to stop), the motor acts as a generator. This "Regenerative Energy" flows back into the drive. The drive's rectifiers block it from going back to the grid, so it accumulates in the DC bus capacitors, raising the voltage until it trips.
1. Decel Time too Short: Trying to stop a heavy flywheel or high-inertia load too fast.
2. No Braking Resistor: The energy has nowhere to go.
3. Braking Transistor Failure: The internal switch meant to divert energy to the resistor is broken.

Solution

Energy management is key here:
1. Increase Decel Time: The simplest fix is to increase the time it takes to stop (Parameter 01-10). This spreads the energy return over a longer period, allowing natural losses to dissipate it.
2. Install Braking Resistor: For fast stops, connect an external braking resistor to the B1/B2 (or +/PB) terminals. Ensure the resistance (Ohms) and Wattage match the drive manual specifications.
3. Enable Over-Voltage Stall Prevention: Most Delta drives have a parameter for "Stall Prevention during Decel." Enable this to let the drive automatically pause deceleration if voltage gets too high.