ocd Over-Current during Deceleration fault in delta drive

ocd Over-Current during Deceleration fault in delta drive troubleshooting

Description

The ocd fault signifies that the output current exceeded the drive’s safety threshold while the motor was slowing down (decelerating). This differs from acceleration faults because it is often linked to regeneration energy and the drive fighting against the motor's kinetic energy to bring it to a stop.

Causes

When a motor is forced to stop faster than it naturally would (coasting), it acts as a generator. However, an Over-Current during this phase usually means the drive is trying to impose a frequency change that results in a high current slip.
1. Deceleration Time too Short: The drive is trying to force the motor to zero speed too aggressively.
2. External Force: A load (like a fan in a draft or a downhill conveyor) is driving the motor faster than the VFD frequency, causing erratic current spikes.
3. Short Circuit: Similar to ocA, intermittent shorts in the windings or cables can trigger this as voltage drops and current spikes.

Solution

Rectifying ocd faults involves managing the stopping energy and checking electrical integrity:
1. Increase Decel Time: Lengthen the deceleration time parameter. This reduces the braking current required to stop the load.
2. Check Braking Hardware: While regeneration usually causes Over-Voltage (ov), severe rapid braking without a resistor can sometimes manifest as current instability. Ensure braking resistors are installed if rapid stopping is required.
3. Electrical Test: Perform insulation resistance tests on the motor and cables. Check for loose connections that might vibrate during speed changes.
4. Change Stop Mode: If precise stopping isn't needed, switch the stop method from "Ramp to Stop" to "Coast to Stop".