Case Study: Repairing a Decanter Centrifuge

A wastewater facility’s centrifuge faced shutdowns due to VFD overheating. Fixing the fan and VFD components restored performance, cutting downtime by 90%.

Background

An industrial wastewater treatment facility relies on a decanter centrifuge system to dewater sludge. This centrifuge is driven by motors controlled by Eaton Variable Frequency Drives, located in a dedicated environmental control panel. These VFDs regulate motor speed and torque, ensuring optimal separation performance under varying load conditions.

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Problem Statement

Operators reported that the centrifuge intermittently failed to reach operational speed, causing the control system to trip and initiate emergency shutdowns. This issue caused:

Frequent downtime
Inconsistent dewatering performance
Increased maintenance costs

Initial Observations

Alarm logs showed VFD fault codes: “Overcurrent”, “Undervoltage”, and “DC Bus Overvoltage”.
The problem appeared during high-torque startup and load surges.
Power to the panel was stable, and no anomalies were found in the main supply.

Diagnosis & Troubleshooting

Step 1: Visual Inspection

No signs of burning or physical damage.
Ambient temperature within enclosure: ~40°C
Dust buildup noted on heatsinks and filters.

Step 2: Electrical Testing

DC Bus Voltage: Spiking during startup
Capacitor Health: Equivalent series resistance increased.
IGBTs: Some thermal stress but not shorted.

Step 3: Control Signal Verification

Analog signals from the PLC were stable.
No loose wiring or grounding issues.
Load sensor feedback was erratic.

Step 4: Environmental Factors

Panel cooling fan had failed; internal temperature often exceeded design specs.
This caused thermal degradation of the VFD components over time.

Root Cause

The cooling system failure led to thermal overstress of VFD internal components, causing:

Degraded DC link capacitors
Intermittent IGBT malfunction
Voltage instability during startup and load changes

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Repair and Resolution

Steps Taken:

Replaced the faulty panel fan and cleaned all filters.
Repaired the VFD:
- Replaced DC capacitors and damaged gate drivers.
- Reapplied thermal paste and reseated the IGBTs.
- Verified heatsink thermal conductivity.
Calibrated and replaced the load sensor.
Updated VFD firmware and reconfigured startup ramp profiles to limit inrush current.

Post-Repair Validation

VFD operated consistently under all load conditions.
Ramp-up/down was smooth with no fault trips.
Temperature inside the panel stabilized to <35°C.
Logged data over 72 hours confirmed normal operation.

Outcome & Recommendations

Results:

Downtime reduced by 90%
Centrifuge throughput increased by 15%
Maintenance intervals extended

Preventive Measures:

Implement a quarterly thermal inspection and VFD capacitor check.
Install temperature monitoring alarms inside the panel.
Schedule annual filter and fan cleaning/replacement.

Case Study: Repairing a Decanter Centrifuge

A wastewater facility’s centrifuge faced shutdowns due to VFD overheating. Fixing the fan and VFD components restored performance, cutting downtime by 90%.

Background

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Problem Statement

Initial Observations

Diagnosis & Troubleshooting

Step 1: Visual Inspection

Step 2: Electrical Testing

Step 3: Control Signal Verification

Step 4: Environmental Factors

Root Cause

Relevant Industries

Repair and Resolution

Post-Repair Validation

Outcome & Recommendations

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