Ground faults in a servo amplifier system can lead to erratic behavior, unexpected shutdowns, or even permanent damage to equipment. A ground fault occurs when an unintended electrical connection exists between a live conductor and ground, causing leakage currents that disrupt normal operation. Diagnosing and fixing these faults promptly is essential for maintaining system reliability and safety.
This article provides a step-by-step guide to identifying and resolving ground faults in servo amplifier systems.
Read more: Servo Amplifiers: Diagnosing and Fixing Ground FaultsRecognizing the Symptoms of a Ground Fault
The quintessential step to repairing a ground fault is being able to recognize and identify symptoms. After all, you can’t fix a problem if you don’t know what the problem looks like. When looking for symptoms of a ground fault keep an eye out for:
Unexpected shutdowns or fault alarms (e.g., “Ground Fault” error on the drive)
Erratic motor behavior (jittering, unexpected movements, or loss of torque)
Burning smells or overheating components
Electrical noise affecting feedback devices (encoders/resolvers)
Tripped circuit breakers or ground fault protection devices
Safety Precautions
Once you’ve recognized the symptoms of a ground fault, you may have that impulse of wanting to go straight into poking around and tinkering with the drive. However, before you do that, you need to take precautionary steps to ensure your safety. Exercising the following precautions will prevent the chances of a hazard occurring, increasing your safety.
- Make sure the power is disconnected and verify with a multi-meter.
- Ensure the capacitors are discharged.
- Use insulated tools and wear personal protective equipment (PPE)
– Companies like RefrigiWear offer a selection of insulated foot wear that protects against high voltage. - Follow lockout/tagout procedures if working in an industrial environment.
Isolating the Fault
Once you are confident that all safety precautions have been taken and that the system is completely off and all power fully dispersed, then you can proceed forwards with isolating the fault. Here are a few ways you can isolate a fault.
Checking the Power Supply
Using a multi-meter, you can check the power supply to see if you get a low resistance rating that would indicate a short in the ground.
Checking the Motor Windings
You can test the motor windings by disconnecting the motor cables from the power supply. Next, measure the resistance between each motor phase and the ground. There should be high resistance (>1MΩ). A low resistance is an indicator of a short in the motor frame.
Check Encoders and Resolver Connections
Another way is to check encoders and resolvers for any exposed or damaged wires. You can check do this by checking for continuity between signal lines and ground. There should be no direct connection.
Inspecting the Servo Amplifier
If you need to check the servo amplifier, look for obvious visual signs like burnt components, blown fuses, or discolored PCBs. Using a multi-meter test the DC bus capacitors for leakage or short circuits. Double check proper grounding of the amplifier chassis.
Repairing the Ground Fault
While diagnosing and isolating faults are lightly challenging but doable for most people, it is advised that if you are not most versed in servo amplifiers then reach out to a professional for repairs.
Repair/Replace Damaged Wiring
If the issue is with the cables then replace any damaged or frayed cables. Also, check for strain relief on connection points to the devices. Good strain relief prevents future wear of cables. Make sure you use shielded cables for motor and feedback connections.
Address Motor Issues
Check your motor bearings as mechanical wear can cause internal shorts. If your motor windings are shorted, replace the motor.
Replacing Components
Replace blown out PCB and capacitors. Double check the amplifier is properly grounded. Be sure to check the specs before doing so.
Verify Grounding Scheme
When verifying the grounding scheme, make sure the system has a single-point ground to avoid ground loops. Also, make sure wires are properly sized and securely connected
After Repair Testing
After repairs are done, before you restore power, make sure to give another test. Use a multimeter to test resistance on motor windings and cables. After that, gradually power up the system and monitor for fault messages. Finally, run the servo motor at low speed and check for any odd sounds or for overheating.
Conclusion
Ground faults in servo amplifier systems can cause significant downtime if not addressed properly. By following a structured diagnostic approach—checking power supplies, motor windings, feedback cables, and amplifier components—you can efficiently locate and resolve the issue. Always prioritize safety, use proper testing equipment, and ensure correct grounding practices to prevent future faults.
Regular preventive maintenance, including insulation resistance checks and visual inspections, can help detect ground faults early and extend the lifespan of your servo system.
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Updated on May 1, 2025 by Ken Cheng