Safety first
Isolate power according to the manufacturer and plant procedure, confirm DC bus discharge, and use correctly rated instruments. Never assume the DC link is safe immediately after the input supply is removed.
Record the fault code, operating frequency, current, DC voltage, motor state and process condition before resetting.
Understand the control chain
A drive fault can be caused by any layer. Confirm whether the problem is electrical, parameter, communication, motor or mechanical.
No display or no power
Check incoming voltage, fuses, isolator, control supply and phase condition. Verify whether the drive uses a separate control power source.
If protection repeatedly opens, do not replace it with a larger rating. Investigate rectifier, DC bus, wiring and short-circuit conditions.
Motor does not start
Confirm the drive is ready, start command source is correct, enable and safety circuits are healthy, frequency reference is present and minimum/maximum limits permit operation.
| Observation | Likely area | Check |
|---|---|---|
| Ready but no run | Command source | Terminal fieldbus or keypad selection |
| Run active but 0 Hz | Reference source | Analog network or fixed speed |
| Drive inhibited | Interlock or safety | STO enable permissive |
| Motor hums | Output or motor | Phases cable motor connection |
Overcurrent fault
Overcurrent may result from short acceleration time, motor cable faults, incorrect motor data, sudden mechanical load or an internal drive problem. Disconnect and test only according to approved procedures.
Compare current during uncoupled or reduced-load operation where mechanically safe.
Overvoltage fault
Regenerative energy during deceleration can raise DC bus voltage. Increase deceleration time, review braking resistor/chopper design and check incoming supply.
High supply voltage or unstable generator power can also cause overvoltage.
Undervoltage fault
Check supply dips, loose terminals, undersized cables, contactor problems and simultaneous starting of large loads. Log input voltage during the event when possible.
Do not ignore recurring undervoltage resets; they may indicate plant distribution problems.
Overload and overheating
Verify motor load, cooling airflow, ambient temperature, carrier frequency, motor parameters and low-speed cooling. A VFD can protect against current but cannot correct an overloaded mechanical process.
Inspect fan operation, heatsink contamination and enclosure ventilation.
Communication faults
Check network power, cable shielding, topology, termination where applicable, addresses, baud rate, telegram/profile and PLC watchdog logic.
Capture both drive-side and PLC-side diagnostics. A communication fault may be a network issue or an application timeout configured too aggressively.
Analog reference instability
Verify signal type, common reference, scaling, grounding and noise. Compare the measured signal with the displayed drive reference.
Use shielded cable and separate low-level analog wiring from motor output cables.
Motor noise and vibration
Check switching frequency, motor condition, cable length, output reactor requirements, speed range and mechanical resonance. Do not mask bearing or alignment problems by changing drive parameters randomly.
At low speed, confirm motor cooling and torque requirements.
Structured troubleshooting record
| Record | Example |
|---|---|
| Fault code and time | Drive alarm with timestamp |
| Operating values | Frequency current DC bus temperature |
| Command path | PLC fieldbus terminal or keypad |
| Recent change | Parameter motor cable or mechanical work |
| Corrective action | Specific tested change |
| Result | Verified under normal production |
A repeatable record turns breakdown experience into preventive knowledge.
Frequently Asked Questions
Can I reset a VFD fault immediately?
Record the code and conditions first. Reset only when the process is safe and the cause does not create a repeated hazard.
Why does a VFD trip during acceleration?
Possible causes include excessive load, short acceleration time, motor/cable fault or incorrect motor data.
Why does it trip during deceleration?
Regenerative energy may raise DC bus voltage. Review deceleration time and braking hardware.
Can a megger be used on a motor connected to a VFD?
Do not test through the drive. Isolate the motor and follow drive and motor manufacturer instructions.
What causes communication loss?
Cable, power, addressing, topology, configuration, network load or watchdog settings.
Why is the motor hot at low speed?
The shaft-mounted cooling fan may provide insufficient airflow while torque demand remains high.
Should motor parameters be auto-tuned?
Use the manufacturer's commissioning procedure and ensure the motor and process are safe for the selected tuning method.
What is the most important troubleshooting habit?
Capture evidence before changing parameters or resetting the fault.
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