What Are the Common Inverter Fault Symptoms and Inspection Methods? A Complete Guide

Common inverter faults mainly include overcurrent, short circuit, ground fault, overvoltage, undervoltage, phase loss, overheating, overload, CPU malfunction, and communication errors. Modern inverters are equipped with comprehensive self-diagnostic, protection, and alarm functions. When any of these faults occurs, the inverter will immediately trigger an alarm or shut down automatically for protection, displaying a fault code or fault type. In most cases, the fault cause can be quickly identified and resolved based on the displayed information. The inspection points and troubleshooting methods for these faults have already been clearly explained above. However, many inverter faults do not trigger alarms or display any indication on the operation panel. Common fault symptoms and inspection methods are listed below

1.Motor does not rotate

(1) Check the main circuit:

1) Verify the supply voltage.

2) Confirm the motor is correctly connected.

3) Check whether the conductor between terminals P1 and P has become disconnected.

(2) Check input signals:

1) Verify that a start signal has been input.

2) Confirm that forward/reverse start signals are properly input.

3) Ensure the frequency reference signal is not zero.

4) When the frequency reference is 4–20 mA, check if the AU signal is ON.

5) Confirm that the output stop signal (MRS) or reset signal (RES) is not active (i.e., not open).

6) When “restart after instantaneous power failure” is enabled (Pr. 57 ≠ “9999”), verify that the CS signal is ON.

(3) Check parameter settings:

1) Verify whether reverse rotation is restricted (Pr. 78).

2) Confirm that the operation mode selection (Pr. 79) is correct.

3) Check if the starting frequency (Pr. 13) is set higher than the operating frequency.

4) Review various operation functions (e.g., three-speed operation), especially ensuring the maximum frequency (Pr. 1) is not set to zero.

(4) Check the load:

1) Determine if the load is too heavy.

2) Check if the motor shaft is locked.

(5) Others:

1) Check if the ALARM indicator is lit.

2) Verify that the jog frequency (Pr. 15) is not set lower than the starting frequency (Pr. 13).

2.Motor rotates in the wrong direction

1) Check if the phase sequence of output terminals U, V, W is correct.

2) Verify that the forward/reverse start signal wiring is correct.

3.Actual speed differs significantly from the set value

1) Confirm the frequency reference signal is correct (measure the input signal value).

2) Check if the following parameters are properly set (Pr. 1, Pr. 2).

3) Check if the input signal is affected by external noise (use shielded cables).

4) Verify if the load is too heavy.

4.Unsmooth acceleration/deceleration

1) Check if acceleration/deceleration time settings are too short.

2) Confirm if the load is too heavy.

3) Check if torque boost (Pr. 0) is set too high, causing the stall prevention function to activate.

5.Speed cannot increase

1) Verify the maximum frequency setting (Pr. 1) is correct.

2) Check if the load is too heavy.

3) Confirm torque boost (Pr. 0) is not excessively high, triggering stall prevention.

4) Check if the braking resistor is incorrectly connected to terminals P and P1.

6. Operation mode cannot be changed

If the operation mode cannot be switched, check the following:

1) External input signals:Ensure the STF or STR signal is OFF (operation mode cannot be changed while STF or STR is active).

2) Parameter settings:Check Pr. 79 (“Operation mode selection”). When Pr. 79 = “0” (factory default), the inverter starts in “External operation mode” upon power-up. To switch to “PU operation mode,” press the [MODE] key twice, then press the [▲] key once. For other settings (1–5), the operation mode is determined by the respective function definitions.

7. Power indicator light is off

Check wiring and installation for correctness.

8. Parameters cannot be written

1) Check if the inverter is running (STF or STR signal is ON).

2) Confirm the [SET] key was pressed for at least 1.5 seconds.

3) Verify the parameter value is within the allowable range.

4) Ensure parameters are not being set while in External operation mode.

5) Check Pr. 77 (“Parameter write disable selection”).

Reference

• IEC 61800-3 

• IEC 61800-5-1 

• IEC 61000-4 

Author: Senior Inverter Repair Engineer | Over 12 years of experience in industrial variable frequency drive system troubleshooting and maintenance (familiar with IEC/GB standards)