Phase Imbalance
The three-phase input power supply exhibits significant voltage or current imbalance exceeding 2-3% tolerance, causing uneven loading of the input rectifier diodes and DC bus ripple. This condition leads to increased component stress, overheating, and potential drive shutdown to prevent damage to power semiconductors and capacitors.
Error Code
108
Severity
Fault
Equipment
AC Drive / VFD
Manufacturer
Schneider Electric
Yellow PHASE or IMBAL LED indicator active on front panel
Fault code F006 or PH displaying voltage imbalance percentage
Motor exhibits increased vibration and audible noise during operation
Individual phase currents vary by more than 5-8% between phases
DC bus ripple voltage exceeds 10% of average value
Drive randomly trips during high load conditions
Loose or corroded input terminal connections causing voltage drops
Failed input fuse or contactor contact creating single-phase operation
Unbalanced utility supply with phase-to-phase voltage differences exceeding 2%
Motor winding fault creating unequal impedance between phases
Worn or damaged input reactor with asymmetrical inductance values
Defective input rectifier diode causing uneven current distribution
Execute lockout/tagout and verify all energy sources are isolated safely
Measure and record all three phase-to-phase voltages with precision multimeter
Check input terminal tightness to manufacturer torque specifications
Test input fuses for continuity and proper current ratings
Verify motor winding resistance balance within 2% using milliohm meter
Replace any failed rectifier diodes after confirming proper gate driver operation
Perform complete phase balance verification test under full rated load conditions
Safety First: Always isolate power and follow LOTO (Lockout/Tagout) procedures before working on electrical components. If unsure, contact a certified repair technician.
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