DC Link Overvoltage

Immediately disconnect AC input power and measure mains voltage with calibrated multimeter at drive input terminals—verify it does not exceed 528V AC phase-to-phase; check for industrial facility switching transients or utility switching events

Measure DC link voltage directly across main capacitor terminals with volt-resistant meter set to 1000V DC range—reading should be 560-650V under no-load condition; readings above 700V confirm overvoltage condition

Inspect line reactor core for saturation (burnt smell, discoloration) and measure DC resistance of all three phases with ohmmeter—resistance variance >10% between phases indicates winding damage; replace if suspected

Examine DC bus capacitor bank for physical swelling, leaking electrolyte, or burnt terminals; measure capacitor ESR with dedicated ESR meter—values >2Ω indicate degradation requiring replacement of entire capacitor block

Test regenerative braking resistor continuity and resistance value with ohmmeter—open circuit or resistance below 50Ω per specification indicates resistor failure; measure drive output PWM frequency (typically 4-16kHz) with oscilloscope to verify chopper circuit switching

Verify control board 24V isolated supply voltage—should measure 24±2V DC; if low, check optocoupler health and gate driver supply capacitors for leakage current using ESR meter

Connect oscilloscope across DC bus capacitors during motor deceleration test—waveform should not exceed 700V peak; sustained overvoltage confirms regenerative load condition requiring external braking resistor installation

Replace DC bus capacitor assembly if ESR exceeds specification or visual inspection shows damage; reinstall drive and perform no-load voltage verification before reconnecting motor load