Armature Overcurrent

Verify mechanical load is free: manually rotate motor shaft by hand (disconnect coupling). Listen for bearing noise or feel binding resistance. Check conveyor/pulley systems for obstacles.

Measure DC bus voltage with multimeter at drive terminals with no load. Should read within ±10% of nameplate (typically 230V, 400V, or 460V DC). Confirm supply phase sequence and absence of phase loss.

Test armature winding insulation resistance using megohmmeter (1000V test): phase-to-ground should read >100 MΩ. If <10 MΩ, motor winding is shorted and requires replacement or rewind.

Inspect thyristor assembly heatsink for burnt components, cracked solder joints, or gate drive circuit board damage. Check gate driver optocoupler LEDs for glow using infrared camera (indicates continuous current draw).

Measure current sense shunt voltage drop across terminals at rated motor current (should match 50-100mV specification in manual). If measurement is erratic or zero, shunt is open-circuit; replace sensing resistor.

Reset drive parameter: Access menu → Current Limit adjustment (typically parameter P07 or I_max) and verify setting is 120-130% of motor nameplate current. Reprogram if corrupted.

If mechanical and electrical checks pass, power-cycle drive and attempt soft-start with no load. Gradually increase load while monitoring current. If fault reoccurs at low torque, thyristor or gate driver circuit requires replacement.

Perform thyristor static test with dedicated thyristor tester or Multimeter continuity mode (thyristor should show forward drop 0.6-0.8V in forward direction, open circuit reverse). Replace defective thyristors as matched pairs.