OC (OC1, OC2, OC3) Overcurrent fault in Toshiba drive
OC (OC1, OC2, OC3) Overcurrent During Acceleration, Deceleration, or Constant Speed fault in Toshiba drive
Description The Overcurrent (OC) fault is the most frequent trip in variable frequency drives. It indicates that the output current going to the motor has exceeded the drive's rated current capacity, typically by 200% or more, for a split second. The drive shuts down the output transistors (IGBTs) instantly to protect the hardware from catastrophic failure. OC1 occurs during acceleration, OC2 during deceleration, and OC3 during constant speed operation. Understanding which phase the drive was in is crucial for diagnosis. This is not a thermal overload (which is slow); this is an instantaneous spike in amperage. Causes
1. Short Circuit: A phase-to-phase short in the motor windings or output cabling.
2. Ground Fault: A phase-to-ground short, often caused by damaged cable insulation or moisture in the motor peckerhead.
3. Mechanical Bind: The load is locked, jammed, or has excessively high inertia (e.g., a fan starting against the wind).
4. Acceleration Time: The acceleration time (ACC) is set too short, requiring more torque (and current) than the drive can supply.
5. Hardware Failure: The drive's internal output transistors (IGBTs) are blown. Solution Begin by isolating the variable. Disconnect the motor cables (U, V, W) from the bottom of the drive. Try to run the drive empty. If the fault persists with no wires attached, the VFD hardware (IGBTs or Current Sensors) is faulty and the unit likely needs replacement.
If the drive runs empty, the issue is external. Perform a "Megger" test (Insulation Resistance) on the motor and cables (ensure VFD is disconnected during this test to avoid blowing the drive). You are looking for a reading above 50 Mega-ohms. If the insulation is good, use a standard multimeter to measure resistance phase-to-phase (U-V, V-W, W-U). They should be balanced.
If the electrical integrity is sound, look at parameters. Increase the Acceleration Time (ACC) significantly. If the load has high inertia (like a large flywheel or centrifuge), the motor draws massive current to get it moving; extending the ramp time reduces this inrush. Check the "Torque Boost" parameter—if set too high, it saturates the motor core, causing excess current. Reduce torque boost. Finally, check for mechanical binding by physically rotating the motor shaft by hand (if safe). If the application requires this much current, the VFD may simply be undersized for the application.
Description The Overcurrent (OC) fault is the most frequent trip in variable frequency drives. It indicates that the output current going to the motor has exceeded the drive's rated current capacity, typically by 200% or more, for a split second. The drive shuts down the output transistors (IGBTs) instantly to protect the hardware from catastrophic failure. OC1 occurs during acceleration, OC2 during deceleration, and OC3 during constant speed operation. Understanding which phase the drive was in is crucial for diagnosis. This is not a thermal overload (which is slow); this is an instantaneous spike in amperage. Causes
1. Short Circuit: A phase-to-phase short in the motor windings or output cabling.
2. Ground Fault: A phase-to-ground short, often caused by damaged cable insulation or moisture in the motor peckerhead.
3. Mechanical Bind: The load is locked, jammed, or has excessively high inertia (e.g., a fan starting against the wind).
4. Acceleration Time: The acceleration time (ACC) is set too short, requiring more torque (and current) than the drive can supply.
5. Hardware Failure: The drive's internal output transistors (IGBTs) are blown. Solution Begin by isolating the variable. Disconnect the motor cables (U, V, W) from the bottom of the drive. Try to run the drive empty. If the fault persists with no wires attached, the VFD hardware (IGBTs or Current Sensors) is faulty and the unit likely needs replacement.
If the drive runs empty, the issue is external. Perform a "Megger" test (Insulation Resistance) on the motor and cables (ensure VFD is disconnected during this test to avoid blowing the drive). You are looking for a reading above 50 Mega-ohms. If the insulation is good, use a standard multimeter to measure resistance phase-to-phase (U-V, V-W, W-U). They should be balanced.
If the electrical integrity is sound, look at parameters. Increase the Acceleration Time (ACC) significantly. If the load has high inertia (like a large flywheel or centrifuge), the motor draws massive current to get it moving; extending the ramp time reduces this inrush. Check the "Torque Boost" parameter—if set too high, it saturates the motor core, causing excess current. Reduce torque boost. Finally, check for mechanical binding by physically rotating the motor shaft by hand (if safe). If the application requires this much current, the VFD may simply be undersized for the application.
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