Load Short-circuit

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This fault occurs when a short circuit is detected in the motor windings or the cabling between the inverter and the motor. It represents an immediate and severe electrical overload. The inverter quickly shuts down its output to prevent catastrophic damage to its power semiconductors (IGBTs) and potentially the motor.

• Direct short circuit between two or more motor winding phases.
• Short circuit from a motor winding phase to the motor frame (ground).
• Damaged motor cable insulation due to mechanical stress, abrasion, or chemical exposure.
• Internal short circuit within the motor windings or motor terminal box.
• Faulty inverter output IGBT (Insulated Gate Bipolar Transistor) causing a continuous short condition.

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1. 1

   1. Disconnect the motor cables completely from the inverter output terminals (U, V, W).

2. 2

   2. Measure the resistance between each motor phase (U-V, V-W, W-U); readings should be balanced and non-zero (e.g., 0.1-5 Ohms).

3. 3

   3. Use a megohmmeter (e.g., 500VDC test voltage) to measure insulation resistance from each motor phase (U, V, W) to the motor frame (PE).

4. 4

   4. Thoroughly inspect the entire length of the motor cables for any physical damage, pinch points, or signs of arcing.

5. 5

   5. If motor and cables test good, perform a diode check across the inverter's output IGBTs (between DC bus +/- and U, V, W terminals) to check for internal shorts.