Failure in Output Stage (IGBT Desaturation)

What does Desat mean?

This fault indicates a desaturation of IGBTs in the output stage, signaling a hard short circuit between phases or phase to earth, or an earth fault. It can also be related to the brake IGBT (up to SX-D4037). If left unresolved, it can lead to severe damage to the drive's power components and connected motor, requiring costly repairs.

• Motor phase-to-phase short circuit due to insulation degradation or mechanical damage.
• Motor phase-to-earth short circuit in winding or terminal box.
• Output cable (motor cable) insulation breakdown, shorting phases or phase to earth.
• Brake IGBT short circuit or faulty gate drive if the drive includes an integrated brake chopper (e.g., SX series).
• Damaged drive output IGBT module (internal hardware fault).

Click steps to track your progress.

1. 1

   Disconnect motor cables from drive output terminals U, V, W.

2. 2

   Measure insulation resistance between motor phases (U-V, V-W, W-U) and each phase to ground using a megohmmeter (1000V DC). Expect > 5 MOhms.

3. 3

   Measure continuity between motor phases and phase-to-ground using a multimeter. Expect open circuit phase-to-ground, low resistance phase-to-phase.

4. 4

   Inspect motor output cable for visible damage, crushed sections, or water ingress.

5. 5

   If drive includes a brake chopper, verify the brake resistor and its cabling for shorts or damage (measure resistance across resistor terminals).