Brake chopper fault

What does 27 mean?

This warning/alarm indicates a short circuit in the brake IGBT, which disables the brake function. A critical consequence is that substantial power is continuously transmitted to the brake resistor, even if the brake function is inactive, creating a high voltage hazard and risking severe overheating of the resistor. This fault can also be triggered by an overheated brake resistor (using Klixon inputs 104 and 106) or in 12-pulse frequency converters if a disconnect or circuit breaker is opened while the unit is operating.

• Internal short circuit of the brake IGBT (Insulated Gate Bipolar Transistor) within the frequency converter.
• Drive internal control circuit failure related to the brake chopper gate driver.
• Damage to the power board where the brake chopper is located (e.g., burnt components).
• External factors like excessive DC-link voltage transients causing IGBT overstress.
• Short circuit in the brake resistor connection (e.g., terminals 81, 82) leading to excessive chopper current.

Click steps to track your progress.

1. 1

   Disconnect main power supply to the frequency converter at the upstream breaker. Verify zero voltage at L1, L2, L3 terminals.

2. 2

   Disconnect the brake resistor cables from the frequency converter's brake terminals (e.g., 81, 82).

3. 3

   Measure resistance between the DC-link (+) and brake resistor terminal (e.g., 81) and DC-link (-) and brake resistor terminal (e.g., 82) using a diode test function on a multimeter. Look for short circuit.

4. 4

   Visually inspect the frequency converter's power board for signs of damage (e.g., burnt components, discoloration) in the brake chopper section.

5. 5

   If resistance measurements indicate a short circuit internal to the drive's brake chopper, the frequency converter power section requires service or replacement.

6. 6

   Before re-powering, verify the brake resistor itself is not short-circuited (e.g., measure resistance at its terminals).