DC Bus Undervoltage

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The DC bus voltage inside the drive has fallen below the trip point (e.g., 190Vdc for 240V AC input or 380Vdc for 480V AC input), which is adjustable via L2-05. Common causes include insufficient incoming AC power, excessively short acceleration times leading to voltage sag, or significant fluctuations in the input voltage quality.

• Insufficient incoming AC line voltage to the drive's L1/R, L2/S, L3/T terminals, possibly due to grid instability or undersized supply transformer.
• Momentary power loss or sag in the main AC supply, causing the DC bus capacitors to discharge below the undervoltage trip level (L2-05).
• Faulty or worn pre-charge resistors/circuitry failing to adequately charge the DC bus capacitors.
• Damaged DC bus capacitors or internal power supply components within the drive, leading to reduced voltage holding capacity.

Klikk på steg for å spore fremgangen.

1. 1

   Measure the incoming AC line voltage at the drive's L1/R, L2/S, L3/T terminals using a multimeter to confirm it is within 10% of the drive's nominal input voltage.

2. 2

   Verify the parameter L2-05 (DC Bus Undervoltage Detection Level) is set correctly according to the drive's nominal input voltage (e.g., 190V for 240V drive or 380V for 480V drive).

3. 3

   Inspect the wiring connections from the main power supply breaker to the drive's input terminals (L1/R, L2/S, L3/T) for loose connections or corrosion.

4. 4

   Monitor the DC bus voltage (dC bus monitor value) on the drive's operator panel during operation to observe its behavior relative to the L2-05 trip point.

5. 5

   If a dynamic braking unit is present, verify its functionality by checking for continuity across the braking resistor terminals and proper connection to the drive (B1, B2).