Lv / LvA / Lvd Low Voltage fault in delta drive

Lv / LvA / Lvd Low Voltage fault in delta drive troubleshooting

Description

The Lv (Low Voltage) fault triggers when the DC bus voltage drops below a minimum threshold (e.g., < 190VDC for a 220V class drive). This ensures the IGBTs have enough voltage to gate properly and prevents the control electronics from shutting down unexpectedly.

Causes

1. Input Phase Loss: One of the three input phases (R, S, T) is missing or a fuse has blown. The drive might run on single phase under light load but will trip Lv under load.
2. Low Mains Voltage: Brownouts or voltage sags in the facility.
3. Contactor Failure: The internal "Charge Relay" or contactor that bypasses the soft-charge resistor may have failed. If this doesn't close, the voltage drops immediately when the motor starts.
4. Sudden Load: A massive starting current draw on a weak grid can sag the voltage.

Solution

Diagnostic steps:
1. Check Input Power: Measure voltage across R-S, S-T, and R-T. All should be balanced and within spec. Check input fuses and circuit breakers.
2. Listen for "Click": When the drive powers up, you should hear a relay click. If you don't, or if the fault happens exactly when you press "Run," the internal charging bypass contactor is likely faulty (requires drive repair).
3. Tighten Screws: Loose input wiring causes high resistance and voltage drop.
4. Power Quality: If the grid is unstable, an external voltage stabilizer or UPS might be required for the control circuit.