Cause : External SCR disable comes when the alarm indicates a series DC-link capacitor voltage imbalance. An alarm indicating a series DC-link capacitor voltage imbalance typically refers to a condition where there is an unequal distribution of voltage across the DC-link capacitors in a power electronic system.

This imbalance can occur due to various factors such as mismatched capacitor characteristics, aging capacitors, or irregularities in the power electronic circuitry.