When capacitors are disconnected from the supply, a DC voltage persists across the terminals of the capacitor unit. Safe handling of capacitor units after de-energisation requires that the stored electric charge in the capacitor unit should be removed to avoid the risk of electric shock to personnel. Any stored charge should be removed gradually — shorting the terminals of a capacitor unit to remove the charge will result in very rapid discharge of a substantial amount of energy that can endanger personnel and result in damage to the capacitor units themselves.
Capacitor units are therefore supplied with a discharge device capable of reducing the voltage between the terminals practically to zero, within a given time, after the capacitor has been disconnected from a network. The question of what this discharge time should be is of interest in this article.
The decision of a shorter discharge time for a capacitor bank may seem safe and harmless. In fact such a decision results in possible long term damage to the the capacitor units, and will always have a significantly higher carbon footprint than the default IEC60871 discharge time.