Restoration time after a transformer blows depends on damage severity, spare availability and system configuration. If only a small distribution transformer fails and a spare is on the truck or nearby depot, utilities can often replace it within a few hours. For larger units requiring crane work, oil handling and testing, replacement can take many hours or even days. In transmission substations, where units are custom sized, utilities rely on spare or mobile transformers and more complex switching, so restoration may involve staged reconfiguration before full capacity returns.