Minor overhauling of a generator is a routine maintenance procedure that is done to keep the generator in good working condition. It typically involves cleaning, inspection, and replacement of worn or damaged components such as bearings, brushes, and seals. The goal of minor overhauling is to prevent major issues from arising and to ensure that the generator is operating at peak efficiency.

Major overhauling of a generator, on the other hand, is a more extensive and involved process that is typically done when the generator has experienced significant wear or damage, or when it has been in operation for an extended period of time. It typically involves disassembling the generator, inspecting and repairing or replacing all major components such as the rotor, stator, and exciter, and reassembling the generator. The goal of major overhauling is to restore the generator to its original condition, or as close to it as possible, and to ensure that it will continue to operate safely and efficiently.