For power generation equipment servicing:

Preventative maintenance is the most important type of power generation equipment servicing. It involves inspecting and replacing parts on a regular basis to prevent them from failing. This can help to extend the life of the equipment and prevent costly repairs.
Service inspections are conducted at regular intervals to check the condition of the equipment. This includes inspecting the engine, generators, turbines, transformers, and other components. Any problems that are found during a service inspection should be repaired immediately.
Major repairs are necessary when the equipment breaks down or becomes damaged. This can involve replacing worn or damaged parts, or rebuilding the equipment to its original specifications. Major repairs are typically performed by qualified technicians.
Upgrades are sometimes necessary to keep power generation equipment up-to-date with the latest technology. Upgrades can improve the efficiency of the equipment, or make it more compatible with new power grid standards.