Foreign Object Damage

Problem: The mechanisms that can introduce a foreign object into a generator range from human errors to material failures. In any case, machine failure is often the result. Once inside the machine, objects gain energy from the spinning rotor and do extensive damage.

Prevention: Rotor fan blades, balance weights, slot wedges, bolts or pantleg washers – any internal component that is prone to failure or can be dislodged – should be inspected a regular basis. Keep in mind that there is also potential danger from items left inside the generator during inspections, testing, and maintenance. If the generator has its rotor pulled, the inspection can be more thorough. Utilize a combination of visual examination and a final crawl through, along with ultrasonic or magnetic particle tests on critical rotating components. In the case shown in the picture at the top left, the replacement fan was designed to eliminate or reduce harmonic vibratory modes and lower stresses. The blades on the new fan were designed to be thicker and stronger with natural blade frequencies significantly higher.