Harmonic suppressor is an iron-cored reactor and is used in the neutral ground connection of a generator so that third harmonic currents are reduced to safe value. If the third harmonics are not suppressed, they can cause dangerous overheating of grounding resistors of grounding transformers or erroneous operation of ground fault protective gear. The reactor is so designed that its core becomes saturated at very low system frequency fault currents.
Thus it presents high impedance to the flow of harmonic currents and low impedance path to the flow of fault currents. Since the harmonic suppressor acts as a reflection point for the travelling waves passing through the machine winding, it becomes necessary to connect a surge diverter between the machine neutral point and ground so as to avoid high voltage build-up. Grounding of generators through individual resistors and harmonic suppressors is illustrated in Fig. 12.12(a).
