SG9101 Interference Distinguishing Partial Discharge (PD) Detector is a new type apparatus developed by the institute after SG-8001 (modeled from Model-5), SG-8201 and SG-8601 PD apparatuses. Basically it keeps the merits and functions of the above three types apparatuses. SG9101 adopts special interference distinguishing logical circuit, which can discriminates the accidental interference. (The interference must be high than a set threshold and last 4 test periods at least, the "effect" will be shown). Cooperating with the time window, it can enhance the ability to discriminate and eliminate external interference.