Diagnostic technique for electrical installation using external electrode method: Relationship between size of metal case and detected signal

The breakdowns between charged objects and grounded metal objects contained in grounded metal cases of electrical installation become the source of accidents such as an electric shock, a fire, and an explosion. The casualties are often caused by the occurrence of the accidents. The detection of corona discharges appeared before the breakdowns (spark discharges) is the first step in eliminating the potential of the accidents. However, the detection of corona discharges generated in the metal cases is difficult. In ongoing study, the external detection of negative corona discharges generated in a grounded metal case has become possible using the proposed method based upon the principle of the external electrode method. In this paper the relationship between the size of metal cases and the detected signals by means of the proposed method is reported. The results of this study are useful for engineers to detect early a foretaste of the accidents associated with electrical discharges generated in the metal cases of electrical installation.