| 摘要 |
PURPOSE:To enable diagnosis of water tree deterioration of a main insulation of a power cable by impressing an AC voltage between the cable and a shield electrode, by changing an amplitude value of the AC voltage and by observing a change in a DC current component of a charge current accompanying the change in the amplitude value. CONSTITUTION:An amplitude Vo of an AC voltage impressed on a power cable C through a transformer T is increased from zero at a prescribed boosting speed, as indicated by a line J, by an autotransformer S. When the amplitude Vo reaches a prescribed value, it is maintained at this value for some time and then decreased at a prescribed step-down speed of the same absolute value. On the occasion, a DC component in a charge current of the cable C is recorded by an ammeter A. Then a current indicated by a line K flows when deterioration exists in the cable C. This current holds either a positive or negative polarity at the time of boosting and a polarity reverse to the above at the time of stepping-down when it flows. In the case when the water tree deterioration is serious, a current value observed in the ammeter A is large as indicated by a line L. By making an operation of boosting or stepping- down, accordingly, the presence or absence of the deterioration and the degree thereof can be diagnosed. |
