>Deterioration diagnosis for XLPE cable	>Deterioration diagnosis for Submarine Cable
	>VISCAS deterioration diagnosis for XLPE cable
	Distinctive features of water-tree deterioration, depending on voltage class
	> 6.6 kV XLPE cable
	Since use stress is low, water-tree sometimes does not immediately result in insulation destruction, even if it progresses enough to penetrate into the insulator (penetrating water-tree).
	> 22-77 kV class XLPE cable
	Since use stress is high, water-tree frequently results in insulation destruction before it penetrates the insulator.
	>Applicability of deterioration diagnosis technique
	>6.6 kV + Penetrating water-tree => Marked drop in insulation resistance, and diagnosis can be done with 1 and 2 > 22-77kV + Non-penetrating water-tree => Drop in insulation resistance is extremely small. -> Detection is difficult with 1 and 2. > tanδ method: Cannot detect local deterioration in the line length direction, and can only determine the average deterioration.	Deterioration diagnosis techniques and their applicability Deterioration diagnosis technique 6.6kV 22-77kV Judgment of local deterioration 1 Measurement of insulation resistance ○ × ○ 2 DC leakage current characteristic ○ × ○ 3 tanδ method ○ ○ ×
	>Two diagnosis methods based on the electrical features of water-tree
	- Low resistance due to unimpaired insulation - Non-linearity in electrical conduction characteristic	->Method based on harmonic component of loss current
	-Accumulation of charge due to DC voltage - Release of charge due to AC voltage application	->Residual charge method
	>Diagnosis of water-tree deterioration of XLPE cable using method based on harmonic component of loss current
	Features 1 Features 2 The size and phase of the 3rd harmonic of loss current is used as an indicator of deterioration. A judgment curve based on the line length is used to enable judgment of local deterioration.
	>Diagnosis of water-tree deterioration of XLPE cable using the residual charge voltage sweep method
	Water-tree deterioration has a significant effect on the service life of CV cable, and accurate diagnosis of such deterioration is an important way to prevent destruction of the insulation of XLPE cable. By using the "residual charge voltage sweep method" it becomes possible to diagnose water-tree deterioration using a non-destructive technique which has previously been regarded as difficult.
		This enables accurate understanding of the residual performance of CV cable a key point for preventing insulation destruction. This system (the residual charge voltage sweep method) has received the following two awards: *IEEJ Technical Development Award (Progress Award) (2003) *Award by the Promotion Foundation for Electrical Science and Engineering (OHM Technology Award) (2002)
	> Features of the residual charge voltage sweep method
	Features 1 Features 2 The strength of the electric field emitted by residual charge is used as an indicator for deterioration diagnosis. This method accurately detects a residual charge signal corresponding to the longest water-tree which has occurred in the XLPE cable. Features 3 Features 4 For deterioration diagnosis, it is possible to know the current breakdown field strength of the line (residual performance). This technique enables deterioration diagnosis which does not depend on the line length.
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