JPS59202075A - Diagnosis of insulation deterioration of power cable - Google Patents

Abstract

PURPOSE:To prevent a dielectric breakdown accident caused by a water treeing of a power cable, by detecting the water treeing generated to the power cable in a hot-line state. CONSTITUTION:A power source transformer 1, an earthing transformer 3 and a cable 4 to be measured are connected to a high voltage matrix line 2 and a DC component measuring apparatus 6 is connected to the earthing wire 5 drawn out from the metal shield layer of the cable 4. AC voltage is applied to the cable 4 while the DC component of the current of the earthing wire 5 is detected and the polarity, the density and the time characteristics thereof are analyzed. By this method, the presence or absence of a water treeing the magnitude and the generating direction of the water treeing in the cable insulator are detected and the propriety in the use continuation of the cable is judged.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to insulation deterioration diagnosis method 1 for plastic insulated electrical cables, mainly cross-linked polyethylene insulated cables ((Σ＼! KEISONO[)ζ-). .

(It is clear that the insulation deterioration of -X Riichinor is mainly due to the water tree.
In order to prevent dielectric breakdown accidents due to severe deterioration of the insulation, it is important to prevent the occurrence of water leakage.

Conventionally, this water tree detection method has been to collect cables taken from so-called stopped lines, that is, cables where an insulation breakdown accident has occurred, or cables whose charging has been stopped and insulation diagnosis has been performed, and one of the cable insulators has been collected from a cable that requires attention. A method in which the presence of water trees can be confirmed only by collecting the parts, boiling them, or staining them and observing them visually or under an optical microscope.
Applying DC voltage to a recently reported stopped line, the application stops t
Measure the charge accumulated on the cable after lr, 7k l-
There are two ways to predict the occurrence of ')-. However, both systems detect water trees after the line has stopped, and cannot reliably prevent insulation breakdown caused by water trees on live lines.

The purpose of the present invention is to eliminate the drawbacks of the prior art described above, to detect water trees occurring in live (or stopped) power cables, and to prevent insulation breakdown accidents due to water trees in power cables. The objective is to provide a new method that can

In other words, the gist of the present invention is to apply AC voltage to a power cable (or stop and remove cable) that is subject to insulation deterioration diagnosis on a live line, detect the DC component from the grounding line current, and determine its polarity. , analyze the size and time characteristics,
The purpose of this method is to detect the presence, size, and direction of water trees and determine whether or not the cable can be continued to be used.

By the way, the present inventors discovered the following new fact in the process of researching the water tree phenomenon.

J: The cable used for DI research is 6 KV, 100-1
150-1250- and 400mACV cables, 4 samples of normal cables and 100 test runs of forcedly degraded cables.

During these trials, AC 3.8 KV, which is the working voltage of 61A1 class Cv cable, was applied from the conductor side of the cable, and the DC component was measured from the cable shielding layer side, and after performing an AC breakdown test in the same trial. , we observed water trees. The effective length of the cable is 10 +++ for each trial.

Volume occupied by cable insulation of observed water trees (%)
) and the DC component per 11n3 (1 due to the difference in conductor size)
Figure 1 shows the relationship between m' (converted by A). In addition,
In the figure, (a) shows the water generated from the inner semiconductive layer side of the cable, -1) -1 so-called inner water guide tree, and (b) shows the water tree generated from the outer semiconductive layer side of the cable, the so-called outer water guide tree. This line shows the case of . It can be seen from this that when the absolute value of the DC component is large, the volume occupied by the insulator of the water tree generated is large.

Figure 2 shows the relationship between the maximum length of the water tree or cable insulator for guiding water inside and outside the volume.

From this result, it can be seen that the larger the volume occupied by the water tree in the cable insulation, the greater the maximum length of the water tree.

Figure 3 shows the relationship between the cable's AC breakdown voltage and the absolute value of the DC component per 1 m°. This result shows that the cable with a large DC component has a lower dielectric breakdown strength against AC voltage.

Based on the above, the following can be said.

(1) The generation of a DC component is due to the generation of water trees; if an internal water tree occurs, a negative polarity DC component is generated, and if an external water tree occurs, a positive polarity DC component is generated.

(2) The larger the absolute value of the target flow, the larger the volume that the water tree occupies in the cable insulation.

(3) The larger the absolute value of the DC component, the longer the water retention occurs.

From the above, by detecting the polarity and magnitude of the DC component, it is possible to know the presence, magnitude, and direction of water in the cable, thereby preventing insulation breakdown accidents during cable operation. It can be prevented.

Next, the present invention will be explained in detail with reference to FIGS. 4 and 5.

Figure 4 shows that when a three-core CV cable is targeted,
FIG. 5 shows an embodiment in which a single-core Cv cable is targeted. In the figure, 1 is the power transformer, 2 kl stomach 1'':,''
H','(i compression wire, 3 is the grounding transformer, 4.4' is the CV cable to be measured, 5.5' is the grounding wire drawn out from the metal shielding layer of the cable. 6 is the DC component) There are measurement devices, p-wave circuit, amplification circuit, performance circuit, base station jFi,
8 This embodiment described above detects the DC component of the ground line current from the metal shielding layer side of the C cable to which an AC voltage is applied, and determines the presence, size, and occurrence of water trees. Since it detects the direction, it can be applied not only to live cables, but also to water tree detection of cables on stop tracks and removed cables by applying a predetermined AC T13) pressure.

As described above, according to the present invention, by detecting the occurrence of water trees in power cables, it is possible to accurately know the state of insulation deterioration of the cables, thereby preventing cable breakdown accidents. It is possible to prevent power outage accidents,
Figure 2 shows the relationship between the maximum length of the inner and outer water guiding trees and the volume that the water tree occupies in the cable insulation;
FIG. 3 is a diagram showing the relationship between the absolute value of the DC component per cable insulator 1++z' and the AC breakdown voltage of the cable, and FIGS. 4 and 5 are detailed explanatory diagrams of the present invention.

(1 power transformer) (2 high voltage bus) (3 grounding transformer) (4, 4', C to ' cable to be measured) (5, 5' grounding wire) (6: DC component measuring device) 2nd Day 7 I (Tree force γ-) 4 insulations (Continued from page 1) Inventor Tadayuki Ikeda Hitachi Cable Co., Ltd. Hidaka Factory 1, 5-1 Hidaka-cho, Hitachi City Case description 1982 Patent Application No. 76885
No. 2 Name of Invention Diagnosis Method for Insulation Deterioration of Electric Capable 3 Person Making Amendment 4 Agent 〒100 5) Boxes 4 and 5 in the drawing to be amended.

(Contents of 5 amendments As per attached sheet.

7 A) Figures 4 and 55 after cuff closure A drawing showing the. 1 or more copies

Claims (1)

[Claims] 11i11 Apply AC voltage to the target power cable, detect the DC component of the grounding wire current, and determine its polarity.
Size and time! The present invention is characterized in that it is possible to determine whether or not to continue using the cable by analyzing the water content and detecting the presence, size, and direction of water in the cable insulator. A method for diagnosing insulation deterioration of power cables.