JPH02156171A - Insulation measuring apparatus - Google Patents

Abstract

PURPOSE:To make it possible to make a coupling capacitor compact and to alleviate working by forming an outer conductor having a specified electrostatic capacitance at the outer surface of the vicinity of the end part of a current applying lead cable through an insulating layer surrounding the conductor. CONSTITUTION:Two trapezoidal parts 26 and 27 are formed on a current applying cable 20. An outer conductor 23 is formed on the outer surface of an intermediate insulating layer 22 at the parts 26 and 27. The outer conductor 23 is electrically connected to a conductor 21 of the cable 20. A high voltage side electrode 24 is embedded in the insulating layer 22 so as to surround the conductor 21 coaxially. The outer conductor 23 and the electrode 24 are both constituted of a wound copper tape layer or a wound braided tape layer. A capacitor having a specified electrostatic capacitance is formed. The cable 20 is directly connected to a jumper wire 4 which is connected to a cable head. The terminal of a partial discharge measuring device 9 and one end of a detecting resistor 10 are connected to a connecting terminal of the conductor 23. The cable 20 is connected to a DC power source 8 through a protecting resistor 6 in series. In this way, the partial discharge and the like can be measured safely without providing a large capacitor.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Field of Application) The present invention relates to an insulation measuring device for measuring insulation characteristics associated with deterioration of cable insulation.

(Prior Art) When the insulation properties of a cable insulator deteriorate for some reason, the direct current resistance between the cable conductor and the shield decreases and leakage current increases. Furthermore, if a void is generated in the insulator for some reason, the electric field will be concentrated in that portion, causing partial discharge. These phenomena have the risk of increasing power transmission loss in the cable or leading to dielectric breakdown.

Therefore, in the past, DC voltage was applied between the cable conductor and the shield at appropriate times to measure leakage current and partial discharge, not only for cables before shipping, but also for power cables that had already been installed. .

FIG. 3 shows a schematic diagram of a conventional apparatus for performing such insulation measurement work.

In the figure, a cable to be measured 1 is terminated in a cable head 2 . A pull-out rod 3 electrically connected inside the cable head 2 to the conductor of the cable to be measured 1
One end of a capacitor 5 is connected to via a jumper wire 4. Also, this jumper wire 4 is connected to a protective resistor 6.
The charging lead cable 7 and the DC power supply 8 are connected in series through the power charging lead cable 7 and the DC power supply 8. The other end of the capacitor 5 is electrically connected to a ground terminal 11 provided on the shield of the cable to be measured 1 via a detection resistor 10. A measurement terminal of a partial discharge measurement device 9 is connected to a connection point between the capacitor 5 and the detection resistor 10.

In this insulation measurement work, first, a high DC voltage is applied to the conductor of the cable to be measured 1 by the DC power supply 8 through the energizing lead cable 7, the protective resistor 6, and the jumper wire 4. When a high DC voltage is applied to the conductor of the cable to be measured 1, a leakage current flows through the insulator, and this leakage current is detected by the partial discharge measuring device 9 through the capacitor 5. Furthermore, if there are voids in the cable insulation, partial discharge occurs in the voids. The current generated by this partial discharge is also detected by the partial discharge measuring device 9 through the capacitor 5.

FIG. 4 shows an equivalent circuit for partial discharge measurement as shown in FIG. 3.

In this equivalent circuit, the cable under test l can be regarded as a capacitor whose shield is grounded.

Here, a high DC voltage is applied to the conductor of the cable to be measured 1 from the DC power supply 8 via the protective resistor 6 . This protective resistor 6 is provided to prevent a partial discharge signal generated in the cable under test 1 from being transmitted to the DC power supply 8 side.

Further, a series circuit including a capacitor 5 and a detection resistor 10 is connected in parallel to the cable 1 to be measured. This capacitor 5 has a role as a so-called coupling capacitor, and prevents a high DC voltage from being applied to the partial discharge measuring device 9 side. Then, a partial discharge signal flows into the detection resistor 10 through the capacitor 5. This allows the partial discharge measuring device 9 to measure the voltage signal generated across the detection resistor IO.

(Problem to be solved by the invention) By the way, in such partial discharge measurement work,
In order to measure minute partial discharge signals with high sensitivity, it is necessary to suppress external noise as much as possible.

Therefore, as shown in FIG. 3, the capacitor 5 is installed as close as possible to the cable head 2.

However, for example, the capacitor 5 used for measuring the insulation of a 22 kV class cable line has a height of about 40 cm and a weight of about 3 kg to 10 kg. Therefore, sufficient consideration must be given to the supporting method and arrangement thereof, and it is also necessary to provide a relatively large space around the cable head 2. However, in reality, sufficient space could not be secured around the cable head 2, which caused problems in measurement.

The present invention has been made in view of the above points, and it is an object of the present invention to provide an insulation measuring device that reduces the size of a coupling capacitor and improves the workability of insulation measuring work.

(Means for Solving the Problems) The insulation measuring device of the present invention is a lead cable for charging that is connected to the terminal end of the cable to be measured when measuring the insulation of the cable, and the lead cable for charging is connected to the terminal end of the cable to be measured when measuring the insulation of the cable. The present invention is characterized in that an external conductor formed to have a predetermined capacitance is provided through an insulating layer surrounding the conductor of the lead cable, and an insulation measurement terminal is connected to this external conductor.

(Example) FIG. 1 shows a longitudinal sectional view of the main parts of a lead cable for charging used in the insulation measuring device of the present invention.

In the figure, this charging lead cable 20 has a conductor 2
1 is coated with an insulating layer 22. This insulating layer 22 has two layers in the longitudinal direction of the charging lead cable 20.
It has two trapezoidal sections 26,27. Both of these trapezoidal portions 26, 27 form a so-called stress cone. An external conductor 23 is formed on the outer periphery of the insulating layer 22 at the intermediate portion sandwiched between the two trapezoidal portions 26 and 27. Further, a high voltage side electrode 24 is embedded coaxially around the outer periphery of the conductor 21 in the insulating layer 22 . One end of this high voltage side electrode 24 is electrically connected to the tip of the conductor 21.

It should be noted that an external shield 25 of the cable is shown in the trapezoidal portion 27 of the energizing lead cable 2o, which continues downward in the figure. Further, a connecting terminal 28 for connecting to a partial discharge measuring device, which is not shown in this figure, is attached to the outer conductor 23.

Conductor 21 and insulator 2 of this power charging lead cable 20
The configuration of 2 is similar to that of a conventional power supply lead cable, and is composed of, for example, a conductor 21 of twisted copper wire and a polyethylene insulator 22. It is also assumed that the shielding body 25 is composed of a semiconductive layer or a copper tape wrap.

Now, as described above, the charging lead cable 20 of the present invention is provided with the high voltage side electrode 24 that is electrically connected to the conductor 21 and coaxially surrounds the conductor 21. The high-voltage side electrode 24 is composed of a copper tape-wrapped layer, a braided tape-wound layer, or the like embedded in the insulator 22. Further, the outer conductor 23 is similarly composed of a copper tape wrapping layer, a braided tape wrapping layer, or the like.

With this configuration, a capacitor having a predetermined capacitance is formed by the high voltage side electrode 24 and the external conductor 23. The value of this capacitance is the value of the outer conductor 23
The length of the formed part, the high voltage side conductor 24 and the outer conductor 2
It is determined by the area facing 3. Further, it also differs depending on the dielectric constant of the insulator 22 sandwiched between the two. Therefore,
When manufacturing this power supply lead cable 20, the size of each part is designed in advance so that a capacitance corresponding to the capacitor 5 as explained in FIG. 3 can be obtained. For example, when trying to obtain a larger capacitance, the insulator sandwiched between the high-voltage conductor 24 and the outer conductor 23 may be made of a wound layer of high-permittivity insulating tape. good.

Now, FIG. 2 shows a schematic diagram of the measurement work when using the power charging lead cable 20 as shown in FIG. 1.

In the figure, the same parts as in FIG. 3 are given the same reference numerals, and redundant explanation will be omitted.

As shown in this figure, when the device of the present invention is used, the lead cable 2o for charging is directly connected to the jumper wire 4 connected to the upper part of the cable head 2. Then, the measurement terminal of the partial discharge measuring device 9 and one end of the detection resistor 10 are connected to the connection terminal 28 explained in FIG. 1 of the external conductor 21 formed on the charging lead cable 20. On the other hand, the charging lead cable 20 is connected in series to a DC power source 8 via a protective resistor 6 .

When the device is configured as shown in this figure, its equivalent circuit is the same as that shown in FIG. 4, and measurements of partial discharge, etc. can be carried out in the same manner as before. Moreover, as shown in the figure, according to the device of the present invention, although the energizing node cable itself becomes slightly larger, there is no need to install a large capacitor near the cable head 2, which eliminates the need to secure installation space and avoid dangerous Installation work etc. can be omitted.

The present invention is not limited to the above embodiments.

The configuration of the charging lead cable 2o is such that an external conductor is formed to have a predetermined capacitance via an insulating layer surrounding the conductor 21 at the center, and the high voltage side electrode 24 is not necessarily required. . However, the provision of the high-voltage side electrode 24 has the effect of increasing the area facing the external conductor 23 and increasing the capacitance. Also, the outer conductor 2
A protective coating or the like may be formed on the outer periphery of 3 to further protect it. Further, the high-voltage side electrode 24 and the insulator and external conductor provided on its outer periphery do not necessarily have to be integrated with the power supply lead cable 20. That is, it may be molded on the outer periphery of the energizing lead cable after it is manufactured.

(Effects of the Invention) The insulation measuring device of the present invention described above has a capacitor built into the terminal end of the lead cable for charging, so there is no need to install a large capacitor as in the conventional case. Therefore, it is not necessary to secure a space for installing the capacitor or to perform preparation work, thereby shortening the working time and making it possible to carry out accurate insulation measurements even in places where there is not enough working space.

[Brief explanation of the drawing]

FIG. 1 is a vertical cross-sectional view of the main parts of a charging lead cable used in the insulation measuring device of the present invention, FIG. 2 is a schematic diagram showing an example of its use, and FIG. 3 is a schematic diagram of a conventional insulation measuring device. Figure 4 shows such a circuit. 20-1----- Lead cable for charging, 21--
------- one conductor, 22-- one-- insulator, 23-- one outer conductor, 24--------m- high voltage side electrode, 25----- --- one shielding body, 26.27 --- trapezoidal part, 28 --- one connecting electrode. (1 person) Figure 2 Figure 3 Figure 4

Claims (1)

[Claims] A charging lead cable that is connected to the terminal end of the cable under test when measuring cable insulation, and a predetermined capacitance is applied to the outer periphery near the end via an insulating layer surrounding the conductor of the charging lead cable. 1. An insulation measuring device, comprising: an external conductor formed to hold the insulation, and an insulation measuring terminal connected to the external conductor.