JPH03214078A - Diagnosis of deterioration in hot-line insulation - Google Patents

Abstract

PURPOSE:To achieve a detection free from effect of a local battery and an earth capacitance by detecting a direct current from an earthing conductor of a cable line in a hot-line condition with a current detector made up of a high permeability magnetic material and a Hall effect element. CONSTITUTION:A high-permeability magnetic material (permalloy(R)) 31 formed in a shape of C is coupled to a earth wire 2 connected between a shielding layer 13 of a CV cable 1 and the ground and a Hall effect element (made of semiconductor material such as InSb)32 is disposed at a gap part thereof to form a current detector 3. Then, a magnetic field generated according to a size of current of the earth wire is caught with a magnetic material 31 and an element 32 outputs a current according to the size of the magnetic field, which allows better detection of both AC and DC components. As the earth wire current is not converted into a voltage, there is no potential difference generated between the cable 1 and the ground. An output of the detector 3 is sent to a measuring device 4 and an AC component is removed with a filter such as lowpass filter to extract a DC component and thus, a water tree deterioration of a insulating body 12 is diagnosed from the size thereof.

Description

[Detailed Description of the Invention] [Industrial Field of Application] The present invention solves the problem of insulation deterioration due to water tree etc. of power cables.
This relates to a method for obtaining information under live wires.

[Conventional technology J The main cause of insulation deterioration in ultra-high voltage Cv cables is water tree deterioration of cross-linked polyethylene, and it is necessary to prevent insulation breakdown accidents due to such deterioration (diagnosis of insulation deterioration under live wire conditions). Various methods have been proposed.

Such live line diagnostic methods include, for example, injecting DC current from the neutral point of a grounding transformer on the line, superimposing the DC current on the transmitted AC current, and as a result, deterioration of water trees in the cable insulation, etc. There is a so-called direct current superimposition method that determines and evaluates insulation resistance based on the direct current component generated in the grounding wire connecting the cable shielding layer and the ground depending on the degree of damage. Furthermore, assuming that the deteriorated part of the water tree has a rectifying effect, a method has been proposed to diagnose the deterioration by detecting the DC component that exists in the grounding wire depending on the length and volume of the water tree when the line is live. There is.

[Problems to be Solved by the Invention] Incidentally, in the above-mentioned live wire diagnostic method, a method shown in FIG. 2 has been adopted to detect a DC component from a ground wire. In the figure, E is an AC power supply, 1 is a sample C cable, 11
12 is a crosslinked polyethylene insulator, 13 is a shielding layer, and 14 is a sheath. An impedance 5 such as a resistor is installed in the middle part of the grounding wire 2 that connects the shielding layer 13 and the ground.
is inserted. With this configuration, the DC current present in the grounding wire 2 is converted into a terminal voltage appearing at both ends of the impedance 5 and detected, and the DC component is measured by the measuring device 6b.

However, in the case of direct current detection from the ground wire 2 as described above, an impedance 5 is inserted in the middle of the ground wire 2, so a potential difference may occur between the pulley 1 and the ground. become. For this reason, there was a problem in that the ground capacitance ffC and the action of the local battery e affected the measurement, making it impossible to obtain accurate measured values.

The influence of the local battery e is particularly noticeable when the insulation resistance of the cable sheath 14 is low, and in such a case, d! In some cases, the DC component caused by water tree deterioration in the grounding wire 2, which should be determined, is not constant. In addition, when applying this method to an existing line, the grounding wire must be cut in order to insert the impedance 5, and there is a problem that it is not desirable to cut the grounding of the live line only temporarily. Moreover, the installation work of the insulation diagnostic device is also complicated.

Therefore, the present invention provides a method for diagnosing live wire insulation by detecting the DC component from the ground wire, which detects the DC component without being affected by local batteries or ground capacitance and without cutting the ground wire. The purpose of this paper is to provide a method for accurately diagnosing insulation deterioration.

[Means for Solving the Problem] The live line insulation deterioration diagnosis method of the present invention was devised to achieve the above object. In the method for diagnosing insulation deterioration based on the DC current, the DC current from the grounding wire is detected by a current detection device comprising a high permeability magnetic material and a Hall effect element. It is characterized by:

If a current detection device made of a high permeability magnetic material and a Hall effect element is used, the current can be extracted from the magnetic field generated by the current flowing in the grounding wire, so the grounding wire does not need to be cut. No ground wire current can be detected.

[Example] An example of the present invention will be described in detail below based on the drawings.

FIG. 1 shows an example of the method of the present invention, in which an alternating current voltage is applied to the conductor 11 of the test CV cable by an alternating current power source E, making it a live wire. 12 is a cross-linked polyethylene insulator, 1
3 is a shielding layer, and 14 is a sheath. Note that when diagnosing insulation deterioration using the DC superimposition method described above, a DC power source with a generated voltage of about 50 V may be connected to the neutral point of the grounding transformer of the line, although not shown.

As shown in the enlarged view of Figure 3, a C-shaped high permeability magnetic material 31 is coupled to the grounding wire 2 that connects the shielding layer 13 of the cable 1 and the ground. , a Hall effect element 32 is provided in the gap between the high permeability magnetic material 31.
is located. Island delivery FJ! A current detector 3 consisting of a magnetic material 31 and a Hall effect element 32 connects the grounding wire 2
Detect the current inside. Here, for example, it is preferable that the gap portion or other portion of the high permeability magnetic material 31 be made openable and closable so that it can be coupled to the ground wire 2 with a single touch using a clamp method. In this case, current detector 3
This makes it easy to attach and detach the ground cotton 2.

As the high permeability magnetic material 31, permalloy, iron, silicon steel, grain-oriented silicon steel, MnZn ferrite, etc. can be used. Further, as the Hall effect element 32, I n
S b * I n As * G a As
* This can be achieved by using semiconductor materials such as Ge and Si.

If the insulation layer 12 of the cable 1 has deteriorated due to water tree,
As mentioned above, due to the presence of the deteriorated portion, a DC current flows through the grounding wire 2. In addition to this, an alternating current that fluctuates at a period comparable to that of the alternating voltage applied to the cable 1 is originally present in the grounding wire z. In general, a current transformer consisting of an iron core and a coil is used to detect the current flowing through an electric wire without contacting the wire.Although ordinary current transformers can detect alternating current components well, DC components necessary for line diagnosis may not be detected. In contrast, in the method of the present invention, the high permeability magnetic material 31 catches the magnetic field generated depending on the magnitude of the ground wire current, and the Hall effect element 3
2 outputs a current according to the magnitude of the magnetic field, so both alternating current and direct current components can be detected satisfactorily. Furthermore, unlike the conventional impedance insertion type, the ground line current is not converted into voltage, so no potential difference occurs between the cable 1 and the ground. Therefore, the influence of the ground capacitance of the cable 1 and the local battery action can be reduced to a negligible level.

The output of the current detection device 3 is sent to the needle row device 4, where it is processed as follows, for example.

That is, in FIG. 3, the output is first filtered by a filtering device 41 such as a low-pass filter to remove the current component in the output current to extract the DC component, and then this DC component is passed to the amplifier 4.
2, the DC component is amplified to a predetermined amount, and the DC component is displayed on the display device 43 to observe its size. Based on the observation results, water tree deterioration of the insulator 12 of the cable 1 is diagnosed.

[Effects] According to the live wire insulation diagnosis method of the present invention as explained above, since current is not converted to voltage unlike the conventional method that uses the terminal voltage of an impedance inserted into the ground wire, there is no difference between the cable and the ground. No potential difference occurs. Therefore, the ground capacitance is small, the influence of local batteries can be ignored, and measurements can be made regardless of the insulation resistance of the sheath. Since the measured values are not affected by ground capacitance or local batteries, live line insulation diagnosis can be performed more accurately by utilizing the DC component in the ground line.

In addition, the DC component required for live line insulation diagnosis can be detected without contact without cutting the ground wire, so even when applied to an existing cable line, all you need to do is couple the high permeability magnetic material to the ground wire. This makes the construction easier. Furthermore, since there is no need to cut the grounding wire, the safety of the cable line is not compromised, and the present invention has excellent effects.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram showing the live wire insulation diagnosis method of the present invention, and FIG.
The figure is an explanatory diagram showing a conventional method, and FIG. 3 is an enlarged view of the main part of FIG. 1. 1- Test CV cable, 11... Conductor, 12... Insulator, 13... Shielding layer, 14... Sheath, 2...
Grounding wire, 3... Current detection device, 31... High permeability magnetic material, 32... Hall effect element, 4... Measuring device

Claims (1)

[Claims] In a method of detecting direct current from the grounding wire of a live cable line and diagnosing insulation deterioration based on the direct current, the detection of the direct current from the grounding wire is performed using a high permeability magnetic material and the Hall effect. 1. A method for diagnosing deterioration of live wire insulation, characterized in that the method is carried out using a current detection device comprising a current detection device.