JPH0484779A - Detection of partial discharge from electric power cable - Google Patents

Abstract

PURPOSE:To enable detection of partial electric discharge simply, with high sensitivity and reliability in the state movable to the length direction by providing wire shield line on the periphery of electric power cable movable to the length direction and arranging a detection coil on the outside. CONSTITUTION:On the periphery of a cable 1 under test, wire shield lines 2 are wound with a long pitch over the whole length. By impressing current to the conductor of the cable 1 from a rotary connector 5 at the end of the impressing terminal 6, and moving the cable 1 from a drum 3 to a drum 4, the high frequency voltage induced in the detection coil is measured with a measuring device 9. When a partial discharge occurs in the cable 1, the partial discharge current flows in the wire shield 2, a voltage is generated between both ends of the detection coil 8 and this voltage is measured with a measuring device 9. If the measurement is done during the moving of cable 1 from the drum 3 to the drum 4, then the maximum voltage generated in the detection coil 8 is attained when passing the partial discharge point on the coil 8. That is, a partial discharge is measured with the highest detection sensitivity.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention provides a method for detecting partial discharges in power cables, in particular, a method for detecting partial discharges in high-voltage type cables that can move in the length direction with high sensitivity and in a simple manner. Regarding how it can be done.

[Conventional technology]

As a method of detecting insulation defects by subjecting the entire length of a high-voltage cable with an external semiconductive layer to a partial discharge test, the test cable is transferred from one drum to another. There is a method to measure partial discharge in between. For example, as described in JP-A No. 63-101774, a test cable on which a simple metal shielding layer has been applied in advance using metal tape or the like is wound from one drum to another, and a simple metal shield layer is placed between the drums. The shielding layer is removed and a partial discharge detection electrode is provided in that area to measure partial discharge. This method is explained in FIG.

A simple metal shielding layer 32 (hereinafter referred to as shielding layer 32) is applied in advance to the outer periphery of the test cable 31 (hereinafter referred to as cable 31), and is wound around a drum 33. cable 31
are sequentially wound onto the winding drum 34. drum 33
The terminal 35 of the cable 31 wound on the winding drum 34 is an insulated blind terminal, and the winding start of the winding drum 34 is connected to the power supply terminal 36 through the inside of the drum's mesh. The power supply terminal 36 has a rotary contact 37 at its tip, and can apply power to the cable 31 even when the winding drum 34 rotates. The shielding layer 32 is removed from the cable 31 between the two drums, between a position A close to the drum 33 and a position B close to the winding drum 34. In the part between A and B where the shielding layer 32 of the cable 31 is removed, the exposed external semiconducting layer 38 is completely grounded, and three partial discharge detection electrodes 39 (hereinafter referred to as electrodes 39
) can be installed.

When performing measurements, the cable 31 wound around the drum 33 is transferred to the winding drum 34 one after another, the shielding layer 37 is removed at position A, and the cable 31 is moved to position B, which is close to the winding drum 34.
A shielding layer 37 is then applied again.

Partial discharge is measured by an electrode 39 attached to the area between A and B where the shielding layer 32 has been removed.

When the measurement of one section of the cable 31 from which the shielding layer 32 has been removed is completed, the shielding layer 32 is applied again from the end B of the section, and the shielding layer 32 of the adjacent new section from the A side is removed, and the electrode 39 is moved to this section, and partial discharge measurement is performed in a new section.

[Problem to be solved by the invention]

However, according to the conventional method described above, the structure around the electrode becomes complicated because it is necessary to move the cable in the length direction while maintaining electrical contact between the partial discharge detection electrode and the outer semiconducting layer of the cable. . It is also difficult to obtain perfect electrical contact between the sensing electrode and the outer semiconducting layer of the cable at all times during movement. Therefore, the reliability of measurement is low.

In addition, with this method, the detection electrode is not only attached partially;
Since a high voltage is applied to the entire cable under test, a metal shielding layer is required to allow the charging current to flow.
This requires a complicated operation in which a metal shielding layer is applied to the test cable in advance, removed during the measurement section, and then reapplied to the section where the measurement has been completed.

Therefore, it is an object of the present invention to detect partial discharges in long high-voltage power cables having an external semiconducting layer easily, with high sensitivity, and with high reliability in a state where they can move in the length direction. It is to realize the method.

[Means to solve the problem]

The present invention provides a method for easily detecting partial discharges in high-voltage long power cables having an external semiconducting layer in a state where they can move in the length direction, with high sensitivity and high reliability. , a wire shield is provided around the outer periphery of a power cable that can be moved in the length direction, a detection coil is placed outside the wire shield, and while the power cable is moved continuously or intermittently, a wire shield is placed between the conductor of the power cable and the wire shield. The electromotive force generated at both ends of the detection coil was measured in the energized state.

The test cable has a conductor, an insulating layer covering the conductor, and an outer semiconducting layer formed by extruding synthetic resin around the conductor.
A homemade cable core may also be used.

In the former case, the cable under test needs to have a wire shield, but since the wire shield is already provided during the manufacturing process, there is no need to provide it again during the measurement. In the latter case, it is necessary to provide a wire shield during the measurement, and after the measurement is completed, the wire shield may be removed as necessary, or the product may be completed as is without being removed. The winding pitch of the wire shield is selected to be an appropriate pitch so as to generate a sufficient electromotive force due to partial discharge current through magnetic coupling to the detection coil. The pitch may be as large as necessary for partial discharge detection (single thread or multiple threads may be used).The present invention is also applicable to a wire shield cable complete product that has a wire shield made of multiple strands and a corrosion-resistant sheath on the outside. It is possible.

The detection coil may be wound around the cable under test, or may be wound around a high frequency iron core, and this iron core may be placed parallel to the cable. Since the detection coil only needs to be magnetically coupled with the wire shield in a high frequency band, it is not necessary to physically contact the wire shield, and there may be a considerable gap between the two. Therefore, it is possible to measure while moving the detection coil and cable relative to each other, and by fixing the detection coil and measuring while moving the cable in the length direction, it is possible to measure the cable wound on a winding means such as a drum. Partial discharge can be measured for the entire length of the wire. In particular, by transferring a power cable wound around one drum, etc. to another drum, etc., and fixing the detection coil at a position between them, the cable can be moved in approximately the same state. Measurements over the entire length can be easily performed. The cable may be fixed and the detection coil may be moved.

[Effect]

When a partial discharge occurs in the cable core when the conductor is energized, a closed circuit is formed through the capacitance between the conductor and the outer semiconducting layer, and the partial discharge current is transferred to the wire wound around the cable. flows to the shield.

This current flowing through the wire shield generates a magnetic flux that has a component in the axial direction of the cable. The interlinkage between this magnetic flux and the detection coil generates an electromotive force between both ends of the detection coil, and by measuring this, the partial discharge current can be measured. Even if there is a considerable air gap between the wire shield and the detection coil, there is sufficient magnetic coupling between the two in the high frequency band (10kHz or higher), so the detection coil can remove the partial discharge generated in the cable core from the outside of the cable. Can be measured with high sensitivity. By moving the cable and sequentially moving the measurement position, partial discharge can be easily detected over the entire length of the power cable.

Hereinafter, the present invention will be explained in more detail with reference to Examples.

[Example 1] FIG. 1 shows an example of a configuration used in the partial discharge detection method of the present invention.

A wire shield wire 2 is wound around the outer periphery of the test cable 1 at long pitches over the entire length, and the wire shield wire 2 is grounded (not shown).

The test cable 1 (hereinafter referred to as cable 1) wound around the first drum 3 is sequentially wound onto the winding drum 4. A blind terminal 5 is attached to the terminal of the cable 1 wound around the drum 3.
and insulated. The beginning of the winding of the winding drum 4 is connected to the power supply terminal 6 through the body of the drum. The charging terminal 6 has a rotary contact 7 at its tip, and can apply power to the cable 1 even when the drum is rotating. A detection coil 8 is installed around the outer circumference of the cable 1 between the drum 3 and the winding drum 4.
will be established. A measuring device E9 for measuring high frequency electromotive force is connected to both ends of this coil 8.

The operation of this configuration is as follows.

Electricity is applied to the conductor of the cable 1 from the rotary contact 5 at the tip of the charging terminal 6, and while the cable 1 is being wound from the drum 3 to the drum 4, the high frequency electromotive force generated in the detection coil 8 is measured by the measuring device 9. When measured, when a partial discharge occurs in the cable 1, a partial discharge current flows through the wire shield wire 2, and the detection coil 8 is detected due to the linkage between the magnetic flux generated by this current and having a component in the axial direction of the cable. An electromotive force is generated between both ends of the coil 8, and this electromotive force is measured by a measuring device 9.

A partial discharge that occurs within the cable l generates a partial discharge current that circulates through the conductor at the point of occurrence and the wire shield wire 2 on both sides of the conductor, but this current is largest at the point where the partial discharge occurs and decreases as the distance increases. do. cable 1 to drum 3
When the electromotive force generated in the detection coil 8 is measured while being wound on the drum 4, the electromotive force generated in the detection coil 8 reaches a maximum when the point of occurrence of partial discharge passes through the coil 8. That is, partial discharge is measured with the highest detection sensitivity.

C Embodiment 2] FIG. 2 shows an example in which feeding and winding are performed using a turntable drum.

The test cable 21 is a half-shaped cable core, and a wire shield 22 is wound around its outer periphery at a long pitch over its entire length, and the wire shield 22 is grounded via a rotating metal roller 23 .

The drums 24 and 25 are turntable drums. Test cable 2 wound around the sending drum 24
One terminal is connected to a power charging terminal 26 having a rotating contactor 27, and can power the cable 21 even when the drum 23 is rotating. The end 28 on the winding side is a blind end bundle. The detection coil 8 and measuring device 9 are the same as in the first embodiment.

The operation in the measurement is the same as in Example 1 except that electricity is applied from the drum 24 on the sending side.

Since a turntable type drum is used, the delivery,
The bending radius of the cable at both winding ends can be relatively large, and it can be applied even when the test cable is thick. The test cable 21 may be a completed cable with a wire shield.

[Example 3] In Example 2, when the test cable 21 is a completed wire shield cable having a wire shield layer and a corrosion-resistant sheath, the drum 25 on the winding side is a normal drum instead of a turntable drum. Use. This allows the product to be shipped as is.

[Embodiment 4] Contrary to Embodiment 3, the sending-out drum 24 in Embodiment 2 is a drum around which the completed cable is wound (having a power charging terminal), and the winding-side drum 25 is a turntable type drum. use

(Effects of the Invention) According to the present invention, detection of partial discharge in a high-voltage cable cable is performed in a state where the cable can move in the length direction.
By using a wire shield and a detection coil, it can be easily performed with high sensitivity and reliability. By sequentially moving the cable in the length direction, partial discharge detection can be performed for sections of arbitrary length, and partial discharge detection can also be easily performed for the entire length of the long cable.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram showing the configuration used in one embodiment of the partial discharge detection method of the present invention, FIG. 2 is an explanatory diagram showing the configuration used in another embodiment of the present invention, and FIG. FIG. 3 is an explanatory diagram illustrating a partial discharge detection method for the entire length of a high-voltage type cable. Explanation of symbols 1-----1 Test cable 2-----1・--Wire shield wire 3--------
-・-Drum 4--------One winding drum 5-----Blind end bundle 6------One charging terminal 7--------・−・Rotating contact 8・−・−1−−−−−Detection coil 9−−−−−−−・−Measuring device 21・・−・・−・−Sample cable 22・・−・− Wire shield layer 23 --- Metal roller 24 --- Drum 25 --- Drum 26 ----------- Power charging terminal 27-・--・・-・One-rotation contactor 2 days-・-・One terminal 31--・・・-- Test cable 32・・-・・・・Simple metal shielding layer 33-- −
・−・−Drum 34−−−−−1・−Drum 35−・−−−−−・Terminal 36・−・−−−−Electrification terminal 37−−−−・One rotation contactor

Claims (1)

[Scope of Claim] A method for detecting partial discharge in a power cable having a conductor, an insulating layer covering the conductor, and an outer semiconducting layer provided on the outer periphery of the power cable, comprising: a wire shield on the outer periphery of the power cable. a fixed detection coil is arranged outside the wire shield, and while the power cable is moved continuously or intermittently in the length direction, an electric current is applied between the conductor and the wire shield, and the detection coil is A method for detecting partial discharge in a power cable, characterized by measuring electromotive force generated at both ends.