JP3175129B2 - Power cable inspection method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a sweep inspection method for a high-voltage power cable having an extruded solid insulator such as a crosslinked polyethylene insulated cable (CV cable).

[0002]

2. Description of the Related Art Performing a full-length quality inspection of a core of a high-voltage power cable having an extruded solid insulator by a sweep inspection based on partial discharge measurement has a long history. There are roughly two methods for this: (1) inspection of the core before shielding in an insulating liquid or semiconductive liquid and inspection of the shielded section of the shielded core. ("Partial discharge detection" FHKrenger
Author. Okada Toru. (See the translation by Katsuhiko Naito)

FIG. 5 is an explanatory diagram of an example of a sweep inspection of a core before shielding in an insulating liquid. The cable core 41 before shielding is passed through the fixed tubular electrode 42 maintained at the test voltage. Since the tubular electrode 42 and the cable core 41 are immersed in the insulating liquid 44 filled in the insulating tank 43, the inside of the tube and the tube end are completely filled, and no discharge that disturbs the test occurs in this portion. It has become. The cable to be tested can extend over a mile and travel from the cable reel through the electrode assembly to another reel. The inner conductor of the cable is grounded. The inner diameter of the electrode is the minimum size that allows the outer diameter of the core to vary. The ends of the electrodes are logarithmic in shape so that the potential gradient is constant along the surface.

FIG. 6 is an explanatory diagram of an example of a sweep inspection of a core before shielding in a semiconductive liquid. Cable core 51 is an insulating tube
Passed through 53. The insulating tube 53 is filled with distilled water 54, and a metal electrode 52 maintained at a high voltage and connected to a detector 55 is placed in the center. End of insulating tube 53 and cable core 51
The conductors inside are grounded. Thus, the voltage applied to the dielectric gradually increases toward the center. Again
Since 54 serves as a medium that completely touches the surface of the cable core 51, the discharge between the cable core 51 and the electrode 52 does not matter.

FIG. 7 is an explanatory diagram of an example of a sweep inspection of a shielded core. FIG. 7A is a mechanical layout diagram, and FIG.
Is a circuit diagram. The principle of this test is to allow the cable core 62 to pass over a metal reel which can be regarded as another separated electrode because the semiconductive shield part has a high resistance as shown in the figure. The cable core 62 is wound on drums 67, 68 having a grounded conductive body, and a test voltage is applied to conductors 61 in the cable core 62. In an actual apparatus, two test reels 65 and 66 connected to the detector 70 via the bridge 69 and two ground reels 63 disposed near the test reels 65 and 66 are used. Cable cores 62b, 62c of the same length on the two test reels 65, 66 serve as two samples having the same dielectric loss. The discharge on one side of the test reel is between the bridge points (Fig. 7 (b)
At points 1 and 2). The discharge between the high voltage part and the ground, for example, the cable cores 62a and 62d on the grounding reel 63 and the drums 67 and 68 is eliminated. In this way,
Cable core 62 passing through test reels 65 and 66
The discharge of b, 62c is detected. In the figure, 64 is a rubber reel for guidance.

[0006]

The sweep inspection of the core before shielding in the insulating liquid or the semiconductive liquid shown in FIGS. 5 and 6 has high safety because the conductor can be set to the ground potential. However, this method is not applicable to high voltage cables because the method of extruding the semiconductive shield layer and the extrusion of the solid insulator are used in order to increase the reliability of the cable. .

On the other hand, in the sweep inspection of the shielded core shown in FIG. 7, since a high voltage is applied to the entire length of the conductor, it is necessary to assemble a high-quality terminal that does not generate a partial discharge at the test voltage. However, since it is installed on a rotating cable drum, the equipment is extremely large in the case of a high-voltage cable, and is not implemented with a transmission cable of 66 kV or more.

[0008]

SUMMARY OF THE INVENTION The present invention solves the above-mentioned problems and provides a method for inspecting a power cable capable of performing a safe and highly sensitive partial discharge measurement. The conductor of the power cable core in a state where the high voltage is applied is grounded, a high voltage is applied to a part of the semiconductive shield layer, and a high voltage is applied to the semiconductive shield layers on both sides of the portion to which the high voltage is applied. used as dividing resistors for sharing a further utilized as the partial pressure resistors Hanshirubedenshi
At least one or more intermediate voltage application sections are provided in the
Partial discharge measurement is performed at a portion where the high voltage is applied .

[0009]

FIG. 1 shows the principle of the inspection method of the present invention. The conductor 1 of the power cable core 2 provided with the semiconductive shield layer is grounded, and a high voltage is applied to a part of the conductor 1 through the partial discharge detector 7 and the measuring electrode 4 from the transformer 8 to measure the partial discharge. Reference numeral 5 denotes a guard electrode for preventing disturbance in measurement. The semiconductive shield layer of the cable core 2 between the guard electrode 5 and the ground electrode 3 shares a voltage in the length direction of the cable and acts as a kind of resistance sharing terminal. However, the resistance of the semiconductive shield layer cannot be made too high to maintain a stable shield function, and the current flowing through the semiconductive shield layer (strictly, the heat generated by the current) must be kept at a realistic value. In the case of a high-voltage cable, a length exceeding 10 m is required as a resistance voltage dividing portion (heat generation per unit length of the cable is proportional to the square of the applied voltage and inversely proportional to the square of the length).

However, when the resistance voltage dividing portion, that is, the distance between the ground electrode 3 and the guard electrode 5 becomes longer, the influence of the capacitance 13 between the semiconductive shield layer 12 and the conductor 11 increases as shown in FIG. A large current flows in the vicinity of the application section, which becomes a bottleneck of heat generation. FIG. 3A shows this state. In order to improve this, an intermediate electrode 6 is provided between the ground electrode 3 and the guard electrode 5 and an appropriate voltage is externally applied to this portion, whereby the heat generation distribution is greatly improved as shown in FIG. You.

However, in the case of a very high-voltage cable such as a 500 kV cable, even if the above-described averaging is performed, several tens of meters are required to suppress the amount of heat generation (correctly, temperature rise due to heat generation) to an allowable value. Length is required. In such a case, it is effective to intermittently apply the voltage to suppress the average heat generation. Since the time constant of the temperature rise of the cable is large, for example, if the power is applied for 10 seconds and no power is applied for 90 seconds, the temperature rise due to heat generation is almost the same as that when the average calorific value becomes 1/10 of continuous power application become.

[0012]

FIG. 4 is an explanatory view of a specific example of an apparatus embodying the above principle. The power cable core 22 provided with the semiconductive shield layer supplied from the supply stand 21 includes:
It reaches the guard electrode 26 via the ground electrode 23 and the intermediate electrodes 24 and 25. The inside of these electrodes is formed of a conductive brush or roller, and maintains electrical contact with the cable core 22 in a slidable manner. Reference numerals 27 and 28 denote measuring electrodes. In this case, the measuring electrode is divided into two parts and a balance method is adopted. 29 is a partial discharge detector. Since the guard electrode 26, the measurement electrodes 27 and 28, and the partial discharge detector 29 are supported at a high voltage by the support insulator 32, the optical fiber 30 transmits the signal detected by the partial discharge detector 29 to the measuring device 31. used. 33 is a high voltage transformer of the section voltage. 34 is a capacitor type voltage divider for supplying an intermediate potential to the intermediate electrodes 24 and 25. In this case, if a transformer capable of supplying a necessary intermediate potential is used, the voltage divider is unnecessary. In this embodiment, the structure for applying the intermediate potential is simplified to be folded at the high voltage portion. However, a linear arrangement as shown in the principle diagram of FIG. 1 is also possible.

[0013]

According to the partial discharge measurement, it has been theoretically clarified that the more sensitive the section to be measured is, the higher the sensitivity can be measured, and it has been desired to realize a sweep test. However, since a feasible and practical means has not been found for a high-voltage cable, a full-length inspection has been performed until now, which cannot always be said to have sufficient sensitivity. By applying the inspection method of the present invention to such a partial discharge measurement of a high-voltage cable, it is possible to perform a partial-discharge measurement with higher sensitivity than ever before, which is effective for improving the reliability of the high-voltage cable.

[Brief description of the drawings]

FIG. 1 is a principle diagram of an inspection method of the present invention.

FIG. 2 is an explanatory diagram of a capacitance in a resistance voltage dividing unit.

FIG. 3 is a comparison diagram of an increase in the amount of heat generated by the influence of the capacitance in the resistance voltage dividing section (A) and an amount of heat generated by the present invention in which the increase is improved (B).

FIG. 4 is an explanatory diagram of a specific example of an apparatus for realizing the inspection method of the present invention.

FIG. 5 is a diagram illustrating an example of a sweep inspection of a pre-shield core in an insulating liquid.

FIG. 6 is an explanatory diagram of an example of a sweep inspection of a pre-shield core in a semiconductive liquid.

FIG. 7 is an explanatory diagram of an example of a sweep inspection of a shielded core.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Conductor 2 Cable core with semiconductive shield 3 Ground electrode 4 Measurement electrode 5 Guard electrode 6 Intermediate electrode 7 Partial discharge detector 8 Transformer

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) G01R 31/12 G01N 27/92 H01B 9/02 G01B 7/04

Claims (2)

(57) [Claims] 1. A high voltage is applied to a part of the semiconductive shield layer by grounding a conductor of a power cable core provided with a semiconductive shield layer, and a half of both sides of a portion to which the high voltage is applied. To share the high voltage applied to the conductive shield layer
As a voltage dividing resistor , and further used as the voltage dividing resistor.
A method for inspecting a power cable, comprising: providing at least one or more intermediate voltage applying portions in a semiconductive shield layer to be used, and performing partial discharge measurement in a portion to which the high voltage is applied . 2. The power cable inspection method according to claim 1, wherein the average heat generation in the semiconductive shield layer is reduced by intermittently applying a high voltage.