JPH067145B2 - Partial discharge measurement method for power cables - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for measuring partial discharge of a power cable for diagnosing insulation deterioration of the power cable and the like.

[Conventional technology]

FIG. 4 (a) shows a conventional partial discharge measuring method. A power cable 1 is usually connected at an intermediate connection 2 and has termination connections 3 at both ends. Normally, the metal sheath of the intermediate connection portion 2 is grounded by the ground wire 4, and the metal sheath of the power cable 1 is grounded by the ground wire 5 near the terminal connection portion 3.

When measuring the partial discharge, the choke coil 7 that serves as a high frequency impedance is connected to the high voltage charging unit 6 to block the high frequency pulse, and the high frequency pulse is removed by the coupling capacitor 8. This high frequency pulse is a partial discharge signal induced in the cable conductor by the partial discharge generated in the insulator, and generates a predetermined potential difference across the detection impedance 9. This is measured by the partial discharge measuring instrument 10.

FIG. 4 (b) shows another conventional partial discharge measuring method. Normally, a detection impedance 9 is inserted in the ground wire 4 of the intermediate connection portion 2, and the high frequency pulse induced in the metal sheath of the power cable 1 is measured by the partial discharge measuring instrument 10.

[Problems to be Solved by the Invention]

However, according to the conventional partial discharge measurement method, it is necessary to connect a coupling capacitor to the high-voltage charging section or remove the ground wire to insert the detection impedance, so preparation for measurement is troublesome and time consuming. Moreover, there is a disadvantage that the measurement cannot be performed in a live state at all times.

Therefore, it is an object of the present invention to provide a method for measuring the partial discharge of a power cable, which does not require special labor for measuring the partial discharge.

Another object of the present invention is to provide a method for measuring a partial discharge of a power cable, which can be always measured in a live state.

[Means for Solving the Problems]

In order to achieve the above object, the present invention provides a predetermined detection electrode near the surface of a plastic sheath that covers a metal sheath, connects one end of the detection impedance, and grounds the other end to form an insulator for a power cable. Provided is a method for measuring a partial discharge of a power cable, which introduces a high frequency pulse based on a partial discharge generated therein to a detection impedance and measures a potential difference across the detection impedance.

When a partial discharge occurs in an insulator of a power cable, a high frequency pulse is induced in a conductive member adjacent to the insulator, such as an electric conductor or a metal sheath. In order to detect this high frequency pulse, a detection electrode is attached so as to face the metal sheath. The mounting position of the detection electrode is not limited to the portion facing the metal sheath for cables, but the outer circumference of the copper body tube of the terminal connection part, the outer circumference of the metal sheath such as the intermediate connection part, the insulation connection part, the outer circumference of the ground wire, etc. May be The detection electrode is connected to the detection impedance, and the output of the detection impedance is input to the partial discharge measuring instrument to measure the high frequency pulse.

〔Example〕

Hereinafter, the method for measuring the partial discharge of the power cable of the present invention will be described in detail.

FIG. 1 is a conceptual view of the present invention, in which a flat electrode (not shown) is usually attached near the intermediate connection portion 2 or the termination connection portion 3 to form a detection capacitor 20. The detection capacitor 20 is connected to the detection impedance 9, and the partial discharge measuring instrument 10 measures the high frequency pulse based on the voltage across the detection impedance 9.

FIG. 2 shows an example in which a flat electrode (ring-shaped) 21 is attached to the ordinary intermediate connecting portion 2 to form the above-mentioned detection capacitor 20, and a vinyl sheath 22 provided on the outer periphery of the ordinary intermediate connecting portion 2 is used. A plane electrode 21 made of copper, aluminum or the like is provided so as to surround it. The flat electrode 21 is the lead wire mounting portion 21.
has a and is connected to the detection impedance 9. The flat electrode 21 normally forms the detection capacitor 20 between itself and the metal sheath of the intermediate connection portion 2, and its size (area) is determined by the frequency band of the high frequency pulse, the value of the detection impedance 9, and the like. In this case, each parameter is determined so that the reactance of the detection capacitor 20 does not become large.

FIG. 3 shows the above-described detection capacitor 20 formed in the insulation connection portion 30, in which flat electrodes (ring-shaped) 21 are provided on both sides of the insulation cylinder 31 of the insulation connection portion 30 and the lead wire mounting portion 21a.
Is connected to the detection impedance 9 via. The connection to the detection impedance 9 is a differential connection, and its midpoint is grounded as necessary. By this differential connection, a potential based on the potential difference between the metal sheaths on both sides of the insulating cylinder 31 is applied to the detection impedance 9, but the detection impedance 9 is connected to each of the flat electrodes 21 on both sides of the insulation impedance 31 and individually measured. You may.

As described above, the high frequency pulse based on the partial discharge is detected by the electrode attached to the outside of the metal sheath, but the shape and attachment position of the electrode are not limited to the embodiment. For example, the following modifications may be made.

(1) It may be provided outside the insulated wire for grounding. For example, the inner conductor of the coaxial cable may be used for grounding and the outer conductor may be used as the detection electrode.

(2) It may be attached in a ring shape near the grounding side metal fitting at the end of the air.

(3) An insulated metal electrode may be attached near the ground side of the air terminating porcelain tube.

(4) When it is necessary to electrically and mechanically protect the metal electrode, a protective layer such as a reinforcing vinyl tape may be provided outside and / or inside.

(5) The electrode is not limited to metal, and metal chemical conversion paper or the like may be used.

(6) The electrodes may be permanently installed, or may be attached only during measurement.

〔The invention's effect〕

As described above, according to the method for measuring the partial discharge of the power cable of the present invention, a predetermined detection electrode is provided near the surface of the plastic sheath that covers the metal sheath, one end of the detection impedance is connected, and the other end is grounded. Then, the high-frequency pulse based on the partial discharge generated in the insulator of the power cable was introduced to the detection impedance, and the potential difference between both ends was measured, which simplifies the preparation work for the measurement, and the live line condition. It is possible to measure at any time.
Further, since the system such as the power cable line is not substantially modified, the reliability of the system is not deteriorated.

[Brief description of drawings]

FIG. 1 is an explanatory view showing the concept of the present invention, FIG. 2 and FIG.
FIG. 4 is an explanatory view showing two embodiments of the present invention, FIG. 4 (a),
(b) is an explanatory view showing a conventional partial discharge measuring method. Explanation of symbols 1 ... Power cable 2 ... Ordinary intermediate connection part, 3 ... Termination connection part 4, 5 ... Ground wire, 6 ... High-voltage charging part 7 ... Choke coil 8 ... Coupling capacitor 9 ... Detection impedance 10 …… Partial discharge measuring instrument 20 …… Detection capacitor, 21 …… Detection electrode 22 …… Vinyl sheath, 30 …… Insulation connection 31 …… Insulation tube

Claims (1)

[Claims] 1. A power cable having a metal sheath covered with a plastic sheath, wherein a predetermined detection electrode for forming a predetermined capacitance with the metal sheath is provided near the surface of the plastic sheath, and the detection is performed. One end of the detection impedance is connected to the electrode, the other end of the detection impedance is grounded, and a high frequency pulse based on partial discharge generated in the insulator of the power cable is guided to the detection impedance via the capacitance. A method for measuring a partial discharge of a power cable, which comprises measuring a potential difference between both ends of the detected impedance caused by the above.