JPH0836005A - Method for measuring dielectric loss tangent of power cable - Google Patents

Abstract

PURPOSE:To obtain dielectric loss tangent even in the case where a charging part is not exposed in an equipment direct-coupled terminal for underground equipment. CONSTITUTION:Voltage phase is detected on the basis of the voltage excited in a detection part of an equipment direct-coupled terminal for underground equipment, which is connected to a cable to be measured. Dielectric loss tangent of the power cable in the operated condition is obtained on the basis of a phase difference between the voltage phase and the current phase flowing in a grounding line of the cable to be measured.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention detects the voltage phase in an underground power distribution system in which the charging part is not exposed and detects the dielectric loss tangent of the cable to be measured from the difference between the voltage phase and the current phase flowing in the ground wire of the cable to be measured. The present invention relates to a method for measuring a dielectric loss tangent of a power cable.

[0002]

2. Description of the Related Art Conventionally, a dielectric loss tangent measuring method has been known as a method for inspecting the insulation performance of a power cable. This dielectric loss tangent is used to detect a current flowing between a test piece such as a power cable and the ground and measure the phase difference between the detected current and the voltage applied to the test piece. A method using a standard capacitor or a resistor is known as a voltage phase detection method for measuring the dielectric loss tangent. The conventional voltage phase detection method using this standard capacitor or resistor is used in the case of a distribution system in which the charging section is exposed.

[0003]

In a recent underground power distribution system, a directly connected terminal for underground equipment or the like may be used, and the charging part may not be exposed. In the case of such an underground distribution system, the voltage phase cannot be detected by the conventional voltage phase detection method using standard capacitors and resistors, and the dielectric loss tangent of the power cable cannot be measured. I have a problem. The object of the present invention is, even when the charging part is not exposed by the equipment direct connection type terminal for underground equipment,
Make the loss tangent required.

[0004]

In order to achieve the above object, the dielectric loss tangent measuring method of a power cable of the present invention is applied to a power detecting section of a directly connected terminal for underground equipment connected to a cable to be measured. The voltage phase is detected from the induced voltage, and the dielectric loss tangent of the power cable in operation is determined from the phase difference between this voltage phase and the current phase flowing through the ground wire of the cable to be measured.

[0005]

Operation: The voltage detection cover of the directly connected terminal for underground equipment is removed, and the voltage induced in the voltage detection section is taken out through the preamplifier. The phase of the extracted voltage, which is deviated by the resistance of the detection unit, is corrected by the phase correction unit and input to the dielectric loss tangent measuring device. The dielectric loss tangent measuring device detects the voltage phase of the cable to be measured and the current phase flowing through the ground wire, and calculates the dielectric loss tangent from the voltage phase and the current phase.
The obtained dielectric loss tangent is used to judge the insulation performance of the power cable.

[0006]

Embodiments of the present invention will be described below. Figure 1 shows the equipment directly connected terminal for underground equipment in the underground distribution system.
It has a configuration as shown in FIG. That is, the terminal 10 directly connected to the underground equipment is connected to the transformer / terminal at the end of the cable.
It is used to connect to devices such as circuit breakers, and is a type that connects to devices without exposing the charging part. Reference numeral 11 is a device body, 12 is a center conductor connected to the device body 11, and 13 is an insulator covered by the center conductor 12. Reference numeral 14 is a terminal to which the tip of the central conductor 12 is connected. Reference numeral 15 is a terminal tightening bolt, and 16 is a compression terminal attached to the terminal 14. The conductor 18 of the power cable 17 is attached to the compression terminal 16. 19 is conductor 1
8 is an insulator coated on, 20 is a semiconductive layer,
It is covered on the insulator 19. Reference numeral 21 is a shielding copper tape, and 22 is a sheath. Reference numeral 23 is a tin-plated soft copper wire (ground wire) connected to the shielding copper tape 21.

A straight cone 24 is coated on the insulator 19 of the power cable 17. The connection cylinder 25 is covered by hanging from the insulator 13 onto the straight cone 24. The connecting tube 25 is made of an insulating synthetic resin, and has an inner semiconductive resin 25A having a predetermined width and a thin inner surface. In addition, at a position on the outer peripheral surface of the connecting tube 25, which is located above the terminal 14, the power detection unit 2
6 is provided. The power detection unit 26 is a unit for detecting whether or not a voltage is supplied from the conductor 18 of the power cable 17 to the central conductor 12. An external semiconductive resin 25B is formed on the outer peripheral surface of the connecting tube 25 so as not to come into contact with the power detecting section 26. 27 is a voltage detection cover,
It has a structure as shown in FIG. That is, the voltage detection cover 27 is made of a conductive material, contacts the voltage detection unit 26, is covered on the voltage detection unit 26, and also contacts the external semiconductive layer 25B. . 28 is a stopper. Reference numerals 29 and 30 denote hose bands for tightening the connecting tube 25. Reference numeral 31 denotes a semiconductive tape, which is peeled off from the sheath 22 and the shielding copper tape 21 and wound around the exposed portion of the semiconductive layer 20. Reference numeral 32 denotes an insulating tape, which is wound around the semiconductive tape 31 and the sheath 22 so as to have an insulating property.

Presence or absence of charging by the power detection unit 26 (power detection)
3, the voltage detection cover 27 is removed as shown in FIG. 3, and the voltage induced in the voltage detection unit 26 is detected by a high voltage voltage detector (not shown).
Confirm by checking in. That is, in the normal case where the detection cover 27 is used, no potential is generated in the detection unit 26 because the detection cover 27 is in contact with the outer semiconductive layer 25B of the connection cylinder 25. Therefore, the power detection cannot be performed with the power detection cover 27. Voltage detection cover 2
An equivalent circuit of the voltage detection unit 26 when the voltage induced in the voltage detection unit 26 is taken out when 7 is removed is as shown in FIG. That is, the electrostatic detection unit 26 has a capacitance C of the high voltage electrode and a resistance R of the high voltage electrode. If this resistor R is neglected, the measurement is basically the same as the conventional measurement using a standard capacitor (usually several hundred pF). However, the value of capacitance C is very small, about 20 pF. Further, the insulating synthetic resin forming the connecting tube 25 is made of EP (ethylene propylene) rubber, and its dielectric loss tangent is about 0.03%, so that the resistance R also exists. Therefore, the phase of the voltage induced in the power detection unit 26 is shifted, and the dielectric loss tangent cannot be correctly measured even if the voltage induced in the power detection unit 26 is directly input to the dielectric loss tangent measuring device.

Therefore, the dielectric loss tangent measuring method of the power cable according to the present invention is measured by a circuit as shown in FIG. In the figure, reference numeral 1 denotes a preamplifier which amplifies a voltage induced in a detection unit to a predetermined magnitude and outputs it. Reference numeral 2 denotes a phase correction unit that corrects a phase shift of the voltage that has been subjected to predetermined amplification in the preamplifier 1. That is, the phase correction unit 2 corrects the phase of the voltage detected by the preamplifier 1 according to the amount of phase shift with respect to the resistance R of the voltage detection unit 26,
The output is adjusted so that the phase shift becomes zero. By doing so, the voltage phase of the voltage induced in the power detection unit 26 can be detected. Reference numeral 3 is a dielectric loss tangent measuring device, which obtains the dielectric loss tangent from the difference between the voltage phase induced in the voltage detector 26 corrected by the phase corrector 2 and the current phase flowing through the ground line.

Next, the operation of this embodiment will be described.
The power detection cover 27 attached to the connection tube 25 of the device 10 directly connected to the underground device is removed to expose the power detection unit 26. A circuit as shown in FIG. 5 is connected to the power detection unit 26. Then, a voltage is induced in the power detection unit 26, and this induced voltage is amplified by the preamplifier 1 and output to the phase correction unit 2. The phase corrector 2 corrects the phase of the induced voltage and outputs it to the dielectric loss tangent measuring device 3. In this dielectric loss tangent measuring device 3, the dielectric loss tangent is obtained from the difference between the voltage phase induced by the voltage detecting section 26 and corrected by the phase correcting section 2 and the current phase flowing through the ground line.

[0011]

According to the present invention, the voltage phase is detected by the voltage detecting section of the equipment direct connection type terminal for underground equipment connected to the cable to be measured, and the voltage phase is detected. Since the dielectric loss tangent of the power cable in the operating state is obtained from the difference, the dielectric loss tangent can be easily obtained even when the charging part is not exposed by the directly connected terminal for underground equipment.

[Brief description of drawings]

FIG. 1 is a front view in which a part of an equipment direct connection type terminal for underground equipment in an underground power distribution system to which the present invention is applied is sectioned.

FIG. 2 is an enlarged cross-sectional view of a part of the equipment direct connection type terminal for underground equipment, showing a state in which a detection cover is attached to the detection unit shown in FIG.

FIG. 3 is a diagram showing a state in which a detection cover of FIG. 2 is removed.

FIG. 4 is an equivalent circuit diagram of the power detection unit shown in FIG.

FIG. 5 is a diagram showing an example of a dielectric loss tangent measuring method for a power cable according to the present invention.

[Explanation of symbols]

1 ………………………………………………………… Preamplifier 2 …………………………………………………… Phase corrector 3 ………………………………………………………… Dielectric loss tangent measuring instrument 10 …………………………………………………… Underground equipment Equipment directly connected terminal 11 …………………………………………………… Equipment main body 12 …………………………………………………… Main Conductor 13 ………………………………………………………… Insulator 14 …………………………………………………… Terminal 16 ……… ………………………………………………… Compression terminal 17 …………………………………………………… Power cable 18 …………………… ……………………………………… Conductor 25 …………………………………………………… Connection tube 26 ……………… ....................................... electroscopic 27 ............................................................ electroscopic cover

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Yoshihiro Hirata 1-20-20 Kitasekiyama, Otaka-cho, Midori-ku, Nagoya, Aichi Chubu Electric Power Co., Inc. Electric Power Research Laboratory (72) Inventor Toshinari Hashizume Ooka, Numazu, Shizuoka Prefecture 2771 Yazaki Electric Wire Co., Ltd. (72) Inventor Tsuneo Tani 2771 Ooka, Numazu City, Shizuoka Prefecture Yazaki Electric Wire Co., Ltd.

Claims (1)

[Claims] 1. A method for measuring a dielectric loss tangent of a power cable in an operating state, wherein a voltage phase is detected from a voltage detecting section of a direct connection type terminal for underground equipment connected to the cable to be measured, and the cable to be measured is detected. A method for measuring the dielectric loss tangent of a power cable, which is characterized in that the dielectric loss tangent of the cable under test is obtained from the difference between the phase of the current flowing through the ground wire of the cable.