JPH0567189B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a partial discharge detection method that can accurately detect partial discharge in a cable or a cable connection part, etc. in a live line state.

[Conventional technology and problems] Insulation deterioration in high-voltage cables manifests as localized corona discharge, but it is extremely important to quickly detect such localized discharges in the maintenance of cable lines. be.

What is shown in FIG. 1 is the above-mentioned partial discharge detection method that has been widely used in the past. In order to measure the partial discharge characteristics of a cable line using this method, first, power transmission on the line is stopped, and the power transformer 21, for example, at the cable head 11 of the power transmission system of the cable 10 is
A detection system 20 consisting of a choke coil 22, a coupling capacitor 23, a detection impedance 24, etc. is connected, and the pulse voltage generated at the detection impedance terminal is amplified to detect partial discharge.

However, in the conventional method as described above, the period to be measured becomes longer, the partial discharge detection pulse voltage decreases, and the pulsed external noise voltage of the measurement system increases, and this ratio, that is, the S/N value As a result, the detection sensitivity of partial discharge decreases.
Moreover, as mentioned above, it is necessary to perform the measurement after a power outage, making it impossible to diagnose insulation in a constantly live state. Since the pulse current generated through the capacitance is detected as the voltage generated in the impedance to ground, it can only be detected when it has a ground electrode, such as the cable head 11 or the ordinary junction box 12 in Figure 1. , it is not possible to detect partial discharge at an intermediate connection portion without a ground electrode like the insulated connection box 13 in the same figure.

[Object of the Invention] The present invention eliminates the drawbacks of the prior art as described above, makes it possible to install a detection system in advance at any appropriate location on a long cable line, and makes it possible to install a detection system in advance in a long cable line in a live line state. The present invention aims to provide a method for detecting partial discharges in cable lines that makes it possible to detect partial discharges with high sensitivity.

[Summary of the Invention] That is, the present invention forms a separation part that is electrically isolated from an external shielding conductor at one end side of a connection part of a cable line, and creates a pulse detection impedance between the external shielding conductors on both sides of the separation part. The main purpose of this system is to install a cable, thereby making it possible to detect partial discharge pulses circulating between the cable's internal conductor and external shielding conductor, thereby enabling constant live line insulation diagnosis. It is.

[Examples] The present invention will be described below based on Examples.

FIG. 2 is an explanatory cross-sectional view showing how the partial discharge detection method according to the present invention is implemented. 1 is a high-voltage inner conductor of the cable, 2 is a cable insulator, and 3 is an outer shielding conductor of the cable.

The connecting portion of the cables 10, 10 configured as described above generally has a configuration as shown in FIG.
Connect the exposed conductors 1 and 1 to the conductor connection fitting 4
After crimping and reinforcing the connection with a connecting portion insulator 5, a semiconducting layer 6 and a connecting portion external shielding conductor 7 are provided, and finally an external insulating protective layer (not shown) is coated. Normally, the cable external shielding conductor 3 and the connection part external shielding conductor 7 are electrically connected as shown in 8 in the figure, but in the present invention, as shown in the figure, the cable external shielding conductor 3 and the connection part external A separation part (edge cut part) 9 is formed which separates the shielding conductor 7 and connects it with only the semiconducting layer 6. Thus, both external shielding conductors 3 in the electrically isolated separation section 9
and 7, a pulse detection impedance (for example, a transformer 30) is connected, and the high-frequency pulse voltage input to this impedance 30 can be extracted.

Although it is of course possible to separately install the above-mentioned detection system when detection is required, it is better to install it in advance at required intervals as part of the cable installation system when installing the cable. Note that installing such a detection system at the terminal connection or intermediate connection (with or without a ground electrode does not matter in the present invention) rather than at the cable main body itself as shown in Figure 2 is because the connection to the main body is This is partly because it is difficult to install, but also because there is a high possibility that partial discharge will occur at the connection part as described above.

FIG. 3 is an explanatory diagram showing the operation of the partial discharge detection system according to the present invention installed as described above.
Here, it goes without saying that the pulse detection impedance 30 in the detection system should have sufficiently low impedance for commercial frequencies of 50 Hz or 60 Hz and be able to withstand ground fault current and the like.

Now, it is assumed that a partial discharge has occurred in the portion of the connection portion insulator 5 shown in the equivalent circuit in FIG. 3. Then, a pulsed current flows as shown by the arrow in FIG. 3 due to the partial discharge, and a part of the pulsed current flows to the pulse detection impedance 30 as shown. Therefore,
By extracting a pulse voltage through this pulse detection impedance 30, the occurrence of the partial discharge is detected.

In the above, pulse detection impedance 3
If the distance between the zero installation location and the point of partial discharge occurrence is large, the generated pulse will propagate as a traveling wave and will gradually attenuate, reducing the pulse detection sensitivity. Therefore, it is desirable to install a detection system after carefully considering the installation interval in anticipation of this.

In addition to the above-mentioned locations, the detection system may also be installed between the cross-bonds used to reduce the sheath circuit current when three single-layer cables are used in three-phase AC power transmission. It is also possible to install an impedance,
It is convenient for installation because it has an edge cut part.

[Effects of the Invention] As described above, by using the partial discharge detection method according to the present invention, the following excellent effects can be achieved.

(1) Unlike the conventional voltage-to-ground detection method, it does not require a ground potential, so there are no restrictions on the installation location, and installation can be done at desired intervals, making maintenance of the entire cable line easier. This makes monitoring much easier.

(2) High-sensitivity detection is possible because it can be selectively installed in terminal connections, intermediate connections, etc. where insulation weaknesses are likely to occur.

(3) Since detection can be performed while the line is in a live line state, so-called live line insulation diagnosis is possible by keeping the detection system connected at all times.

[Brief explanation of the drawing]

Figure 1 is an explanatory diagram showing the conventional partial discharge detection method.
FIG. 2 is an explanatory sectional view showing a specific example of the detection method according to the present invention, and FIG. 3 is an explanatory view showing a partial discharge detection situation in FIG. 2. 1: Cable internal conductor, 2: Cable insulator,
3: cable external shielding conductor, 5: connection part insulator, 6: semiconducting layer, 7: connection part external shielding conductor,
10: Power cable, 11: Cable head, 3
0: Impedance for pulse detection.

Claims (1)

[Scope of Claims] 1. In a cable line having an external shielding conductor in a cable and its connecting portion, etc., the cable external shielding conductor and the connecting portion external shielding conductor are connected at one end side of the connecting portion, and the other end of the connecting portion On the side, the cable external shielding conductor and the connecting part external shielding conductor form an electrically isolated part connected only through a semiconductor conductor or its equivalent, and an impedance for pulse detection is created between the two separated external shielding conductors. A partial discharge detection method in a cable line, which is characterized in that the pulse voltage due to partial discharge generated in the cable line is extracted through a pulse detection impedance. 2. The partial discharge detection method according to claim 1, wherein the pulse detection impedance is installed in advance as part of the cable installation system. 3. The partial discharge detection method according to claim 1 or 2, wherein a pulse detection impedance is inserted and installed between cross bonds for sheath current low range.