JPH0628485B2 - Discharge detection circuit of power cable transmission system - Google Patents

Description

TECHNICAL FIELD The present invention relates to a discharge detection circuit for a power cable transmission system.

[Problems of Prior Art] The power cable transmission system is required to have higher reliability of insulation than the devices installed in the substation.

This is because the equipment installed in the substation is relatively easy to manage because it is inside the substation building, and it is relatively easy to replace it in the event of an accident. This is because if a problem occurs in the power cable transmission system, it is usually difficult to identify its position, and replacement (installation replacement) requires a great deal of labor and expense.

On the other hand, conventional discharge detection of this type of power cable transmission system has been performed by collectively viewing the entire power cable transmission system at the terminal end provided at the end of the line. However, with this means, not only the partial discharge pulse from a distant place (such a partial discharge pulse in a long cable line is almost all) is considerably attenuated by the time the end portion is reached, but also from the outside to the line. The amount of noise that had entered would increase, making it difficult to detect the partial discharge pulse. Moreover, the charge amount of partial discharge due to voids in the power cable insulating layer is usually a very small charge amount of several PC to several + PC, and the power cable transmission system has many long power cables. Since the capacitance is increased due to the connection, the partial discharge pulse voltage to be detected is reduced, which makes the detection more difficult.

As described above, there is a difficulty in detecting partial discharge in the power cable transmission system, which is essentially different from detection of partial discharge in devices in the substation.

An object of the present invention is to solve this problem, to prevent damage to the power cable due to discharge in the power cable power transmission system, and to prevent power transmission stoppage due to complete destruction of the damaged cable. An object is to provide a discharge detection circuit for a power cable transmission system.

By the way, the power cable line has a connecting portion every several hundred meters, but since the power cable itself is manufactured in a factory under strict quality control, there is almost no trouble. On the other hand, since the connection part is manufactured locally, and also in a narrow space such as a manhole, quality control is not performed like when the power cable is manufactured, which is not always sufficient. Therefore, statistically most of the troubles in the power cable transmission system occur at or near the connection part. In view of these findings, the present inventors provide the following solution.

[Means for Solving the Problems] A discharge detection circuit according to the present invention is a power cable insulating layer between a well-known external shielding layer or a metal sheath of an intermediate connection portion provided in the middle of a power cable transmission system and the ground. A means for detecting partial discharge and other discharges inside is connected.

[Embodiment] FIG. 1 is an electric circuit diagram showing an embodiment of a discharge detection circuit according to the present invention.

Due to the actual situation as described above, the occurrence of partial discharge and other discharges in the power cable line often occurs around the intermediate connecting portion rather than the main body portion of the power cable. Further, the pulsed current due to the discharge has many high-frequency components and is attenuated as it propagates through the power cable. Therefore, in the present invention, it is extremely important to connect the discharge detecting means to the intermediate connection portion where the occurrence of discharge is concerned. Also, it is of special significance to identify the location of the intermediate connection, which is unique to the power cable transmission system.

Now, in the figure, reference numeral 1 is an intermediate connection portion, and usually the outer shielding layer of the power cable or the metal sheath 2 is directly grounded, but in the present invention, a pulse detection transformer 3A as a discharge detection means is inserted. More specifically, in the pulse detection transformer 3A, the primary winding is connected between the outer shield layer or the metal sheath of the intermediate connection portion 1 and the ground, and the output is taken out from the secondary winding individually. Therefore, by connecting a corona measuring device (not shown) to the secondary winding,
Pulsed discharge can be detected.

In the figure, 4 is an insulating type intermediate connecting part (or insulating type intermediate oil stop connecting part) in which the outer shielding layer or the metal sheath is cut (insulated) in the middle of the connecting part.
In this case, the primary winding of the pulse detection transformer 3B may be connected between the outer shield layer or the metal sheath at both ends thereof via the insulating portion (edge cutting portion) and via the surge protector 5 or a capacitor for overvoltage protection. Then, as in the case of the intermediate connection portion 1, by connecting a corona measuring device (not shown) to the secondary winding of the pulse detection transformer 3B, pulsed discharge can be detected. With this configuration, the commercial high-frequency voltage is not applied to the pulse detection transformer 3B, and the iron core of the pulse detection transformer 3B does not saturate.

In the circuit of FIG. 1, the charging current of the power cable and the current flowing through the external shielding layer or the metal sheath flow in the pulse detection transformer 3A in a superimposed manner. Therefore, if the pulse detection transformer 3A with an iron core is used, the magnetic flux of the iron core may be saturated. In that case, as shown in FIG. 2, the air-core coil 6 is used instead of the pulse detection transformer 3A to prevent the saturation phenomenon from occurring, and the coupling capacitor 7 is provided between the intermediate connection portion 1 and the air-core coil 6. Should be connected. In addition, FIG. 3 shows a pair of terminals in which the secondary side of each pulse detection transformer 3C is commonly connected, and a pulsed voltage is generated at the terminals regardless of which of the three intermediate connection portions 1 is discharged. It was done like this.

[Effects of the Invention] According to the present invention, the detection of the discharge occurrence in the power cable transmission system is completely different from the conventional contents, that is, the external shielding layer or the metal of the intermediate connection part provided in the middle of the system. By connecting a means for detecting partial discharge in the power cable insulation layer and other discharges between the sheath and the ground, it was possible to detect the occurrence of discharge in the power cable transmission system, which was considered difficult in the past, and It is possible to constantly monitor the discharge generation position and the like in a live state, and therefore, it is possible to prevent the ground fault accident due to the discharge generation and to prevent the power transmission function from stopping.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is an electric circuit diagram of an embodiment of the present invention, and FIGS. 2 and 3 are electric circuit diagrams of modified examples of the present invention. 1; Intermediate connection part, 2; External shield layer or metal sheath of power cable, 3A, 3B, 3C; Pulse detection transformer, 4; Insulation type intermediate connection part (or insulation type intermediate oil stop connection part), 6; Air core coil.

Front page continuation (72) Inventor Junichi Minato 5-1-1 Hidaka-cho, Hitachi City, Ibaraki Hitachi Cable & Cable Research Laboratories (56) References JP-A-51-10338 (JP, A) JP-A-SHO 52-110445 (JP, A)

Claims (4)

[Claims] 1. A pulse which is connected between an external shielding layer or a metal sheath of an intermediate connection portion provided in the middle of a power cable transmission system and the ground, and causes partial discharge or other discharge in an insulating layer of a power cable at an operating voltage. A discharge detection circuit for a power cable transmission system, characterized in that the discharge detection circuit is provided with a means for detecting a discharge current. 2. The pulse detecting transformer, wherein the detecting means is a pulse detecting transformer in which the primary winding is connected between the outer shield layer or the metal sheath of the intermediate connecting portion and the ground and the output is taken out from the secondary winding. Discharge detection circuit of the power cable transmission system described. 3. The discharge detection circuit of a power cable transmission system according to claim 1, wherein the detection means is an air-core coil connected between the outer shield layer of the intermediate connection portion or the metal sheath and the ground. 4. The pulse detecting transformer according to claim 2, wherein the detecting means is a pulse detecting transformer in which the primary winding is connected between the outer shield layer or the metal sheath of the intermediate connecting portion and the ground, and the secondary winding is connected in common. Discharge detection circuit of the power cable transmission system described.