JPS59195167A - Detection of defective linear connection of high tension power cable - Google Patents

Abstract

PURPOSE:To enable decision of an internal defective connection with ease and sureness by providing measuring electrodes to the right and left sheath insulating layers of a power cable at the linear juncture thereof and measuring the induced voltage of the electrodes. CONSTITUTION:If the connection at the part of a connector 7 is defective, the potential of the core on the side where a metallic shielding body 4' is not grounded is divided by the electrostatic capacitities A, A' of main insulating layers 2-1, 2-2, and the electrostatic capacities B, B' of cable sheath insulating layers 5-1, 5-2 to the ground, then a potential is generated in a metallic shielding body 4' which is not grounded. This potential is induced according to the potential of the body 4' in electrodes 8-1, 8-2 attached to the layers 5-1, 5-2 and is measured with voltmeters 9-11. Whether the connecting condition is satisfactory or not is discriminated from the values measured by such voltmeters.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for detecting a connection failure in a straight connection of a high voltage electrical cable.

As shown in Fig. 1, the high-voltage electric cable consists of a core wire 11 through which a load current is passed, main insulating layers λ,
In addition to the semiconducting tape 3, a metal shield to equalize the electric field of the main insulating layer 2, and a shield to protect it from external damage, the insulating layer S is also protected.

If the high-voltage electric cable has a long extension distance, use straight-line connections at several points along the way to electrically connect the core wires and metal shields, respectively, to extend the cable. The cable's metal shield is grounded on one end. Grounding of metal shields is generally done at the cable end.

For this reason, if there is a poor connection in the metal shield at the straight connection point in the middle, the metal shield at the end will receive an induced voltage from the core wire, causing tracking in the outer insulation layer. There is a risk that the layer may also be burnt out, leading to further failure.

In order to detect the connection status of straight connections that cause these failures, there is a method of internal diagnosis using X-ray photography.
It requires a great deal of labor and expense to handle the equipment on site.

In the present invention, a high-voltage electric cable is put into use, measurement electrodes are provided on the outer insulating layer of the electric cable on the left and right of the straight connection part, and internal connection failures are detected by measuring the voltage induced in the electrodes. This is a method of detection, and aims to provide a method that is easy to use and can be used to make a reliable determination.

Embodiments of the present invention will be described in detail below with reference to the drawings.

FIG. 2 is a sectional view showing a detection state by the method of the present invention.

In the dark, the core wires of the left and right high-voltage cables are connected by the straight connection part A, and the metal shield G' and the connecting metal fittings connect the high-voltage cable's metal shield G' and connecting metal fittings. , Guco is connected.

The outer insulating layer of the power cable on both sides of the straight connection part connected in this way! ;-/,! ;-- Voltmeter for measuring the induced voltage on the surface and between the ground 9. /Cause// is what people do.

If there is a connection failure in the connection fitting 20, the potential of the core wire on the side where the metal shield G' is not grounded will be lower than the electrostatic capacitance A of the main insulating layer Corpanoule, as shown in the circuit shown in Fig. 3. , A', and the cable jacket insulating layer 3-/, 3-1 are voltage-divided by the main capacitances B and B' relative to the ground, producing a potential in the ungrounded metal shield. This potential is the outer insulation layer of the cable,! A voltage as shown in FIG. 7 is induced between the electrodes attached to S-2 and / and Z-λ according to the potential of the metal shield, and 9, lθ, //
It can be measured with a voltmeter.

The measured value of the voltmeter 9 will be zero if the metal shields 4-/S goo-ni of the left and right power cables are completely connected, but the value measured by the voltmeter 10. // measurement noise occurs when the grounding point of a distant metal shield is incomplete.

Therefore, it is possible to determine whether the connection state is normal or abnormal from the measured values of these voltmeters 9,101//.

Many of the early failures of high-voltage electrical cables are caused by poor connection of metal shields at straight connections. However, by using the measurement method of the present invention, it is possible to determine the quality of the connection inside the straight connection, which cannot be confirmed visually, to prevent power outage accidents due to insulation breakdown, and to extend the life of the cable. The effect of reducing the expense angle j can be expected.

[Brief explanation of drawings]

Figure 1 is a schematic diagram of the high voltage electric cable, Figure 1 is a sectional view showing the detection state by the method of the present invention, Figure 3 is an equivalent circuit diagram including the measurement circuit, and Figure 3 is a metal shield. FIG.

Claims (1)

[Claims] A method for measuring connection failure in a straight connection part of a power cable connected to a high-voltage distribution line in a live line state, the method comprising:
Electrodes were provided on the surface of the outer insulating layer of the power cable on both sides of the straight connection, and the voltages between these electrodes and between each electrode and the ground were measured, and the results showed that there was a defect inside the straight connection. A method for detecting a defective straight line connection of a high voltage electric cable, characterized by detecting the following.