JPS60225074A - Partial discharge measuring apparatus of power cable - Google Patents

Abstract

PURPOSE:To accurately measure partial discharge of a power cable by connecting a plurality of capacitors in parallel to a conductor at the final terminal section of a power cable in such a manners to be symmetrical to the axial direction of the cable to cancel noise with a capacitor circuit arranged in a phase symmetry. CONSTITUTION:A plurality of parallel circuits of connection capacitors 12 (C1, C2,...) and an impedance circuit 13 are connected in series between a power cable 10' and a metal sheath 11 in such a manner as to be symmetrical to the axial direction of the cable. A measuring device 14 is connected accross the impedance circuit 13 to detect a partial discharge. When the measuring apparatus thus arranged receives an electromagnetic induction through a mutual inductances MS from a noise source I, noise current I1 and I2 flows to C1 and C2 of the connection capacitors 12 in the same direction as the noise source. Then, noise currents I1 and I2 flows through the impedance circuit 13 in the opposite direction to offset the noise current. In this manner, as a plurality of capacitors are arranged symmetrically to the axial direction of the power cable, invading noises can be removed.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a partial discharge measuring device for electric power cables, and particularly to this type of device that removes noise due to electromagnetic induction during measurement.

[Technical Background of the Invention] Conventionally, partial discharge measurements of power cables have been carried out as one of the control tests for power cables, as shown in FIG. That is, a series circuit of a capacitor 3 and an impedance circuit 4 is connected between the conductor via and the metal sheath 2 at the terminal end of the power cable 1 in parallel to the power cable 1 .

Further, a measuring device 5 for detecting discharge is connected in parallel to the impedance circuit 4. The terminal end of the power cable l is connected to a terminal 6 to which a high voltage is to be applied.

In this case, the measurement is 1! When a partial discharge occurs at a certain point in the cable l, the current flowing through the measurement circuit of the power cable capacitor 3, impedance circuit 4, and metal sheath 2 changes minutely, and this is detected by the measuring device 5, and the occurrence It measures position.

[Problems with the background art] However, since partial discharge is a weak electrical signal,
It is easily affected by external noise caused by electrostatic induction and AT* conduction, and in particular electromagnetic induction is the main cause. That is, as shown in FIG. 1, the mutual inductance Ms due to the noise source I
A current In flows through the measuring circuit through the measuring circuit, and the measuring device 5 detects this, and there is a problem in that it is not possible to determine whether it is due to partial discharge or noise.

Currently, the smaller the spatial loop formed by the power cable 1 and the capacitor 3, the less the noise will invade due to this electromagnetic induction.

is almost defenseless.

[Object of the Invention] The present invention has been made in view of the above-mentioned conventional difficulties.By connecting a plurality of capacitors in parallel with the conductor at the terminal end so as to be symmetrical with respect to the axial direction of the electric power cable,
It is an object of the present invention to provide a partial discharge measuring device for electric power cables that cancels and removes intruding noise using capacitor circuits that are symmetrical to each other and accurately measures partial discharge.

[Summary of the Invention] In order to achieve such an object, the present invention provides a plurality of wires connected in parallel symmetrically with respect to the axial direction of the electric power cable between the conductor and the sheath at the terminal end of the electric power cable. A partial discharge measuring device for an electric power cable includes a capacitor, an impedance circuit connected in series to the plurality of capacitors, and a measuring device for detecting partial discharge of the electric cable at both ends of the impedance circuit. do.

[Embodiments of the invention] Preferred embodiments of the present invention will be described below with reference to the drawings.

In FIG. 2, the basic principle of the partial discharge measuring device for power cables according to the present invention is shown in FIG.

A parallel circuit of a plurality of coupling capacitors 12 (CIIC21...) and an impedance circuit 13 are connected in series between the conductor 10' and the metal sheath 11 at the terminal end of the power cable IO, symmetrically with respect to the axial direction of the power cable. A measuring device 14 for detecting partial discharge is connected to both ends of the impedance circuit 13.

The terminal end of the power cable IO is connected to a terminal 15 for applying a high voltage.

Incidentally, since the coupling capacitors 12 are provided symmetrically with respect to the axial direction of the power cable IO, an even number of coupling capacitors 12 is naturally required.

When the power cable partial discharge measuring device configured in this manner receives electromagnetic induction from the noise source I through the mutual inductance Ms, first, the coupling capacitor 12 (C
+ ), a noise current line 1 flows in the same direction as the noise source I. Then, the noise current 2 flows through the coupling capacitor 12 (C2) in the same direction as the noise source I. Therefore, the noise currents 1 and 2 are in opposite directions with respect to the impedance circuit 13, and the noise currents theoretically cancel out and flow through the impedance circuit 13, so that they are not detected by the measuring device 14.

In fact, although some noise current flows through the impedance circuit, electromagnetic induction is removed to the extent that it does not affect the measurement of one partial discharge.

That is, by experiment, it was possible to reduce the conventional noise current level to 1/3 to 115.

It should be noted that what is shown in FIG. 2 is a principle diagram of the device according to the present invention, and in reality, the coupling capacitor 12 is connected as shown in FIG.
It is implemented by having a cylindrical shape and covering the terminal end of the electric power cable 10. In this case, as shown in Figure 3, the configuration is made up of four (or more) coupling capacitors, and by doing so, the symmetry increases and the noise suppression effect becomes greater. .

[Effects of the Invention] As is clear from the embodiments described above, according to the present invention, a plurality of coupling capacitors are connected in parallel with the conductor at the terminal end symmetrically with respect to the axial direction of the power cable, By removing noise that enters through a capacitor circuit that is symmetrical, it is possible to reduce and eliminate noise caused by electromagnetic induction, which was previously unprotected, and it is possible to accurately measure partial discharges in power cables. .

[Brief explanation of drawings]

Fig. 1 is a principle diagram showing a conventional electric cable partial discharge measuring device, and Fig. 2 is a principle diagram showing a device according to the present invention.
FIG. 3 is a conceptual diagram of a partial discharge measuring device for power cables showing one embodiment of the present invention. 10...Electric cable 10'...Conductor 11...Metal sheath 12...Coupling capacitor 13...
・・・・Impedance circuit 14 ・・・・Measuring device representative Patent attorney Moritani-O Figure 1 Figure 2 Figure 3

Claims (1)

[Claims] A plurality of capacitors connected in parallel symmetrically with respect to the axial direction of the power cable between the conductor and the sheath at the terminal end of the power cable, an impedance circuit connected in series to the plurality of capacitors, and the impedance circuit. A partial discharge measuring device for an electric power cable, characterized in that a measuring device for detecting partial discharge of the electric power cable is provided at both ends of a circuit.