JPH0315707B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for measuring partial discharge in cables.

BACKGROUND OF THE INVENTION Conventionally, partial discharge measurement of cables has been carried out as one of cable management tests using a pulse circuit as shown in FIG. Since the pulse circuit handles minute pulses, the blocking coil L
A lead wire L1 connected to a high-voltage power supply E via a lead wire _L1 and a grounded lead wire _L2 are arranged above and below, and a coupling capacitor C and a detection element Z are connected between the lead wire _L1 and the ground.
The cable under test 1 is constructed by inserting the lead wire l ₁ into the cable conductor at one terminal 2.
and the lead wire below it into the metal sheath of the cable.
l Measured by connecting ₂ .

Since the pulse circuit is configured and spatially assembled as described above, external noise due to electrostatic induction or electromagnetic induction is likely to enter. Noise that enters the circuit includes noise V ₁ that enters from the high-voltage power supply E through the lead wire L ₁ as schematically shown in Figure 1, and electrostatic induction that enters through stray capacitance with the circuit. Noise V ₂ caused by high voltage charging, corona V ₃ generated at the cable end 1b due to high voltage charging
There is also noise V ₄ due to electromagnetic induction that enters through the mutual inductance M.

Conventionally, the following methods have been adopted to remove these noises. In other words, the blocking coil L ( _first
(Fig.) and a balance circuit. When using the blocking coil L, it is reduced to about 1/100 to 1/1000. To prevent noise _V2 caused by capacitance, store the pulse circuit together with the cable in a shielded room and avoid placing any metal objects nearby.
In this case, not only the occupied space becomes large, but also the equipment cost becomes high. For corona _V3 , the cable end portion 1b is enlarged to maintain a small creeping electric field. Regarding the noise V ₄ caused by electromagnetic dielectric, the noise V ₄ is caused by the cable under test 1 and the coupling capacitor C.
The smaller the spatial loop created, the smaller the intrusion, but it is almost defenseless.

Therefore, in the conventional measuring method, the equipment becomes large and the equipment cost becomes expensive, and there are also disadvantages in that all noise cannot be effectively removed.

The present invention has been made in view of such conventional difficulties.One end of the cable to be measured is inserted into a grounded metal case, and the other end is connected to a coupling capacitor via a pulse sensor in another grounded metal case. Partial discharge of a cable that is connected to a dual-purpose charging cable, applies a high voltage to the cable under test through the charging cable, and as a result, the partial discharge generated in the cable under test is extracted as an optical signal by the above-mentioned pulse sensor. The purpose is to provide a measurement method.

The present invention will be described below with reference to the drawings.

FIG. 2 shows an example of a pulse circuit for implementing the present invention, in which a cable to be measured 3 is connected to a power supply cable 5 via a pulse sensor 4 at its terminal 3a.
The exposed terminals 3a, 5a of these conductors and the pulse sensor 4 are electrically shielded with a grounded metal case 6 to eliminate stray capacitance. Similarly, the other open end 3b of the cable 3 is also shielded by a grounded metal case 7. Further, the terminal 3b is formed in a large size in order to suppress the generation of corona _V3 . The other terminal 5b' of the charging cable 5 is fitted with an insulator 8, and the conductor 9 of the cable 5 drawn out from this is fitted with a blocking coil L.
A high-voltage power supply E is connected via the. The blocking coil L is for removing noise _V1 of the high voltage power supply. The energizing cable 5 also serves as a coupling capacitor C, and the capacitor C is electrically shielded by the metal sheath of the energizing cable 5 itself. By using the energizing cable 5 also as the coupling capacitor C in this way, the spatial configuration of the pulse circuit can be made smaller. The pulse sensor 4 consists of an impedance Z and an E/O converter that converts the voltage generated across the impedance Z into an optical signal.
Partial discharge generated in the cable 3 is extracted from the sensor 4 as an optical signal by an optical fiber 10.
The signal is then converted into an electrical signal by the monitor 11, amplified, and displayed on the oscilloscope 12 as an electrical waveform.

In the present invention, the pulse circuit is configured as described above to measure partial discharge of a cable, and various noises are removed as follows.

First, the high voltage is applied to the power supply cable 5 by the high voltage power supply E.
The noise V ₁ of the high-voltage power supply E is applied between the conductor of the cable 3 to be measured and the metal sheath through the blocking coil L. Further, corona V ₃ generated at the open terminal 3b of the cable 3 is suppressed by increasing the size of the terminal 3b. To prevent noise V ₂ caused by electrostatic induction, the terminals 3a and 3b of the cable 3, the terminal 5a of the charging cable 5, and the pulse sensor 4 are shielded by grounded metal cases 6 and 7, and the cables 3 and 5 themselves are shielded. Since it is shielded with its own metal sheath, stray capacitance is removed from the entire pulse circuit so that it no longer occurs. In addition, for noise V ₄ due to electromagnetic induction,
By using a energizing cable that also serves as a coupling capacitor, the coupling capacitor is omitted and the spatial configuration of the pulse circuit is made small, thereby suppressing the occurrence.
Further, since the partial discharge measurement signal is converted into an optical signal by the pulse sensor 4 and taken out by the optical fiber 10, it can be easily guided to the oscilloscope 12 without being affected by external electrical influences.

FIG. 3 shows another example of a pulse circuit for implementing the present invention, in which the blocking coil L shown in FIG.
Instead, a balance detection circuit or a polarity discrimination circuit is provided to remove the noise V ₁ from the high-voltage power supply E, and the other noises V ₂ , V ₃ , and V ₄ are the same as the pulse circuit in Figure 2. It is removed by a similar action. That is, in this pulse circuit, the terminal tip 5a of the energizing cable 5 which also serves as a coupling capacitor is branched within the metal case 6, and is connected to the pulse sensor 4', respectively.
4'' to the terminal 3a of the cable under test 3 and the terminal 13a of the coupling capacitor cable 13.The open terminal 13b of the coupling capacitor cable 13 is grounded in the same way as the terminal 3b of the cable 3. Shielding is provided by a metal case 14, and a pulse capacitor 4',
4'', monitors 11' and 11'', and a detector 15 for determining balance or polarity constitute a detection circuit. Note that 10' and 10'' are optical fibers, and 12 is an oscilloscope.In this detection circuit, in addition to the noise _V1 from the high-voltage power supply E, the open terminal 3b of the cable under test 3 is detected.
It is also effective in removing corona _V3 .

As explained above, according to the present invention, one end of the cable to be measured is inserted into a grounded metal case, and the other end is placed in another grounded metal case and charged with a coupling capacitor via a pulse sensor. A high voltage is applied to the cable under test through the energizing cable, and the partial discharge generated in the cable under test is measured using the above-mentioned pulse sensor as an optical signal. It can effectively eliminate noise from high-voltage power supplies, noise caused by electrostatic induction, noise caused by electromagnetic induction, and corona discharge, eliminating the need for a shield room. It is also easy to form the terminal of the cable under test.
Another advantage is that the pulse circuit including the cable under test can be easily assembled at any location.

Note that the present invention is applicable not only to cables but also to partial discharge measurements of cable connections, units, etc.

[Brief explanation of the drawing]

Figure 1 is a conceptual diagram showing a conventional pulse circuit, Figure 2 is a conceptual diagram showing a conventional pulse circuit.
3 are conceptual diagrams showing pulse circuits used in the present invention. 3... Cable under test, 3a, 3b... Terminal,
4, 4', 4''... Pulse sensor, 5... Power supply cable that also serves as a coupling capacitor, 6, 7, 14... Grounded metal case.

Claims (1)

[Claims] 1 One end of the cable to be measured is inserted into a grounded metal case, and the other end is inserted into another grounded metal case through a pulse sensor equipped with an E/O converter that converts electrical signals into optical signals. A high voltage is applied to the cable to be measured through the energizing cable that also serves as a coupling capacitor, and the partial discharge generated in the cable to be measured is extracted as an optical signal by the pulse sensor. Characteristic cable partial discharge measurement method.