JPH0233996B2 - DENRYOKUKEEBURUNOBUBUNHODENSOKUTEIHOHO - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improvement in the determination of partial discharge in a power cable, which is useful in detecting the presence or absence of partial discharge in a power cable.

Generally, as shown in Figure 1, when the insulation of the power cable under test deteriorates, a partial discharge occurs due to high voltage between the conductor of the power cable under test and the sheath shielding layer. As a type of test to measure the insulation deterioration of the power cable 1 under test, the partial discharge signal generated in the insulation of the power cable 1 under test is
Conductor and sheath shielding layer 16 of power cable 1 under test
There is a partial discharge isolation circuit which is measured by a sensor 31 via a coupling capacitor 4 in series between the two.

However, the coupling capacitor 4 is large in size and occupies a large space because the required insulation distance must be increased in order to increase the measurement voltage. Furthermore, since the partial discharge separation circuit is assembled spatially, it is susceptible to electrostatic induction and electromagnetic induction. On the other hand, there is a method in which the partial discharge separation circuit is connected in the form of a cable to reduce the space factor, and the entire partial discharge separation circuit is hermetically sealed with a grounded metal sheath to avoid induced noise.
In this case, the partial discharge separation circuit is miniaturized,
Although induced noise is removed, low-pass filters still have the disadvantage of being large and subject to induced noise, making it difficult to measure partial discharge signals.

The present invention has been made focusing on the above points,
The present invention aims to provide a method for measuring the presence or absence of partial discharge in a power cable using a shielded cable that has a low-pass filter function.

The present invention will be explained below with reference to Examples.

A power source 2 (for example,
In a method for measuring partial discharge of a power cable, in which a high voltage is applied by a DC power source, a commercial power source) and a partial discharge signal generated in the power cable insulator is measured, a high voltage side terminal 61 of the power source 2 is connected from the power source. Connect the input end of a circuit of a low-pass filter, which has the characteristics of a low-pass filter that blocks noise and is not affected by external noise due to the shielding 41b, and also has the function of a coupling capacitor to separate the high voltage of the power supply 2 and the partial discharge signal. , one end 12 of a sensor 33 disposed at the end of the power cable under test is connected to the output end of the low-pass filter circuit, and the other end 13 of the sensor is connected to the end of the conductor 1a of the power cable 1 under test. Further, the ground side terminal 71 of the power source 2, the ground side terminal of the low-pass filter circuit, and the sheath shielding layer 1b of the power cable 1 under test are connected, for example, as one element of the circuit for separating the partial discharge signal. Measure the partial discharge signal at both ends 12, 13 of the sensor 33 as follows.

That is, in FIG. 4, one terminal 12 of the pure resistor 11 is connected to the high voltage side terminal of the low-pass filter circuit, and the other terminal 13 is connected to the conductor 1a of the power cable 1 under test. An amplifier 17 is connected to the terminals 12 and 13 via a voltage dividing capacitor 16, and an electrical and optical converter 19 connected to the output terminal of the amplifier and its input terminal generates electricity in the power cable insulation under test. The electrical signal of the partial discharge signal is converted into an optical signal and further sent to the optical fiber 18. The optical signal transmitted by the optical fiber 18 is converted by a monitor 21 into an electrical signal corresponding to the electrical signal of the partial discharge, and the electrical signal is measured by an oscilloscope 22.

When a partial discharge signal is extracted from both ends of the sensor, the voltage dividing capacitor 16 is used for electrical protection of the circuit including the amplifier 17 and the electrical/optical converter 19, and the capacitor 16 shares the transient voltage to prevent damage to each circuit. are doing.

Furthermore, sensors including amplifiers do not necessarily need to convert the partial discharge signal into an optical signal; for example, it may be converted into electromagnetic waves, and the partial discharge signal can be measured by taking measures to sufficiently electrically insulate the measurement circuit. good. Note that the sensor is installed near a cable head 91 that is gas insulated (for example, SF ₆ ).

It has the characteristics of a low-pass filter that blocks noise from the power supply and does not receive external noise due to the shield 41b.
Furthermore, it also functions as a coupling capacitor that separates the high voltage of the power supply and partial discharge. The low-pass filter cable 41, which is an embodiment of the low-pass filter circuit, is made of a magnetic material with good flexibility (for example, ferrite powder mixed with rubber and extruded with an extruder, as shown in FIGS. 3 and 5 a). )
It has a structure in which an insulator 8 is provided on a coiled conductor 41a which may be covered with a semiconductor tape 7 as a shield which may have a shielding layer 41b thereon, and a shielding layer 41b is provided thereon. Moreover, the sheath 41b,
It may be provided.

The low-pass filter circuit has the characteristics of blocking and shielding the noise from the power supply by the characteristics of the low-pass filter, thereby preventing external noise from being received, and at the same time separating the high voltage of the power supply and the partial discharge signal. However, the low-pass filter circuit may be constructed by connecting the low-pass filter 41 and the coupling capacitor cable 43 as follows.

The coupling capacitor cable 43 has a conductor 43a provided with an insulator 8', a shield layer 43b provided thereon, and a sheath 43b' provided thereon, as shown in FIG. 3B, for example.

Note that in order to increase the capacitance corresponding to the capacitor 411c of the low-pass filter circuit shown in FIG. 1, the diameter of the conductor 43a is made as large as possible.
Further, the coupling capacitor cable may be composed of power cables of other phases arranged in parallel.

In the method of the present invention described above, the low-pass filter circuit of the conventional partial discharge signal measurement circuit is made into a cable, and the measurement circuits are connected in the form of a cable, so that the measurement circuit path becomes small and the electrostatic induction・There is no electromagnetic noise, and there is no need for a large and expensive shield room.

[Brief explanation of drawings]

Figure 1 is an explanatory diagram of the conventional partial discharge measurement method;
FIG. 2 is a diagram illustrating an embodiment of the method of the present invention;
FIG. 3 is a vertical sectional view of a low-pass filter cable which is an embodiment of the low-pass filter circuit used in the method of the present invention, and FIG. 4 is a vertical sectional view of an embodiment of the sensor of the partial discharge separation circuit used in the method of the present invention. The block diagram and FIGS. 5a and 5b are cross-sectional views of a low-pass filter cable and a coupling capacitor cable used in another embodiment of the present invention. 1... Power cable under test, 1a... Conductor of power cable under test, 1b... Sheath shielding layer, 18
...Optical fiber, 2...Power supply, 21...Monitor,
22...Oscilloscope, 3...Magnetic material, 33
...Sensor of discharge separation circuit, 41...Low pass filter cable, 42...Coupling capacitor cable, 43...Connection part, 43a...Conductor of coupling capacitor cable, 43b...Sheath shielding layer of coupling capacitor cable, 43b' ... sheath of the coupling capacitor cable, 41b ... sheath shielding layer of the low-pass filter cable, 41b' ... sheath of the low-pass filter cable, 61 ... high voltage side terminal, 7 ... semiconducting tape as a shielding layer of the coil, 71... Earth side terminal of power supply, 8... Insulator of low pass filter cable, 8'... Insulator of coupling capacitor cable, 41a... Conductor of low pass filter cable, 91... Gas insulated cable head, 11 ...Pure resistance, 12, 13...
...Terminal, 17...Amplifier, 19...Electric/optical converter, 16...Voltage dividing capacitor.

Claims (1)

[Claims] 1. Partial discharge measurement of a power cable, in which a high voltage is applied between the conductor of the power cable and the shielding layer through a low-pass filter circuit, and a partial discharge signal generated inside the power cable is measured. In the method,
Partial discharge of a power cable, characterized in that the circuit of the low-pass filter is constituted by a cable consisting of a coiled conductor, an insulator provided on the outer periphery of the coiled conductor, and a shielding layer provided on the outer periphery of the insulator. Measuring method. 2. A low-pass filter cable in which the cable is composed of a coiled conductor, an insulator provided on the outer periphery of the coiled conductor, and a shielding layer provided on the outer periphery of the insulator, and a low-pass filter cable in which the conductor is provided with an insulator and a shielding layer is provided on the insulator. 2. The method for measuring partial discharge of a power cable according to claim 1, wherein the power cable is connected to a coupling capacitor cable provided therein.