JPH06317626A - Resonant partial discharge detecting device - Google Patents

Abstract

PURPOSE:To improve the S/N ratio by providing a high frequency partial discharge sensor comprising a signal detecting electrode disposed on the peripheral surface of a power cable and an inductance element connected to the electrode. CONSTITUTION:A noise removing part 1 is disposed between a high frequency partial discharge sensor 10 and a measuring device 2. The noise removing part 1 comprises plural band pass filters which are narrow band (e.g. +2.5MHz) filters and have different passing frequency bands and a switching device for putting a specified band pass filter out of the above band pass filters in its connecting state between the sensor 10 and the measuring device 2.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a resonance type partial discharge detecting device having a high frequency partial discharge sensor which is composed of electrodes arranged on the peripheral surface of a power cable and an inductance element connected to the electrodes.

[0002]

2. Description of the Related Art Conventionally, as a partial discharge detecting device for detecting a partial discharge (PD) generated in a power cable, there is a partial discharge detecting device using, for example, a tuning type detection method and a method using an AE (acoustic emission) sensor. Proposed.

As shown in FIG. 6, a tunable detection device using the tuned detection method has a terminal portion 22 of a power cable 21.
The coupling capacitor 23 and the detection impedance 24 are connected in series between the inner conductor of a or 22b and the metal shielding layer, and the potential difference generated across the detection impedance 24 is adjusted by the tuning amplifier 25 having a tuning frequency of several hundred kHz. I took it out.

However, this tunable detection device has a problem that it is difficult to detect the signal under the hot line because it is necessary to take out a signal from the inner conductor of the power cable, and a dedicated coupling capacitor is also required. . Further, since the tuning frequency in this device is several hundred kHz, it is easily affected by ambient noise, and although good detection accuracy can be obtained in an experiment in a shielded room, it is difficult to apply it to a cable after installation.

On the other hand, the detection device using the AE sensor is
Although an AE sensor detects elastic waves propagating inside the insulator by partial discharge, this device is not affected by electrical noise, but it is strong because the ultrasonic waves have straightness. It has directivity, and there is a problem that the detection sensitivity is extremely lowered depending on the detection position.

As a method for detecting partial discharges that solves these drawbacks, a metal shield layer is insulated in a connection portion of a power cable, and a potential difference generated between the two metal shield layers sandwiching the insulating portion when a partial discharge occurs is determined by measuring the potential difference between both metal shield layers. A detection method has also been proposed in which detection is performed using a detection impedance connected between shield layers (“Partial discharge test results for the Minamiikegami 275kV CV cable line”; Katsuta et al., Institute of Electrical Engineers, Insulation Material Research Material EIM-90-20). .

However, this method is limited in its application only to the connection portion where the metal shield layer is insulated, and the metal shield layer is in a non-grounded state, resulting in a lack of safety when a short-circuit accident occurs. There is. In addition, there is a drawback that the device becomes large and requires skill in measurement.

Therefore, the inventors of the present application have proposed a resonance having a sensor (high frequency partial discharge sensor) composed of an electrode disposed on an insulating coating layer (sheath) of a power cable and an inductance connected to this electrode. A type partial discharge detection device was proposed (Japanese Patent Application No. 2-310197).

FIG. 7 is a sectional view showing a sensor portion of this resonance type partial discharge detection device.

On the outer circumference of the power cable 21, an electrode 31 formed of a conductive paint or a metal tape is provided over the entire circumference. The electrode 31 includes an insulating cylinder 33a attached to the power cable 21, a brass cylinder 33b arranged on the outer circumference of the insulating cylinder 33a, and a lead tape 34 covering the outer circumference.
It is housed in a shield container formed by.
A coaxial connector 35 such as a BNC connector is attached to the brass tube 33b.
A coil 32 as an inductance element is connected between the inner conductor of the electrode and the electrode 31. The shield container is connected to the ground wire to which the metal shield layer of the power cable 21 is connected.

The power cable 21 to be detected is, for example, a 275 kV CV cable, and the inner conductor 36, the inner semiconductive layer 37, and the cable insulator (XLPE:
cross-linked polyethylene) 3
8. A metal shielding layer 39 as an outer metal layer and a plastic sheath 40 as a coating layer are coaxially arranged.

FIG. 8 is a block diagram showing the structure of a partial discharge detecting device using this high frequency partial discharge sensor.
This apparatus includes a sensor 30 having the above-described structure, a wide band amplifier 41 that amplifies the output of the sensor 30, and a digitizing oscilloscope 42 that performs signal processing such as averaging on the output of the wide band amplifier 41. Has been done.

A plurality of power cables 21 are connected to each other via connecting portions 43a and 43b so as to have a predetermined length, and inner conductors 36 of terminal portions 44a and 44b thereof are connected to a high voltage power supply line 45. In addition, the metal shield layer 39 of the power cable 21 includes the end portions 44a and 44b and the connecting portion 43.
It is properly grounded at a, 43b and the like.

Next, the operation of the partial discharge detection device constructed as described above will be described.

The equivalent circuit of the power cable 21 is generally considered as a circuit as shown in FIG. That is, the ground lines of the inner conductor 36, the metal shielding layer 39, the terminal ends 44a and 44b, and the connecting portions 43a and 43b form an RL series circuit. The inner conductor 36 and the metal shielding layer 39 are capacitively coupled via a cable insulator 38 interposed therebetween. Further, the detection unit D is composed of the coupling capacitance determined by the electrode 31 of the sensor 30 and the plastic sheath 40 of the power cable 21, the inductance of the coil 32 provided in series with this capacitance, and the input impedance of the measuring instrument. Composed. The coupling capacity of the electrode 31 can be adjusted by, for example, the length of the electrode 31 in the cable longitudinal direction.

When a partial discharge occurs in the cable insulator 38, the pulsating current generated by the partial discharge is i2 in the figure.
, I2 ′, ... and the coaxial modes i1 and i1 in FIG.
.., i3, i3 ', ... Propagate separately in the earth return mode. As a result, the detection section D has i1 + i
Since the current indicated by 1'flows, the sensor 30 detects this current.

In the partial discharge detection device thus constructed, the metal shield layer 3 of the electrode 31 and the power cable 21 is used.
The coupling capacitance formed by 9 and the high frequency resonance circuit formed by the coil 32 detect a signal in a predetermined band of a traveling wave in a wide band generated by partial discharge.

This resonance type partial discharge detection device has the advantages that the sensor can be easily installed on the power cable, the safety is high, and the partial discharge can be detected in a live state.

[0019]

However, the above-mentioned resonance type partial discharge detection device has the following problems. That is, the resonance type partial discharge detection device described above is an LC series filter including a coupling capacitance C between the electrode coated on the cable anticorrosion layer and the cable shielding layer, and an inductance L connected in series thereto. By the action, the signal of a specific frequency component of the signal based on the partial discharge is detected. As shown in FIG. 10, the function of this LC serial filter has a gain of 1/2 at frequencies 0.8 and 1.2 times the center frequency f0. However, since the gain is not 0 when the frequency is less than 0.8f0 and exceeds 1.2f0, noise components other than the signal due to partial discharge are also input to the measuring instrument. Since the partial discharge sensor shown in FIG. 7 is a kind of fixed filter, f
If there is a noise component near 0, the S / N ratio will drop significantly.

The present invention has been made in view of the above problems, and it reduces noise input to a measuring instrument and increases the S value.
It is an object of the present invention to provide a resonance type partial discharge detection device capable of obtaining the / N ratio.

[0021]

A resonance type partial discharge detection device according to the present invention comprises a signal detection electrode disposed on the peripheral surface of a power cable and an inductance element connected to the signal detection electrode. A high-frequency partial discharge sensor, a noise removal unit that passes a specific frequency component of the signal output from the high-frequency partial discharge sensor, and a measuring device that processes the signal given through the noise removal unit. The noise removing unit selectively connects a plurality of bandpass filters having different pass frequency bands and a specific filter of the bandpass filters between the high frequency partial discharge sensor and the measuring instrument. And a switching means for performing the switching.

[0022]

According to the present invention, the noise eliminator is provided between the partial discharge sensor and the measuring device, and only the signal in the specific frequency band of the signals output from the partial discharge sensor is input to the measuring device. To do. The noise removal unit, a plurality of band pass filters different in pass frequency band from each other,
The switching means selectively connects a specific one of these bandpass filters between the sensor and the measuring instrument. The band pass filter has a narrow pass band of ± 2.5 MHz, for example, and passes a signal in a band having a small noise component among the signals output from the partial discharge sensor. Therefore, the noise component is significantly reduced as compared with the case without the bandpass filter, and as a result, the S / N ratio is improved.

If the frequency band of the main component of noise is constant, only one bandpass filter having a constant pass frequency band needs to be provided between the sensor and the measuring instrument. However, since the frequency band of the main component of noise propagating through the power cable may be different between daytime and nighttime, if there is only one bandpass filter, a high S / N ratio and high sensitivity measurement can be performed during the daytime. Even if it is possible, at night, it becomes difficult to discriminate between noise and signals due to partial discharge, and the sensor's original measurement sensitivity may not be obtained. Therefore, in the present invention, as described above, a plurality of bandpass filters having mutually different pass frequency bands are prepared, and the bandpass filter of the noise removing unit is appropriately changed by the switching means according to the frequency band of the main component of noise. Be able to switch.
As a result, the measurement frequency can be adjusted according to the environment, and the partial discharge can always be detected with a good S / N ratio.

[0024]

Embodiments of the present invention will now be described with reference to the accompanying drawings.

FIG. 1 is a schematic diagram showing a resonance type partial discharge detection device according to an embodiment of the present invention.

The present embodiment is different from the conventional one in that the noise removing unit 1 is provided between the sensor 10 and the measuring instrument 2, and the other structure is basically the same as the conventional one.

That is, the partial discharge sensor 10 is mounted on the power cable 11. This partial discharge sensor 10 is the same as the sensor shown in FIG.
The electrode is attached to the peripheral surface of the coil, a coil (not shown) connected to the electrode, and a shield container that houses the electrode and the coil. This sensor 10
The output of is input to the measuring device 2 via the noise removing unit 1. The noise eliminator 1 electrically connects between the sensor 10 and the measuring device 2 by selecting a plurality of bandpass filters having different pass frequency bands from each other and selecting a specific one of these bandpass filters. And a switching device.

Each bandpass filter constituting the noise removing section 1 has a narrow band (for example, ± 2.5 MHz or less), and the bands are different from each other. FIG. 2 is a graph showing an example of band characteristics of a bandpass filter with the horizontal axis representing frequency and the vertical axis representing gain, and FIGS. 3A and 3B.
FIG. 6 is a graph showing a specific characteristic example of a bandpass filter. The bandpass filter shown in FIG. 3A has a peak frequency of 20 MHz and a cutoff frequency of (20 ±
2.5) MHz. The peak frequency of the bandpass filter shown in FIG. 3B is 25 MHz, and the cutoff frequency is (25 ± 2.5) MHz. The noise component of the signal output from the sensor 10 is removed by the narrow band pass filter in this way, and the measurement device 2
Given to.

FIG. 4 is a waveform diagram showing a signal applied to the measuring instrument via the bandpass filter, and FIG. 5 is a waveform showing a signal applied to the measuring instrument in the conventional partial discharge detecting device without the bandpass filter. It is a figure. As is clear from FIGS. 4 and 5, the S / N ratio can be remarkably improved by providing the bandpass filter between the sensor and the measuring device.

In the present embodiment, the output of the sensor is passed through a noise removing section provided with a plurality of band pass filters having different band characteristics to remove noise components and then input to the measuring instrument. For this reason, the signal input to the measuring device has a very small noise component, and the S / N ratio is remarkably improved as compared with the conventional case. Further, the noise eliminator is provided with a switch so that the plurality of band pass filters can be switched according to the band noise component and an optimum band pass filter can be selected and used. Therefore, the resonance type partial discharge detection apparatus according to the present embodiment is extremely useful for measurement in a situation where the band of the noise component is unstable in the actual line or the like.

[0031]

As described above, the resonance type partial discharge detection apparatus according to the present invention includes a plurality of band pass filters having different pass frequency bands between the sensor and the measuring instrument, and these band pass filters. Since a noise removing unit configured by a switching unit that selectively connects a specific one of the above to the sensor and the measuring instrument is provided, the noise component is effectively removed according to the operating environment. Thus, the partial discharge generated in the power cable can be detected with high sensitivity and high S / N ratio.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing a resonance type partial discharge detection device according to an embodiment of the present invention.

FIG. 2 is a graph showing an example of characteristics of a bandpass filter.

3A and 3B are graphs showing the characteristics of a bandpass filter.

FIG. 4 is a waveform diagram showing an example of a partial discharge signal given to a measuring instrument through a bandpass filter.

FIG. 5 is a waveform diagram showing an example of a partial discharge signal given to the measuring instrument when there is no bandpass filter.

FIG. 6 is a block diagram showing a conventional tunable partial discharge detection device.

FIG. 7 is a cross-sectional view showing a sensor section of a resonance type partial discharge detection device.

FIG. 8 is a block diagram showing a configuration of a conventional resonance type partial discharge detection device.

FIG. 9 is an equivalent circuit diagram of a power cable and a detection system.

FIG. 10 is a graph showing the output characteristics of the partial discharge sensor.

[Explanation of symbols]

 1; Noise removing unit 2; Measuring device 10, 30; High frequency partial discharge sensor 11, 21; Power cable 31; Electrode 32; Coil 36; Inner conductor 39; Metal shielding layer 40; Sheath

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Yasuhiro Takahashi 1-5-1 Kiba, Koto-ku, Tokyo Fujikura Ltd. (72) Inventor Masayuki Tan 1-5-1 Kiba, Koto-ku, Tokyo Shareholders Inside Fujikura

Claims (1)

[Claims] 1. A high frequency partial discharge sensor comprising a signal detection electrode arranged on the peripheral surface of a power cable and an inductance element connected to the signal detection electrode,
The noise removal unit includes a noise removal unit that allows a specific frequency component of the signal output from the high-frequency partial discharge sensor to pass through, and a measuring device that processes the signal provided via the noise removal unit. It is composed of a plurality of bandpass filters having mutually different pass frequency bands and switching means for selectively connecting a specific filter of these bandpass filters between the high frequency partial discharge sensor and the measuring instrument. A resonance type partial discharge detection device characterized in that