JPH04140673A - Partial discharge detection device - Google Patents

Abstract

PURPOSE:To enable PD pulse and noise to be identified easily by observing an output of detection means which resonates due to high-frequency constituents included in a partial discharge (PD) pulse further through a spectrum analyzer. CONSTITUTION:When a piezoelectric sensor 6 receives a PD pulse, influence of noise constituents can be fully excluded if the high-fequecy constituents included in 1t range from 5 MHz to 60 MHz, thus enabling the PD pulse to be detected with a high sensitivity. On the other hand, noise with high-frequency constituents are mixed abruptly, the output appears from the sensor 6. However, since the output of the sensor 6 is further supplied to a spectrum analyzer 8, an abrupt noise will not appear as a spectrum. On the other hand, once the PD occurs, it occurs continuously and the frequency increases before a power cable 1 breaks down. Therefore, the PD pulse is displayed on the analyzer 8 and is observed, thus enabling the PD pulse and other noises to be clearly identified simply by observing them as a spectrum on the analyzer 8.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention is directed to a partial discharge that occurs inside an insulator of a power cable and at an insulator-conductor interface.
The present invention relates to a partial discharge detection device that detects arge; PD).

[Prior art] Conventionally, a P
As the D detection device, a tunable detection method and a method using an AE (acoustic emission) sensor have been proposed.

A tuned detection device connects a coupling capacitor and a detection impedance in series between the internal conductor at the end of a power cable and a metal shielding layer, and tunes the potential difference generated across the detection impedance to a frequency of several hundred kHz. It is designed to be extracted by a tuned amplifier with a frequency.

However, this tunable detection device has problems in that it is difficult to measure under live wires because it is necessary to extract the signal from the internal conductor, and a dedicated coupling capacitor is also required. Moreover, the tuning frequency in this device is several hundred kilohertz.
z, it is easily affected by surrounding noise, and although good detection accuracy can be obtained in a shielded room, it is difficult to apply to cables after installation.

Additionally, a device using an AE sensor uses the AE sensor to detect elastic waves propagating inside an insulator due to partial discharge, but while this device does not receive electrical noise, it does not receive ultrasonic waves. Since it has a straight-line property, it has strong directivity, and there is a problem that detection sensitivity is extremely reduced depending on the position.

Therefore, a high-bandwidth PD detection method has been proposed as one of the tunable detection methods to solve these drawbacks. That is, when frequency analysis of partial discharge pulses and ambient noise is performed, several M
It is known that around Hz, the level of ambient noise is very low and only the frequency component of the partial discharge pulse is detected. The multi-band PD@output method focuses on this point and detects frequency components of 5 MHz to 80 MHz of the partial discharge pulse using a high band tuning circuit.

[Problems to be Solved by the Invention] By the way, when this type of PD detection device is applied to a power cable monitoring system in a live line state, when an operator
A system is needed that can easily distinguish between D-pulses and noise.

However, in the conventional high-band PD detection method described above,
There is a problem in that when noise with high frequency components suddenly enters, it is not easy to distinguish between this and the PD pulse.

The present invention has been made in view of such problems, and an object of the present invention is to provide a partial discharge detection device that can easily distinguish between partial discharge pulses and noise.

[Means for Solving the Problems] A partial discharge detection device according to the present invention is installed on a corrosion protection layer of a power cable or a coating layer such as a plastic source, and detects a partial discharge generated inside the power cable by a partial discharge pulse and a metal sheath or It has a detection means that receives a high frequency component of a signal propagating through an outer metal layer such as a metal shielding layer through the coating layer and resonates with the high frequency component, and a spectrum analyzer that outputs a spectrum of the output of the detection means. It is characterized by

[Function] According to the present invention, when the detection means receives a partial discharge pulse, the detection means resonates with a specific high frequency component included in the partial discharge pulse, and amplifies and outputs only the signal of the high frequency component. Here, the above high frequency component is 5MHz
When the frequency is between 60 MHz and 60 MHz, the influence of noise components is sufficiently eliminated, and partial discharge pulses can be detected with high sensitivity.

On the other hand, if noise with high frequency components suddenly enters the
Although an output appears from the detection means, in the present invention, the output of the detection means is further supplied to a spectrum analyzer, so that sudden noise does not appear as a spectrum.

On the other hand, once a partial discharge occurs, it occurs continuously, and its frequency increases before the object to be monitored is destroyed. Therefore, this PD pulse will be displayed and observed on the spectrum analyzer.

Therefore, according to the present invention, P
D-pulses and other noise can be clearly distinguished, and the burden on workers performing monitoring work can be reduced.

It is also possible to store the patterns on the screen of the spectrum analyzer in a computer and construct an automatic insulation diagnosis system using pattern recognition technology.

[Embodiments] Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.

FIG. 1 is a block diagram showing the configuration of a partial discharge detection device according to a first embodiment of the present invention.

This device includes a sensor 6 attached to a power cable 1 to detect partial discharge, a wideband amplifier 7 that amplifies the output of this sensor 6, and a spectrum analyzer 8 that displays the spectrum of the output of this wideband amplifier 7. It is configured.

The power cable 1 to be detected is, for example, a 275 kV Cv cable, and as shown in FIG.
internal semiconducting layer 12, cable insulator (XLPE) 13,
A metal shielding layer 14 as an outer metal layer and a plastic source 15 as a covering layer are coaxially arranged in this order from the center. As shown in FIG.
A plurality of terminals 2 a + 2 are connected via b.
The internal conductor 11 of b is connected to the high voltage power supply line 3. Moreover, the metal shielding layer 1 of this power cable 1
4 is the terminal part 2 a + 2 b and the connecting part 4 a + 4 b
etc., and are appropriately grounded.

Sensor 6 connects plastic source 15 of power cable 1
attached to the outer periphery of the An example of this sensor 8 is shown in FIG. That is, the metal shield case 21 has an opening formed on one side thereof. This opening is closed by an insulating plate 22 made of alumina or the like. A piezoelectric element 23 having an electrode 24 formed on one side by vapor deposition is housed inside the shield case 21 . The piezoelectric element 23 is
The surface opposite to the electrode forming surface is closely fixed to the insulating plate 22. This piezoelectric element 23 is made of, for example, lead zirconate titanate (PZT), and together with the plastic source 15 of the power cable 1, has a capacitance of about 500 pF and high frequency filter characteristics of 10 MHz or more. The electrode 24 of this piezoelectric element 23 is connected via a lead wire 25 to an internal conductor of a coaxial connector 26 attached to the shield case 2.

Next, the operation of the partial discharge detection device according to this embodiment configured as described above will be explained.

Now, it is common to think that the equivalent circuit of the power cable 1 is as shown in FIG. That is, the inner conductor 11,
Metal shielding layer 14, termination portion 2a + 2b, and connection portion 4
The ground wires a and 4b form an RL series circuit. Internal conductor 1
1 and the metal shielding layer 14 are coupled through the capacitance of the cable insulator 13 interposed between them. Further, the detection section is composed of a combined capacitance of the sensor 6 and the plastic source 15, and an input impedance of the measuring instrument.

When a partial discharge occurs in the cable insulator 13, the resulting pulsed current is 12+j2', ·
The coaxial mode indicated by ... and 1++11 + ・ in the same figure
...+ 13+ 13'+ It propagates separately from the ground return mode shown by . As a result, a current shown as li+1% flows through the detection section, and the sensor 6 detects this current.

FIG. 5A shows the frequency response results of the measurement system using the sensor 6. However, the power cable 1 is 20 m, and the distance from the discharge point and grounding point to the sensor 6 is 2 m +
It was assumed that the distance was 4m. Further, for comparison, the frequency response of the conventional tunable measurement method is shown in B in the figure. As can be seen from the figure, the high frequency component can be detected even from above the plastic source 15. For example, when a partial discharge occurs with the true discharge charge amount toopc, the high frequency component only has a frequency of about 20 MHz.
I was able to get V. The resonant frequency of the measurement system when the sensor 6 is used varies slightly depending on the power cable 1, the distance to the grounding point, etc., but can be set in the range of 30 MHz to 80 MHz.

On the other hand, considering external noise, as shown in Figure 5, the airborne noise area N due to heaters, motors, etc.
! is distributed below 3 MHz, and the noise region N2 due to broadcast radio waves is distributed around 80 MHz and 200 MHz. Therefore, in the conventional tuning method shown in FIG.
to Ei OMHz exists in the region with the least noise and can perform good S/N measurements.

The output of this sensor 6 is amplified by a broadband amplifier 7, and then its spectrum is extracted by a spectrum analyzer 8. Measurement with the spectrum analyzer 8 is performed because the time sweep of the measuring instrument is slow, on the order of ms or S, and cannot be observed unless several signals are received during that time. Therefore, sudden noise components do not appear as a spectrum. On the other hand, partial discharges are repeated at a slow cycle immediately after occurrence, and the frequency of occurrence tends to increase just before the power cable 1 is destroyed, so that it appears as a spectrum on the spectrum analyzer 8. Therefore, it can be determined that the spectrum appearing on the spectrum analyzer 8 is due to partial discharge.

Figure 6 shows the partial discharge pulse and its frequency components, Figure 7 shows the signal appearing on the plastic source 15 and its frequency components, and Figure 8 shows the output signal of the sensor 6 and its spectrum observed with a spectrum analyzer. It is a graph figure which shows each.

External noise is superimposed on the spectrum shown in FIG. 6(b) of the partial discharge pulse shown in FIG. 6(a). Moreover, the same figure (b) on the plastic source 15 shown in FIG. 7(a)
Although the spectrum shown in ) does not include low-frequency noise, noise in the broadcast frequency band has not been removed. On the other hand, in the spectrum shown in 111(b) of the output signal of the sensor 6 shown in FIG. 8(a), only the PD pulse component from which the noise component has been removed is observed.

The monitoring worker only has to judge that a partial discharge is occurring when this pattern force is detected.
It becomes extremely easy to identify PD pulses. Furthermore, by automatically detecting this pattern, it is also possible to realize an automatic PD pulse monitoring system.

[Effects of the Invention] As described above, according to the present invention, by further observing the output of the detection means that resonates due to the high frequency component contained in the PD pulse through a spectrum analyzer,
It becomes possible to easily distinguish between PD pulses and other noise, and the effect is that monitoring work can be facilitated and automated.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a PD detection device according to a first embodiment of the present invention, FIG. 2 is a sectional view of a power cable in the same device, FIG. 3 is a sectional view of a sensor in the same device, and FIG. 4 is a sectional view of a sensor in the same device. An equivalent circuit diagram of the power cable and detection system in the device,
Figure 5 is a graph showing the frequency response characteristics of the detection system in the same device, Figure 6 is a graph showing the partial discharge pulse and its frequency components, and Figure 7 is the signal appearing on the plastic source and its frequency components. Graph, FIG. 8 is a graph showing the output signal of the sensor and the spectrum observed by the spectrum analyzer. 1: Power cable, 2a+2b; Termination part, 3: Voltage power line, 4a, 4b; Joint part, 6; Sensor, 7; Broadband amplifier, 8; Spectrum analyzer, 11; Internal conductor, 12; Internal semiconducting layer, 13 : cable insulator, 14;
metal barrier layer, 15; plastic source,

Claims (2)

[Claims] (1) The high-frequency components of the signals generated inside the power cable by partial discharge pulses that are mounted on the anti-corrosion layer or the coating layer such as the plastic source of the power cable and propagate through the outer metal layer such as the metal sheath or the metal shielding layer. A partial discharge detection device comprising: a detection means that receives through the coating layer and resonates with the high frequency component; and a spectrum analyzer that outputs a spectrum of the output of the detection means. (2) The partial discharge detection device according to claim 1, wherein the detection means comprises a piezoelectric sensor whose resonance frequency is 5 MHz to 60 MHz.