JPH0339670A - Partial discharge measuring method - Google Patents

Abstract

PURPOSE:To easily diagnose insulation with high accuracy by specifying a frequency range and fitting high impedance which has a specific value to the cross-bond line of an insulated connection part. CONSTITUTION:In an underground long channel, noises are attenuated abruptly at frequencies above an intermediate wave (up to 1.6MHz), so the frequency range is set to 1.5 - 20MHz. High-frequency iron cores 3a - 3c which provide effective impedance at a measurement frequency are fitted to the cross-bond lines of insulated connection parts 1a - 1c which have sheath insulating cylinders 2 on a long three-phase AC power cable line laid in this underground channel. Their cross-bond terminals are connected to detection impedance elements 4a - 4c through signal lead-out lead lines (a) - (c) and their outputs are amplified 5a - 5c and detected 6a - 6c independently. The signals after the detection are supplied to a judgement circuit 7 to decide noises and outputted 8 only when judged to be partial discharge signals.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a partial discharge measuring method for diagnosing insulation deterioration of electric cables, etc., and particularly relates to a partial discharge measuring method for diagnosing insulation deterioration of electric cables, etc. This invention relates to a partial discharge measurement method that allows highly accurate insulation diagnosis of cable lines.

[Background technology]

As a conventional partial discharge measuring method, there is a method shown in FIG. 4, for example. The power cable lO is connected by an intermediate connection 11 and is connected to a high voltage charging part 13 via a terminal connection 12. The sheaths of the intermediate connection 11 and the end connection 12 are grounded via a ground conductor 14.15. Here, when measuring the partial discharge of the insulator of the power cable 10, remove the grounding wire 15 and insert the detection impedance 16 there.
A partial discharge measuring device 17 is connected to the terminal. Since the partial discharge of the insulator is a high frequency pulse, a potential difference is generated between both ends of the detection impedance 16 based on the high frequency pulse. This is detected by the partial discharge measuring device 17. The detected data is subjected to predetermined data processing, whereby the power cable 10
Diagnose deterioration of insulators.

According to the conventional partial discharge measurement method, it is necessary to remove the grounding wire 15, insert the detection impedance 16, and return it to the original state after the measurement is completed, which reduces the reliability of the power cable line as a system. In addition, there were problems such as system operation had to be stopped because measurements could not be taken when the line was live. As a solution to this problem, for example, patent application No. 63-3
A partial discharge measuring method shown in No. 09273 has been proposed. According to this partial discharge measuring method, a high inductance iron core is directly attached to a lead wire such as a grounding wire from the outside, and a partial discharge measuring device is connected in parallel to the lead wire to measure a partial discharge signal.

Generally, the signal due to partial discharge is O(DC) ~ 10MHz
It is said that it contains frequency components of approximately This partial discharge can be detected and detected with high sensitivity in long cable lines.
To make measurements, it is necessary to distinguish between partial discharge signals and noise that enters the measurement system through electromagnetic induction. Therefore,
■Reduce noise intrusion. ■Measure under conditions that prevent noise from entering as much as possible. ■Measures such as using logic circuits to distinguish between noise and partial discharge pulses are used for detection and measurement.

[Problem to be solved by the invention]

However, the conventional partial discharge measurement method and the
According to the partial discharge measurement method of No.-309273, ■～■
There have been problems such as it being difficult to take countermeasures and requiring the use of expensive measuring equipment. In particular, in cable lines having insulated connections, noise from other phases enters through cross-bond lines, making highly accurate measurement even more difficult.

Therefore, an object of the present invention is to provide a partial discharge measuring method that allows easy and highly accurate insulation diagnosis of a long Cv cable line.

Another object of the present invention is to provide a partial discharge measuring method for detecting partial discharge pulses in a power cable line having an insulated connection portion with high sensitivity and high accuracy.

[Means to solve the problem]

In order to achieve the above-mentioned object, the present invention installs a measuring device in an underground tunnel, sets the measurement frequency range to 1.5 to 2 [Mn2, and attaches a predetermined high frequency impedance to the cross bond wire of the insulated connection. To provide a partial electrodynamic measurement method that detects partial discharge pulse signals from both sides of a connection part, independently amplifies and detects each signal, and then compares signals from each phase to distinguish between partial discharge pulses and noise. It is something.

That is, the partial discharge measuring method of the present invention includes the following item 1.

■Frequency range 15 to 20 Mtlz The reason why the frequency range for measurement is set to 1.5 to 20 Mtlz is as follows. In long underground tunnels, medium waves (1, 6 MH2
It was found that the noise at frequencies above (up to 100%) is rapidly attenuated. On the other hand, the partial electrodynamic pulse includes pulse components up to a high frequency region. Therefore, if the partial discharge pulse is detected in a high frequency region with less noise by setting the measurement point inside the underground tunnel, the S/N ratio will be improved and high sensitivity detection will be possible.

■Installing a predetermined value of high-frequency impedance to the cross-bond wire Since the metal sheath of the insulated connection part is cross-bonded, it is also suitable for measurements of human faces, for example.

C-phase noise is mixed in. In other words, if a partial discharge occurs in the A phase, not only the A phase but also the B discharge occurs.

Even in the C phase, some amount of light is detected and measured. This makes it difficult to distinguish it from noise. So, for example,
A high frequency iron core is attached to each cross bond wire to increase the impedance of that part at high frequencies and achieve electrical isolation at high frequencies. In this way, even if a partial discharge occurs in the A phase, it will not spread to the B and C phases, making it easy to detect partial discharge pulses in each phase.

■Comparing the signals from each phase after amplification and detection In the three-phase electric cable cable line in a long underground tunnel, each single-core cable is laid almost symmetrically. Therefore, the appearance of noise is almost the same for each wire core. However, in high frequency tuning method measurements, it is difficult to cancel (differential method) considering the phase of noise in the original signal. For this reason, a comparison is made in the low frequency region where the time constant after amplification and detection is long.

〔Example〕

Hereinafter, the partial discharge measuring method of the present invention will be explained in detail with reference to FIGS. 1 to 3.

Figure 1 shows a long three-phase AC power cable installed in an underground tunnel.
Insulated connection part 1 with sheath insulation tube 2 in pull line
This shows a, lb, and lc. High-frequency iron cores 3a, 3b, and 3c are attached to each cross bond wire to provide effective impedance at the measurement frequency.

Each three-phase cross bond terminal is provided with lead wires a, b, and c for signal extraction.
, c through the detection impedance 4a.

Connected to 4b and 4c. Detection impedance 4
Signals from a+4b and 4c are each sent to a high frequency tuned amplifier (tuned frequency range 1.5-20MHz) 5a
, 5b, 5c, and the detectors 6a, 6b
, 6C. When the judgment circuit 7 receives the detected signal, it discriminates between noise and a partial discharge signal.
Output signal 8 is output only when it is determined to be a partial discharge signal.

Figures 2(a) and 2(b) are examples of ambient electromagnetic wave spectra measured near the insulated connections above ground and in underground tunnels using a dipole antenna with a length of 2 m. As shown in Figure (a), on the ground, various noises,
A wireless signal or the like is received. On the other hand, as shown in the same figure (b), the noise in the underground tunnel is rapidly attenuated above the MHz order. Broadcast waves, etc. are received, but this is mainly done through electric cables, control cables, etc. installed inside the tunnel.
This is thought to be due to ground noise being propagated through security-related cables. Of course, the spectrum shown in FIG. 2(b) is thought to vary depending on the conditions inside the tunnel, the type of installed cable, the intensity of noise, etc. In any case, it can be seen that noise is rapidly attenuated within the sinus at frequencies above the MHz order.

Next, the effects of the high frequency iron cores 3a, 3b, and 3c were investigated when a noise signal oscillator was connected to the lead L'A a in the circuit shown in FIG. 1, and reception was received through the lead C.

FIG. 3(a) shows the case without an iron core, and FIG. 3(ω) shows the case with an iron core attached. As is clear from the figure, a damping effect of 20 db or more was obtained at 5 MHz by installing the iron core. The degree of attenuation depends on the iron core material, shape, and number of iron cores, so it can be selected as necessary. Various methods for distinguishing between internal partial discharge and external noise have already been proposed. In the present invention, after amplification by high frequency tuning, the signal is detected and converted to a low frequency signal, and the low frequency signal is used for discrimination. Basically, the noise inside the tunnel is received under the same conditions for each phase of A, B, and C in the circuit shown in Figure 1, so
If the low frequency signals a, 6b, and 6c are the same, it is determined to be noise, and the output 8 from the determination circuit 7 is not generated.

That is, when the input signal from the A phase is Ia, the human input signal from the B phase is Ib, and the input signal from the C phase is Ic, if IayIb>Ic, it is determined to be noise and output 8 is not generated. here,
It is assumed that a partial discharge occurs in the C phase portion and is superimposed on noise to generate a partial discharge signal Is. In this case, each phase signal is subtracted as signal arithmetic processing.

Ia −Ib −0 Ib −(Ic +Is ) =−Is(Ic +Is
) -1a = +Is In other words, if a partial discharge occurs in a certain phase, an output is generated in the signal of the phase related to it, and it does not occur in an unrelated phase. Then, among the three signal outputs obtained by the subtraction process between the two phases, one is 0.1 is negative polarity,
One is that a positive output waveform is obtained. The determination circuit 7 determines that a partial discharge has occurred when the above-mentioned relationship is satisfied, and outputs an output signal 8 indicating the occurrence of a partial discharge. In the present invention, this subtraction processing is performed using the detected low frequency signal, so it is easier than processing using the original signal having high frequency components.

The present invention has a tuning frequency range of 1.5 to 20 MHz for measurement.
z, but of course the method of the present invention can be applied if the same effect is expected outside this range, for example. Further, depending on the arrangement of the connecting portions, the cross bond wire becomes long, and if the lead wire itself has a high impedance at high frequencies and produces an isolation effect, it is not necessary to use an iron core. Furthermore, a method for distinguishing between partial discharge pulses from connections and external noise is also available.
It goes without saying that the method is not limited to the embodiment, and other methods may be used.

〔Effect of the invention〕

As explained above, in the partial discharge measurement method of the present invention, the measurement point is set in an underground tunnel, the frequency range for measurement is 1.5 to 20 MHz, a high frequency impedance is attached to the cross bond wire of the insulated connection, Partial discharge pulse signals are detected from both sides of the insulated connection, each of which is independently amplified and detected, and the signals from each phase are compared to distinguish between partial discharge pulses and noise. Highly sensitive insulation diagnosis of ultra-high voltage long CV cable lines with
It was possible to do this with high precision.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram showing one embodiment of the present invention. Figure 2(a)
, (b) shows an example of the ambient electromagnetic wave spectrum near the ground and underground tunnel insulated connections, Figure (a) shows the ambient electromagnetic wave spectrum above ground, and Figure (b) shows the ambient electromagnetic wave spectrum in the tunnel. . FIGS. 3(a) and 3(b) are diagrams for explaining the isolation effect of the high-frequency iron core. FIG. 4 is a diagram for explaining a conventional partial discharge measuring method. Explanation of symbols 1 a, 1 b, 1 c ------Insulating connection part 2 - Sheath insulating tube 3 a
, 3 b, 3 c----------1 High frequency iron core 4 a, 4 b, 4 c-----
-Detection impedance 5a, 5b, 5c
------------High frequency tuned amplifier (tuned frequency range 1.5 to 20 MHz 6 a, 6 b, 6 c) ------- Detector 7 -------・Judgment circuit 8-・-
・−・Output signal)

Claims (1)

[Claims] (1) In a partial discharge measurement method that detects partial discharge in the insulator of a long three-phase AC power cable line and diagnoses the deterioration of the insulator, the frequency range for measurement is 1.5 to 20 MHz, and A high frequency impedance of a predetermined value is attached to the cross bond wire of the insulated connection part of the insulated connection part, a partial discharge pulse signal is detected from both sides of the insulated connection part, the signal is amplified and detected, and the signals from each phase are compared and the partial discharge pulse signal is detected. A partial discharge measuring method characterized by distinguishing between discharge pulses and noise.