JPH02176579A - Measurement of partial electric discharge - Google Patents

Abstract

PURPOSE:To improve measurement sensitivity by measuring a partial electric discharge in the manner of detecting an intermediate frequency signal which is produced by mixing a signal having the frequency swept at a specified cycle to a high frequency pulse signal based on the partial discharge. CONSTITUTION:The high frequency pulse based on the partial discharge appeared as a potential difference on both ends of detection impedance 6 is attenuated to a specified level in an attenuator 8 after passing through a high- pass filter 7. An output of the attenuator 8 is amplified in an amplifier 9 and mixed with a local oscillating signal coming from a local oscillator 15 by a mixing device 11. As a result, the intermediate frequency signal (beat signal) is outputted and detected 13 after amplified by the amplifier 12. Since the frequency of the local oscillating signal in the detected signal is being swept, this detected signal is the one corresponding to the high frequency pulse with the frequency range corresponding to the sweeping width, and converted to a digital signal in an A/D conversion circuit 14. This digital signal is processed in a signal memory processing part 10, and a decision of the partial discharge is made by the size and the quantity per unit time then displayed 16.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a method for measuring partial discharge in a power cable or the like in which a high voltage is applied to an insulator.

[Conventional technology]

FIG. 3 shows a conventional partial discharge measuring method. A power cable 1 laid underground has a metal sheath grounded and is connected to a high voltage charging terminal 3 via a terminal connection part 2. A blocking coil 4 is provided between the terminal connection portion 2 and the high voltage charging terminal 3, and a coupling capacitor 5 is connected to the power cable 1 side of the blocking coil 4. The coupling capacitor 5 is grounded via a detection impedance 6 , the detection impedance 6 is connected to a high-pass filter, and the high-pass filter 7 is connected to an attenuator 8 . The attenuator 8 is connected to an amplifier 9, and the amplifier 9 is connected to a signal memory processing section 10.

In the above configuration, the high voltage charging terminal 3 is connected to the AC high voltage (
For example, 275 KV) is applied to make the underground power transmission line constituted by the power cable 1 live. When a partial discharge occurs in the insulator of the power cable 1 in this state, a high frequency pulse is induced between the conductor of the power cable 1 and the metal sheath. The high frequency pulse of the conductor is blocked by the blocking coil 4 and flows through the detection impedance 6 via the coupling capacitor 5 together with a current based on the alternating current applied voltage, and a potential difference is generated across the impedance. A high-frequency component of the signal based on the potential difference passes through a high-pass filter 7 and is attenuated by an attenuator 8 to a predetermined level. The subsequent signal is amplified by an amplifier 9, and a signal memory processing section 10
, where it undergoes predetermined signal processing. In this signal processing, partial discharge is measured by detecting the magnitude of high-frequency pulses and the number of high-frequency pulses per unit time, and insulation deterioration of the power cable 1 is diagnosed.

[Problem to be solved by the invention]

However, according to the conventional partial discharge measurement method, if the level of the high-frequency pulse based on partial discharge is small, it will be masked by noise entering from the outside and the noise of the amplifier itself, making it difficult to measure partial discharge. There is. In addition, the generation period of partial discharge pulses is not constant,
Furthermore, when AC voltage is applied, the high-frequency pulse changes polarity between positive and negative depending on the cycle of the AC voltage, so if the high-frequency pulse is averaged over several cycles, the output becomes zero and partial discharge cannot be measured. There is an inconvenience that it disappears.

Accordingly, an object of the present invention is to provide a partial discharge measuring method in which the measurement results are not easily influenced by noise entering from the outside.

Another object of the present invention is to provide a partial discharge measuring method that improves measurement sensitivity by averaging high-frequency pulses.

[Means to solve the problem]

In order to achieve the above object, the present invention generates an intermediate frequency signal (beat signal) by mixing a high frequency pulse signal based on partial discharge and a local oscillation signal output from a frequency sweep type local oscillator, and generates an intermediate frequency signal (beat signal). A partial discharge measuring method is provided for measuring partial discharge by detecting a signal.

Here, if the frequency sweep period is T, then nT (n=1
．． If the measurement is performed over a period of time of 2.3...-m---...-) and the average value is calculated by dividing the measurement result by n, the measurement accuracy will be improved.

〔Example〕

Hereinafter, the partial discharge measuring method of the present invention will be explained in detail.

FIG. 1(a) shows an embodiment of the present invention, and parts common to FIG. 3 are indicated by common reference numerals, so duplicate explanations will be omitted, but the following configuration is added to the configuration of FIG. It has been added. That is, the output of the amplifier 9 is connected to the mixer 11 together with the output of the frequency sweep type local oscillator 15, and the output of the amplifier 9 is connected to the mixer 11.
is connected to amplifier I2 for outputting an intermediate frequency signal. The amplifier 12 is connected to a detection circuit 13, and the detection circuit 13 is connected to an A/D conversion circuit 14 that A/D converts the detected signal.
It is connected to the. The A/D conversion circuit 14 is connected to a signal memory processing section (having a memory for storing digital signals and performing arithmetic processing on the digital signals) lO, and the signal memory processing section 10 is connected to the control section 17. Local oscillator I5, display section 16, signal memory processing section 10, etc. are controlled by control section 17. The local oscillator 15 outputs a local oscillation signal having a frequency that changes with a period T, for example, as shown in FIG. 1(b).

The present invention will be explained in detail below.

A high frequency pulse based on a partial discharge appearing as a potential difference between both ends of the detection impedance 6 passes through a band pass filter 7 (low frequency components and DC components are cut), and is attenuated to a predetermined level by an attenuator 8. The output of the attenuator 8 is amplified by the amplifier 9, and the mixer 1 generates a local oscillation signal from the local oscillator 15 (for example, as shown in FIG. 1 (1)), the frequency changes linearly with respect to time. Although it is a signal,
(including but not limited to). This mixing in the mixer 11 outputs an intermediate frequency signal (beat signal), which is amplified by the amplifier 12 and then detected by the detection circuit 13. Since this detection signal is a local oscillation signal whose frequency is swept, it corresponds to a high-frequency pulse in a frequency band corresponding to the sweep width, and this is the signal that is detected by the A/D conversion circuit 14.
is converted into a digital signal. The digital signal is processed by the signal memory processing section 10, and partial discharge is determined based on its magnitude and number per unit time.

The measurement results are displayed on the display section 16.

Here, partial discharge is measured once over time nT while sweeping the frequency with period T, and the measurement results of each time are added up in the signal memory processing section 10, and when the added value is divided by n, the average value is obtained. can be calculated. Through such averaging processing, the level of random noise is reduced to 1/J]
It is known that the mouth is weakened. For example, if n=10', random noise (7) L/< Luha1 /, /
TO''r=1/100 f. Therefore, it is possible to measure partial discharges up to a level of 1/100 compared to when no averaging process is performed.

FIG. 2(a) shows the frequency spectrum of the high-frequency pulse based on the partial discharge measured in this manner. If the frequency of the high-frequency pulse is fs and the frequency of the local oscillation signal is fL, then the frequency ffi of the intermediate frequency signal is determined by f, , = f, -f, and when f is constant, f is shown in Fig. 1 (
By sweeping as shown in b), a frequency spectrum f (0 to 2000 MH2') shown in FIG. 2(b) is obtained.

FIG. 2(b) shows a noise spectrum measured when no current is applied to the high voltage charging terminal 3. As is clear from the frequency spectrum, there is a U
Continuous periodic large noise from HF television broadcasting is mixed in. As is clear from the comparison of Figure 2 (al, (bl), partial discharge occurs up to about 100,100 O, and 1
It can be seen that a level difference of about 0.5 scale is detected near 00100O.

〔Effect of the invention〕

As explained above, according to the partial discharge measuring method of the present invention, a high frequency pulse signal based on partial discharge and a local oscillation signal output from a frequency sweep type local oscillator are mixed to generate an intermediate frequency signal, and this intermediate frequency Partial discharge is measured by detecting the signal, and if necessary, partial discharge is determined by averaging the results of one measurement, so that the following effects can be achieved.

(11) It is possible to obtain highly accurate measurement results that are not affected by noise entering from the outside.

(2) Accuracy can be further improved by averaging the results of one measurement.

(3) Even partial discharges that occur randomly over time can be accurately measured.

(4) Partial discharge deteriorates the insulator and shortens its lifespan, but the initial partial discharge is of low level (and the number of parts is small. Even in such a state, measurement is possible, so the process up to treatment can be You will have more time and it will be easier to take countermeasures.

[Brief explanation of the drawing]

FIGS. 1(a) and 1(bl) show an embodiment of the present invention, and (a)
) is a block diagram, (b) is an explanatory diagram showing the frequency sweep characteristics of the local oscillator, Fig. 2 (al), (bl is an explanatory diagram showing the measurement results of partial discharge and noise, and Fig. 3 is a conventional partial discharge measurement A diagram illustrating the method. Explanation of symbols 1 - - - Power cable 2 - - - - - - - One end connection part 3 - - - - - - - - - - - - - - - - - - - - - - - - ------ - High voltage charging terminal blocking coil coupling capacitor detection impedance high pass filter attenuator signal memory processing section mixer detection circuit A/D conversion circuit 15 Display section 17 9.12 Amplifier/local oscillator control section

Claims (2)

[Claims] (1) In a partial discharge measurement method for diagnosing deterioration of an insulator by measuring partial discharge in an insulator to which a high voltage is applied, the frequency is swept at a predetermined period in a high-frequency pulse signal based on the partial discharge. A partial discharge measurement measurement signal, characterized in that the partial discharge is measured by mixing signals of the partial discharge to generate an intermediate frequency signal; and detecting the intermediate frequency signal to measure the partial discharge. (2) The partial discharge is measured over n cycles (n=1, 2, 3...), and the partial discharge is measured by averaging the n measurement results. How to measure partial discharge.