JPH067149B2 - Partial discharge measurement method - Google Patents

Description

The present invention relates to a method for measuring partial discharge of an electrode 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 metal sheath of the power cable 1 laid in the ground is grounded, and is connected to the high-voltage charging terminal 3 via a terminal connecting portion 2. A blocking coil 4 is provided between the terminal connection portion 2 and the high-voltage charging terminal 3, and the blocking coil 4 is provided.
A coupling capacitor 5 is connected to the power cable 1 side of the. The coupling capacitor 5 is grounded via a detection impedance 6, the detection impedance 6 is connected to a high pass filter 7, and the high pass filter 7 is connected to an attenuator 8. The attenuator 8 is connected to the amplifier 9, and the amplifier 9 is connected to the signal memory processing unit 10.

In the above-described configuration, an AC high voltage (for example, 275 KV) is applied to the high voltage charging terminal 3 to bring the underground power transmission line configured by the power cable 1 into a live state. 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. High frequency pulse of conductor is blocking coil 4
Is blocked by the electric current and flows through the detection impedance 6 through the coupling capacitor 5 together with the current based on the AC applied voltage, and a potential difference is generated across the detection impedance 6. The high-pass component of the signal based on the potential difference passes through the high-pass filter 7 and is attenuated to a predetermined level by the attenuator 8. The subsequent signal is amplified by the amplifier 9 and input to the signal memory processing unit 10, where it undergoes predetermined signal processing. In this signal processing, the partial discharge is measured by detecting the size of the high-frequency pulse and the number of high-frequency pulses per unit time, and the insulation deterioration of the power cable 1 is diagnosed.

[Problems to be Solved by the Invention]

However, according to the conventional partial discharge measuring method, the high frequency pulse measuring circuit in the signal memory processing unit has only a certain frequency band, whereas the high frequency pulse is 100
It is distributed over a wide band above 0 MHz. Therefore,
Since the measurement cannot be performed over the entire band in which the high-frequency pulse is distributed, the measurement accuracy decreases. Further, if the level of the high-frequency pulse based on the partial discharge is small, it may be masked by noise invading from the outside, noise of the amplifier itself, and the like, which may make it difficult to measure the partial discharge.
Further, the generation cycle of the partial discharge pulse is not constant, and further,
When the AC voltage is applied, the high-frequency pulse changes its polarity between positive and negative depending on the cycle of the AC voltage. Therefore, if the high-frequency pulse is averaged over several cycles, the output becomes zero and the partial discharge cannot be measured. There is.

Therefore, an object of the present invention is to provide a partial discharge measuring method capable of measuring over the entire band in which high frequency pulses based on partial discharge are distributed.

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

[Means for Solving the Problems]

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

Here, when the frequency sweep period is T, nT (n =
The measurement accuracy is improved by performing the measurement over the time of 1, 2, 3 ..., And calculating the average value by dividing the measurement result by n.

[Action]

The high frequency pulse due to the partial discharge in the insulator is distributed over a wide band. The detectable band of the intermediate frequency signal (beat signal) obtained by mixing the high-frequency pulse with the local oscillation signal swept over a predetermined frequency width at a predetermined cycle is the frequency of the high-frequency pulse according to the sweep frequency of the local oscillation signal. The band will be swept in the same cycle. Generally, the detection band of the detection means is narrower than the distribution band of high frequency pulses. However, by generating an intermediate frequency signal between the high frequency pulse and the swept local oscillation frequency, it becomes possible to perform measurement over a wide band of the high frequency pulse.

〔Example〕

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

FIG. 1 (a) shows an embodiment of the present invention, and the portions common to FIG. 3 are shown by common reference numerals, and thus duplicated description will be omitted, but the following configuration is added to the configuration of FIG. Has been added. That is, the output of the amplifier 9 is a frequency sweep type local oscillator.
Connected with the output of 15 to a mixer 11, which is connected to an amplifier 12 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 detection signal. The A / D conversion circuit 14 is connected to a signal memory processing unit (having a memory that stores a digital signal and processing the digital signal) 10. The signal memory processing unit 10 controls the control unit 17
It is connected to the. The local oscillator 15, the display unit 16, the signal memory processing unit 10, and the like are controlled by the control unit 17. The local oscillator 15 outputs a local oscillation signal having a frequency that changes in a cycle T, as shown in FIG.

The operation of the present invention will be described below.

A high-frequency pulse based on partial discharge that appears as a potential difference across the detection impedance 6 passes through the high-pass filter 7 (low-pass component and direct-current component are cut) and is attenuated to a predetermined level by the attenuator 8. The output of the attenuator 8 is amplified by the amplifier 9, and the mixer 11 generates a local oscillation signal from the local oscillator 15 (for example, a signal whose frequency changes linearly with time as shown in FIG. 1 (b)). But not limited to this). An intermediate frequency signal (beat signal) is output by this mixing in the mixer 11, and the amplifier
After being amplified by 12, it is detected by the detection circuit 13. Since the local oscillation signal is swept in frequency, this detection signal corresponds to a high frequency pulse in a frequency band corresponding to the sweep width, and this is converted into a digital signal by the A / D conversion circuit 14. The digital signal is processed by the signal memory processing unit 10, and the partial discharge is determined based on the size and the number per unit time. The measurement result is displayed on the display 16
Is displayed in.

Here, while sweeping the frequency at the cycle T, the partial discharge is measured n times over the time nT, the measurement results of each time are added by the signal memory processing unit 10, and the added value is divided by n to obtain the average value. Can be calculated. The level of random noise is It is known to decay to. For example, if n = 10 ⁴ , the random noise level is Becomes Therefore, it is 1/10 compared to when averaging is not performed.
It is possible to measure up to 0 level partial discharge.

FIG. 2 (a) is a frequency spectrum of the high frequency pulse based on the partial discharge thus measured. On the other hand, FIG. 2 (b) is a frequency spectrum measured in a state where no line voltage is applied to the high voltage charging terminal 3 (that is, a state in which there is no partial discharge and only noise is present). Fig. 1
As shown in (b), by sweeping the local oscillation signal ₁ from 0 to a certain frequency, the intermediate frequency signal _n (= _s to ₁ ) of a predetermined frequency is changed to the frequency _{s of} the high frequency pulse.
Can be obtained for the entire band (0 to 2000 MHz).

As is clear from the frequency spectrum in Fig. 2 (b),
Noise with a large continuous periodicity of UHF television broadcasting is mixed in the vicinity of about 700 MHz. As is clear from the comparison between FIGS. 2 (a) and 2 (b), it is understood that partial discharge occurs up to about 1000 MHz, and a level difference of about 0.5 scale is detected in the vicinity of 1000 MHz.

〔The invention's effect〕

As described above, according to the partial discharge measuring method of the present invention, the high frequency pulse signal based on the partial discharge and the local oscillation signal output from the frequency sweep type local oscillator are mixed to generate an intermediate frequency signal. The partial discharge is measured by detecting the signal, and if necessary, the partial discharge is determined by averaging the measurement results of n times. Therefore, the following effects can be obtained.

(1) Measurement is possible in the entire band of high frequency pulse based on partial discharge.

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

(3) The accuracy can be further improved by averaging the measurement results of n times.

(4) Partial discharge that occurs randomly with respect to time can be accurately measured.

(5) Partial discharge deteriorates the insulator and shortens the life, but the initial partial discharge has a small level and a small number. Even in such a state, the measurement can be performed, so that the time margin until the processing becomes long and the measure can be easily taken.

[Brief description of drawings]

1 (a) and 1 (b) show one embodiment of the present invention, (a) is a block diagram, (b) is an explanatory view showing frequency sweep characteristics of a local oscillator, and FIGS. 2 (a) and (a). b) is an explanatory diagram showing the results of measuring partial discharge and noise, and FIG. 3 is a block diagram showing a conventional partial discharge measuring method. Explanation of reference numerals 1 ... Power cable, 2 ... Termination connection part 3 ... High-voltage charging terminal 4 ... Blocking coil 5 ... Coupling capacitor 6 ... Detection impedance 7 ... High-pass filter 8 ... Attenuator , 9, 12 …… Amplifier 10 …… Signal memory processing section 11 …… Mixer 13 …… Detection circuit 14 …… A / D conversion circuit, 15 …… Local oscillator 16 …… Display section, 17 …… Control section

Claims (2)

[Claims] 1. A partial discharge measuring method for diagnosing deterioration of an insulator by measuring partial discharge in an insulator to which a high voltage is applied, wherein a high frequency pulse signal based on the partial discharge has a frequency at a predetermined cycle. A partial discharge measuring method comprising: mixing a swept local oscillation signal to generate an intermediate frequency signal; detecting the intermediate frequency signal to measure the partial discharge. 2. The partial discharge is measured by measuring the partial discharge over n cycles (n = 1, 2, 3, ...), and averaging the measurement results of the n times to measure the partial discharge. Partial discharge measurement method described.