JPH0750143B2 - Partial discharge position locator - Google Patents

Description

The present invention relates to a partial discharge position locator.

(Prior Art) When a voltage higher than a certain value is applied to an insulator, dielectric breakdown occurs and partial discharge occurs. Conventionally, an abrupt change in voltage or current when partial discharge occurs is measured by an electrical method,
It is widely practiced to determine the location of partial discharges.
There is also a method in which ultrasonic waves generated due to mechanical vibration generated by partial discharge are detected by a plurality of ultrasonic sensors, the time difference between them is calculated, and the position of partial discharge is calculated.

(Problems to be Solved by the Invention) However, it is difficult for the conventional electrical method to accurately measure the partial discharge in various noisy field environments, and much more, the position of the partial discharge is accurately located. This is extremely difficult. On the other hand, even with the method using the ultrasonic sensor, it is difficult to accurately select the time difference between the two ultrasonic signal waveforms by selecting the corresponding ultrasonic signal from various ambient noises, and the position of the partial discharge is located. There is a problem that it is almost impossible to do.

The present invention has been made in view of the above circumstances, and detects ultrasonic waves generated during partial discharge with a plurality of ultrasonic sensors, and obtains a cross-correlation coefficient between signal waveforms to determine the position of partial discharge. It is an object of the present invention to provide a partial discharge position locating device for locating.

(Means for Solving the Problems) In order to achieve the above object, according to the present invention, a plurality of ultrasonic sensors installed at different positions for detecting ultrasonic waves generated by partial discharge and converting them into electric signals A waveform storage device that converts the output electric signal waveform of each of the ultrasonic sensors into a digital electric signal waveform and stores the digital electric signal waveform, and reads the digital signal waveform to calculate a cross-correlation coefficient for each of the two digital signal waveforms. Partial discharge position consisting of an arithmetic unit for calculating the arrival time difference of the ultrasonic wave from the value to the ultrasonic sensor, calculating the distance difference by multiplying the arrival time difference by the ultrasonic velocity, and calculating the position of the partial discharge An orienting device is provided.

(Function) A plurality of ultrasonic sensors each detect an ultrasonic wave generated during partial discharge and convert it into an electric signal waveform, and the waveform storage device converts these analog electric signal waveforms into digital signal waveforms and stores them. The arithmetic unit reads one cycle or several cycles of each digital signal waveform, calculates the cross-correlation coefficient, finds the difference in the arrival time of ultrasonic waves to each ultrasonic sensor from the maximum value, and calculates the position of partial discharge. To do.

(Example) Hereinafter, an example of the present invention will be described in detail with reference to the accompanying drawings.

FIG. 1 is a block diagram showing an embodiment of the partial discharge position locating device of the present invention. In this embodiment, the partial discharge position locating device of the present invention comprises four ultrasonic sensors 3a, 3b, 3c, 3d, a waveform storage device 5, and a computing device 6. The four ultrasonic sensors 3a, 3b, 3c, 3d are attached at the partial discharge position of the connection portion 2 of the power cable 1, for example, at the position where it is easy to detect ultrasonic waves due to mechanical vibration associated with the partial discharge generated at 4,
The ultrasonic wave generated in the connection portion 2 is detected and output as an electric signal. The waveform storage device 5 is composed of an AD converter and a digital memory, and converts the analog electric signal waveform from the ultrasonic wave connecting portions 3a, 3b, 3c, 3d into a digital electric signal waveform,
The time of arrival of each waveform is stored in the digital memory. The arithmetic unit 6 reads the digital electric signal waveform for one cycle or several cycles stored in the waveform storage unit 5, and cross-correlation coefficient ρ _{xy (j)} (j = 0, 1, 2, ...
1) The maximum value is calculated, the arrival time difference from the partial discharge position 4 of the ultrasonic waves to the ultrasonic sensors 3a, 3b, 3c, 3d is calculated, and the position of the partial discharge in the connection portion 2 is calculated and determined.

Next, the operation of the partial discharge position locating device of the present invention will be described with reference to FIGS. 1 and 2.

FIG. 2 is a diagram showing the output waveforms x _i and y _{i of} the ultrasonic sensor and the waveform of the cross-correlation coefficient ρ _xy thereof. In general, two digital data waveforms of two time series data are calculated as x _i (i
= 1,2, ... N) and y _i (i = 1,2, ... N), the cross-correlation coefficient ρ _{xy (j)} of these two waveforms is defined by the following equation.

here, The mutual covariance coefficient R _{xy (j)} given by the equation (2) indicates the similarity between the waveform x _m and the waveform y _{m + j} , and takes the maximum value when the two waveforms are the most similar. The mutual covariance coefficient R _{xy (j)} can be obtained by directly calculating from the equation (2), but the Fourier transform of the mutual covariance coefficient R _{xy (j)} may correspond to each component of the cross power spectrum. Since it has been proved, the cross power spectrum of the waveform x _m and the waveform y _{m + j} is usually obtained, and the inverse covariance coefficient R _{xy (j)} is obtained by inverse Fourier transforming this.
Is asked. Fast Fourier transform (FFT) and fast Fourier inverse transform are used as the Fourier transform and the inverse Fourier transform, respectively. Further, R _{x (0)} and R _{y (0)} are the values of the autocovariance coefficients R _{x (j)} and R _{y (j)} when j = 0, respectively, given by the following equations.

The self-covariance coefficients R _{x (j)} and R _{y (j)} are also efficiently obtained by calculating the power spectrum of the waveforms x _m and y _m and subjecting this power spectrum to the inverse Fourier transform.
The cross-correlation coefficient ρ _{xy (j)} given by the equation (1) is obtained by normalizing the cross-covariance coefficient R _{xy (j)} by the self-covariance coefficients R _{x (0)} and R _{y (0)} , It takes a maximum value of 1 when both waveforms x _m and y _{m + j} are most similar.

As a result of actually detecting the ultrasonic waves generated by the partial discharge of the connection portion 2 of the voltage cable 1 by the ultrasonic sensors 3a and 3b, respectively, and by the ultrasonic sensors 3a and 3b respectively, the ultrasonic sensors 3a and 3b are detected. The output waveform of is the waveform x _{i of} Fig. 2 (a)
And the waveform y _{i in} FIG. 2 (b), the cross-correlation coefficient ρ
_{xy (j)} was calculated by the arithmetic unit 6 as shown in FIG. The time that gives the maximum value of the cross-correlation coefficient ρ _{xy (j)} ,
That is, it was calculated that the time difference ΔT between the waveforms x _i and the waveform y _i reaching the ultrasonic sensors 3a and 3b was 48 μs.

If this time difference ΔT is multiplied by the sound velocity v in the material of the connecting portion 2, for example, 1900 m / sec, the distance difference ΔS = ΔT from the partial discharge occurrence position 4 to the ultrasonic sensor 3a and the ultrasonic sensor 3b.
Xv is required. Therefore, in the example of FIG. 2, the distance difference ΔS
Is ΔS = 48 × 10 ⁻⁶ × 1900 = 0.0912 (m) = 9.12 (cm). This distance difference ΔS indicates the difference in length between the ultrasonic wave propagation path A and the ultrasonic wave propagation path B in FIG.

The calculation of the time difference described above is also performed between the ultrasonic sensor 3c and the ultrasonic sensor 3d to obtain the distance difference, and if the difference between the ultrasonic wave propagation path C and the propagation path D is obtained, The partial discharge position 4 can be accurately calculated and determined.

(Effects of the Invention) As described above, according to the present invention, a plurality of ultrasonic sensors installed at different positions to detect ultrasonic waves generated by partial discharge and convert them into electric signals, and the ultrasonic sensor A waveform storage device that converts each output electric signal waveform into a digital electric signal waveform and stores the converted waveform, and a cross-correlation coefficient is calculated for each of the two digital signal waveforms by reading the digital signal waveforms. It requires a special skill by being composed of an arithmetic unit that calculates the arrival time difference at the sound wave sensor, calculates the distance difference by multiplying the arrival time difference by the ultrasonic velocity, and calculates and determines the position of the partial discharge. Instead, the time difference between the two waveforms can be calculated accurately and quickly from the output of a noisy ultrasonic sensor, and the position of the partial discharge can be located using this, and the partial discharge can be reliably measured. In addition, it is possible to prevent a dielectric breakdown accident in advance, and there is no need for manual adjustment, so that it is possible to achieve complete automation.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of the partial discharge position locating device of the present invention, and FIG. 2 is an output waveform x _i , y _{i of an} ultrasonic sensor.
FIG. 7 is a diagram showing a waveform of a cross correlation coefficient ρ _xy . 1 ... voltage cable, 2 ... connection part, 3a, 3b, 3c, 3d ...
Ultrasonic sensor, 4 ... Partial discharge position, 5 ... Waveform storage device, 6 ... Computing device.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Yoshio Maruyama 6 Yawata Kaigan Dori, Ichihara City, Chiba Furukawa Electric Co., Ltd. Chiba Cable Manufacturing Co., Ltd. (72) Yasuhiro Yamashita 6 Hachiman Kaido Dori, Ichihara City, Chiba Furukawa Electric Co., Ltd. Company Chiba Electric Wire Works

Claims (1)

[Claims] 1. A plurality of ultrasonic sensors installed at different positions to detect ultrasonic waves generated by partial discharge and convert them into electric signals, and output electric signal waveforms of the ultrasonic sensors are converted into digital electric signal waveforms. A waveform storage device that converts and stores the digital signal waveform, calculates a cross-correlation coefficient for each of the two digital signal waveforms, calculates a difference in arrival time of ultrasonic waves from the maximum value to the ultrasonic sensor, A partial discharge position locating device, comprising: an arithmetic unit for calculating and determining the position of the partial discharge by calculating a distance difference by multiplying the time difference by the ultrasonic velocity.