JPH09133731A - Partial discharge measuring method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To accurately measure partial discharge by obtaining a calibration ratio of high accuracy with due consideration of an impedance effect across the sheath and the ground. SOLUTION: An insulated connection part 2 is supplied with a calibration pulse from a calibration pulse generator 3 and voltage V generated across the sheaths of an insulated connection part 2 is measured with a partial discharge detector 4, thereby finding a calibration ratio. In addition, the calibration ratio is used to measure a charge amount for partial discharge. At a calibration process, impedance elements R of different resistance values are connected across the sheaths of the insulated connection part 2, and voltage V detected with each impedance element R connected is obtained. Also, the calibration ratio is found from the value of the resistance of each impedance element R and the voltage V. Alternatively, low impedance elements are connected across the sheaths of the insulated connection part 2, or across the sheath and the ground to reduce the effect of an impedance fluctuation between the sheath and the ground, thereby finding the calibration ratio.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of measuring a partial discharge of a power cable line, and more particularly to a method of measuring a partial discharge capable of calibrating a partial discharge charge amount with high accuracy.

[0002]

2. Description of the Related Art FIG. 5 is a diagram showing a configuration example of a power cable line. In the figure, U, V and W are power cables,
1UJ, 1VJ, 1WJ, 2UJ, 2VJ and 2WJ are insulation connection parts, 3UJ, 3VJ and 3WJ are normal connection parts. As shown in Fig. 5, the power cable line for ultra high voltage is
Since the grounding method is a cross-bond method, the line configuration is a combination of an insulating connection part and a normal connection part. In the above-described insulating connection portion for cross-bonding, a slit portion for cutting off the shielding layer is provided.

Considering the coaxial power cable as a transmission line for a partial discharge signal, the presence of the slit causes impedance unmatching. Therefore, the partial discharge signal generated at the connection portion or the like, or the partial discharge signal that propagates and reaches the insulating connection portion is demultiplexed to the ground side at this slit portion, so that the partial discharge pulse can be measured. However, in the case of the ordinary connection part, since there is no slit part like the insulated connection part, the partial discharge cannot be directly calibrated and measured.

Therefore, when measuring the partial discharge charge amount generated in the ordinary connection portion or the like, the partial discharge signal propagated from the ordinary connection portion or the like is measured in the adjacent insulating connection portion. Then, in advance, a calibration ratio of the partial discharge charge amount Q generated at the normal connection portion or the like to the voltage V1 detected at the insulating connection portion is obtained, and when the partial discharge occurs,
If the voltage V1 is detected at the insulating connection portion and the partial discharge charge amount is obtained from the voltage V1 using the calibration ratio, the partial discharge charge amount generated at the normal connection portion or the like can be measured.

In order to obtain the above-mentioned calibration ratio, as shown in FIG. 6, two adjacent insulating connection portions 2 and 2'having the same distance between the normal connection portion to be calibrated and the insulating connection portion are used. Then there is a method to do as follows. A calibration pulse generator 3 is provided on one insulation connection 2 and the other insulation connection 2 '
And a partial discharge detector 4 is provided. A predetermined calibration pulse is injected from the adjacent insulating connection portion 2 separated by the distance L. This calibration pulse propagates in the power cable 1'with attenuation,
The other insulated connection portion 2 ′ corresponding to the detection point is reached. In this method, the arrived calibration pulse is detected by the partial discharge detector 4.

Next, a method for obtaining the calibration ratio will be described. FIG. 7 is a diagram showing an equivalent circuit when a calibration pulse is injected from the insulating connection portion. This figure shows the voltage V that arrives at the adjacent insulating connection when the current I corresponding to the charge amount Q is injected, and Zc is the surge impedance of the cable (hereinafter referred to as the cable impedance), Zs.
1, Zs2 is the impedance between the cable sheath and the ground, and Zi is the impedance between the sheaths of the cable connecting portion.

According to the figure, the detection voltage v1 obtained at the detection point P when the current I corresponding to the charge amount Q is injected is obtained as follows. Here, Y1 = 1 / (2Zc),
Y2 = 1 / (Zs1 + Zs2), Y3 = 1 / Zi,
If d is a cable attenuation factor and M is a proportional constant (ratio of incoming voltage to the detection point P and detection voltage), impedance Z
The current I1 flowing through c is expressed by the following equation. I1 = {Y1 / (Y1 + Y2 + Y3)} I Therefore, the voltage V1 detected at the detection point P is expressed by the following equation (1). V1 = {Y1 / (Y1 + Y2 + Y3)} I ・ Zc ・ d ・ M (1)

On the other hand, the voltage detected when the partial discharge having the charge amount Q is generated at the distant ordinary connection portion separated by the distance L is expressed by the following equation (2). V2 = (Zc · I · d · M) / 2 (2) Here, similarly to the above, Zc is the impedance of the cable, d is the attenuation factor of the cable, and M is a proportional constant. From the above equations (1) and (2), the calibration ratio k is obtained as in the following equation (3). k = V1 / V2 = 2Y1 / (Y1 + Y2 + Y3) (3) Here, when Zs = Zs1 + Zs2, and the above equation (3) is represented by Zc, Zs, and Zi, the following equation (4) is obtained. k = 2Zs / {2Zc + Zs + (2ZsZc / Zi)} (4) The calibration ratio k is obtained in advance as described above, and V is detected by the detector.
When the voltage is observed, the corresponding calibration charge Q1
On the other hand, the partial discharge charge amount Q generated at the normal connection part is Q
= KQ1 can be calculated.

In order to accurately obtain the calibration ratio, it is necessary to obtain the sheath / ground impedance Zs and the sheath-to-sheath impedance Zi of the cable connecting portion for each insulation connecting portion as described above. Calculated the calibration ratio on the assumption that the sheath / earth impedances Zs1 and Zs2 and the sheath-to-sheath impedance Zi of the cable connecting portion are sufficiently larger than the cable impedance Zc. That is, from the idea that all the charges injected from the pulse generator reach the detection point,
s1, Zs2 >> Zc, Zi >> Zc, that is, Y2 <
Assuming that << Y1 and Y3 << Y1, Y2 and Y3 are ignored in the equation (3), and the calibration ratio is k = 2 to obtain the partial discharge charge amount.

[0010]

As described above, in the prior art, the sheath / earth impedances Zs1 and Zs are conventionally used.
2 and impedance between sheaths of cable connection part Z
Assuming that i is sufficiently larger than the impedance Zc of the cable, the sheath-to-ground impedance and the sheath-to-sheath impedance of the cable connecting portion are ignored to obtain the calibration ratio, and the partial discharge charge amount is measured. Therefore, there were the following problems.

(1) An accurate calibration ratio could not be obtained, and the amount of partial discharge charge normally generated at the connection portion could not be obtained accurately. In particular, the impedance Zi between the sheaths of the cable connecting portion is the impedance Z of the cable.
The impedance Zs between the sheath and ground is several times the impedance Zc of the cable, although it can be ignored by assuming that it is sufficiently larger than c. The accuracy has decreased.

(2) The number of connecting portions is very large depending on the length of the power cable line and the number of lines. For example, the number of connecting portions of the 275 kV class CV cable line constructed up to now ranges from several tens to several hundreds. Therefore, in order to obtain an accurate calibration ratio in consideration of the impedance Zs, it is necessary to measure the impedance Zs between the sheath and the ground of each of the above-mentioned connecting portions, and for this, new work is added. Become. In addition, since the calibration ratio obtained by the operation differs for each insulation connection portion, an accurate charge amount is calculated using those coefficients individually, which is very complicated.

The present invention has been made to solve the above-mentioned problems of the prior art. The first object of the present invention is to obtain a highly accurate calibration ratio in consideration of the impedance between the sheath and the ground. , It is to measure the partial discharge that normally occurs at the connection part etc. accurately. The second object of the present invention is to prevent the influence of the impedance between the sheath and the ground from becoming a practical problem, so that
It is possible to accurately calibrate the charge amount of the partial discharge pulse without measuring the impedance between the ground and to accurately measure the partial discharge generated at the normal connection portion.

[0014]

In the present invention, the above problems are solved by the following methods (1) and (2). (1) Calculate an accurate calibration ratio in consideration of the impedance between the sheath / ground and the impedance between the sheaths of the cable connection part. In the invention of claim 1 of the present invention,
An accurate calibration ratio k is obtained as follows.

(A) Measurement of Y1 + Y2 + Y3 As shown in FIG. 1 (a), a new impedance R is connected between the sheaths of the insulation connection part to which the calibration pulse generator 3 is attached. The equivalent circuit in this case is as shown in FIG. In the figure, Zc is the impedance of the cable, Zs1 and Zs2 are the impedance between the cable sheath and the ground, Zi is the impedance between the sheaths of the cable connecting portions, and R is the above-mentioned added impedance.

Here, as in FIG. 7, Y1 = 1 / (2Z
c), Y2 = 1 / (Zs1 + Zs2), Y3 = 1 / Z
Assuming that i and G = 1 / R, d is the cable attenuation factor, and M is a proportional constant (ratio of the arrival voltage to the detection point P and the detection voltage), the voltage v at the detection point P is as follows.

V = {Y1 / (Y1 + Y2 + Y3 + G)}
Zc · I · d · M When the impedance R is R = R1 and G1 = 1 / R1, the following equation (a1) is established. v1 = {Y1 / (Y1 + Y2 + Y3 + G1)} Zc · I · d · M (a1) Further, the impedance R is R = R2, G2 = 1 / R.
If the value is 2, the following expression (a2) is established. v2 = {Y1 / (Y1 + Y2 + Y3 + G1)} Zc · I · d · M (a2)

From the equations (a1) and (a2), the following equation (a3) is obtained. Y1 + Y2 + Y3 = (-AG1 + G2) / (A-1) (a3) Here, A = v1 / v2. That is, different impedances are connected between the sheaths of the insulation connection portion, and Y1 + Y2 + Y3 can be obtained from the detection voltage when the respective impedances are connected, by the above equation (a3).

(B) Calculation of Y1 The impedance Zc of the cable can be accurately calculated from the following formula (b1) from the structure / dimension of the cable and the relative dielectric constant of the material. Zc = (60 / √ (ε)) log (D2 / D1) (b1) where D1 is the outer diameter of the conductor, D2 is the outer diameter of the insulator, and ε is the relative dielectric constant of the insulator. As mentioned above, Y1 = 1 /
Since it is (2Zc), Y1 can be obtained by calculating Zc by the above equation (b1).

(C) Calculation of calibration ratio Since the calibration ratio k can be calculated by the above equation (3),
An accurate calibration ratio k can be obtained from Y1 + Y2 + Y3 and Y1 obtained by the methods shown in (a) and (b) above.

(2) Impedance Z between sheath and ground
The influence on the calibration ratio due to the difference in s is reduced. An accurate calibration ratio k can be obtained by the above (1), but as described above, since the impedance Zs between the sheath and the ground is different for each insulation connection part, the calibration ratio is calculated for each insulation connection part. Is complicated. Therefore, in the invention of claim 2 of the present invention, a resistance is added to the calibration pulse injecting circuit, and the impedance Z between the sheath and the ground is practically used.
The effect of the difference in s is reduced.

The principle of the second aspect of the present invention will be described below. From the equivalent circuit of FIG. 7, the equation (4) is obtained as described above. Here, assuming that Zi is sufficiently larger than Zs and Zc, (2ZsZc / Zi) ≠ 0, and α = Z
Setting s / Zc, the above equation (4) can be modified as follows. k = 2α / (2 + α) (c1)

As described above, the value of the calibration ratio k changes depending on the value of α. FIG. 2 is a diagram showing the relationship between the value of α and the calibration ratio k. As shown in (1) above, the impedance Zc of the cable is constant if the structure is the same. Therefore, if the impedance Zi between the sheaths of the cable connection portion is sufficiently large, the calibration ratio k is between the sheath / ground. It is determined by the impedance Zs. That is, sheath /
Even if the value of the impedance Zs between the ground changes greatly,
This problem can be solved by adopting a circuit configuration in which the rate of change of the calibration ratio k becomes small. In the present invention, the impedance elements Za, Zb, Zc shown in FIG. 3 are inserted in the calibration pulse generation circuit. By doing so, the above problem is solved.

In FIG. 3, (a) shows the case where the above impedance is not added, (b) shows the case where the impedance element Za is attached to the shielding layers (between the slits) on both sides of the insulating tube of the insulating connection part, (c). Shows an equivalent circuit when impedance elements Zb and Zc are attached between the shield layers on both sides of the insulating cylinder and the ground, and Zs' in the figure is the equivalent impedance between the sheath and the ground. When the equivalent impedance Zs ′ between the sheath and the ground is obtained from the equivalent circuit of FIG. 3, the following (c4) (c5) (c
6) is obtained.

In the case of (a) Zs' = Zs1 + Zs2 (c4) In the case of (b) Zs' = {Za (Zs1 + Zs2)} / (Za + Zs1 + Zs2) (c5) In the case of (c) Zs' = {ZbZs1 / (Zb + Zs1) } + {ZcZs2 / (Zc + Zs2) (c6)

For the above equation (c4), equations (c5) and (c
6) shows that mounting the impedance elements Za, Zb, Zc makes it possible to mitigate the effects of variations in the equivalent impedances Zs1, Zs2 between the sheath and ground, and substantially reduces the effects of Zs1, Zs2. I am trying to By inserting the impedance element between the slits or between the shield layer and the ground as described above, the calibration ratio k can be treated as a practically constant value.

According to the first aspect of the present invention, as described in (1) above, calibration is performed by connecting impedance elements having different values between shield layers sandwiching the insulating cylinder of the insulating connection portion for injecting the calibration pulse. The voltage generated when a pulse is injected and each impedance element is connected is detected by the partial discharge detector, and calibrated based on each voltage detected by the partial discharge detector and the value of the connected impedance element. Since the ratio is calculated, the calibration ratio can be obtained with high accuracy, and the partial discharge generated in the normal connection part or the like can be measured with high accuracy.

According to the second aspect of the present invention, as described in the above (2), the impedance of the cable between the shield layers sandwiching the insulation cylinder of the insulation connection portion for injecting the calibration pulse, or between the shield layer and the ground. Connect an impedance element having a value equal to or less than the above, and calibrate by injecting a calibration pulse with the impedance element reducing the effect of impedance variation when looking at the ground side from the shield layer of the insulation connection part Since the ratio is calculated, the effect of the impedance between the sheath and the ground can be reduced to a level that does not pose a problem in practice, and more accurate partial discharge calibration can be performed, which occurs at ordinary connection parts. Partial discharge can be measured accurately.

[0029]

Embodiments of the present invention will be described below. (1) Calculation of calibration ratio (a) Calculation of Y1 + Y2 + Y3 When a 100V resistance is connected to the shield layers (between slits) on both sides that sandwich the insulating cylinder of the insulated connection part of the 275kV class CV cable line. Then, Y1 + Y2 + Y3 was measured in the case of not connecting. In this case, G1 = 0 and G2 = 1 / R = 1/100
= 0.01.

When the above resistor was connected, the measured value was V1 = 0.025V, and when the resistor was not connected, the measured value was V2 = 0.018V. From this, A = V1 / V2 = 1.38,
Y1 + Y2 + Y3 was obtained as follows. Y1 + Y2 + Y3 = (-1.38 * 0 + 0.01) / (1.38-1) = 0.263

(B) Calculation of Y1 The impedance Zc of the cable was calculated from the conductor outer diameter of 45 mm and the insulation outer diameter of 103 mm. Zc = 60 / √ (2.3) log (103/49) = 29.4Ω Y1 = 1/2 Zc = 0.170

(C) Calculation of calibration ratio The calibration ratio k is obtained from the above equation (4) as follows. k = 2Y1 / (Y1 + Y2 + Y3) = (2 × 0.0170) /0.0263=1.29

(D) Evaluation When the impedance Zc of the cable, the impedance Zs between the sheath and the ground, and the impedance Zi between the sheaths of the cable connecting portion were measured, Zc = 29Ω, Zs
= 55Ω, Zi is 1 MΩ or more, and the measured value is Y1 +
Calculation of Y2 + Y3 gave the following 0.0262. Y1 + Y2 + Y3 = 0.192 + 0.009 = 0.0
262 When the calibration ratio k is calculated from this, k = (2 × 0.017
2) /0.0262=1.31, which is substantially in agreement with the values obtained in the above (a) to (c), and it was confirmed that the calculation method according to the present invention was correct.

(2) Impedance Z between sheath and ground
Reduction of influence on calibration ratio due to difference in s The target cable was implemented as a 275 kV, 1400 sq CV cable (insulation thickness 27 mm). The insertion position of the impedance element was between the shield layers on both sides of the insulating tube. The equivalent circuit is shown in FIG. In the figure, Zs = Zs
1 + Zs2, α = Zs / Zc, Zs ′ = Za · Zs /
Assuming (Za + Zs) and α ′ = Zs ′ / Zc, the calibration ratio k ′ after newly inserting Za is as follows. k ′ = 2α ′ / (2 + α ′) (d1) Here, since Za has an impedance equal to or less than Zc, the calibration ratio is obtained with Zs ′ = Za and calibration is performed.

Considering that the impedance Zc of the cable is 29Ω, the value of the impedance to be newly inserted is set to 20Ω. α'is α '= Zs' / Zc = Za
/Zc=0.69, the calibration ratio k ′ is k ′ = 2α ′ /
(2 + α ′) = 0.51. Therefore, in the insulated connection portion in which the impedance element of 20Ω is inserted, the calibration is performed with the calibration ratio of 0.51.

The effectiveness of the above-mentioned calibration method was verified at three insulated connection parts. As a result of actually measuring Zs at three places,
The values were 82Ω, 106Ω, and 120Ω, respectively. (C
When the calibration ratio k is calculated from the equation 1), 1.17 and
It becomes 1.29 and 1.35. Compared with the calibration ratio 2 used in the conventional method, the variation is 59% to 68.
%. When the calibration ratio k'is obtained from the equation (d1), it becomes 0.43, 0.45, and 0.6, respectively. Compared with the calibration ratio of 0.51 used in this example, the variation is 84 to 90%. As described above, by performing the method of the present invention as compared with the conventional method, more accurate calibration becomes possible.

[0037]

As described above, in the present invention,
The following effects can be obtained. (1) The voltage generated when the impedance pulse is injected by connecting impedance elements of different values between the shield layers sandwiching the insulation cylinder of the insulation connection part for injecting the calibration pulse, and the impedance elements are connected to the above Partial discharge The calibration ratio is calculated based on each voltage detected by the partial discharge detector, each voltage detected by the partial discharge detector, and the value of the connected impedance element, so the calibration ratio can be calculated accurately. Therefore, it is possible to accurately measure the charge amount of the partial discharge generated at the normal connection part or the like with the partial discharge detector provided in the insulating connection part.

(2) An impedance element having a value equal to or less than the impedance of the cable is connected between the shield layers sandwiching the insulation cylinder of the insulation connection portion for injecting the calibration pulse, or between the shield layer and the ground, and Since the impedance factor is used to calculate the calibration ratio by injecting the calibration pulse while reducing the influence of the impedance variation when the shield layer of the above-mentioned insulated connection is viewed from the ground side, the impedance ratio between the shield layer and ground is calculated. The impact can be reduced to a level that does not pose a problem in practice, the partial discharge can be calibrated with higher accuracy, and the partial discharge generated in the ordinary connection part can be accurately measured with the partial discharge detector provided in the insulation connection part. It can be measured well. Further, it is not necessary to measure the impedance between the sheath and the ground for each insulation connection portion, and the efficiency of the calibration work can be further improved.

[Brief description of the drawings]

FIG. 1 is an equivalent circuit for explaining the principle of the present invention.

FIG. 2 is a diagram showing a change in a calibration ratio k with respect to a change in an α value.

FIG. 3 is a diagram showing an example of inserting an impedance element.

FIG. 4 is an equivalent circuit when an impedance element is inserted between the shield layers.

FIG. 5 is a diagram showing a configuration example of a power cable line.

FIG. 6 is a diagram illustrating a method of calculating a calibration ratio.

FIG. 7 is a diagram showing an equivalent circuit when charges are injected from an insulating connection portion.

[Explanation of symbols]

1,1 ', 1 "Power cable 2,2' Insulated connection part 3 Calibration pulse generator 4 Partial discharge measurement device Zc Cable impedance Zs, Zs1, Zs2, Zs' Sheath / ground impedance Zi Insulation impedance between insulation connections Zo, Za, Zb Insertion impedance

Claims (2)

[Claims] 1. A charge pulse is injected into an insulation connection portion of a power cable line, a voltage generated at that time is detected by a partial discharge detector attached to the insulation connection portion adjacent to the insulation connection portion, and the injected charge is detected. In the partial discharge measuring method for calculating the calibration ratio based on the amount and the detected voltage signal, and measuring the partial discharge charge amount generated at the location distant from the partial discharge detector based on the calibration ratio, The calibration pulse is injected by connecting impedance elements with different values between the shield layers sandwiching the insulating tube of the insulating connection to be injected, and the voltage generated when each impedance element is connected to the partial discharge partial discharge detector. And calculate the calibration ratio based on each voltage detected by the partial discharge detector and the value of the connected impedance element. Partial discharge measurement method characterized. 2. A calibration pulse is injected into an insulation connection portion of a power cable line, a voltage generated at that time is detected by a partial discharge detector attached to the insulation connection portion adjacent to the insulation connection portion, and the injected charge is injected. In the partial discharge measurement method, the calibration ratio is calculated based on the detected voltage signal and the amount of the partial discharge charge generated at the location distant from the partial discharge detector based on the calibration ratio. In the partial discharge measuring method of calculating the calibration ratio based on the detected voltage signal, and measuring the partial discharge generated at the location distant from the partial discharge detector based on the calibration ratio, the insulation for injecting the calibration pulse Impedance element with a value equal to or less than the impedance of the cable between the shield layers sandwiching the insulating tube of the connection part, or between the shield layer and the ground A partial discharge characterized in that the calibration ratio is obtained by injecting a calibration pulse in a state in which the influence of the fluctuation of impedance seen from the shield layer of the insulating connection part to the ground side is reduced by the impedance element. Measuring method.