KR101649990B1

KR101649990B1 - Diagnosis method to examine state of power cable using length conpensation

Info

Publication number: KR101649990B1
Application number: KR1020150080628A
Authority: KR
Inventors: 김현주; 이건호; 임장섭; 김용현; 박나래; 이인회; 이원석
Original assignee: 대한전선 주식회사; 엘에스전선 주식회사; 목포해양대학교 산학협력단
Priority date: 2015-06-08
Filing date: 2015-06-08
Publication date: 2016-08-23

Abstract

The present invention relates to a method of diagnosing a state of a power cable using length compensation, which evaluates the long-term reliability of an accelerated water tree test by compensating the length of a low-frequency carbon delta, which is a power cable water tree diagnosis method. A method of diagnosing a state of a power cable using length compensation according to an embodiment of the present invention includes the steps of (a) accumulating tangent delta (tan delta) measured at a predetermined applied voltage and performing wipe modeling, ) Calculating a correction coefficient for each measured distance and a Weibull distribution function for the accumulated tan delta, and then converting the accumulated tan delta to a reference distance; (c) (D) interpolating the tan delta divided by the trend line by the quantitative analysis unit, and outputting the interpolated result.

Description

[0001] DESCRIPTION [0002] DIAGNOSIS METHOD TO EXAMINE STATE OF POWER CABLE USING LENGTH CONNECTION [0003]

The present invention relates to a method of diagnosing a state of a power cable using length compensation, and more particularly, to a method of diagnosing a state of a power cable by using an accelerated water tree test (AWTT) The present invention relates to a method of diagnosing a state of a power cable using length compensation to evaluate the long-term reliability of the power cable.

Generally, a very low-frequency tan delta (VLF tan δ) measurement method in a power system measures the change in tan delta of a cable or an electric power facility by applying various kinds of applied voltages to detect abnormality such as water tree generation in the insulator, Is the most representative method to diagnose.

When a water tree occurs inside the insulator operated for a long time, deterioration such as decrease of insulation resistance and increase of loss current occurs. This phenomenon eventually appears as a change in tan delta. Through the measurement of the change, it is judged whether the insulator is abnormal or deteriorated. In particular, high voltage insulators have very high insulation resistance and capacitance, so that leakage current and voltage are 90 degrees out of phase. However, this is the theoretical conclusion that appears in an ideal state of the circuit. Actually, a slight deviation occurs due to the resistance component inside the insulator. That is, the larger the tan delta, the more the insulator is abnormal.

In other words, it is necessary to evaluate the long-term reliability of the cable. It is known that it is effective to use Accelerated Cable Lifetime Test (ACLT) and Accelerated Water Tree Test together as a technique for evaluating long- It has been proposed and standardized in many ways around the world.

However, due to differences in voltage and frequency of each country, some evaluation rules are adopted for appropriate experimental conditions in each country. The most common cable The cable acceleration life test proposed by the Electric Power Research Institute (EPRI) for the long-term reliability test is as follows.

First, after applying various conditions to the cable acceleration life test for the cable samples, the acceleration factor calculation formula proposed by the Power Research Center is used to predict the degree of deterioration.

As the acceleration factor calculation formula proposed by the North American Power Research Center, the average operation condition of the MV grade 15kV cable, which is commonly used in North America, is 8.66kV (15kV /

), And the conductor operating temperature is set at 45 占 폚.

The cable accelerated life test conducted by the North American Power Research Center is based on the MV-rated 15kV cable accelerated life test. In addition, after determining the operating voltage and temperature, the operating life of the cable is predicted by using the method of accelerating deterioration of the cable under harsh conditions by increasing the operating voltage and temperature compared to the operating condition and using the weave distribution function which is a statistical method.

Generally, the progress of the deterioration progress of the short-distance line of about 10m and the progress of the dielectric strength is inferred by using a numerical method to the result of the actual line taking into account the economic aspects of the experiment.

Next, in order to obtain the acceleration lifetime characteristic curve of the cable, the acceleration coefficient of each North American and domestic MV cable is modeled through the acceleration factor calculation formula and the matrix of the North American Power Research Center mentioned above. In particular, The acceleration coefficient is modeled according to the cable length, the conductor temperature, and the operating voltage.

The three-dimensional model of the deterioration acceleration coefficient of 30 ft (about 9.1 m) and a probability distribution of 63.2% for each type of stress is shown in FIG. 1 according to the North American conditions through the acceleration factor of the North American Power Research Center mentioned above Respectively.

FIG. 1 is a graph showing the life time (63.2%) of an insulation deterioration model according to acceleration conditions (conductor temperature, operating voltage, remaining life) of the prior art.

As shown in FIG. 1, as the operating voltage increases and the temperature of the conductor increases, the life span tends to decrease drastically from 70 years to less than one year.

The Vt characteristic curve showing the tendency for the estimated accelerated life is shown in Figs. 2 (a), (b) and (a) and (b) Based on the coefficients, it shows the remaining service life at 10%, 20% and 63.2% (10% is shown as triangle, 20% as circle, and 63.2% as square) in North American and domestic operating conditions.

FIG. 2 (a) is an acceleration lifetime estimation curve at a cable conductor temperature of 45 ° C. in North America, and FIG. 2 (b) is a graph of an acceleration lifetime estimation curve at a cable conductor temperature of 45 ° C. FIG. 3 (a) is an accelerated lifetime estimation curve at a cable conductor temperature of 90.degree. C. applied in North America, FIG. 3 (b) is an accelerated lifetime estimation curve at a cable conductor temperature of 90.degree. It is a curve graph.

As shown in FIGS. 2 (a) and 2 (b), the Vt curve for operating conditions in North America and Korea shows that the test conditions corresponding to the acceleration conditions according to the applied voltage (the predicted life : may be represented by Estimated lifetime), wherein the U ₀ is there is a reference voltage, in particular, the applied voltage is the remaining service life in the interval of increased to 2U ₀ in 1U ₀ is the drastically reduced than the remaining lifetime at another voltage increasing section Respectively.

In addition, the remaining life at 63.2% of the remaining life at 10% and 20% tends to sharply decrease. Therefore, as the accelerated life test of the cable accelerates, the variation of the error may increase sharply, and thus the range of the effect becomes wider.

The Vt curve for North American and domestic operating conditions shown in Figs. 3 (a) and 3 (b) can be calculated by a method proposed in a variation of the estimated lifetime according to each applied voltage with respect to a conductor temperature of 90 ° C. This is a result. In particular, since the crosslinked polyether-type cable tends to decrease as the applied voltage increases in the state of normal operating conditions of 90 ° C, the normal operating conditions, namely, 10% and 20% remain as in the case where the conductor temperature is 45 ° C There is a tendency that the remaining service life of 63.2% is more rapidly reduced than the service life.

In addition, it can be inferred that the deterioration rate of cable can be further shortened in Korea due to the fact that power lines are operated at about 50 ° C to 60 ° C due to the increase in domestic power consumption.

As a result, ultra-low-frequency tan delta method is mainly used as a method for evaluating the abnormality of the cable.

Extremely low frequency tan delta measurement is a method of diagnosing cables or transformers with various types of applied voltage for abnormal signs such as water tree growth or voids inside the insulator. If a water tree is formed inside the insulator, the insulation resistance is decreased and the loss current is increased. This phenomenon is eventually seen as an increase of the tan delta, and the change of the insulator is judged by the abnormality or the deterioration state.

More specifically, because the high-voltage insulator has very high insulation resistance and capacitance, the leakage current and voltage ideally have a phase difference of 90 degrees. However, this is an ideal circuit, and a slight variation occurs due to the resistance component inside the insulator. These deviations are expressed as delta. In general, the larger the tan delta, the more the influence of the resistance component of the leakage current inside the insulator increases, indicating that an abnormality occurs in the insulator.

More specifically, the deteriorated cable shows a tendency that the increase in the tan delta increases largely nonlinearly with increasing voltage, while the new cable tends to have little change in tan delta value.

The system for diagnosing the deterioration of the cable using the ultra-low-frequency tan delta method for evaluating the abnormality of the above-mentioned cable has been introduced to the domestic market since 2002 and is being operated from 2010. In recent years, Has been revised to the standard of judgment criterion and has become a standard of new deterioration diagnosis technique.

However, the above-mentioned extremely low frequency tan delta measurement method has the following problems.

First, because the time constraints and economic aspects of the development of the new cable are very important, it is necessary to approach through the accelerated or shortened experiments and the statistical analysis of the measured values. However, to be.

In particular, statistical methods for estimating the deterioration progress of cables operated for more than 20 years, and representative conditions under which the reliability area is different depending on the operating conditions of the cable, namely, the degree of undergroundization, rainfall, There is no consideration of the environmental conditions such as the current situation and the country specificity of the cable type and development.

Second, technological dependence on technologically advanced European countries is inevitable unless the ongoing statistical verification and development of proprietary technologies for the judgment criteria suitable for domestic site conditions are carried out.

In particular, since the measurement data and the analytical technology have been rapidly being paid for in recent years, there has been a vicious cycle of introducing the judgment technology into the technical analysis technique while paying back the technical data for the background data to foreign countries. Is very high.

Accordingly, there is a need for a new method for state diagnosis and long-term reliability evaluation for accelerated life test such as evaluation of reliability concerning a short cable and an acceleration coefficient obtained in an accelerated life test.

On the other hand, there are also problems concerning the diagnosis of nondestructive state and the rate of change of acceleration test.

In this regard, FIG. 4 is a graph showing the AC dielectric breakdown strength according to the operating period of the prior art.

4 shows the results of the AC breakdown test (breakdown electric field, Unit: Kv / mm) for 20% and 30% of the cables operated in the field by using the Weibull distribution function for each operation period. , 50%, 63.2%, 80% and 99% cumulative probability, the number of the original mark starting with Nx means the sample subjected to the accelerated deterioration test for new cable for x months, starting with Ux The number of the original mark indicates that the accelerated deterioration test was carried out on the cable which has been operated for 20 years in the field.

Since the 50% value of the destructive electric field and the trend line are coincident with each other, the ACBD strength is small enough to estimate the operation life through the insulation breakdown value of the sample with the operation period of 10 years or more. Lifetime estimates are good for estimating lifetime for cable samples with an operating period of less than 10 years, but not for cable samples over 10 years.

In conclusion, the AC insulation breakdown test can be used to compare the initial tree growth and the initial tree growth for the initial new product, but it is not a suitable absolute value for the lifetime or probabilistic approach to dielectric breakdown.

Accordingly, there is a need for compensating the length of the cable in the accelerated life test in some cases. More specifically, since the acceleration life test has various expense and various limitations, the acceleration deterioration test is performed with a unit length of about 10 m.

However, as shown in FIG. 5, which is a graph showing the tan delta distribution for each voltage in the test section of the prior art (less than 0 to 1500 m), the tan delta distribution for each voltage in the test section (less than 0, It can be seen that the tan delta according to each section (110m, 220m, 330m, 440m, 550m, 660m, 770m, 880m, 990m, 1100m, 1210m, 1320m, 1430m, 1500m have different distribution characteristics, There is a tendency for the tan delta to be high with respect to the track, so a method or technique for compensating the length is necessary.

(Patent Document 1) KR10-1466623 B1

In order to solve the above problems, a technical problem to be solved by the present invention is to provide a method of diagnosing whether a power cable is in a deteriorated state during an acceleration test using a very low frequency carbon delta signal generated in a cable dispersed in a wide area And to provide a method for diagnosing a state of a power cable using compensation.

The present invention also relates to a method and apparatus for statistically processing a correlation between a deterioration phenomenon occurring in a power cable operated in the field and an acceleration test in a group of extremely low frequency tan delta measurement data, The present invention provides a method of diagnosing a state of a power cable using a length compensation method for diagnosing a state of a complex electric power cable with respect to a long-distance line.

The present invention also provides a system and method for diagnosing a cable state, comprising: compensating a length of a cable to improve the reproducibility of a field measurement; performing a long-term reliability evaluation of the cable to diagnose a clear condition; The present invention provides a method of diagnosing a state of a power cable using length compensation.

According to an aspect of the present invention, there is provided a method of driving a vehicle, including: (a) accumulating tidal delta (tan?) Measured at a predetermined applied voltage to perform wiped modeling; (b) calculating a correction coefficient for each of the measured distances and a Weibull distribution function for the accumulated tan delta, and converting the accumulated tan delta to a reference distance; (c) linear interpolating the converted tan delta by dividing the converted tan delta into a trend line; And (d) a quadratic interpolator for subtracting the tan delta divided by the trend line from the quantitative analysis part, and outputting the interpolated result.

In one embodiment of the present invention, the step (b), (b1) the test duration (more than 0 to less than 1500m) the accumulated Tan delta ₀ 0.5U, 1.0U _0, for a cable length of _0, and 1.5U Comparing the distribution by the tan delta deviation; (b2) setting a length of a cable length and a unit representative length; (b3) deriving 20%, 30%, 50%, 63.2%, 80%, and 99% of the accumulated tan delta by the unit representative length using the Weibull distribution function; And (b4) outputting 20%, 30%, 50%, 63.2%, 80%, and 99% of the derived tan delta to a box plot, Can be divided into 110m, 220m, 330m, 440m, 550m, 660m, 770m, 880m, 990m, 1100m, 1210m, 1320m, 1430m, and 1500m.

In one embodiment of the present invention, in the step (b), the correction coefficient may satisfy the following formula (1).

... Equation (1)

In one embodiment of the present invention, the step (d) may be performed by applying the correction coefficient to the converted tan delta.

In one embodiment of the present invention, the step (c) may be performed by a linear interpolation function or an exponential interpolation function of the converted tan delta for each section of the cable length of the step (b) have.

In one embodiment of the present invention, the reference distance may be 300 m.

According to the present invention, it is confirmed that the long-term reliability verification can be combined with the field suitability by presenting the rationale based on the statistical basis and the probability distribution for the power cable deterioration criterion obtained from the acceleration test based on the data obtained from the actual site .

In addition, according to the present invention, the analysis of the deterioration state of the power cable according to the conventional failure test acceptance criterion can lead to the problem of long-term reliability, and it is effective to proceed with follow-up (reinforcement, replacement).

Further, according to the present invention, it is possible to reduce the long-term reliability investment cost when the criteria set forth in the present invention are applied to the same cable.

In addition, according to the present invention, since the remaining life of the power cable can be predicted and the occurrence timing of the fault caused by the statistical probability can be predicted, it is possible to provide a basis for establishing a planned operation policy for the electric power facility.

It should be understood that the effects of the present invention are not limited to the above effects and include all effects that can be deduced from the detailed description of the present invention or the configuration of the invention described in the claims.

FIG. 1 is a graph showing the life time (63.2%) of an insulation deterioration model according to acceleration conditions (conductor temperature, operating voltage, remaining life) of the prior art.
FIG. 2 (a) is an acceleration lifetime estimation curve graph at a cable conductor temperature of 45.degree. C. applied in North America. FIG.
FIG. 2 (b) is an acceleration lifetime estimation curve graph at a cable conductor temperature of 45.degree.
FIG. 3 (a) is an acceleration lifetime estimation curve graph at a cable conductor temperature of 90.degree. C. applied in North America. FIG.
FIG. 3 (b) is an acceleration lifetime estimation curve graph at a cable conductor temperature of 90.degree.
4 is a graph showing the AC dielectric breakdown strength according to the operating period of the prior art.
5 is a graph showing the tan delta distribution for each voltage in the test section of the prior art (less than 0 to 1500 m).
FIG. 6 is a block diagram illustrating the components necessary for explaining a method of diagnosing a state of a power cable according to an embodiment of the present invention.
7 is a flowchart illustrating a method of diagnosing a state of a power cable according to an embodiment of the present invention.
FIG. 8 is a graph showing a tan delta distribution after a length compensation in a test period (less than 0 to 1500 m) in a process of a method for diagnosing a state of a power cable according to an embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described with reference to the accompanying drawings. The present invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. In order to clearly illustrate the present invention, parts not related to the description are omitted, and similar parts are denoted by like reference characters throughout the specification.

Throughout the specification, when a part is referred to as being "connected" to another part, it includes not only "directly connected" but also "indirectly connected" . Also, when an element is referred to as "comprising ", it means that it can include other elements, not excluding other elements unless specifically stated otherwise.

The term " tan delta " used in the present invention is defined as tan delta when a very low frequency is applied throughout the specification.

Also, the term 'U ₀ ' used in the present invention is defined as a reference voltage which is a voltage between a ground and a conductor to integrate the transmission /

In addition, the term 'Box Plot' used in the present invention means that a maximum value, a minimum value, a median value, and a quadrant deviation are used throughout the specification to easily understand the shape of the measured values of the data. .

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

FIG. 5 is a graph showing a tan delta distribution for each voltage in a test period (less than 0 to 1500 m) of the prior art. FIG. FIG. 7 is a flowchart illustrating a method of diagnosing a state of a power cable according to an embodiment of the present invention. FIG. 8 is a flowchart illustrating a method of diagnosing a state of a power cable according to an exemplary embodiment of the present invention. 0 to < RTI ID = 0.0 > 1500m) < / RTI >

As shown in FIG. 7, a method for diagnosing a state of a power cable according to an embodiment of the present invention includes the steps of (a) accumulating tangent delta (tan delta) measured at a predetermined applied voltage by the wired modeling unit 100, (B) The ternary delta transforming unit 200 calculates a weighing distribution function and a correction coefficient for the measured distance for the accumulated tan delta, and then converts the accumulated tan delta into a reference distance (C) a step (S530) of performing linear interpolation by dividing the tan delta converted by the length compensating unit 300 into trend lines (S530), and (d) the quantitative analysis unit (400) And outputting the second interpolation result (S540).

As shown in FIG. 5, the tan delta distribution for each voltage tends to show a high tan delta with different distribution characteristics when the accelerated deterioration test is carried out at a field length of 10 m, It is the same as the tan delta in the 110m ~ 550m section.

Therefore, length compensation for 10m cable is indispensable, and a detailed explanation will be given below.

First, in the step (a), the cable length of about 12,000 km in the measurement of the extremely low frequency carbon delta of the power distribution cable is used as the basis of the measurement database, and the extremely low frequency carbon delta according to the measurement length is accumulated, The model is statistically compensated.

To do this, the data of the extremely low-frequency tan delta (TD) signal measured at 11 different voltages (0.5, 0.6, 0.7, 0.8, 0.9, 1.0, 1.1, 1.2, 1.3, 1.4 and 1.5 U ₀ ) Accumulate and perform weave modeling.

Here, the extremely low frequency Tan delta measurements for domestic since the base voltage is the voltage between ground and the conductor is approximately 13.2kV, which is a measurement reference voltage is defined as 1U _0. Therefore, U ₀ is used as a basis for the basic applied voltage rating because the country's transmission and distribution voltage ratings are different.

Next, in step (b), the accumulated tan delta for the length compensation is converted, and the compensation distribution for the measurement length is compared with the statistical distribution for each measurement distance to determine a normal line distance (= reference distance) Normalize the absolute compensation data. That is, the reference distance is preferably 300 m, but it may be 299 ~ 301 m depending on the user's intention or situation.

More specifically, by using a weave distribution for all data and a correction coefficient for each measurement distance, the tan delta converted for each unit length of the entire data is converted into a typical line distance (300 m).

For this purpose, the transformation of the tan delta is performed using a statistical distribution, and the tan delta data of the corresponding length is converted by the correction formula obtained by the equation.

As a result of comparing the tan delta measured in the field up to 2012 and the tan delta of the 10 m short-distance line used in the accelerated life test, the above-mentioned performance was analyzed with the result that the value of the short- The measurement period can be applied differently if necessary.

This step (b), (b1) comparing the test period by dividing the distribution of accumulated tan delta as 0.5U _0, 1.0U _0, 1.5U ₀ and tan delta deviation for the length of the cable (more than 0 to less than 1500m) 30%, 50%, 63.2%, and 80% of the tan delta accumulated for each unit length by using the Weibull distribution function, (b2) setting the length of the cable length and the unit representative length, % And 99%, and (b4) outputting 20%, 30%, 50%, 63.2%, 80% and 99% of the derived tan delta to a box plot.

In this case, the unit length of the cable length is divided into 110m, 220m, 330m, 440m, 550m, 660m, 770m, 880m, 990m, 1100m, 1210m, 1320m, 1430m and 1500m. The unit representative length is set in order to check the delta of the cable length over a longer cable length than the conventional technique in which the cable length is set to 10 m.

In the step (b), the correction coefficient is obtained by dividing an average of 50% values of each section of the cable length before correction by the pre-correction delta, and is expressed by the following equation (1) 1).

Also, correction factors were calculated for each voltage (0.5U ₀ , 1.0U ₀ , 1.5U ₀ , and DTD) and intervals by using the above-described equation (1) Respectively.

Calibration factor according to cable length at 0.5U ₀ Length [m] Less than 110 220 or less 330 or less 440 or less 550 or less 660 or less 770 or less Correction coefficient 0.47 0.71 0.82 0.92 0.98 1.18 1.12 Length [m] 880 or less 990 or less 1100 or less 1210 or less 1320 or less 1430 or less 1500 or less Correction coefficient 0.99 1.08 1.67 1.18 1.34 1.81 1.90

Correction factor according to cable length at 1.0U ₀ Length [m] Less than 110 220 or less 330 or less 440 or less 550 or less 660 or less 770 or less Correction coefficient 0.42 0.92 0.84 0.90 0.91 1.18 1.10 Length [m] 880 or less 990 or less 1100 or less 1210 or less 1320 or less 1430 or less 1500 or less Correction coefficient 1.09 1.09 2.02 1.18 1.41 2.08 2.22

Correction factor according to cable length at 1.5U ₀ Length [m] Less than 110 220 or less 330 or less 440 or less 550 or less 660 or less 770 or less Correction coefficient 0.38 0.62 0.86 0.87 0.89 1.21 1.10 Length [m] 880 or less 990 or less 1100 or less 1210 or less 1320 or less 1430 or less 1500 or less Correction coefficient 1.13 1.06 2.14 1.25 1.42 2.31 2.18

Correction factor according to cable length in tan delta deviation Length [m] Less than 110 220 or less 330 or less 440 or less 550 or less 660 or less 770 or less Correction coefficient 0.35 0.62 0.82 0.93 0.85 1.27 1.00 Length [m] 880 or less 990 or less 1100 or less 1210 or less 1320 or less 1430 or less 1500 or less Correction coefficient 1.27 1.04 2.90 1.27 2.80 4.00 4.00

The above Table 1 to Table 4 are each an 0.5U _0, 1.0U _0, 1.5U ₀ and the correction coefficient according to the cable length variation in tan delta.

As shown in FIG. 8, since the distribution of the tan delta after the length compensation is different, length compensation is necessary. For this, the length is compensated by applying the correction coefficient.

In the step (c), the box-delimited tan delta is represented by a two-dimensional tan delta / tan delta conversion map. More specifically, the tan delta obtained through the steps (a) and (b) is positioned (filled circle mark 2) by the two-dimensional tan delta / tan delta conversion map shown on the right side of [Table 5].

The trend line used in the step (c) is derived by the linear interpolation function or the exponential interpolation function of the converted tan delta for each section of the cable length in the step (b).

Next, a compensation point is generated by two interpolation methods, which are estimated by the conversion formula. Here, the conversion formula expresses the hypothetical point of the accelerated test cable test length from the tangent delta estimated from about 20,000 solid lines to show the degree of matching between the actual measured tan delta and the field operated line, .

If the length to be estimated is close to the real line, it can be seen that T / 2012 and T / 2014 have a similar distribution and therefore show a high degree of linearity and a linear trend.

On the other hand, in general, the short-distance cable performs linear interpolation and the long-distance cable performs exponential interpolation. The measured tan delta is an irregular nonlinear trend and the short distance cable of about 10m is effective for exponential interpolation.

In addition, the interpolated line has two virtual points for the length-converted delta according to the length of the accelerated test cable. At this time, the hypothetical point uses the exponential interpolation method such as T / 2014 for the extreme short-distance or long-distance cable, and uses the linear interpolation formula such as T / 2012 for the cable of the distance close to the measurement data.

Next, the position of the measured tan delta is mapped to the position of the two-dimensional tan delta / tan delta deviation while performing the accelerated life test as shown on the left side of [Table 5]. (Filled circle mark) along the line of the accelerator, and compensates for the position change by compensating for 2, 4, 6 (empty circle mark) along the trend line (the empty circle mark of 4 is 6 empty Mark on the circle mark). For example, if the acceleration period corresponds to 2, 4, ... n months, the value of the compensated tan delta can be expressed as T2, T4, ..., Tn.

Next, the step (d) is performed by applying the correction coefficient to the converted tan delta. That is, in the step (d), the correction coefficient for each interval obtained through the correction coefficient calculation formula is applied to the converted tan delta.

The present invention as described above provides a mathematical model for expressing a change slope according to a line length represented by a tan delta as a trend line and a method for comparing the matching degree with a tan delta group operated for several decades in the field Respectively.

Also, the present invention confirms a two-dimensional position of the quantified value, that is, a two-dimensional tan delta / tan delta conversion map, converts the position level similar to the deteriorated state of the operated tan delta group, The mathematical model that can be used is presented, and the quantified values are combined with the slope of the virtual line, so that the invalid data and valid data for the delta size, shape, and measurement error represented by the delta group can be represented as one arithmetic value It was.

It will be understood by those skilled in the art that the foregoing description of the present invention is for illustrative purposes only and that those of ordinary skill in the art can readily understand that various changes and modifications may be made without departing from the spirit or essential characteristics of the present invention. will be. It is therefore to be understood that the above-described embodiments are illustrative in all aspects and not restrictive. For example, each component described as a single entity may be distributed and implemented, and components described as being distributed may also be implemented in a combined form.

The scope of the present invention is defined by the appended claims, and all changes or modifications derived from the meaning and scope of the claims and their equivalents should be construed as being included within the scope of the present invention.

100: Wavelet modeling unit
200: tan delta conversion part
300: Length compensator
400: Quantitative analysis section

Claims

(a) accumulating tangent delta (tan?) measured at a predetermined applied voltage and performing wipe modeling;
(b) calculating a correction coefficient for each of the measured distances and a Weibull distribution function for the accumulated tan delta, and converting the accumulated tan delta to a reference distance;
(c) linear interpolating the converted tan delta by dividing the converted tan delta into a trend line; And
(d) a quantitative analysis unit for performing second-order interpolation of tan delta divided by the trend line,
The step (b)
(b1) comparing the test period, the accumulated cost Tan delta of 0.5U _0, 1.0U _0, 1.5U ₀ and tan delta distribution by dividing the deviation of the cable length (more than 0 to less than 1500m);
(b2) setting a length of a cable length and a unit representative length;
(b3) deriving 20%, 30%, 50%, 63.2%, 80%, and 99% of the accumulated tan delta by the unit representative length using the Weibull distribution function; And
(b4) outputting 20%, 30%, 50%, 63.2%, 80% and 99% of the derived tan delta by box plot,
Wherein the unit lengths of the cable lengths are divided into 110m, 220m, 330m, 440m, 550m, 660m, 770m, 880m, 990m, 1100m, 1210m, 1320m, 1430m and 1500m. State diagnostic method.

delete

The method according to claim 1,
In the step (b)
Wherein the correction coefficient satisfies the calculation formula (1).

... Equation (1)

The method of claim 3,
And the step (d) is performed by applying the correction coefficient to the converted tan delta.

The method according to claim 1,
The step (c)
Wherein the trend line is derived by a linear interpolation function or an exponential interpolation function of the converted tan delta for each section of the cable length in the step (b).

The method according to claim 1,
Wherein the reference distance is 300 m.