KR20150000583A - Advanced Transformer Deterioration Diagnosis System Based on AE sensor with New Piezoelectric material - Google Patents

Abstract

The preset invention relates to a transformer safety inspection system, comprising: a sensing data obtaining unit receiving an electrical signal from an acoustic emission sensor and sampling the received electrical signal according to a preset scheme to generate sampling data; and an event determining unit performing reliability estimation on the sampling data to determine whether a partial discharge event has occurred.

Description

TECHNICAL FIELD [0001] The present invention relates to a transducer safety diagnosis system based on an acoustic emission sensor using a piezoelectric material,

The present invention relates to an acoustic emission sensor-based transformer safety diagnosis system employing a piezoelectric material, and more particularly, to a transformer safety diagnosis system based on an acoustic emission sensor using a piezoelectric material, To an acoustic emission sensor based transformer safety diagnosis system.

In Korea, the maintenance method of power transformer is applied by a mixed method of time - based preventive maintenance and state - based repair. Currently, the global trend in maintenance and preventive maintenance technology is in the stage of introduction and activation of the concept of condition based maintenance in advanced countries including Japan, USA and Canada. Most of the high-voltage transformers used in power facilities are inflow transformers. The lifetime of the inflow transformer is determined by the abnormal voltage of the surge and the open / close surge in the insulating material, the deterioration due to the electrical and mechanical stress of the external short circuit, and the deterioration due to the heat caused by the overload. Is very important for preventive maintenance. In recent years, demand for safety and disaster prevention of substation facilities, which are increasing in urban areas, is increasing in recent years. In order to satisfy these installation conditions, the demand for mold transformer, which is a flame retardant transformer, is increasing instead of the existing inflow transformer, and development of technology for expanding the scope of application is proceeding. The main part of mold transformer made of synthetic resin such as epoxy resin is composed of solid insulator and has high initial insulation performance, but it is still difficult to perform visual inspection or state analysis of the internal state of insulator. Therefore, it is very important to accurately diagnose the internal state of the device from the viewpoint of quality control of equipment manufacturing process and maintenance of equipment. In particular, deterioration factors caused by high-voltage transformers are thermal degradation, mechanical damage, and partial discharge degradation due to high-temperature right and short-circuit. Such deterioration causes the electrical performance and mechanical performance of the transformer to deteriorate. As a result, in the transformer, the mechanical strength is lowered, the vibration is increased and the combustible gas is generated. There are several methods for detecting the abnormal state of the transformer, such as the method of analyzing the insulating oil gas, the method of measuring the partial discharge, the method of measuring the temperature, and the method of measuring the partial discharge is an electric method And an acoustic emission signal (ultrasonic signal) are most often used. As the operation time elapses, the transformer generates a partial discharge in a portion where the insulation is weak, and if such a partial discharge continues, it may lead to insulation breakdown. When a partial discharge occurs in the transformer, a local heat is generated at that part, and the surrounding oil is compressed rapidly by the generated heat, and an acoustic emission signal is generated due to the shock wave. The generated acoustic emission signal spreads radially through the insulating oil in the transformer. At this time, the acoustic emission signal attached to the outer wall of the transformer can be used to detect the acoustic emission signal. Particularly, in the case of a conventional inflow-type transformer, a method of attaching an acoustic emission sensor to a surface of a transformer has a problem that the adhesion force of the sensor decreases with time and the distance of transmission of the acoustic emission signal becomes long, The sensitivity of the sensor is deteriorated due to exposure to various noise sources.

Accordingly, the present invention provides a transformer safety diagnosis system capable of diagnosing a partial discharge in a transformer while minimizing the influence of an external noise source.

Other objects of the present invention will become readily apparent from the following description of the embodiments.

According to another aspect of the present invention, there is provided a transformer safety diagnosis system based on an acoustic emission sensor using a piezoelectric material, the system comprising: A sensing data acquisition unit for generating sampling data by sampling in accordance with a set method; And an event determiner for evaluating the reliability of the sampling data to determine whether a partial discharge event has occurred.

The acoustic emission sensor includes a front alignment member, a rear alignment member to be inserted into the front alignment member, and a piezoelectric element disposed between the front alignment member and the rear alignment member. The piezoelectric element includes a PMN-PT piezoelectric single- Lt; / RTI >

The piezoelectric element has a resonance characteristic at 1 Mhz, and the piezoelectric element may have a thickness of 1.6 to 1.8 mm, a width of 1.9 to 2.1 mm, and a length of 1.8 to 2.2 mm.

(여기서, Z₁=압전 소자의 음향 임피던스, Z₃=변압기에 사용되는 절연유의 음향 임피던스, Z₂는 전면정합체에 사용되는 재료의 음향 임피던스임)에 의해 결정되고, 상기 전면정합체는, 음향임피던스가 5.4 내지 5.6 MRayL일 수 있다.Also, the acoustic impedance of the front mating body is expressed by the following equation

Wherein Z ₁ = acoustic impedance of the piezoelectric element, Z ₃ = acoustic impedance of the insulating oil used in the transformer, and Z ₂ is the acoustic impedance of the material used for the front mating body, The acoustic impedance may be between 5.4 and 5.6 MRayL.

Also, the acoustic impedance of the rear mast is 5 to 8 MRayL, the rear mast includes epoxy and tungsten powder, and the mixing ratio of the epoxy and tungsten powder may be 1: 4 to 6.

The sensing data acquisition unit may generate sampling data at a preset number of times per second and a predetermined number of times during the predetermined period, and the event determination unit may divide the predetermined period into at least one phase interval, The phase value of at least one sampling data in the divided phase section is set to 1 in the phase interval in which the sampling data exceeds the reference value, A ratio of the event value 1 to a ratio of the event value 1 in the phase section and a ratio of 0, and determines whether at least one of the calculated ratio of 1 and the ratio of 0 exceeds the predetermined reference confidence value The reliability of the event value for each phase section is evaluated, and the reliability of the event value As a result of the reliability evaluation, if there is at least one phase interval in which the ratio of the event value 1 exceeds the reference reliability value and at least one phase interval in which the ratio of the event value 0 exceeds the reference reliability value, .

INDUSTRIAL APPLICABILITY As described above, the present invention diagnoses a partial discharge in a transformer using data satisfying reliability among data acquired through a sensor, thereby diagnosing a partial discharge in a transformer in a state of eliminating the influence of noise There is an advantage that it can be.

Further, by extracting an acoustic signal generated during partial discharge through a sensor inserted in an insulating oil passage, the influence of noise on collection of data for partial discharge diagnosis can be minimized.

1 is a schematic diagram of a transformer safety diagnosis system according to a preferred embodiment of the present invention.
Fig. 2 shows an installation state of the acoustic emission sensor of Fig. 1. Fig.
3 is an exploded perspective view of the acoustic emission sensor of Fig.
4 is a graph illustrating resonance characteristics of a PMN-PT piezoelectric device according to an embodiment of the present invention.
5 is a diagram for explaining a method of obtaining the ultrasonic velocity of the insulating oil.
Figure 6 shows a KLM model of the acoustic emission sensor of Figure 1;
7 shows a transmission line representation of the KLM model of FIG.
8 shows a partial discharge time domain simulation signal.
9 shows a partial discharge frequency domain simulated signal.
10 shows simulation results of receiving characteristics of an acoustic emission sensor according to the conditions for manufacturing the rear matching layer.
11 is a functional block diagram of the diagnosis unit of FIG.
FIG. 12 shows a table for explaining a method for determining whether or not a partial discharge event is generated by the event determination unit.

While the invention is susceptible to various modifications and alternative forms, specific embodiments thereof are shown by way of example in the drawings and will herein be described in detail. It should be understood, however, that the invention is not intended to be limited to the particular embodiments, but includes all modifications, equivalents, and alternatives falling within the spirit and scope of the invention.

Like reference numerals are used for like elements in describing each drawing. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in detail with reference to the accompanying drawings.

The terms first, second, etc. may be used to describe various components, but the components should not be limited by the terms. The terms are used only for the purpose of distinguishing one component from another.

For example, without departing from the scope of the present invention, the first component may be referred to as a second component, and similarly, the second component may also be referred to as a first component.

And / or < / RTI > includes any combination of a plurality of related listed items or any of a plurality of related listed items.

It is to be understood that when an element is referred to as being "connected" or "connected" to another element, it may be directly connected or connected to the other element, .

On the other hand, when an element is referred to as being "directly connected" or "directly connected" to another element, it should be understood that there are no other elements in between.

The terminology used in this application is used only to describe a specific embodiment and is not intended to limit the invention.

The singular expressions include plural expressions unless the context clearly dictates otherwise. In the present application, the terms "comprises" or "having" and the like are used to specify that there is a feature, a number, a step, an operation, an element, a component or a combination thereof described in the specification, But do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, or combinations thereof.

Unless defined otherwise, all terms used herein, including technical or scientific terms, have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs.

Terms such as those defined in commonly used dictionaries are to be interpreted as having a meaning consistent with the contextual meaning of the related art and are to be interpreted as either ideal or overly formal in the sense of the present application Do not.

Hereinafter, a transformer safety diagnosis system according to a preferred embodiment of the present invention will be described with reference to FIGS. 1 to 12 attached hereto.

Referring to FIG. 1, the transformer safety diagnosis system 1 may include an acoustic emission sensor 100 and a diagnosis unit 200. The diagnostic unit 200 may collect the output signal of the acousto-electronic sensor 100 through the signal line 300 and may use the collected output signal to determine whether a partial discharge in the transformer has occurred.

The front mast 110 has a spherical shape and may have a rectangular parallelepiped insertion hole 111 into which the rear mast 120 is inserted and fixed. The rear mast 120 may have a rectangular parallelepiped shape and the piezoelectric elements 130 may be attached on four sides. The output ends of the piezoelectric elements 130 on the four sides can be joined to the signal line 300 on the upper surface of the rear mast 120. As is well known, the piezoelectric element 130 can convert a sound wave generated during partial discharge into an electrical signal and output it. The acoustic emission signal of the piezoelectric element 130 can be easily collected by locating the piezoelectric element 130 between the front and rear masts 110 and 130, Can be prevented. Also, by the structure in which the piezoelectric element 130 is positioned on the four sided sides of the spherical front mast 110, it is possible to collect acoustic output signals in a non-directional manner.

As the piezoelectric element 130, PZT and PMN-PT piezoelectric single-crystal elements can be used. The characteristics of the PZT and PMN-PT piezoelectric single crystal devices can be as shown in Table 1 below.

Properties PZT ceramics PMN-PT
단일 결정 PZT-5A PZT-5H Electro-mechanical coupling factor, k _r 0.49 0.505 0.65-0.75 Piezoelectric charge constant, d ₃₃ (10 ^-12 C / V) 374 593 1,500-2,500 Piezoelectric voltage constant, g ₃₃ (10 ^-3 VM / N) 24.8 19.7 35 Curie Temperature, (占 폚) 36.5 190 150 Sound velocity (m / s) 4,350 4,560 3,600 Density (kg / m ³ ) 7,750 7,500 8,000 Acoustic impedance, (10 ⁶ kg / m ² s) 34 34 28.8 Frequency constant, N _t (Hz) 1,890 2,000 1,800-1,900

The PMN-PT piezoelectric single crystal has a piezoelectric constant of g ₃₃ The reception characteristic of the acoustic response signal can be good because the value is very high. Therefore, it is preferable that PMN-PT piezoelectric single crystal is used as the piezoelectric element 130. [

Since the frequency range of the acoustic emission signal is less than 1 MHz, the center frequency of the acoustic emission sensor is preferably 1 MHz.

The thickness t of the piezoelectric element 120 in the acoustic emission sensor can be calculated by the following equation (1).

Here, f = frequency (Hz)

With the above equation, it is preferable that the thickness of the piezoelectric element 120 is 1.6 to 1.8 mm. In consideration of the resonance characteristics, it is preferable that the width of the piezoelectric element 120 is 1.9 to 2.1 mm and the length is 1.8 to 2.2 mm. Referring to FIG. 4, a PMN-PT piezoelectric device having a thickness of 1.8 mm, a width of 2 mm, and a length of 2 mm may exhibit resonance characteristics at 1 Mhz.

It may be desirable that the front mats 110 are machined to the shape of the device to an appropriate thickness to maximize the permeability of the sound waves by protecting the piezoelectric elements and reducing the acoustic impedance difference between the element and the test body. Since the acoustic emission signal generated inside the transformer is propagated in an arbitrary direction, it may be desirable that the acoustic emission signal is formed in the form of an integral sphere so that the acoustic emission signal can be detected in various directions. The material of the front mating body 110 can be selected by the following equation (2).

Where Z ₁ = the acoustic impedance of the piezoelectric element, Z ₃ = the acoustic impedance of the insulating oil used in the transformer, Z ₂ is the acoustic impedance of the material used for the front mating body

As seen in Table 1 above, the acoustic impedance of the PMN-PT piezoelectric element can be 28.8 (10 ⁶ kg / m ² s).

To measure the acoustic impedance of the transformer insulation oil, the acoustic impedance of a Far East essential oil (No. 1, No. 4), commonly used as transformer insulation oil, was measured. Far-end oil (No. 1, No. 4) Specifications of insulating oil may be as shown in Table 2 below.

Specific gravity, 15/4 C 0.825 Kinematic viscosity cs (f) m2 / s 40 C 8.520 100 C 2.450 Pour Point C -40 Flash point C PM 150 Evaporation rate,%, 98 C, 5 hours 0.17 reaction neutrality Computers, mg KOH / g 0.01 Corrosiveness Noncorrosive Myth stability 120 C, 75 hours Sludge, wt% 0.09 Computers, mg KOH / g 0.27 Moisture, ppm 15 Breakdown voltage, 25mm, kV 60 Dielectric loss tangent, 80 C,% 0.0017

By applying the ultrasonic wave reflection method of measuring the ultrasonic velocity of the insulating oil by measuring the ultrasonic signal reflected from the surface of the metal specimen in the insulating oil by using the ultrasonic transducer after the metal specimen is filled in the insulating oil after the container is filled with the insulating oil, Impedance was measured.

5, the relationship between the time difference ( Δt ) between the first and second ultrasonic signals reflected from the surface of the metal test piece passing through the insulating oil, and the distance (D) between the metal test piece and the ultrasonic probe, v _p can be obtained.

The ultrasonic velocity of the insulating oil measured using each of the different ultrasonic transducers can be as shown in Table 3 below.

2.25 Mhz probe 5 Mhz probe 10 Mhz transducer Street
(mm) time
(? T / 2) speed
(m / s) Street
(mm) time
(? T / 2) speed
(m / s) Street
(mm) time
(? T / 2) speed
(m / s) 3 2.16 1388.89 2 1.42 1408.45 2 1.45 1379.31 4 2.88 1388.89 3 2.16 1388.89 3 2.17 1382.49 11 7.98 1378.45 10 7.20 1388.89 4 2.93 1373.31 12 8.70 1379.31 12 8.68 1382.49 6 4.34 1382.88

The average value of the dielectric oil ultrasonic velocity based on Table 3 is about 1390 m / s and the specific gravity of the dielectric oil is about 0.8, which can be 800 kg / m ³ in terms of density.

Therefore, the acoustic impedance, i.e., the acoustic impedance of the insulating oil, which is the product of the ultrasonic velocity and the density, can be 1.112 MRayL.

Substituting the acoustic impedance of the PMN-PT piezoelectric element, 28.8 (10 ⁶ kg / m ² s), and the acoustic impedance of the insulating oil, 1.112 MRayL, into the above equation 2 gives the acoustic impedance Z ₂ ) May be about 5.57 MRayL.

Therefore, it is preferable that a material having an acoustic impedance of 5.4 to 5.6 MRayL is used as the material of the front mast 110. Teflon, Plexiglas, Acryl, Backlite, PMMA (polymethyl methacrylate) and the like having an acoustic impedance of about 5 MRayL may be used as the front mating body 110.

The rear mast 130 serves as a damping material capable of restricting the vibration of the piezoelectric element 120, thereby adjusting the bandwidth of the sensor. Thus, by analyzing the acoustic emission reception characteristics, it may be desirable to select the appropriate backing jersey 130 material.

In order to analyze the acoustic emission reception characteristics, a KLM model as shown in FIG. 6 was used. It is possible to obtain the impulse response of the acoustic emission sensor by constructing the acoustic emission sensor in the form of a network in the KLM model and expressing it as a reciprocating transfer function. Through the simulation process, the design value of the rear mast 130 It is possible to predict the response signal in accordance with the received signal. The KLM model and transmission line theory can be used to analyze the response signal of the acoustic emission sensor while changing the conditions of the rear matching layer. Therefore, a transmission line model for the acoustic emission sensor as shown in FIG. 7 can be constructed based on the basic structure of the acoustic emission sensor.

In the equivalent circuit, the overall transfer matrix can be expressed as the following equation (3) as a product of transfer matrices for each network.

Table 4 summarizes the respective transfer matrices.

Transfer matrix Meaning Formulation Remark N1 electrical coupling transformer with n turns

n: ratio of input and output voltage N2 matrix with series inductance, L

ω: angular frequency N3 matrix with capacitances, C _o and C ^'

N4 변환기 매트릭스

Φ : transformer ratio N5 matching matrix between backing and piezo-material

Z _b : acoustic impedance of backing N6 piezo-matrix connected to the matching layer

Z _c : acoustic impedance of piezo-material N7 전칭 매칭 층

Z _f : acoustic impedance of front matching layer

In Table 4, the phase angle? ₁ included in the transfer function at the front matching side can be expressed by the following Equation (4).

Here, t ₁ = ultrasound transmission time of the front mast, ω = angular frequency, v ₁ = ultrasonic velocity of the front mast

In Table 4, C _o represents the capacitance _{of the} piezoelectric material, and C ^' can be represented by the following equation (5).

는 압전 재료의 전기기계결합계수이며, sinc=sin(πx)/πx임
here,

Is the electromechanical coupling coefficient of the piezoelectric material, and sinc = sin (? X) /? X

The winding ratio? Of the piezoelectric material can be expressed by the following equation (6).

Assuming that the partial discharge is transmitted through the insulating oil in order to obtain the transfer function representing the reception characteristic of the acoustic emission signal transmitted from the transformer partial discharge, the transfer matrix representing the insulating oil as the transfer medium can be expressed as Equation (7) .

Here, Z _m = acoustic impedance of insulating oil, θ 2 = phase angle in insulating oil, which can be obtained by using the sound wave transmission time, frequency, and sound wave velocity of the transmission medium

The final transfer matrix that can represent both the partial discharge sound source, the transfer medium (insulating oil), and the acoustic emission receiver can be expressed by the following Equation (8).

Here, Ns = the transfer matrix of the acoustic output signal generated by the partial discharge

Finally, the transfer function of the acoustic emission signal transmitted from the partial discharge acoustic emission signal source to the acoustic emission sensor for reception can be expressed as Equation (9).

Where Z _i = electrical input impedance, Z ₀ = electrical output impedance n _ij = element of the transfer matrix N _TR

To apply Equation (9), a transfer matrix capable of representing a partial discharge signal is required. The acoustic emission signal generated by the partial discharge has a time response as shown in FIG. 8 and may have a frequency response as shown in FIG. The results of simulation of the received signal characteristics of the acoustic emission sensor while inputting the frequency response of FIG. 9 to the KLM model and varying the acoustic impedance of the rear matching layer using design conditions of the acoustic emission sensor and dielectric oil characteristics, ≪ / RTI > The simulation program is written in Matlab program.

It can be seen from FIG. 10 that as the acoustic impedance of the back material increases, the size of the received signal decreases and the frequency bandwidth increases.

It can be seen from the above simulation results that the acoustic impedance of the rear matching layer of the acoustic emission sensor can secure a suitable frequency bandwidth of the sensor without significantly reducing the signal size in the range of about 5 to 8 MRayL .

The backing material may be prepared by blending an epoxy and a tungsten powder having an average particle size of 25 mu m. The acoustic impedance according to the mixing ratio of epoxy and tungsten powder can be as shown in Table 5 below.

Ratio
(epoxy: powder) Density
(Kg / m3) Velocity
(㎧) Acoustic impedance (MRayl) 1: 0
1: 2
1: 4
1: 6 1150
1710
3570
5050 2836
2395
1704
1720 3.3
4.1
6.1
8.5

In order for the acoustic impedance of the rear matching layer to be in the range of about 5 to 8 MRayL, the mixing ratio of epoxy and tungsten powder may preferably be 1: 4 to 6.

The above acoustic emission sensor 100 can receive the acoustic emission signal 1 inserted into the insulating oil passage 2 on the transformer and propagated at the partial discharge generation point P omnidirectionally. At this time, the acoustic emission signal (1) can be easily collected by the piezoelectric element (120) by the front matching layer (110). The rear matching layer 110 acts as a damper for restricting the vibration of the piezoelectric element 120 at the rear portion of the piezoelectric element 120 when the piezoelectric element 120 receives the acoustic emission signal, And can broaden the frequency bandwidth.

Referring to FIG. 11, the diagnosis unit 200 may include a sensing data acquisition unit 210, an event determination unit 220, and a partial discharge diagnosis unit 230. The sensing data acquisition unit 210 can receive an electrical signal corresponding to the acoustic emission signal 1 from the piezoelectric element 120 through the signal line 300. [ At this time, the sensing data acquisition unit 210 may amplify the electrical signal received from the piezoelectric element 120, and may sample the received electrical signal according to a predetermined sampling scheme. The sensing data acquisition unit 210 may sample the electrical signal received at a preset number of times per second and a predetermined number of times per one cycle. For example, the sensing data acquisition unit 210 can perform sampling of 3840 times per second by performing 60 sampling cycles per second and 64 sampling cycles per one second.

Then, the event determination unit 220 divides one period into a predetermined phase interval, for example, eight phase intervals, and then determines whether there is at least one of the sampled electric signals exceeding the reference value Cutoff Can be determined. The event determination unit 220 may assign "1 " as an event value to the phase interval in which at least one of the sampled electric signals exceeds the reference value (Cutoff). Alternatively, the event determination unit 220 may assign "0" as an event value to a phase interval that does not exceed the reference value (Cutoff) among the sampled electric signals. This process can be performed for all cycles. Through this process, the same information as the table of FIG. 12 can be prepared. FIG. 12 shows a case where the sensing data acquisition unit 210 samples six cycles per second and one period is divided into eight phase intervals.

As described above, when the application of the event value to all the cycles is completed, the event determination unit 220 can evaluate the reliability of the event value.

The event determination unit 220 may perform a reliability evaluation on an event value for each phase. The event determination unit 220 can calculate at least one of the ratio of the event value "1 " and the ratio of" 0 "in each phase interval as a result of assigning the event value to all the periods. The event determination unit 220 may determine whether the ratio of the event value "1 " or the ratio of" 0 "in the phase interval exceeds a preset reference confidence value. Here, the reference confidence value may be any number greater than 50%. The event determination unit 220 determines that the ratio of the event value " 1 "exceeds the predetermined reference confidence value in at least one phase interval and the ratio of the event value" 0 " Value, it can be determined that the partial discharge event has occurred. 12, the reliability of the ratio of event value "1" exceeds 80%, which is the reference confidence value, and the phase interval is 0 to 45, 45 to 90, 225 to 270, 270 to 315, The event determination unit 220 can determine that the partial discharge event has occurred because the reliability of the event value "0 " at 360 exceeds the reference reliability value of 80%. In this way, by determining that a partial discharge event has occurred only when an instantaneous peak waveform has occurred, the resolution between the noise and the partial discharge can be very high. That is, when a signal exceeding a continuous reference value is received, it can be detected and treated as noise.

The partial discharge diagnosis unit 230 may diagnose a partial discharge when it is determined by the event determination unit 220 that a partial discharge has occurred. At this time, the partial discharge diagnosis unit 230 can diagnose the partial discharge risk level, the partial discharge type, and the like by comparing the stored partial discharge pattern with the signal obtained through the acoustic emission sensor 100. The present invention does not limit the diagnostic method of the partial discharge diagnosis unit 230. [ That is, the partial discharge diagnosis unit 230 analyzes the partial discharge using various methods such as phase resolved patrial discharge (PRPD), pulse sequence analsys (PSA), and chaotic analysis of partial discharge (CAPD) .

100: acoustic emission sensor
110: Front fitting
120: piezoelectric element
130: rear surface assembly
200:
210: Sensing data acquisition unit
220: Event determination unit
230: partial discharge diagnosis unit
300: Signal line

Claims (6)

An acoustic emission sensor-based transformer safety diagnosis system using a piezoelectric material,
A sensing data acquisition unit for receiving the electrical signal from the acoustic emission sensor and sampling it according to a predetermined method to generate sampling data; And
And an event determiner for determining whether a partial discharge event is generated by performing reliability evaluation of the sampling data. The method according to claim 1,
Wherein the acoustic emission sensor comprises:
A front mating body, a rear mating body to be inserted into the front mating body, and a piezoelectric element placed between the front mating body and the rear mating body,
Wherein the piezoelectric element is a PMN-PT piezoelectric single crystal device. 3. The method of claim 2,
The piezoelectric element includes:
1 MHz, resonance characteristics,
Wherein the piezoelectric element has a thickness of 1.6 to 1.8 mm, a width of 1.9 to 2.1 mm and a length of 1.8 to 2.2 mm. The method of claim 3,
The acoustic impedance of the front mating body may be,
Equation

(Where Z ₁ = acoustic impedance of the piezoelectric element, Z ₃ = acoustic impedance of the insulating oil used in the transformer, and Z ₂ is the acoustic impedance of the material used for the front mating body)
Lt; / RTI >
Wherein the front mating body comprises:
Wherein the acoustic impedance is 5.4 to 5.6 MRayL. 5. The method of claim 4,
The acoustic impedance of the rear mast is 5 to 8 MRayL,
Wherein the rear mating body comprises an epoxy and tungsten powder,
The mixing ratio of the epoxy and the tungsten powder,
1 < / RTI >:< RTI ID = 0.0 > 4-6. ≪ / RTI > The method according to claim 1,
The sensing data acquisition unit
Generating sampling data at a predetermined number of times per second and a predetermined number of times during the predetermined period,
The event determination unit may determine,
The method of claim 1, further comprising the steps of: dividing the predetermined period into at least one phase interval and providing an event value for each of the divided phase intervals, wherein, in the phase interval in which at least one sampling data exceeds the reference value in the divided phase interval, And assigns 0 as an event value to the phase section in which all the sampling data is equal to or less than the reference value in the divided phase section,
By calculating at least one of a ratio of the event value 1 and a ratio of 0 in the phase section and determining whether at least one of the calculated ratio of 1 and the ratio of 0 exceeds the predetermined reference confidence value, Evaluating the reliability of the values,
As a result of the reliability evaluation of the event value, if there is at least one phase interval in which the ratio of the event value 1 exceeds the reference reliability value and at least one phase interval in which the ratio of the event value 0 exceeds the reference reliability value, Discharge event has occurred in the transformer safety diagnosis system.

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