Abstract:
The present invention relates to a device for detecting a partial discharge for a power transformer which detects an electromagnetic signal occurring due to faulty insulation. The device includes an antenna unit receiving electromagnetic waves, an insulator including the antenna unit, a metallic air-tight unit that seals a connector connected to the insulator and connecting a coaxial cable, and the coaxial cable exposed to the outside of the metallic air-tight unit. Thus, it is possible to enhance broadband properties through an internal conductor of a drain valve.

Description:
TECHNICAL FIELD 
       [0001]    The present invention relates to a device for detecting partial discharge for a power transformer that detects partially discharged electromagnetic wave signals caused by faulty insulation. 
       BACKGROUND ART 
       [0002]    A general partial discharge detecting device for a power transformer is disposed within electric power equipment while maintaining a predetermined insulating distance, and detects partially discharged signals. 
         [0003]    When the partial discharge detecting device is disposed within a drain valve of the power transformer, the partial discharge detecting device does not additionally include a separate inspection window, and sensors can be arranged at various locations. 
         [0004]      FIG. 1  illustrates a partial discharge detecting device according to the related art. 
         [0005]    Referring to  FIG. 1 , a partial discharge detecting device according to the related art is disposed within a drain valve. 
         [0006]    The partial discharge detecting device  10  is separately provided with a signal input end  11  and a signal output end  13 . The partial discharge detecting device  10  detects partially discharged signals with receiving units  12   a  and  12   b,  in which the receiving units  12   a  and  12   b  are connected to the input end and the output end, respectively, in the form of a parallel coupler. 
         [0007]    Although a frequency band of signals generated during partial discharge corresponds to a wideband, the partial discharge detecting device generally detects signals in the frequency band of 0.3 to 1.5 GHz of the Ultra High Frequency (UHF) band (0.3˜3 GHz) less affected by noise. In order to receive signals of the wide UHF band, wideband properties are required. It is impossible to have a wideband through a single shape and an identical shape since a wavelength is physically restricted, and therefore, it is necessary to design a receiving unit having several wavelengths. 
       DETAILED DESCRIPTION OF THE INVENTION 
     Technical Problem 
       [0008]    An aspect of the present invention is to provide a partial discharge detecting device for a power transformer that can detect partially discharged signals, which are the result of an abnormality in the power transformer, through multiple sub-bands. 
       Technical Solution 
       [0009]    In accordance with one aspect of the present invention, a device for detecting partial discharge for a power transformer is provided. The device includes: an antenna unit receiving an electromagnetic wave; an insulating sealing unit including the antenna unit and protecting a coaxial cable; a metal sealing unit connected with the insulating sealing unit and a metal handle; the metal handle sealing a connector connecting the metal sealing unit and the coaxial cable; and the coaxial cable extracted to an outside of the metal sealing unit. 
         [0010]    The insulating sealing unit cover from the antenna unit to a contact part of an internal conductor of a drain valve. 
         [0011]    The sum of a length of the insulating sealing unit and a length of the metal sealing unit may be proportional to a wavelength for a resonant frequency, the length of the insulating sealing unit obtained by subtracting a length of the antenna unit from a length of the drain valve. 
         [0012]    The antenna unit may receive division frequencies configured with a plurality of divided signal bands of a received frequency band for detecting partial discharge signals of the power transformer. 
         [0013]    The device may further include a measuring unit connected through the coaxial cable and measuring the electromagnetic waves received by the antenna unit. 
       Advantageous Effects 
       [0014]    As described above, according to the present invention, the partial discharge detecting device can receive signals in a wide range of frequency bands through multiple sub-bands. 
         [0015]    Furthermore, according to the present invention, the partial discharge detecting device can detect signals of a frequency band having a different wavelength for each of multiple sub-bands. 
         [0016]    In addition, according to the present invention, performance of an antenna can be improved using characteristics of an internal conductor of a drain valve to which an antenna is attached. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0017]      FIG. 1  illustrates a partial discharge detecting device according to the related art; 
           [0018]      FIG. 2  is a longitudinal sectional view of a partial discharge detecting device according to an embodiment of the present invention; 
           [0019]      FIG. 3  illustrates an example for explaining a resonant frequency and an equivalent wavelength depending on an antenna in a partial discharge detecting device according to an embodiment of the present invention; and 
           [0020]      FIG. 4  is a detailed view of the ground structure and the metal handle illustrated in  FIG. 2 . 
       
    
    
     MODE FOR CARRYING OUT THE INVENTION 
       [0021]    Hereinafter, an embodiment of the present invention will be described in detail with reference to the accompanying drawings. 
         [0022]    The embodiment of the present invention relates to a system for diagnosing a power transformer by detecting partially discharged signals of the Ultra High Frequency (UHF) band. 
         [0023]    An antenna unit included within a drain valve is sealed by an insulating sealing unit. According to the sum of a length of the drain valve but excluding the antenna unit and a length of a conductor boundary by a metal sealing unit, a bandwidth of the antenna is increased by periodic resonance of the antenna unit, which is sealed with the insulating sealing unit, by an E-field distribution within the valve. 
         [0024]      FIG. 2  is a longitudinal sectional view of a partial discharge detecting device according to an embodiment of the present invention. 
         [0025]    Referring to  FIG. 2 , a partial discharge detecting device  200  may be disposed in a drain valve  260  at an upper or lower portion of a power transformer  210 . 
         [0026]    The partial discharge detecting device  200  may operate in conjunction with a partial discharge signal processing device  240  through an N-type connector  220  and a coaxial cable  230 . 
         [0027]    In order to detect partial discharge signals in an Ultra High Frequency (UHF) band of 0.5 to 1.5 GHz occurring in the power transformer, the partial discharge detecting device  200  may include an antenna unit  201  for detecting signals in multiple sub-bands. 
         [0028]    The antenna unit  201  of the partial discharge detecting device  200  may have different wavelengths for the respective multiple sub-bands of the partial discharge signal band (e.g., four frequency bands: a first frequency band of 0.5 to 0.75 GHz, a second frequency band of 0.75 to 1.00 GHz, a third frequency band of 1.00 to 1.25 GHz, and a fourth frequency band of 1.25 to 1.5 GHz). 
         [0029]    The antenna unit  201  receives division frequencies configured with a plurality of divided signal bands for detecting the partial discharge signals of the power transformer among frequency bands. 
         [0030]    The antenna unit  201  of the partial discharge detecting device  200  may detect an electromagnetic wave caused by the partial discharge. The detected electromagnetic wave may be transmitted to the measuring device  240  through an insulator  202  including the antenna unit  201 , a metal sealing unit  203 , a metal handle  206 , and the coaxial cable  230 . At this time, a specific structure of a ground unit and the metal handle  206  is the same as illustrated in  FIG. 4 . 
         [0031]    The measuring device  240  is connected with the partial discharge detecting device  200  through the coaxial cable, and measures intensity of the electromagnetic wave detected by the antenna unit  201 . Based on the measurement result, the measuring device  240  may determine whether the partial discharge occurs within the power transformer  210 . 
         [0032]    A resonant frequency and a bandwidth of the antenna unit  201  may be determined depending on the size thereof. Furthermore, the resonant frequency and the bandwidth may be determined depending on the sum of a length of an internal conductor of a drain valve  260  and  250  to which the insulating sealing unit  202  other than the antenna unit  201  is attached and a length of a conductor boundary by the metal sealing unit. 
         [0033]    The insulating sealing unit  202  may be configured in the form of an airtight container such as a pipe to include the antenna unit  201 . The insulating sealing unit  202  includes the antenna unit  201 . The insulating sealing unit may be configured to extend to a contact surface of the internal conductor of the drain valve  260  and  250 . The bandwidth of the resonant frequency and the wavelength may be proportional depending on the length of the internal conductor of the drain valve  260  and  250  corresponding to the length of the insulating sealing unit  202  other than the antenna unit  201  and the length of the conductor boundary by the metal sealing unit. 
         [0034]    Referring to  FIG. 2 , the partial discharge detecting device  200  for the power transformer may include a flange  204  in a single tube form such that the large-sized antenna unit  201  may also be attached to the drain valve  250  and  260 . 
         [0035]    That is, a sensor is attached to the power transformer while the drain valve is closed to prevent insulating oil from leaking. At this time, a space between the drain valve and the flange is narrow, and therefore, the antenna may have a limitation in size to be attached between the drain valve and the flange. In order to solve the above-described problem, the flange is made in the single tube form, thereby increasing the space between the drain valve and the flange to make the antenna unit larger. 
         [0036]    Referring to  FIGS. 2 and 4 , the partial discharge detecting device  200  may include a structure (a ground unit  207 ) for spacing a shield line of an antenna cable  205  apart from the conductive pipe  203  to maintain an insulating distance and grounding the shield line and the conductive pipe at the end portion of the conductive pipe for a distribution of E-field within the drain valve and the conductive pipe. 
         [0037]    Furthermore, the partial discharge detecting device  200  may include the metal handle  206  that seals the connector connecting the metal sealing unit and the coaxial cable and is covered with a waterproof tube to enable the regular measurement. 
         [0038]    That is, the metal handle  206  is a structure for sealing the connector  220  connecting the metal sealing unit and the coaxial cable  230 . When the cap of the metal handle  206  is removed, a connection with the coaxial cable may be made, and when the handle is covered with the waterproof tube, the regular measurement may be carried out. 
         [0039]      FIG. 3  illustrates an example for explaining a resonant frequency and an equivalent wavelength depending on an antenna in a partial discharge detecting device according to an embodiment of the present invention. 
         [0040]    (A) to (D) of  FIG. 3  represent wavelengths (λ) eof the sum of the length of the insulating sealing unit  202  but excluding the antenna unit  201  and the length of the metal sealing unit  203  according to a resonant frequency (f). That is, (A) to (D) of  FIG. 3  represent the wavelengths (λ) when a predetermined length (d1) of a total length (d1+d2) of the insulating sealing unit  202  and the metal sealing unit  203  other than the length of the antenna unit  201  is included in the insulating sealing unit  202 . Namely, the length d1 of the insulating pipe (the insulating sealing unit) may be determined as “the length of the drain valve−the length of the antenna unit (effective length)”. At this time, d2 is the length of the conductive pipe (the metal sealing unit). 
         [0041]    In (A) of  FIG. 3 , when the predetermined length (d1) of the total length (d1+d2) of the insulating sealing unit  202  and the metal sealing unit  203  other than the length of the antenna unit  201  is included in the insulating sealing unit  202 , a wavelength may be identical to the length of d1+d2 for a resonant frequency f1 of 0.58 GHz. 
         [0042]    In (B) of  FIG. 3 , when the predetermined length (d1) of the total length (d1+d2) of the insulating sealing unit  202  and the metal sealing unit  203  other than the length of the antenna unit  201  is included in the insulating sealing unit  202 , a wavelength may be 1.5 times longer than the length of d1+d2 for a resonant frequency f2 of 0.84 GHz. 
         [0043]    In (C) of  FIG. 3 , when the predetermined length (d1) of the total length (d1+d2) of the insulating sealing unit  202  and the metal sealing unit  203  other than the length of the antenna unit  201  is included in the insulating sealing unit  202 , a wavelength may be 2 times longer than the length of d1+d2 for a resonant frequency f3 of 1.125 GHz. 
         [0044]    In (D) of  FIG. 3 , when the predetermined length (d1) of the total length (d1+d2) of the insulating sealing unit  202  and the metal sealing unit  203  other than the length of the antenna unit  201  is included in the insulating sealing unit  202 , a wavelength may be 2.5 times longer than the length of d1+d2 for a resonant frequency f4 of 1.37 GHz. 
         [0045]    A phase by the length d1 and a phase by the length d2 satisfy “Phase by d1+Phase by d2=2π”. At this time, the phase by the length d1 may be defined as β1d1 (β1: propagation constant of medium 1), and the phase by the length d2 may be defined as β2d2 (p2: propagation constant of medium 2). The length of d2 (the conductive sealing unit) satisfying the condition β1d1+β2d2=2π″ may be defined by the following equation. 
         [0000]        d 2=1/β2(2π−β1 d 1)   Equation
 
         [0046]    Accordingly, as described above, according to the present invention, when the antenna unit  201  is included in the insulating sealing unit  202  by the predetermined length, properties of the wideband frequency can be improved. 
         [0047]    Although the present invention has been described by the restricted embodiments and the drawings as described above, the present invention is not limited to the above-described embodiments and various modifications and alterations can be made from the descriptions by those skilled in the art to which the present invention pertains. 
         [0048]    Accordingly, the scope of the present invention should not be determined by the above-described embodiments, and should be determined by not only the following claims but also their equivalents.