Description

SYSTEM AND METHOD FOR DETECTING PARTIAL

DISCHARGE POSITION

Technical Field

[1] The present invention relates to a system and a method for monitoring an electric device, particularly which can detect a partial discharge position. Background Art

[2] There has been a difficulty in detecting and removing an electric discharge source because its size is usually too small to find. Accordingly, it has been recognized as one of important schemes to estimate the partial discharge position with more accuracy in order to prevent the possible breakdown of electric devices.

[3] Schemes for estimating a partial discharge position are largely classified into one of using the attenuation of an electromagnetic discharge signal that is generated by the discharge and one of using a difference in arrival time of electromagnetic discharge signals at a partial discharge sensor.

[4] FIG. 1 is a view for illustrating a method of detecting a partial discharge position according to the prior art.

[5] Referring to FIG. 1, an electric device, for example, a gas insulated bus (GIB) 10 includes a central conductor 12, a box 14, and a plurality of partial discharge sensors 16. The box 14 is insulated from and wraps around the central conductor 12. The partial discharge sensors 16 detect the occurrence of partial discharge signals at the GIB 10.

[6] When a partial discharge occurs at the GIB 10, a partial discharge sensor 16, which is positioned near a partial discharge position DP, may detect a strong partial discharge signal and another partial discharge sensor 16 that is far off the partial discharge position DP may detect a relatively weak partial discharge signal. The position DP may be approximately estimated by performing the interpolation in a graph of position- signal strength of the partial discharge signals that are sensed by the partial discharge sensors 16.

[7] FIG. 2 is a view for illustrating a method of detecting a partial discharge position using a difference in arrival time of an electromagnetic discharge signal at a partial discharge sensor according to the prior art.

[8] In this method, as shown in FIG. 2, first and second partial discharge sensors 26 and

28 are mounted in an electric device under detection to estimate a partial discharge position. The first and second partial discharge sensors 26 and 28 are spaced from each other by a predetermined interval Dt at the electric device. When a partial discharge is

created, its partial discharge signal is detected by the first and second partial discharge sensors 26 and 28, and its arrival time when the signal reaches the sensors 26 and 28 is calculated by a measurement unit 23. The arrival time varies depending on the distance between the discharge sensors 16 and the position DP, and therefore, a first distance Dl between the first partial discharge sensor 26 and the position DP and a second distance D2 between the second discharge sensor 28 and the position DP may be calculated using the arrival time. Disclosure of Invention Technical Problem

[9] The conventional methods described above require multiple partial discharge sensors for estimating the discharge position. Accordingly, the partial discharge sensors need to be installed sufficiently narrow between each other to be capable of detecting a weak discharge signal. This leads to a difficulty in installing such sensors, for example, in a complicated electric device.

[10] On the other hand, when the interval between the sensors is set to be wide, it may be difficult to wire the sensors to a measurement unit, and the signal can be attenuated or deformed while the signal is transmitted from the sensors to the measurement unit. This may deteriorate the reliability of methods of estimating the partial discharge position. Technical Solution

[11] An aspect of the present invention provides a system and a method of detecting a partial discharge position by employing a single partial discharge sensor.

[12] Another aspect of the present invention provides a system and a method of detecting a partial discharge position, which are capable of improving the accuracy by employing a single partial discharge sensor.

[13] An exemplary embodiment of the present invention provides a system of detecting a partial discharge position comprising: a partial discharge sensor detecting an electromagnetic partial discharge signal; a waveform monitoer measuring a waveform of a partial discharge signal detected by the partial discharge sensor; a conversion module converting the waveform and dividing the partial discharge signal according to each transmission mode; and a calculation module calculating a distance between the partial discharge sensor and the partial discharge position through an arrival time and a frequency of the divided partial discharge signal.

[14] The conversion module may have an algorithm for simultaneously analyzing time and frequency.

[15] The algorithm may comprise STFT (Short Time Fourier Transform) or WT (Wavelet

Transform).

[16] The calculation module may yield a group velocity of a signal for each transmission mode and calculate a distance between the partial discharge sensor and the partial discharge position through group velocities of signals of two transmission modes and a difference in arrival time of the two signals.

[17] Another exemplary embodiment of the present invention provides a method of detecting a partial discharge position comprising: measuring a waveform of a partial discharge signal; converting the measured waveform and dividing the partial discharge signal according to each transmission mode; calculating a group velocity of a signal for each transmission mode through a frequency of the divided partial discharge signal; and calculating a partial discharge position through group velocities of two signal of two transmission modes and a difference in arrival time of the two signals.

[18] Dividing the converted waveform may comprise dividing the partial discharge signal using an algorithm for simultaneously analyzing time and frequency.

[19] The group velocity may be calculated from Equation 1 as below:

[20] [Equation 1]

[22] where "C" refers to the speed of light, "fc" refers to a cutoff frequency of a signal of each mode, and "f ' refers to a frequency at an arrival time of the signal of corresponding mode.

[23] Calculating a partial discharge position may comprise selecting a first transmission mode and a second transmission mode; calculating a difference in arrival time of two signals of the first and second transmission modes; and calculating a distance between the partial discharge sensor and the partial discharge position by entering the difference in arrival time and group velocities of the two signals at the arrival times in Equation 3 as below:

[24] [Equation 3]

[26] where "L" refers to the distance between the partial discharge sensor and the partial discharge position, "vgl" and "vg2" refer to group velocities of two signals of the first and second transmission modes, respectively, and "δt" refers to the difference in arrival time.

Advantageous Effects

[27] The present invention can provide further improved reliability in detecting a partial

discharge position compared to conventional methods that employ a plurality of partial discharge sensors. [28] And, since a single partial discharge sensor is provided, costs can be saved.

Brief Description of the Drawings

[29] The invention is described more fully hereinafter with reference to the accompanying drawings, in which embodiments of the invention are shown. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set for the herein:

[30] FIGS. 1 and 2 are views for illustrating a method of detecting a partial discharge position according to the prior art;

[31] FIG. 3 is a view for illustrating a method of detecting a partial discharge position according to an exemplary embodiment of the present invention;

[32] FIG. 4 is a flowchart for illustrating a method of detecting a partial discharge position according to an exemplary embodiment of the present invention;

[33] FIG. 5 is a graph showing a waveform of a partial discharge signal;

[34] FIG. 6 is a graph showing a relationship between arrival time and frequency of a partial discharge signal; and

[35] FIG. 7 is a view showing a system of detecting a partial discharge position according to an exemplary embodiment of the present invention. Best Mode for Carrying Out the Invention

[36] The invention is described more fully hereinafter with reference to the accompanying drawings, in which embodiments of the invention are shown. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure is thorough, and will fully convey the scope of the invention to those skilled in the art. In the drawings, the size and relative size of layers and regions may be exaggerated for clarity. Like reference numerals in the drawings denote like elements. Hereinafter, exemplary embodiments of the present invention will be described in more detail with reference to accompanying drawings.

[37] FIG. 3 is a view for illustrating a method of detecting a partial discharge position according to an exemplary embodiment of the present invention.

[38] Even though a gas insulation bus (GIB) that includes a box 32 and a central conductor 34 has been described as an example in the exemplary embodiment, the present invention is not limited thereto, and may also be applicable to various electric equipment, such as gas insulated switchgears, transformers, and electric cables.

[39] Referring to FIG. 3, when a partial discharge occurs at a partial discharge position

DP in an electric device, for example, a coaxial-structured GIB, an electromagnetic

partial discharge signal is generated and propagates in summed one of various transmission modes, such as a transverse electric and magnetic (TEM) mode and transverse electric (TE) modes TEI l, TE21, TE31, and TE41.

[40] Theoretically, the signals of transmission modes other than TEM mode have their own unique cutoff frequencies, and electromagnetic signals alone that have greater frequencies than such cutoff frequencies are transmitted in their corresponding modes.

[41] The signal is transmitted at different speed depending on each mode, so that the time when a partial discharge sensor 36 detects the signal varies according to each mode. Accordingly, a distance L between the sensor 36 and the partial discharge position DP may be estimated through the arrival time for a signal of each mode.

[42] When a partial discharge occurs at an electric device, a signal of TEM mode that is transmitted in the light speed C is firstly detected by the sensor 36. Then, signals of the other modes propagate at group velocities vg and detected by the sensor 36. The detected discharge signals can be measured by a waveform monitor 38, such as oscilloscopes, and therefore, the distance L can be calculated from the measured values.

[43] FIG. 4 is a flowchart for illustrating a method of detecting a partial discharge position according to an exemplary embodiment of the present invention, FIG. 5 is a graph showing a waveform of a partial discharge signal, and FIG. 6 is a graph showing a relationship between arrival time and frequency of a partial discharge signal.

[44] Referring to FIGS. 4, 5, and 6, a waveform of a partial discharge signal detected by the sensor 36 is measured using the waveform monitor 38 (Step Sl).

[45] The partial discharge signal is one synthesized from signals of various transmission modes as shown in FIG. 5.

[46] Each arrival time and each frequency of the signals of different modes are calculated to yield a group velocity (vg) from the measured waveform (Step S2).

[47] For the first time, a signal of TEM mode that has the fastest group velocity is detected at a first time point 52 in FIG. 5. Then, a signal of TEl 1 mode that has the second fastest group velocity is detected at a second time point 54 and synthesized with the signal of TEM mode.

[48] The arrival times and frequencies of the signals can be more accurately calculated through a scheme that can analyze the signals according to arrival times and frequencies for respective modes.

[49] As an example, schemes high time and frequency resolution, such as STFT (Short

Time Fourier Transform) and WT (Wavelet Transform), can be introduced to analyze the partial discharge signals.

[50] The relationship between frequency and time can be acquired by performing STFT on the measured partial discharge signals as shown in FIG. 6. It can be seen that the partial discharge signals may be divided with respect to each transmission mode by

STFT. A signal that arrives at a first time point 62 is one for TEM mode, and a signal that arrives at a second time point 64 is one for TEl 1 mode, which is the second fastest signal except for the signal for TEM mode, wherein the frequency 66 of the signal for

TEI l mode is 668MHz. [51] Each group velocity is calculated using the arrival time and frequency for each signal for each transmission mode (Step S3). [52] The signal for TEM mode propagates in the light velocity C of light, and the group velocities vg of the signals other than the signal for TEM mode may be yielded from

Equation 1 as below: [53] [Equation 1]

[55] where, "fc" refers to a cutoff frequency of each signal for each mode, "f" refers to each frequency of each signal for each mode at each arrival time, and "C" refers to the light velocity.

[56] The difference (δt) in arrival time can be expressed as Equation 2:

[57] [Equation 2]

[59] where, "tl" and "t2" refers to the arrival time of signals for a first transmission mode and a second transmission mode, respectively, "vgl" and "vg2" refer to the group velocities of the first transmission mode and the second transmission mode, respectively, and "L" refers to a distance between the partial discharge sensor and discharge position (DP).

[60] The discharge position DP is calculated through the group velocities and difference in arrival time between signals for two transmission modes (Step S4).

[61] As can be seen in Equation 2, the difference in arrival time can be expressed by the group velocities and distance. The distance L between the sensor 36 and the discharge position DP may be calculated by Equation 3 that is rewritten in terms of "L" from Equation 2.

[62] [Equation 3]

[63]

L= M

^V SI - ^V S2

[64] The group velocity of the signal for each transmission mode can be calculated

through the arrival time and the frequency at the arrival time of the partial discharge signal divided according to each transmission mode. As a consequence, the distance between the partial discharge sensor and the partial discharge position DP can be calculated by entering the group velocity and difference in arrival time between signals of two transmission mode in a simple equation. For example, a distance L between the partial discharge sensor and the partial discharge position DP may be calculated using the difference in arrival time between the signal of TEM mode and the signal of TEl 1 mode and the group velocities.

[65] According to an exemplary embodiment of the present invention, a partial discharge position (DP) can be detected even with a single partial discharge sensor, so that some disadvantages, such as delays or deformations in signal and restrictions in measuring region, which can occur at existing methods that employ a plurality of partial discharge sensors, can be eliminated.

[66] FIG. 7 is a view showing a system of detecting a partial discharge position according to an exemplary embodiment of the present invention.

[67] Referring to FIG. 7, a detection system 70 includes a partial discharge sensor 72, a waveform monitor 74, a conversion module 75, a calculation module 76, and a storage unit 78. The partial discharge sensor 72 detects a partial discharge signal. The waveform monitor 74 measures a waveform of the partial discharge signal detected by the partial discharge sensor 72. The conversion module 75 performs a transform on the detected waveform and divides the transformed waveform according to each transmission mode. The calculation module 76 calculates the distance between the partial discharge sensor 72 and a partial discharge position through a predetermined equation. The storage unit 78 stores the equation therein.

[68] The conversion module 75 has a conversion algorithm therein for converting a partial discharge signal in which various transmission modes are synthesized into a time- frequency distribution signal having high time and frequency resolution. For example, at least one of various conversion algorithms such as STFT (Short Time Fourier Transform) and WT (Wavelet Transform) may be embedded in the conversion module 75.

[69] The partial discharge signals may be divided according to their arrival times and frequencies through the conversion algorithm. At this time, the arrival times and frequencies are different from one another according to transmission modes of the partial discharge signals, so that the divided signal can be correspondent to transmission modes.

[70] The calculation module 76 receives frequencies and arrival time for two signals of two transmission modes from the conversion module 75 to calculate group velocities of the two signals, and estimates the distance between the partial discharge position

and the partial discharge sensor 72 through the difference in arrival time and the group velocities.

[71] The conversion module 45 and the calculation module 46 may be either programmed in a microprocessor or implemented with hardware. For example, the conversion module 45 and the calculation module 46 may be semiconductor chips or a single chip that can carry out their functions. The storage unit 48 may be a memory that is separately mounted in the system or integrated with the conversion module 45 and/or the calculation module 46.

[72] In exemplary embodiments of the present invention, a single partial discharge sensor is provided to detect a partial discharge position. A distance between the partial discharge sensor and the partial discharge position may be estimated through difference in arrival time and group velocities of partial discharge signals that are divided according to transmission modes.

[73] The exemplary embodiments of the present invention can provide further improved reliability in detecting a partial discharge position compared to conventional methods that employ a plurality of partial discharge sensors.

[74] And, since a single partial discharge sensor is provided, costs can be saved.

[75] Although the illustrative embodiments of the present invention have been described herein with reference to the accompanying drawings, it is to be understood that the present invention should not be limited to those precise embodiments and that various other changes and modifications may be affected therein by one of ordinary skill in the related art without departing from the scope or spirit of the invention. All such changes and modifications are intended to be included within the scope of the invention as defined by the appended claims.

[76]

[77]