WO2009017275A1

WO2009017275A1 - Self-examination type cast resin transformer

Info

Publication number: WO2009017275A1
Application number: PCT/KR2007/004849
Authority: WO
Inventors: Ji-Hong Kim; Won-Chang Jung
Original assignee: Kp Electric Co., Ltd.
Priority date: 2007-07-31
Filing date: 2007-10-04
Publication date: 2009-02-05
Also published as: KR100831960B1

Abstract

Provided is a self-examination-type cast resin transformer. A partial discharge measurement device of the self-examination-type cast resin transformer includes a high- voltage hybrid sensor, which is molded using an epoxy resin and disposed on one side of the transformer to detect radio-frequency (RF) partial discharge induced in a high-voltage winding. Thus, the partial discharge measurement device can measure partial discharge even in gaseous, liquid, and solid states. Also, the partial discharge measurement device is embedded in the transformer to minimize the ingress of noise and transmission loss. Further, partial discharge can be precisely measured at highest measuring sensitivity using a high-voltage hybrid sensor having a good signal-to-noise ratio (SNR).

Description

SELF-EXAMINATION TYPE CAST RESIN TRANSFORMER

Technical Field

[1] The present invention relates to a self-examination-type cast resin transformer, and more particularly, to a self-examination-type cast resin transformer in which a high- voltage hybrid sensor having a good signal-to-noise ratio (SNR) and an examination unit are integrally formed with a transformer so that line impedance can be reduced to maximize measuring sensitivity and partial discharge can be measured even in gaseous, liquid, and solid insulated states. Background Art

[2] In recent years, the increased demand for power leads to a strong need for high- capacity ultra high- voltage transformers, and transformer substations are showing a tendency to become unmanned. A fault that occurs in a high-capacity transformer has far-reaching effects, such as enormous economical loss and serious psychological unrest. Therefore, it becomes increasingly necessary to diagnose insulation to prevent transformer faults.

[3] Thus, a vast amount of research has been conducted on developing continuous monitoring devices for continuously monitoring unusual signs of faults during driving of a transformer so as to increase the reliability of the transformer and stably supply power. Also, fault prevention/diagnosis systems are being developed. The fault prevention/diagnosis systems are aimed to continuously store data in the foregoing continuous monitoring devices to decide the advance of a fault based on the tendency of the data to rise, decide the type of the fault based on correlation between detected abnormal data, and stop operating the transformer and adopt proper measures when an unusual sign makes dangerous progress.

[4] On-line fault detection techniques, which are applied to continuously monitor transformers, may include a technique of analyzing gases dissolved in insulating oil of transformers, a technique of measuring partial discharge, and a technique of measuring temperatures. Here, since internal insulation failure, which causes serious faults to a transformer, involves partial discharge, it is generally accepted that the partial discharge is closely associated with the life span of the transformer. In particular, the partial discharge is rapidly responsive to a sign of a fault, so that a transformer fault can be prevented by measuring the partial discharge. When partial discharge occurs in a transformer, insulating oil is suddenly compressed due to the partial discharge, thus generating pulse-type ultrasonic waves.

[5] An example of a monitoring device for measuring partial discharge is disclosed in the following Document 1.

[6] Japanese Patent Laid-open Publication No. 60-100060 (hereinafter, referred to as

Document 1) discloses a partial discharge detection device in which an ultrasonic sensor installed at an outer wall of a transformer converts an ultrasonic signal into an electric signal, and a wave detector converts the electric signal into a square wave signal. When an acoustic signal passes through the wave detector, a pulse wave signal, which is delayed by an arbitrarily set time from a point in time at the acoustic signal passes through the wave detector, is generated by a pulse generator. When the ultrasonic signal that has passed through the wave detector is input to a decision unit at the same time as the pulse wave signal generated by the pulse generator, the decision unit recognizes the ultrasonic signal as a partial discharge signal induced in the transformer and indicates the partial discharge signal using a meter. The partial discharge detection device is based on the fact that the ultrasonic signal due to the partial discharge induced in the transformer lasts for a longer duration of time than a signal generated due to externally induced noise. Since the signal generated due to externally induced noise lasts only for a short duration of time, when the pulse generator delays a pulse wave signal by an arbitrarily set time and generates the delayed signal, the signal generated due to the externally induced noise already fades and cannot be input to the decision unit at the same time as the ultrasonic signal, so that the decision unit cannot recognize the signal generated due to the externally induced noise as the ultrasonic signal.

[7] Another example of a monitoring device for measuring partial discharge is disclosed in the following Document 2.

[8] Korean Patent Registration No. 0482305 (registered on March 31 , 2005)

(hereinafter, referred to as Document 2) is directed to an ultrasonic on-line detector for measuring partial discharge induced in a transformer. According to Document 2, the ultrasonic on-line detector continuously measures only an ultrasonic signal due to partial discharge induced in the transformer during driving of the transformer and transmits only important data of the ultrasonic signal to a prevention/diagnosis system during the driving of the transformer, so that the prevention/diagnosis system can continuously monitor if partial discharge occurs in the transformer and how the partial discharge makes progress.

[9]

Disclosure of Invention Technical Problem

[10] However, the partial discharge detection device disclosed in Document 1 includes a simple logic circuit and a meter and is designed for a tester to carry and diagnose a transformer fault at regular time intervals. Therefore, the partial discharge detection device disclosed in Document 1 is inadequate for a continuous monitoring device that involves continuously measuring an ultrasonic signal at all times during driving of a transformer and transmitting the measurement result to a prevention/diagnosis system to monitor an advanced state of partial discharge. In particular, the foregoing partial discharge detection device is capable of removing external induced noise, which lasts for a shorter duration of time than an ultrasonic signal due to partial discharge induced in the transformer. However, proper oscillation, which occurs during steady driving of the transformer, and mechanical sounds, which are made by a cooling fan, a cooling pump, and a tap changer, last for longer durations of time than the ultrasonic signal due to the partial discharge induced in the transformer. Thus, the partial discharge detection device cannot eliminate noises, such as the proper oscillation of the transformer and the mechanical sounds. Furthermore, since there are a wide variety of complicated ultrasonic signals, for example, corona noise made by an incoming line, in the transformer, it is impossible to eliminate all noises using such a simple analog circuit, such as a logic circuit.

[11] Also, according to the ultrasonic continuous monitoring device disclosed in

Document 2, an ultrasonic sensor is located outside a transformer to measure discharge in a liquid insulated state. Since the discharge is measured outside the transformer, measuring sensitivity is low. Also, a measured signal is transmitted through an ultrasonic signal line to the ultrasonic on-line detector located outside the transformer, so that measuring efficiency deteriorates due to line impedance, and it is actually difficult to measure discharge in a solid insulated structure.

[12] The present invention is directed to a self-examination-type cast resin transformer in which a high-voltage hybrid sensor having a good signal-to-noise ratio (SNR) and an examination unit are embedded, so that line impedance can be reduced to maximize measuring sensitivity and partial discharge can be measured even in gaseous, liquid, and solid insulated states. Technical Solution

[13] One aspect of the present invention provides a self-examination-type cast resin transformer, which is molded using a resin and includes a high-voltage hybrid sensor molded using the resin and disposed on one side of the self-examination-type cast resin transformer to detect radio-frequency (RF) partial discharge induced in a high- voltage winding.

[14] The self-examination-type cast resin transformer may further include an examination unit for examining the partial discharge in response to a sense signal output from the high- voltage hybrid sensor and transmitting a current state wirely or wirelessly to display the current state on a display unit in real-time to output a warning message when the current state is decided to be dangerous, wherein the examination unit is disposed on one side of the self-examination-type cast resin transformer.

[15] The high- voltage hybrid sensor may include a capacitor including, as an electrode, a metal mesh formed a predetermined distance apart from a central conductor connected to a high- voltage terminal by an insulator; and a high- voltage coupler formed of a resistor connected in parallel with the high- voltage terminal and the metal mesh to adjust a duration time from a wave head to a wave tail of a partial discharge signal, wherein the insulator is the resin.

[16] The high- voltage hybrid sensor may further include a dummy for dividing an output voltage of the high-voltage coupler.

[17] The high- voltage hybrid sensor may be integrally molded with a protrusion that protrudes from an upper portion of a main body of the self-examination-type cast resin transformer, and a line connected between the high- voltage winding and the high- voltage terminal may be combined with the high- voltage hybrid sensor in the protrusion.

[18] According to the present invention, a self-examination-type cast resin transformer is capable of measuring partial discharge even in gaseous, liquid, and solid insulated states.

[19] Also, a partial discharge measurement device is embedded in the self-examination-type cast mold transformer, thereby minimizing the ingress of noise and transmission loss.

[20] Also, partial discharge can be precisely measured at highest measuring sensitivity using a high-voltage hybrid sensor having a good signal-to-noise ratio (SNR).

[21] Furthermore, the sensor embedded in the self-examination-type cast mold transformer is capable of measuring partial discharge continuously so that a fault of the transformer due to the partial discharge can be prevented to supply good quality power.

[22]

Brief Description of the Drawings

[23] FIG. 1 is a plan view of a partial discharge measurement device of a self- examination-type resin cast resin transformer according to an exemplary embodiment of the present invention.

[24] FIG. 2 is a cross-sectional view of the partial discharge measurement device shown in FIG. 1.

[25] FIG. 3 is a circuit diagram of a hybrid sensor according to an exemplary embodiment of the present invention.

[26] FIG. 4 is an equivalent circuit diagram of the hybrid sensor shown in FIG. 3. [27] FIG. 5 is an equivalent circuit diagram of a conventional hybrid sensor.

[28]

Mode for the Invention

[29] The present invention provides a transformer 100, which is integrally formed with a high- voltage hybrid sensor 200 and an examination unit 300, so that line impedance can be reduced to maximize measuring sensitivity, and partial discharge can be measured even in gaseous, liquid, and solid insulated states.

[30] The present invention will now be described more fully hereinafter with reference to the accompanying drawings, in which exemplary embodiments of the invention are shown. This invention may, however, be embodied in 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 complete and fully conveys the scope of the invention to one skilled in the art. The same reference numerals are used to denote the same elements throughout the specification, and a description of the same elements will not be repeated.

[31] FIG. 1 is a plan view of a partial discharge measurement device of a self- examination-type resin cast resin transformer according to an exemplary embodiment of the present invention, and FIG. 2 is a cross-sectional view of the partial discharge measurement device shown in FIG. 1.

[32] A conventional hybrid sensor is highly capable of eliminating noise and has good stability and sensitivity. But, since measures current using a ground line as shown in Fig.5, the conventional hybrid sensor cannot be used under a high voltage.

[33] In order to overcome this drawback, the present invention provides a self- examination-type resin cast transformer as shown in FIGS. 1 and 2. The self- examination-type resin cast transformer includes a high-voltage hybrid sensor 200 and an examination unit 300. The high-voltage hybrid sensor 200 is molded using an epoxy resin and disposed on one side of a transformer 100 to detect radio-frequency (RF) partial discharge of a high-voltage terminal that is connected to a high-voltage winding. The examination unit 300, which is also disposed on one side of the transformer 100, examines partial discharge using a sense signal output from the high- voltage hybrid sensor 200, wirelessly displays a current state in real-time, and outputs a warning message when it decides that the current state is dangerous.

[34] Also, as shown in FIGS. 3 and 4, the high-voltage hybrid sensor 200 includes a capacitor Cl, a high-voltage coupler C , and a resistor R2. The capacitor Cl includes a metal mesh (not shown), which is formed a predetermined distance "d" apart from a central conductor connected to the high-voltage terminal 400 by an insulator (i.e., the epoxy resin). The high- voltage coupler C is formed of a resistor Rl that is connected

HV in parallel with the high- voltage terminal 400 and the metal mesh in order to adjust a duration time from a wave head to a wave tail of a partial discharge signal. The resistor R2 is a dummy resistor that divides an output voltage of the high- voltage coupler C .

[35] Accordingly, the capacitance of the capacitor Cl can be expressed as shown in

Equation 1:

[36]

(1),

[37] wherein C denotes the capacitance of the capacitor Cl, ε denotes a dielectric constant (=3.4) of the epoxy resin, S denotes the area of the metal mesh, and "d" denotes the distance between the metal mesh and the central conductor.

[38] The connection of the high-voltage hybrid sensor 200 with the high-voltage winding of the transformer 100 will now be described in detail. The transformer 100 is a conventional mold transformer that includes a winding unit (not shown) having a low- voltage winding and a high-voltage winding and an iron core unit around which the winding unit is wound. Also, in the transformer 100, the winding unit is molded using the epoxy resin like in the conventional art.

[39] The winding unit passes through the molded epoxy resin and the low- voltage winding and the high-voltage winding are connected to a low- voltage terminal and the high- voltage terminal 400, respectively, so that power can be supplied to the molded high- and low- voltage windings.

[40] Also, as shown in FIG. 1, the high-voltage hybrid sensor 200 is integrally molded with a protrusion that protrudes from an upper portion of a main body of the transformer 100, and a line connected between the high- voltage winding and the high- voltage terminal 400 is combined with the high- voltage coupler C of the high- voltage hybrid sensor 200 in the protrusion of the transformer 100.

[41] Hereinafter, a process of measuring partial discharge using the partial discharge measurement device of the self-examination-type resin cast resin transformer will be described.

[42] As shown in FIGS. 3 and 4, a high- voltage current is supplied from the high- voltage terminal 400 through different paths according to the state.

[43] Specifically, an inductor La causes low impedance due to an inductive reactance X to form a signal path for an audio-frequency (AF) power signal (e.g., a 60-Hz power signal). Here, the inductive reactance X is equal to 2πfL, wherein "f" denotes the frequency of the power signal and L denotes the inductance of the inductor La. That is, the inductive reactance X varies in proportion to the frequency "f" of the power signal. Thus, low impedance is caused in response to an AF power signal to pass the AF power signal, while high impedance is caused in response to an RF power signal not to pass the RF power signal.

[44] Next, the capacitor Cl causes high impedance and forms a signal path for an RF partial discharge current. In general, a capacitive reactance X is equal to l/2πfC, wherein "f" denotes the frequency of the power signal and C denotes the capacitance of the capacitor Cl. That is, the capacitive reactance X varies in inverse proportion to the frequency of the power signal. Thus, impedance increases in response to an AF power signal, while the impedance decreases in response to an RF power signal. Thus, the capacitor Cl inhibits the AF power signal or noise and allows only an RF partial discharge current to pass therethrough. A voltage corresponding to the RF partial discharge current is applied to both ends of the resistor R and output as an RF partial discharge detection signal through first and second output terminals (+, -) connected to both ends of the resistor R.

[45] Therefore, surge and breakdown signals (ultra high-frequency signals) are applied through the high-voltage coupler C HV , a capacitor Cb, and an output terminal "output", and a power frequency and ground noise (AF signals) are applied through the high- voltage coupler C HV , the inductor La, an inductor Lb, and the output terminal "output".

However, since a partial discharge current (an RF signal) is applied through the high- voltage coupler C HV , the dummy resistor R2, and the resistor R, the examination unit

300 examines through the signal path of the partial discharge current if partial discharge occurs.

[46] Examination results output by the examination unit 300 are transmitted wirely or wirelessly and displayed on a monitor 500 in real-time. When the examination result is that a current state is dangerous, the examination unit 300 outputs a warning message, such as a vocal or text message, to an operator.

[47] While the invention has been shown and described with reference to certain exemplary embodiments thereof, it will be understood by one skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims. Industrial Applicability

[48] The present invention provides a technique of preventing a breakdown in a cast resin transformer by measuring partial discharge of the cast resin transformer. The technique according to the present invention can be applied to continuous monitoring devices for continuously measuring signs of faults during the driving of a transformer.

[49]

Claims

[1] A self-examination-type cast resin transformer, which is molded using a resin, comprising a high- voltage hybrid sensor molded using the resin and disposed on one side of the self-examination-type cast resin transformer to detect radio- frequency (RF) partial discharge induced in a high-voltage winding.

[2] The self-examination-type cast resin transformer according to claim 1, further comprising an examination unit for examining the partial discharge in response to a sense signal output from the high- voltage hybrid sensor and transmitting a current state wirely or wirelessly to display the current state on a display unit in real-time to output a warning message when the current state is decided to be dangerous, wherein the examination unit is disposed on one side of the self-examination-type cast resin transformer.

[3] The self-examination-type cast resin transformer according to claim 1, wherein the high-voltage hybrid sensor comprises: a capacitor including, as an electrode, a metal mesh formed a predetermined distance apart from a central conductor connected to a high- voltage terminal by an insulator; and a high- voltage coupler formed of a resistor connected in parallel with the high- voltage terminal and the metal mesh to adjust a duration time from a wave head to a wave tail of a partial discharge signal, wherein the insulator is the resin.

[4] The self-examination-type cast resin transformer according to claim 3, wherein the high-voltage hybrid sensor further comprises a dummy for dividing an output voltage of the high- voltage coupler.

[5] The self-examination-type cast resin transformer according to claim 1, wherein the high-voltage hybrid sensor is integrally molded with a protrusion that protrudes from an upper portion of a main body of the self-examination-type cast resin transformer, and a line connected between the high-voltage winding and the high- voltage terminal is combined with the high- voltage hybrid sensor in the protrusion.