KR102295214B1 - Partial discharging detection-diagnosis system of distribution panel using high frequency current transformer - Google Patents

Abstract

The present invention relates to a system for detecting and diagnosing the partial discharge of a distribution panel using a high-frequency current sensor and, more specifically, to a system for detecting and diagnosing the partial discharge of a distribution panel using a high-frequency current sensor, capable of diagnosing power equipment by detecting a defect cause for partial discharge by analyzing a frequency component detected from a high-frequency current sensor and recognizing a pattern through characteristics of partial discharge. To achieve the objective, according to the present invention, the system for detecting and diagnosing the partial discharge of a distribution panel using a high-frequency current sensor includes: a high-frequency current sensor installed on an earthing line of power equipment, and detecting a discharge pulse signal generated by a current flowing through the earthing line; a detection/diagnosis device checking whether there is partial discharge based on the discharge pulse signal detected from the high-frequency current sensor, and determining the type of the partial discharge; and a shielding box shielding the high-frequency current sensor and the detection/diagnosis device. The detection/diagnosis device includes: a detection part outputting detection data by removing and amplifying a noise of the discharge pulse signal detected from the high-frequency current sensor; and a diagnosis part diagnosing the type of the partial discharge by comparing the detection data outputted from the detection part with comparison data collected through data acquisition (DAQ).

Description

Partial discharge detection and diagnosis system of a switchboard using a high-frequency current sensor

The present invention relates to a system for detecting partial discharge of a switchboard using a high-frequency current sensor, and more particularly, by analyzing a frequency component detected from a high-frequency current sensor and detecting a defective source of the partial discharge through the characteristics of the partial discharge ( It relates to a system for detecting and diagnosing partial discharge using a high-frequency current sensor for electric power devices in high-voltage switchgear, low-voltage switchgear, distribution board, motor control panel, etc.).

Partial discharge refers to a dielectric breakdown that occurs locally in a solid or liquid insulation system due to high voltage stress.

Partial discharge is defined as a local discharge that occurs before dielectric breakdown occurs at the inside or interface of an insulating material, and is largely divided into internal discharge and external discharge.

Internal discharge is generally generated in voids or voids inside a solid or liquid insulator, and refers to partial discharge generated by voids or internal conductive or non-conductive materials formed inside the insulator. The onset of the internal discharge phenomenon appears in different forms depending on the size or location of the void or the cause of the internal discharge.

The external discharge can be divided into a surface partial discharge in which the discharge current of an insulator is formed on the surface of the insulator, and a corona partial discharge generated in a gas surrounding the insulator.

In the case of surface partial discharge, the concentration of electric field is formed horizontally with the surface of the insulator and occurs mainly, and may occur at the end of a bushing, a power cable, and a terminal of a rotating machine winding.

When a partial discharge occurs, high-energy electrons or accelerated ions collide with the surface of the material to cause physical and chemical changes, and when these changes are accumulated, the performance as an insulator is reduced and deterioration occurs.

The detection of such a partial discharge is based on the phenomenon of exchange of energy accompanying the discharge, and this exchange of energy appears in the form of an electrical impulse signal, dielectric loss, light, sound, increase in gas pressure, and chemical reaction.

As one of techniques for detecting partial discharge, a partial discharge detection system is disclosed in Korean Patent Registration No. 10-2130271.

The technology includes a sensor unit including at least one sensor, a Variable Timing Filtering Method (VTFM) unit that separates a partial discharge signal and a noise signal from signals detected for each channel through the sensor unit and removes a noise component, each channel The peak holder unit that detects and outputs the level of each peak part in the partial discharge signal from which the noise component has been removed through the VTFM unit, and the peak level of the partial discharge signal output from the peak holder unit for each channel and a preset partial discharge analysis reference value are compared Then, the level of the partial discharge signal is calculated using the level comparison result of the comparison amplification unit amplifying and outputting the result, and the comparison amplification unit for each channel, and the control unit determines whether partial discharge occurs or not based on the operation result value. A signal arithmetic unit for discriminating, and controlling the parameter setting of the sensor unit, VTFM unit, peak holder unit, and comparison amplifier unit for each channel, and processing results of the VTFM unit, peak holder unit, comparison amplifier unit, and signal calculation unit for each channel It determines the caution or danger state of the partial discharge event based on the It is configured to include a control unit for displaying or outputting.

However, since the above technique uses a partial discharge signal detected for each channel, a plurality of channels must be provided, a process of processing the partial discharge signal detected for each channel is complicated, and a plurality of channels must be installed. have.

In addition, a partial discharge diagnostic device is disclosed in Korean Patent Publication No. 10-2183462.

The technology is an Ultra High Frequency (UHF) sensor that measures the partial discharge signal of the switchboard, a preprocessor that extracts a preset feature amount from the detection signal of the ultrahigh frequency, and learns the feature amount extracted by the preprocessor and a learning unit providing a weight, and a diagnosis unit diagnosing partial discharge according to the feature amount extracted by the pre-processing unit and the weight from the learning unit.

The above technique extracts the signal detected from the UHF sensor and the set feature amount to diagnose the partial discharge according to the weight, but the type of partial discharge, for example, internal discharge or external discharge, cannot be distinguished and diagnosed. have.

Registered Patent Publication No. 10-2130271 (2020. 06. 30.) Registered Patent Publication No. 10-2183462 (2020. 11. 20.)

The present invention has been devised to solve the above problems, and the problem to be solved in the present invention is to analyze a frequency component detected from a high-frequency current sensor to recognize a pattern through the characteristics of a partial discharge to detect a defect source of the partial discharge. An object of the present invention is to provide a diagnostic system for detecting partial discharge of a switchboard using a high-frequency current sensor that can be used.

The partial discharge detection and diagnosis system of a switchboard using a high-frequency current sensor according to the present invention for solving the above problems is a power device in the switchboard, for example, a transformer, a switchgear, a circuit breaker, a cable, a bus bar, a ground wire such as a transformer box bushing, or a high-frequency current sensor installed on a line and detecting a discharge pulse signal generated by a current flowing through the ground line or the line; a detection and diagnosis device for checking whether a partial discharge is present and determining a type of partial discharge based on the discharge pulse signal detected from the high-frequency current sensor; and a shielding box for shielding the high frequency current sensor and the detection and diagnosis device, wherein the detection and diagnosis device includes: a detection unit that removes and amplifies the noise of the discharge pulse signal detected by the high frequency current sensor and outputs detection data; and a diagnosis unit for diagnosing a type of partial discharge by comparing the detection data output from the detection unit with comparison data collected through DAQ (Data Acquisition).

Here, the detection unit includes: a noise removal filter for removing noise from the discharge pulse signal output from the high-frequency current sensor; a coupling capacitor connected in series to the noise removal filter to pass the AC component of the discharge pulse signal and block the DC component; a detection impedance connected in series with the coupling capacitor; and an amplifier for amplifying a voltage at both ends of the detection impedance, wherein the detection impedance may be configured as an RLC tuning circuit.

In addition, the noise removal filter includes: a clock pulse generator for generating a frequency clock with respect to the discharge pulse signal; a first flip-flop for outputting a signal by synchronizing the discharge pulse signal with a rising edge of a clock pulse generated by the clock pulse generator; a second flip-flop for generating a signal by synchronizing the signal from the first flip-flop at a rising edge of the clock pulse; a third flip-flop for generating a signal by synchronizing the signal from the second flip-flop at a rising edge of the clock pulse; a fourth flip-flop for generating a signal by synchronizing the signal from the third flip-flop at a rising edge of the clock pulse; an AND gate and a NOR gate for receiving the output pulses of the second to fourth flip-flops and outputting a predetermined value that has been calculated; and a JK type flip-flop that synchronizes output pulses of the AND gate and the NOR gate at the rising edge of the clock pulse to output a noise-removed signal. characterized by being

In addition, the amplifier may be configured as a two-stage amplifier circuit having an input offset voltage of 3 mV and an amplification degree of 40 dB.

In addition, the power device is characterized in that one selected from a transformer, a transformer, a cable, a bus bar, a circuit breaker, a switchgear, and an enclosure of the power device.

In addition, the high-frequency current sensor is composed of an iron core made of an alloy of nickel and zinc and an induction coil composed of a toroid of brass material, and the iron core is wound 20 to 50 times around the induction coil. .

In addition, the type of partial discharge diagnosed by the diagnosis unit is characterized in that one selected from corona discharge, internal discharge, surface discharge, and random discharge.

According to the present invention, the partial discharge detection and diagnosis system of the switchboard can be installed only by installing the high-frequency current sensor on the ground wire without deforming or disassembling the power device.

In addition, since the location of the partial discharge with respect to the power device can be easily derived by providing the type of the generated partial discharge, there is an advantage in that it is possible to improve the reliability of the maintenance of the power device inside the switchboard.

1 is a schematic configuration diagram of a state in which a partial discharge detection diagnostic system of a switchboard using a high-frequency current sensor according to the present invention is installed;
2 is a schematic configuration diagram of a partial discharge detection diagnostic system of a switchboard using a high-frequency current sensor according to the present invention;
3 is a configuration diagram of a detection unit of a detection diagnostic device applied to a partial discharge detection diagnostic system of a switchboard using a high-frequency current sensor according to the present invention;
4 is a circuit diagram of a noise removal filter applied to a diagnostic system for detecting partial discharge of a switchboard using a high-frequency current sensor according to the present invention;
5 is an equivalent circuit diagram of a detection unit applied to a partial discharge detection diagnostic system of a switchboard using a high-frequency current sensor according to the present invention;
6 is a circuit diagram of an amplifier applied to a diagnostic system for detecting partial discharge of a switchboard using a high-frequency current sensor according to the present invention;
7 is a graph showing a PRPD pattern for a type of partial discharge stored in comparative data applied to a diagnostic system for detecting partial discharge of a switchboard using a high-frequency current sensor according to the present invention;
8 is a diagram showing the configuration of a diagnostic unit applied to a diagnostic system for detecting partial discharge of a switchboard using a high-frequency current sensor according to the present invention.

Next, a preferred embodiment of a system for detecting partial discharge of a switchboard using a high-frequency current sensor according to the present invention will be described in detail with reference to the drawings.

Hereinafter, the same reference numerals are used for technical elements having the same function, and repeated detailed descriptions are omitted to avoid overlapping descriptions.

In addition, the examples described below are illustratively shown in order to effectively show the preferred embodiments of the present invention, and should not be construed to limit the scope of the present invention.

The present invention relates to a diagnostic system for detecting partial discharge of a switchboard using a high-frequency current sensor, and more particularly, by analyzing a frequency component detected from a high-frequency current sensor and detecting a defective source of the partial discharge through the characteristic of the partial discharge. It relates to a partial discharge detection diagnostic system of a switchboard using a high-frequency current sensor capable of diagnosing

1 is a schematic configuration diagram of a state in which a diagnosis system for detecting partial discharge of a switchboard using a high frequency current sensor according to the present invention is installed, and FIG. 2 is a schematic diagram of a diagnosis system for detecting partial discharge of a switchboard using a high frequency current sensor according to the present invention It shows the composition diagram.

1 and 2, the diagnostic system for detecting partial discharge of a switchboard using a high-frequency current sensor according to the present invention includes a high-frequency current sensor 10, a detection diagnostic device 20, and a shielding box 30. is composed

The high frequency current sensor 10 is installed on the ground line of the power device 1 and detects a discharge pulse signal generated by a current flowing through the ground line.

As the power device 1, it can be applied to various power devices such as transformers, transformers, cables, busbars, circuit breakers, switchgear, and enclosures of power devices such as switchboards or distribution boards, and any power device with a grounding wire may be used.

Looking at the example of the power cable, an unbalanced electric field is generated due to a void or foreign material in the main insulation system of the power cable. When this unbalanced electric field becomes above the threshold electric field value designed in the insulation system, the first discharge phenomenon occurs.

Since the insulation system is not restored to its normal state, the discharge phenomenon gradually develops, and a bridge is formed between the grounding wire and the main conductor, leading to the main insulation breakdown.

Although there may be differences in the standards defining such partial discharge, KS C IEC 60270 was established in accordance with the European standard IEC 60270 in Korea. Looking at this standard, partial discharge is defined as “a local electric discharge that occurs partially in an insulator between conductors, and may or may not occur adjacent to a conductor.” In addition, the partial discharge phenomenon generates an energy conversion phenomenon, and is converted into the form of a discharge current, electromagnetic wave, sound, chemical by-product, and the like.

The high-frequency current sensor measures the energy conversion phenomenon caused by the partial discharge through various coupling methods.

As such, the High Frequency Current Transformer (HFCT) is an inductive sensor, composed of a donut-shaped ferromagnetic iron core and an induction coil wound around the iron core, and is formed between a sheath of a power cable and a ground terminal. Alternatively, it is installed on various grounding wires such as the grounding wire between the enclosure of high voltage equipment and the grounding terminal.

That is, the HFCT, which is the high-frequency current sensor, is disposed through an iron core, and when a current flows through the ground line, the current of the ground line is induced in the induction coil, and a voltage is output by the current induced in the induction coil. At this time, the voltage induced in the induction coil, that is, the secondary side is output in proportion to the change in the primary side current and the mutual inductance, which is a proportional constant.

However, while the donut-shaped coil sensor has a wide frequency bandwidth, it has a disadvantage in that it includes a non-linear element dependent on temperature and magnetic flux density. Therefore, the HFCT, which is a high-frequency current sensor applied to the present invention, should be designed to detect a specific frequency.

In other words, in the initial stage of discharge of the current pulse, a rising time of several nanoseconds is exhibited, which outputs an important spectral component of several hundred MHz or more.

The high frequency range frequency component of the discharge pulse generated according to the partial discharge is filtered when it propagates to the grounding conductor to which the HFCT sensor is connected. Therefore, it should be designed to have a response characteristic of 40 MHz or less in order to detect partial charge when partial discharge occurs.

For example, the iron core of the HFCT is made of an alloy of nickel and zinc having high magnetic permeability, and the induction coil is configured in a toroidal shape made of brass, so that the iron core is wound dozens of times. Preferably, the induction coil may be configured to be wound within the range of 20 to 50 times.

According to such a configuration, the response characteristic of the HFCT has a range of 100 kHz to 30 MHz.

The detection and diagnosis apparatus 20 checks whether a partial discharge is present based on the discharge pulse signal detected from the high frequency current sensor 10 and determines the type of partial discharge.

Referring to FIG. 2 , the detection and diagnosis apparatus 20 includes a detection unit 100 and a diagnosis unit 200 .

The detection unit 100 performs a function of removing and amplifying the noise of the discharge pulse signal detected by the high-frequency current sensor and outputting detection data.

3 is a diagram showing the configuration of a detection unit of a detection and diagnosis apparatus applied to a partial discharge detection and diagnosis system using a high-frequency current sensor according to the present invention.

Referring to FIG. 3 , the detection unit 100 includes a noise removal filter 110 , a coupling capacitor 120 , a detection impedance 130 , and an amplifier 140 .

The noise removal filter 110 removes the noise of the discharge pulse signal output from the high-frequency current sensor.

Pulse noise such as corona occupies a frequency band similar to that of the discharge pulse signal generated by partial discharge, so it has a disadvantage that it cannot be removed by the frequency tuning method. However, noise generated by corona, etc. can be removed by using a noise gating circuit.

The noise gating circuit uses a high-speed analog switch or a digital switch, and the circuit is opened to a noise signal to block the output of the signal, and to a non-noisy scene, the circuit is closed to output a signal. am. In this case, the open time of the gate may be configured to be variable within the range of about 1 to 50 μs.

4 is a circuit diagram of a noise removal filter applied to a diagnostic system for detecting partial discharge of a switchboard using a high-frequency current sensor according to the present invention.

4, the noise removal filter 110 includes a clock pulse generator 111 that generates a frequency clock with respect to a discharge pulse signal, and a rising edge of a clock pulse generated by the discharge pulse signal from the clock pulse generator. a first flip-flop 112 for outputting a signal in synchronization with A third flip-flop 114 that generates a signal by synchronizing the signal from the second flip-flop 113 at the rising edge of the clock pulse, and the signal from the third flip-flop 114 at the rising edge of the clock pulse A fourth flip-flop 115 for generating a signal in synchronization, and an AND gate 116 for receiving output pulses of the second to fourth flip-flops 112 to 115 and outputting a predetermined value after operation and the output pulses of the NOR gate 117 and the AND gate 116 and the NOR gate 117 are synchronized at the rising edge of the clock pulse to generate a noise-removed signal It is configured to include a JK type flip-flop that outputs (JK type flip-flop) 118 .

In the above configuration, it is possible to remove noise included in the discharge pulse signal according to the clock pulse generated by the clock generator 111 .

Accordingly, the noise removal filter 110 has the advantage of being able to set the range of noise to be removed by adjusting the clock pulse generated by the clock generator 111 .

The coupling capacitor 120 is connected in series to the noise removal filter to pass the AC component of the discharge pulse signal and block the DC component.

That is, the constant coupling capacitor 120 is connected in series to the signal terminal to remove the DC component transferred to the serially connected detection impedance 130 .

The detection impedance 130 is connected in series with the coupling capacitor 120 to generate a voltage by the current flowing in the circuit.

5 is an equivalent circuit diagram of a detection unit applied to a partial discharge detection diagnostic system of a switchboard using a high-frequency current sensor according to the present invention.

5, the detection impedance 130 is composed of an RLC tuning circuit.

In this configuration, the voltage V output to both ends of the detection impedance 130 is expressed by Equation 1 below.

Equation 1)

where V is the voltage output from both ends of the detection impedance, q is the amount of discharge charge, a is the stray capacitance (capacitance inside the circuit), C is the capacitance of the detection impedance, k is the capacitance of the coupling capacitor, and R is The resistance of the detection impedance, m, is the combined capacitance of the circuit.

Also, ω is expressed by the following equation (2).

Equation 2)

Here, L is the inductor capacitance of the detection impedance.

According to Equations 1 and 2, the voltage across the detection impedance is proportional to the amount of discharge charge q and the coupling capacitor k, and the magnitude of the discharge charge can be calculated as the output voltage. At this time, since the frequency of the partial discharge pulse is different according to the type of discharge, the partial discharge can be detected by appropriately adjusting the RLC constant.

The amplifier 140 performs a function of amplifying the voltage across both ends of the detection impedance.

6 is a circuit diagram of an amplifier applied to a diagnostic system for detecting partial discharge of a switchboard using a high-frequency current sensor according to the present invention.

Referring to FIG. 6 attached, the amplifier 140 may be configured as a two-stage amplifier circuit.

The current flowing to the ground wire due to partial discharge is small. In addition, since the high frequency current sensor 10 detects by inducing the primary side current of the ground line to the secondary side, the discharge pulse signal detected by the high frequency current sensor is also small. Therefore, it is necessary to amplify the voltage at both ends of the detection impedance.

In addition, the amplifier 140 should have a frequency range sufficient to detect partial discharge by applying an operational amplifier, and should be configured to have a low noise level.

Accordingly, the amplifier 140 applied to the present invention may be configured as a two-stage amplifier circuit having an input offset voltage of 3 mV and an amplification degree of 40 dB.

In addition, a low-pass filter is configured on the output side of the amplifier 140 to pass the frequency of the discharge pulse signal and take external or internal radiation noise into consideration.

Next, the diagnosis unit 200 of the detection and diagnosis apparatus 20 will be described.

The diagnosis unit 200 performs a function of diagnosing the type of partial discharge by comparing the detection data output from the detection unit 100 with comparison data collected through DAQ (Data Acquisition).

The comparative data collected through DAQ (Data Acquisition) was measured with a PD sensor by randomly generating a set partial discharge, and the measured signal was calculated and accumulated by a peak detection method and stored.

As the identification factors of peak detection, the magnitude (mV) and phase of the discharge were set and stored.

7 is a graph showing PRPD patterns for types of partial discharges stored in comparative data applied to a diagnostic system for detecting partial discharge of a switchboard using a high-frequency current sensor according to the present invention.

The discharge pulse signal due to partial discharge can be expressed in the form of a pulse having phase information for each cycle of the output voltage, which is called PRPD (Phase Resolved Partial Discharge). am. That is, when looking at the pattern generated by PRPD for the same type of partial discharge, a predetermined area is derived in a clustered form. do.

7 (a) is a PRPD pattern of corona discharge, (b) is a PRPD pattern of internal discharge, (c) is a PRPD pattern of surface discharge, (d) is a PRPD pattern of random discharge.

Here, the random discharge means a state in which at least two or more partial discharges from among corona discharge, internal discharge, and surface discharge are generated in combination.

The magnitude (voltage) of the discharge with respect to the discharge pulse signal is expressed by the following Equation 3 according to Faraday's law of electromagnetic induction.

Equation 3)

Here, e is the secondary induced voltage, Φ is the magnetic flux density, n is the number of turns, A is the cross-sectional area, H is the magnetic field, and μ ₀ is the vacuum permeability.

In this case, the secondary-side induced voltage is proportional to the change in the current flowing through the primary and the mutual inductance, which is a proportionality constant, which is expressed by Equation (4).

Equation 4)

Here, e is the secondary-side induced voltage, M is the mutual inductance, and i is the primary-side current.

In order to analyze the frequency and amplitude change of the discharge pulse signal for a predetermined time, a TF (Time-Frequency) method may be applied in the present invention.

In the TF method, the detected discharge pulse signal is classified into regions according to time and frequency to form a Time-Frequency (T-F) Map, and noise is removed and processed through a normalization process.

As a method for diagnosing partial discharge, a fuzzy neural network intelligent algorithm can be selectively applied in the diagnosis unit 200 or an embedded processor, and partial through clustering and pattern classification using each feature value detected in the diagnosis unit 200 discharge can be detected.

The diagnosis unit 200 calculates the detection data output from the detection unit 100, that is, the detection signal s(t), as a normalized signal s'(t), and converts the normalized signal s'(t) to the normalized signal s'(t). When expressed as a standard deviation in the time and frequency domains, it is expressed as in Equation 5 below.

Equation 5)

Here, σ _T is the standard deviation in the time domain, σ _f is the standard deviation in the frequency domain, s(t) is the normalized signal for the detection signal, and t ₀ is the center of gravity of the normalized signal.

Accordingly, by using Equation 5 above, the discharge pulse signal measured at the positive polarity (0 to 180°) and the negative polarity (181 to 360°) of the power frequency (60 Hz) is analyzed in terms of time and size of the discharge to perform partial discharge. characteristics can be analyzed.

For example, the pulse by the partial discharge is output in the form of attenuated vibration, and may be divided into a first vibration that occurs first and a second vibration that occurs second. At this time, if the sum of the rise time (0 ~ Vmax) and the fall time (Vmax ~ 0) in each vibration is defined as the vibration width, the amplitude of the first vibration is T _w1 and the width of the second vibration is T _w2 . can

In addition, a physical shape method for analyzing a pulse of a partial discharge using kurtosis and skewness can be applied.

The kurtosis analyzes the sharpness of the pulse. If the value is positive (+), it is called leptokurtic, when it is negative (-), it is called flatykurtic, and when it is 0, it forms a normal distribution. It can be defined as a mesokurtic distribution.

In this way, the diagnosis unit 200 extracts a parameter having a characteristic from the detection data detected by the detection unit 100 and the comparison data stored in the DAQ, and classifies the extracted parameter into a pattern using an operator vector, so that the detected data and and to determine the type of partial discharge with respect to the detection data by comparing the correlation of the comparison data.

8 is a diagram showing the configuration of a diagnostic unit applied to a diagnostic system for detecting partial discharge of a switchboard using a high-frequency current sensor according to the present invention.

8, the diagnosis unit 200 identifies an identification element extraction module 210 for extracting identification elements from detection data or comparison data, and identification elements extracted from the identification element extraction module 210 A pattern classification module 220 for classifying a pattern of an identification element using an element vector, a detection data pattern for the detection data and a comparison data pattern for the comparison data based on the pattern classified by the pattern classification module 220 It is configured to include a comparison module 230 for comparing and a diagnostic module 240 for diagnosing a type of partial discharge with respect to the pattern derived from the comparison module 230 .

The identification factors set in the identification factor extraction module 210 include skewness (Sk), kurtosis (Ku), correlation coefficient (CCk), ratio between discharge amounts (Q), number of discharges (N) and maximum discharge size. It is constructed including the ratio (Qmax).

Skewness Sk may be expressed by the following Equation (6).

Here, Sk is the skewness, x _i is a data value (comparison data or detection data), p _{i is the probability of x i} occurring at the i-th phase angle, μ is _{the average value of x i} , and σ is the standard deviation.

The skewness is a measure of the degree of deviation from the central axis compared to the normal distribution, and is calculated as a positive value (+) when the distribution is skewed outward from the center of the whole.

The kurtosis (Ku) indicates the sharpness of the distribution and is expressed by the following Equation (7).

Equation 7)

Here, Ku is the kurtosis, x _i is the data value (comparison data or detection data), p _{i is the probability of x i} occurring at the i-th phase angle, μ is _{the average value of x i} , and σ is the standard deviation.

The correlation coefficient CCk indicates the degree of similarity between the x-distribution and the y-distribution, and is expressed by the following Equation (8).

Equation 8)

Here, CCk is the correlation coefficient, μ _x is the average value of x, μ _y is the average value of y, σ _x is the standard deviation of x, and σ _y is the standard deviation of y.

As the value calculated through the correlation coefficient approaches 1, the correlation is high, and it can be determined that there is no correlation as it approaches 0.

The ratio Q between the discharge amounts is expressed by the following Equation (9).

Equation 9)

Here, Q is the ratio between the discharge amounts, q _i + is the average discharge amount of the i-th phase angle generated during the + half cycle, and q _i - is the average discharge amount of the i-th phase angle generated during the - half cycle.

The number of discharges (N) is the number of discharges in each cycle and is expressed by the following Equation (10).

Equation 10)

Here, N is the number of occurrences of the discharge amount, n _i + is the average number of discharges of the i-th phase angle generated during the + half cycle, and q _i - is the average number of discharges of the i-th phase angle generated during the - half cycle.

That is, the number of discharge occurrences (N) means the ratio of the maximum amount of discharge generated during the +half cycle and the -half cycle.

The ratio (Qmax) of the maximum discharge magnitude is expressed by the following Equation (11).

Equation 11)

Here, Qmax is the ratio of the maximum discharge size, Qmax+ is the discharge size generated during the +half cycle, and Qmax- is the discharge size generated during the -half cycle.

The pattern classification module 220 regards each of the identification elements extracted by the identification element extraction module 210 as one selected vector, and performs a function of grouping similar patterns.

For example, an identification element group consisting of n identification elements can be viewed as one vector, and since the vector has n elements, it becomes an n-dimensional identification element vector. That is, when 6 identification elements are calculated from the discharge pulse signal detected 30 times from the same voltage and the same electrode system, 30 6-dimensional identification element vectors are generated. The generated 30 vectors each have slightly different values, but generally form a constant group, and this group is defined as a cluster in the present invention.

According to this, as the angle between the two vectors selected from the group is smaller, it may be determined that the two selected vectors are due to the same partial discharge.

The comparison module 230 compares the cluster of the identification element vector for the comparison data detected through the DAQ and the identification element vector for the detected detection data, and the identification element of the comparison data close to the identification element vector for the detected detection data. It performs the function of detecting a vector.

That is, the comparison module 230 stores in advance a cluster of identification element vectors for each of corona discharge, internal discharge, surface discharge, and random discharge, and performs an operation on the detection data detected by the detection unit 100 to identify the element After deriving the vector, the derived identification element vector is compared with a vector in the stored cluster of identification element vectors, and the identification element vector having the minimum angle between the two vectors is derived.

The diagnosis module 240 diagnoses the type of the partial discharge with respect to the identification element vector derived from the comparison module 230, and provides the diagnosed partial discharge to the HMI for display.

According to the diagnosis unit 200, when the detection data detected by the detection unit 100 is input in a state in which a cluster of identification element vectors is stored in advance according to the type of partial discharge, a valid identification element is extracted from the input detection data, After classifying the pattern, it is possible to diagnose the type of partial discharge with respect to the detection data detected by the detection unit 100 through comparison with the cluster of the previously stored identification element vectors.

Next, the shielding box (30, see FIG. 2) will be described.

In order to detect a small-scale partial discharge pulse, it must be able to effectively block external noise. That is, in partial discharge detection, the minimum detection sensitivity should be at least twice the noise level. Therefore, in order to accurately detect the partial discharge pulse, an effective noise countermeasure is applied by analyzing the cause of the noise, and a method of adjusting the frequency band of the detection circuit is applied to the noise that is not suppressed other than the partial discharge. signal must be separated.

In partial discharge detection, noise can be largely divided into radiated noise from the outside and ground noise from the grounding side.

Among the noises, ground noise is the ground noise generated due to an unstable grounding system. Most of the high-frequency noise generated when electric and electronic devices are used is caused by an increase in the ground potential due to a lightning strike or a ground fault in the power system. . Accordingly, in order to block the ground noise, a single grounding method may be applied and shielding may be performed using a grounding filter.

Radiated noise is a high-frequency communication signal having a band of several tens of MHz transmitted from a broadcasting station, etc., and noise caused by a radiation component generated from an external device.

The radiation noise may be blocked by applying a shielding technique or the like.

The shielding technique is a measure to remove radiated noise from broadcast carriers, and is shielded with metal with high conductivity such as copper and aluminum so that broadcast frequencies and communication signals are not detected in the lead-in line of the power supply, the coupling capacitor used in the coupling network, and the detection circuit. As a way to do this, in the present invention, the shielding box 30 is used.

Since the shielding effect of the shielding box 30 is greatly affected by the material properties of the metal material, a material having high electrical conductivity may be used.

The shielding box 30 applied to the partial discharge detection diagnostic system of a switchboard using a high-frequency current sensor according to the present invention is composed of a double shielding structure.

The outer shielding box constituting the outside of the shielding box 30 may use a material having high magnetic permeability, and the inner shielding box may be made of a material having high conductivity.

As described above, in the shielding box 30 of the double structure, the shielding box in the range of 350 to 400 dB is used, and the shielding box is composed of a shielding box of 170 to 200 dB, 520 for radiated noise from the outside. It is configured to expect a shielding effect of ~600dB.

If such a shield box 30 is applied, radiation noise can be effectively blocked, but there is no countermeasure against the power line applied to the detection and diagnosis device 20 driven therein and the signal line output from the detection and diagnosis device 20 . Disadvantages may arise.

Accordingly, a filter may be installed at the output terminal of the power supply source to remove conduction noise for the power line and the signal line, or a sealing member capable of shielding the filter may be installed.

At this time, the filter installed on the power line passes the signal for the power frequency, but a filter for power supply that can block the noise signal in the tens of KHz band is applied.

According to the present invention, the partial discharge detection and diagnosis system of the switchboard can be installed only by installing the high-frequency current sensor on the ground wire without deforming or disassembling the power device.

In addition, by providing the type of the generated partial discharge, it is possible to easily derive the location of the partial discharge with respect to the power device, there is an advantage that can improve the reliability of the maintenance of the power device.

In the above, a preferred embodiment of a system for detecting partial discharge of a switchboard using a high-frequency current sensor according to the present invention has been described, but the present invention is not limited thereto, and within the scope of the claims, the description of the invention, and the accompanying drawings. Various modifications are possible, and this also falls within the scope of the present invention.

10: high-frequency current sensor 20: detection and diagnosis device
30: shield box 100: detection unit
110: noise removal filter 120: coupling capacitor
130: detection impedance 140: amplifier
200: diagnostic unit 210: identification element extraction module
220: pattern classification module 230: comparison module
240: diagnostic module

Claims (7)

a high-frequency current sensor installed on a grounding line of a power device in a switchboard and detecting a discharge pulse signal generated by a current flowing through the grounding line;
a detection and diagnosis device for checking whether a partial discharge is present and determining a type of partial discharge based on the discharge pulse signal detected from the high-frequency current sensor; and
a shielding box for shielding the high-frequency current sensor and the detection and diagnosis device;
consists of,
The detection and diagnosis device,
a detection unit for removing and amplifying the noise of the discharge pulse signal detected by the high-frequency current sensor and outputting detection data; and
a diagnosis unit for diagnosing a type of partial discharge by comparing the detection data output from the detection unit with comparison data collected through DAQ (Data Acquisition);
including,
The detection unit,
a noise removal filter for removing noise from the discharge pulse signal output from the high-frequency current sensor;
a coupling capacitor connected in series to the noise removal filter to pass the AC component of the discharge pulse signal and block the DC component;
a detection impedance connected in series with the coupling capacitor; and
an amplifier for amplifying a voltage across the detection impedance;
is made, including
The detection impedance is a partial discharge detection diagnostic system of a switchboard using a high-frequency current sensor, characterized in that composed of an RLC tuning circuit.
delete The method according to claim 1,
The noise removal filter is
a clock pulse generator for generating a frequency clock with respect to the discharge pulse signal;
a first flip-flop for outputting a signal by synchronizing the discharge pulse signal with a rising edge of a clock pulse generated by the clock pulse generator;
a second flip-flop for generating a signal by synchronizing the signal from the first flip-flop at a rising edge of the clock pulse;
a third flip-flop for generating a signal by synchronizing the signal from the second flip-flop at a rising edge of the clock pulse;
a fourth flip-flop for generating a signal by synchronizing the signal from the third flip-flop at a rising edge of the clock pulse;
an AND gate and a NOR gate for receiving the output pulses of the second to fourth flip-flops and outputting a predetermined value that has been calculated; and
A JK type flip-flop that synchronizes the output pulses of the AND gate and the NOR gate at the rising edge of the clock pulse to output a noise-removed signal. Partial discharge detection diagnostic system of a switchboard using a high-frequency current sensor, characterized in that.
The method according to claim 1,
The amplifier is
Partial discharge detection and diagnosis system of a switchboard using a high-frequency current sensor, characterized in that it consists of a two-stage amplifier circuit having an input offset voltage of 3mV and an amplification of 40dB.
The method according to claim 1,
The power device is
Partial discharge detection and diagnosis system of a switchboard using a high frequency current sensor, characterized in that it is one selected from a transformer, a transformer, a cable, a busbar, a circuit breaker, a switchgear, and an enclosure of a power device.
The method according to claim 1,
The high-frequency current sensor,
A switchboard using a high-frequency current sensor, characterized in that it consists of an iron core made of an alloy of nickel and zinc and an induction coil in the form of a toroid made of brass, and the iron core is wound 20 to 50 times on the induction coil. Partial discharge detection diagnostic system.
The method according to claim 1,
The type of partial discharge diagnosed by the diagnostic unit is,
A diagnostic system for detecting partial discharge of a switchboard using a high-frequency current sensor, characterized in that one selected from corona discharge, internal discharge, surface discharge, and random discharge.

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