RU2700368C1 - Method for determining technical state of a digital transformer based on parameters of partial discharges in insulation - Google Patents

Abstract

FIELD: electrical engineering.

SUBSTANCE: invention relates to high-voltage engineering and can be used for diagnostics of technical state of digital transformers. Digital transformer is equipped with a resistive voltage divider and an inductive sensor placed inside the reference insulator. Inductive sensor is connected between electrostatic screen and earthed parts of transformer. Voltage of industrial frequency is recorded by resistive voltage divider. High-frequency voltage pulse from partial discharge current is detected by inductive sensor. Registered signals are filtered and digitized. Phase of high-frequency voltage pulse from partial discharge current is calculated relative to industrial frequency voltage, amplitude and polarity of high-frequency voltage pulse from partial discharge current, number of high-frequency voltage pulses from partial discharge currents during period of industrial frequency voltage change, apparent charge, maximum apparent charge value during observation, average value of apparent charge during observation, average current and power of partial discharges during period of voltage variation of industrial frequency, energy of partial discharge. Performing normalization and Fourier transformation and calculating effective time and frequency of high-frequency pulses. Time-frequency distribution of high-frequency voltage pulses from partial discharge currents is constructed. Amplitude-phase-frequency distribution of high-frequency voltage pulses from partial discharge currents and period of change of industrial frequency voltage are plotted on one graph, from which noise and other discharge processes are separated from internal partial discharges and ranges of phases of occurrence of partial discharges are determined. Dependences of the apparent charge amplitude and the actual value of the industrial frequency voltage on time are plotted, from which the value of the partial discharge ignition voltage and the apparent charge value are determined. Value of apparent charge during observation is compared with threshold value. Results of comparison are used to draw conclusions on possibility of further operation of transformer.

EFFECT: higher reliability of digital transformers.

1 cl, 4 dwg

Description

The present invention relates to high voltage technology and can be used to diagnose the technical condition of digital transformers by the parameters of partial discharges in isolation.

Digital current and voltage transformers are widely known (for example, “Digital current and voltage transformer” according to utility model patent No. 174411, IPC G01R 19/00, 2017, “High-voltage combined digital device for measuring current and voltage” according to the utility model patent No. 159 201 MPK G01R 19/00 ,, 2017, etc.) comprising a supplying electromagnetic transformer, a measuring electromagnetic current transformer, a magnetotransistor converter and a Rogowski belt, covering the current-carrying conductor with a measured current, cylindrically the first shunt with an internal cavity, included in the dissection of the current lead and the primary voltage Converter, placed inside the reference insulator. Digital measuring transformers are designed to convert current and voltage values in primary circuits to a digital code in secondary circuits, containing information on instantaneous values of currents and voltages, which are used for measurement purposes, determination of electric power quality parameters, electric power accounting, relay protection and automation. During laboratory, acceptance tests, as well as during operation, the insulation of digital measuring transformers is exposed to high voltage. Moreover, inside the insulation, at the interfaces of insulating materials and near conductive parts, discharge processes of various intensities with different development mechanisms can occur. Some of these discharges are associated with the processes of ionization of the near-cathode or near-anode space or are surface discharges, the other part is the result of poor manufacturing quality of insulating materials or the development of an internal insulation defect. Particularly dangerous for measuring transformers are precisely internal partial discharges that cause insulation degradation. These discharges begin as local overlap of the defective zones of the dielectric and, over time, can cause breakdown of insulation.

Thus, to ensure reliable operation of digital current and voltage transformers and to prevent accidents associated with damage to insulation from partial discharges, it is necessary to monitor discharge processes, determine their quantitative and qualitative characteristics, development trends.

A known method for monitoring partial discharges in an electrical system (Patent for the invention of the Russian Federation No. 2532142 "Method and system for monitoring partial discharges", IPC G01R 31/12 (2006.01), 2014), in which: take a pulse from the electrical system; identify whether the pulse is a noise or a duplicate signal; if the pulse is noise or a duplicated signal, then this pulse is discarded; break the pulse into two or more frequency components; normalize these two or more frequency components to the maximum level view; comparing two or more normalized frequency components associated with the received pulse, with another stored set of normalized, predefined frequency components associated with other pulses, to identify similar pulses indicating a known failure state; if the pulse is identified as a pulse indicating a known failure state, data is stored in the database, linking the pulse to two or more normalized frequency components and a known failure state; grouping the spectrum of pulse failures with similar normalized frequency components in a scatter diagram stored in a database; if the normalized frequency components of the pulse are not similar to the normalized frequency components of the current group, create a new group of the spectrum of failure pulses stored in the database; and if the pulse is identified as indicating a known failure state, notify the user of the presence of the failure state.

The disadvantages of this method include the lack of tracking the processes of development of the apparent charge, discharge intensity and energy characteristics of partial discharges, since the spectral content of the recorded signals alone does not give a complete picture of the high-frequency processes taking place.

There is a Method of monitoring partial discharges in an electrical system (Patent for the invention of the Russian Federation No. 2505828 "Device for monitoring partial discharges", IPC G01R 31/12 (2006.01), 2014), which consists in determining the lower trigger threshold and the upper threshold trigger, while the lower and upper thresholds of the trigger are the levels of the amplitude of the electrical pulses, and the upper threshold of the trigger corresponds to a higher amplitude than the lower threshold of the trigger, determine the duration is less about the time interval, at least one phase of the electrical system is monitored in order to detect an impulse over a shorter time interval, the maximum amplitude of the impulse arising in the electrical system over the shorter time interval is determined, it is determined whether the measured maximum amplitude of the impulse exceeds the trigger trigger threshold and (or) the upper threshold of the trigger, assign a pulse ripple coefficient if the maximum amplitude of the pulse exceeds the lower trigger trigger threshold and / or trigger trigger threshold, record the pulse or information relating to it if the ripple coefficient corresponding to the pulse is less than a predetermined threshold ripple coefficient in a shorter time interval, apply the time shift of the movable trigger, so if the pulse exceeds the lower the trigger threshold, but not the upper trigger threshold, and the ripple coefficient is equal to a predetermined number of ripples, record the interval during nor during the shorter time interval in which this takes place, and the registration of pulses with an amplitude exceeding the lower trigger threshold, but not the upper trigger threshold, is stopped until this time interval occurs in the next shorter time interval, and reset to zero in time of the time shift of the movable trigger, and registration is started over the next shorter time interval of pulses with an amplitude exceeding only the lower threshold Igger, after the magnitude of the time shift of the movable trigger becomes equal to the value of a shorter time interval, and the registered pulses are stored in the storage device.

The disadvantage of this method is the low reliability of the results due to the inability to control the frequency characteristics of high-frequency bursts, as well as the phase of occurrence relative to the supply voltage, and the possible imposition of signals with a lower or higher frequency from various types of natural discharge processes (for example, from corona discharge) .

A known method for the diagnosis of high-voltage equipment according to the parameters of partial discharges (Patent for the invention of the Russian Federation No. 2536795, IPC G01R 31/12 (2006.01), 2014), which consists in the fact that the electromagnetic field of partial discharges in isolation is perceived by inductive and capacitive sensors, the output signals which are filtered, amplified and multiplied one by one and in accordance with the sign of the product form informative signals, the first of these signals is proportional to the current average value of the apparent charge of partial discharges, and the second to the current the average value of the duration of current pulses caused by partial discharges, using the first signal, adjusts the rate of change of the electric field strength in the insulation, stabilizing the current average value of the apparent charge of partial discharges, and using the second determines the dependence of the duration of current pulses caused by partial discharges on the voltage on high-voltage input of the diagnosed equipment.

The disadvantage of this method is the low reliability of the results due to the use of amplifiers that introduce distortion into the measured high-frequency signal and loss of information about the frequency spectrum and pulse duration of high-frequency discharges due to the use of an averaging RC circuit and an amplitude modulator, as well as due to the lack of the possibility of fixing the intensity of the occurrence of individual partial discharges and the inability to determine the type of discharge.

All of the above methods are not suitable for use in actual use to determine the technical condition of a digital transformer by the parameters of partial discharges. The applicant does not know how to determine the technical condition of digital transformers by the parameters of partial discharges in isolation, which are highly accurate and ensure the reliability of the results.

The basis of the invention is the task of developing a method for determining the technical condition of digital transformers, based on reliable real measurements of an expanded number of features that uniquely characterize the type and quantitative characteristics of partial discharge pulses, indicating the development of defects inside the insulation.

The technical result of the invention is to increase the reliability of the operation of digital transformers due to the accuracy and timeliness of identifying the development of defects inside the insulation according to the parameters of partial discharges.

The technical result is achieved by the fact that, in the method for determining the technical condition of a digital transformer by the parameters of partial discharges in isolation, a digital transformer equipped with a resistive voltage divider placed inside the reference insulator is additionally equipped with an inductive sensor, which is placed inside the reference insulator and connected between the electrostatic screen and the grounded parts of a transformer; industrial frequency voltage is recorded by a resistive voltage divider, a high-frequency voltage pulse from a partial discharge current is recorded by an inductive sensor; registered signals are filtered, analog-to-digital conversion is performed; for the digitized signals, the phase of the high-frequency voltage pulse from the partial discharge current relative to the industrial frequency voltage is calculated, the amplitude and polarity of the high-frequency voltage pulse from the partial discharge current, the number of high-frequency voltage pulses from the partial discharge currents for the period of variation of the industrial frequency voltage, apparent charge, maximum value of the apparent charge during the observation, the average value of the apparent charge during the observation, the average current and power are partial x discharges for a period of voltage variation of industrial frequency, partial discharge energy; normalize and Fourier transform the high-frequency voltage pulses from the partial discharge currents, calculate the effective time and frequency of these pulses; constructing the time-frequency distribution of high-frequency voltage pulses from partial discharge currents, plotting the amplitude-phase-frequency distribution of high-frequency voltage pulses from partial discharge currents and the period of variation of the industrial frequency voltage, by which noise and other discharge processes are separated from internal partial discharges and determine the ranges of the phases of the occurrence of partial discharges, build the dependences of the amplitude of the apparent charge and action Enikeev frequency voltage value from the time at which ignition voltage value is determined of partial discharge and the magnitude of the apparent charge, comparing the magnitude of the apparent charge during the observation with the threshold value from the comparison result that the potential of further operation of the transformer.

The invention is illustrated by drawings. In FIG. 1 shows a device that implements a method for determining the technical condition of a digital transformer by the parameters of partial discharges in isolation. In FIG. Figure 2 shows the time-frequency distribution of high-frequency voltage pulses from partial discharge currents. In FIG. 3 shows the amplitude-phase-frequency distribution of high-frequency voltage pulses from currents of partial discharges and the period of variation of the voltage of the industrial frequency. In FIG. Figure 4 shows the dependences of the amplitude of the apparent charge and the effective value of the industrial frequency on time.

In FIG. 1 shows a digital transformer including a current converter 1 and provided with a resistive voltage divider comprising a resistive element of the upper arm 2 and a resistive element of the lower arm 3 placed inside the support insulator 4. The digital transformer is additionally equipped with an inductive sensor 5 that is placed inside the support insulator 4 and connected between the electrostatic screen 6 of the primary winding of the current transducer 1 and the grounded parts of the transformer.

The resistive element of the upper arm 2 and the resistive element of the lower arm 3 of the resistive voltage divider are connected through a low-pass filter 7 to the analog-to-digital converter of the low-frequency signal 8. The inductive sensor 5 is connected through the high-pass filter 9 to the analog-to-digital converter of the high-frequency signal 10. The outputs of the analog- a digital low-frequency signal converter 8 and an analog-to-digital high-frequency signal converter 10 are connected to a digital signal processing controller 11 connected to the memory window 12, connected through a data transfer unit 13, with an external database 14.

A method for determining the technical condition of a digital transformer by the parameters of partial discharges in isolation is as follows. A digital transformer equipped with a resistive voltage divider placed inside the reference insulator 4 is additionally equipped with an inductive sensor 5, which is placed inside the reference insulator 4 and connected between the electrostatic screen 6 and the grounded parts of the transformer.

During the operation of the digital transformer, a load current flows through the primary winding of the electromagnetic current transducer 1, and a phase voltage of industrial frequency is applied to the transformer relative to the grounded parts, which, after a large-scale conversion, is recorded in the resistive element of the upper arm 2 of the resistive voltage divider in the resistive element of the lower arm 3 of the resistive voltage divider. The registered signal is subjected to low-pass filtering in a low-pass filter 7 to eliminate high-frequency interference and digitized in the analog-to-digital converter of the low-frequency signal 8. Under the influence of high voltage inside the insulation, at the interfaces of insulating materials and near conductive parts (for example, in the insulation of the primary winding of the electromagnetic converter current, in isolation of the secondary winding of the electromagnetic current transformer from the primary winding, in a fiberglass-based, in the outside and it is mainly the insulation layers) may experience discharge processes. In this case, a voltage drop occurs in the inhomogeneities of the insulation and redistribution of the charge between the insulation capacitance and the capacitors connected in parallel to it, which generates a high-frequency current in the electric circuit detected as a high-frequency voltage pulse by the inductive sensor 5. The registered signal is subjected to high-frequency filtering in a high-pass filter 9 for elimination of interference and digitize in the analog-to-digital Converter of the high-frequency signal 10. In the controller processing the digital signal 11 for the digitized signals, the phase of the high-frequency voltage pulse from the partial discharge current relative to the industrial frequency voltage is calculated, the amplitude and polarity of the high-frequency voltage pulse from the partial discharge current, the number of high-frequency voltage pulses from the partial discharge current for the period of variation of the industrial frequency voltage, apparent charge, maximum value of the apparent charge during the observation, the average value of the apparent charge during the observation, average current and partial power discharges for a period of voltage variation of industrial frequency, partial discharge energy. Also, in the controller for processing the digital signal 11, normalization and Fourier transform of the high-frequency voltage pulse from the partial discharge current are performed, the effective time and frequency of the specified pulse are calculated.

The Fourier transform of a digital signal is carried out after determining the phase of its occurrence.

The digital signal is normalized after determining its phase by the expression:

где

Where

s is the i-th sample of the vector of signal values;

N is the number of samples of a discrete signal. Equivalent time is calculated by the expression:

где

Where

- спектральная плотность мощности нормализованного сигнала;

- spectral power density of the normalized signal;

N _i is the value of the i-th time reference. The equivalent frequency is calculated by the expression

где

Where

s _ni (f _i ) - Fourier transform of the normalized high-frequency signal;

f _i - i-oe value of the frequency of the discrete Fourier transform.

The obtained calculation results are stored in the memory unit by the memory unit 12 and transmitted through the data transfer unit 13 to an external database 14. The information stored in the external database 14 is used to construct the time-frequency distribution of high-frequency voltage pulses from partial discharge currents (Fig. 2), when building on one graph the amplitude-phase-frequency distribution of high-frequency voltage pulses from the currents of partial discharges and the period of variation of the voltage of the industrial frequency (Fig. 3), when building awns apparent charge current amplitude value and frequency voltage versus time (FIG. 4), providing obtaining a better understanding of the processes occurring high and the possibility of determining the type of discharge. According to the graph of the time-frequency distribution of high-frequency voltage pulses from the partial discharge currents (Fig. 2), discharge regions with similar energy characteristics are distinguished. According to the graph of the amplitude-phase-frequency distribution of high-frequency voltage pulses from partial discharge currents and the period of variation of the industrial frequency voltage (Fig. 3), noise and voltage pulses of other discharges from different types of discharge processes (for example, from corona discharge) are separated for the selected areas. The phase range of the occurrence of high-frequency voltage pulses is determined by which the high-frequency voltage pulses from internal partial discharges are determined. The dependences of the amplitude of the apparent charge (solid line in Fig. 4) and the effective voltage of the industrial frequency versus time (dashed line in Fig. 4) determine the magnitude of the partial discharge ignition voltage and the magnitude of the apparent charge. The value of the apparent charge during the observation is compared with a threshold value (dash-dotted line in Fig. 4), determined empirically or, for example, regulated by GOST 7746-2015 and GOST 1983-2015, based on the comparison results draw conclusions about the possibility of further operation of the transformer.

The proposed method allows to monitor the discharge processes, determine their quantitative and qualitative characteristics, accurately and timely detect the development of defects inside the insulation by the parameters of partial discharges, prevent accidents associated with damage to the insulation from partial discharges, providing increased reliability of the operation of digital transformers.

Claims (1)

A method for determining the technical condition of a digital transformer by the parameters of partial discharges in isolation, characterized in that the digital transformer equipped with a resistive voltage divider placed inside the reference insulator is additionally equipped with an inductive sensor, which is placed inside the reference insulator and connected between the electrostatic screen and the grounded parts of the transformer; industrial frequency voltage is recorded by a resistive voltage divider, a high-frequency voltage pulse from a partial discharge current is recorded by an inductive sensor; registered signals are filtered, analog-to-digital conversion is performed; for the digitized signals, the phase of the high-frequency voltage pulse from the partial discharge current relative to the industrial frequency voltage is calculated, the amplitude and polarity of the high-frequency voltage pulse from the partial discharge current, the number of high-frequency voltage pulses from the partial discharge currents for the period of variation of the industrial frequency voltage, apparent charge, maximum value of the apparent charge during the observation, the average value of the apparent charge during the observation, the average current and power are partial x discharges for a period of voltage variation of industrial frequency, partial discharge energy; normalize and Fourier transform the high-frequency voltage pulses from the partial discharge currents, calculate the effective time and frequency of these pulses; construct the time-frequency distribution of high-frequency voltage pulses from partial discharge currents, construct the amplitude-phase frequency distribution of high-frequency voltage pulses from partial discharge currents and the period of variation of the industrial frequency voltage, which separate noise and other discharge processes from internal partial discharges and determine the ranges phases of the occurrence of partial discharges, build the dependence of the amplitude of the apparent charge and action uyuschego frequency voltage value from the time at which ignition voltage value is determined of partial discharge and the magnitude of the apparent charge, comparing the magnitude of the apparent charge during the observation with the threshold value from the comparison result that the potential of further operation of the transformer.

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