High-voltage instrument transformer and method for identifying partial discharge

Abstract

The invention relates to a high-voltage instrument transformer (1) having a measuring assembly (3, 4) and an insulator (5), and having at least one sensor (9) for partial discharge measurement. A method for detecting partial discharges in a high-voltage instrument transformer (1) according to the invention comprises detecting a signal from at least one sensor (9) for partial discharge measurement, in particular a transient voltage-to-ground sensor.

Description

Technical Field

[0001] The invention relates to a high-voltage instrument transformer having a measuring assembly and an insulator, and to a method for detecting partial discharges. Background Art

[0002] High-voltage instrument transformers measure high voltages from one kilovolt to over one kilovolt. In transmission networks and / or at high-voltage units such as high-voltage switches, bushings, surge arresters, and / or transformers, high-voltage instrument transformers measure voltages to monitor the proper functioning of the units and / or to switch units, for example, in the event of overvoltage. The faultless, reliable, and continuous operation of high-voltage instrument transformers is essential for transmission networks and / or electrical units to prevent costly damage and failures.

[0003] For proper operation, instrument transformers must be monitored during operation. Currently, time-based maintenance, based on continuous measurements taken during service operations, is preferred over condition-based maintenance. Partial discharges are one of the most obvious indicators leading to failure prediction. Monitoring the development of partial discharges is therefore of fundamental importance. Partial discharges occur at or in solid insulators and in the insulating fluids, such as SF6, clean air, and / or oil.

[0004] Partial discharges in or on solid insulators initiate within voids, cracks, impurities, or inclusions, particularly at the conductor-dielectric interface, and in liquids, particularly within bubbles, impurities, or inclusions. Because the partial discharge is confined to a portion of the insulation, the discharge only partially bridges the distance between the conductors. Following the onset of a partial discharge, a high-frequency transient current pulse appears and lasts for a few nanoseconds to a few microseconds. The current pulse then disappears and repeatedly reappears when the sine wave passes through the zero crossing. Due to the high voltage and high levels of electrical background noise, the detection and measurement of partial discharges is difficult, complex, and cost-intensive. Partial discharges in high-voltage applications, in particular, are difficult to identify and determine during operation, and the damage and / or electrical losses can be significant.

[0005] Partial discharge measurements are performed, for example, using external antennas and / or external sensors. For example, a grounded metal support frame of an electrical unit, spaced apart from the instrument transformer, is used to measure partial discharge signals. Partial discharges induce voltage spikes on the surface of grounded metalwork, such as the grounded metal support frame of the electrical unit, which are measured as voltage and / or current signals. Another method for detecting partial discharges uses ultrasonic sound sensors spaced apart from the instrument transformer. In particular, the methods described above offer only low sensitivity during field measurements and require cost-intensive, highly complex equipment. Summary of the Invention

[0006] The object of the present invention is to overcome the above-mentioned problems. In particular, the object of the present invention is to increase the sensitivity of partial discharge identification and determination, to enable continuous measurements during service operations, to reduce costs by using less complex equipment for partial discharge measurements, thereby reducing noise and improving measurement results.

[0007] The above object is achieved by a high-voltage instrument transformer having a measuring assembly and an insulator, wherein the high-voltage instrument transformer comprises at least one sensor for partial discharge measurement.

[0008] A sensor for partial discharge measurement that is not separated from the high-voltage instrument transformer but is included in the high-voltage instrument transformer increases the sensitivity of partial discharge identification and determination, enables continuous measurement during service operations, reduces costs by using less complex equipment to perform partial discharge measurement, reduces noise and improves measurement results.

[0009] At least one sensor may be a transient earth voltage sensor. Transient earth voltage sensors are used, for example, to measure induced voltages on the earth shield of gas-insulated switchgear, but are also capable of capturing conducted signals. The at least one transient earth voltage sensor included in the high-voltage instrument transformer can measure partial discharges, particularly in the form of voltage and / or current peaks, directly at and / or in the insulator of the high-voltage instrument transformer, thereby increasing the sensitivity and reliability of the partial discharge measurement and enabling continuous measurement during service operation.

[0010] At least one sensor, particularly a transient voltage-to-ground sensor, can be arranged, particularly directly, on the ground shield. At least one sensor, particularly a sensor, can be electrically connected to the ground shield, particularly the sensor being arranged on the ground shield. The transient voltage-to-ground sensor can be arranged on the ground shield and electrically connected to the ground shield. Partial discharges preferably propagate along capacitive paths. In the case of a high-voltage instrument transformer, when a partial discharge initiates, it propagates through the capacitance of the bushing, for example, represented by an aluminum multi-shield, to the shielded ground conductor, thereby creating a closed loop. Extracting a measurable signal from this closed loop is difficult. However, because high-voltage instrument transformers are designed, for example, with an outer bushing connected to the ground shield, the connection of the at least one sensor, particularly the transient voltage-to-ground sensor, enables highly sensitive, time-continuous partial discharge measurements using simple equipment with low cost and complexity. After flowing through the bushing, the signal passes through the ground shield, "closing" the circuit and thus enabling reliable partial discharge measurements.

[0011] Alternatively and / or additionally, the outer shield of the bushing of the high voltage instrument transformer may be electrically connected to the ground shield.

[0012] Alternatively and / or additionally, the at least one sensor can be arranged on, in particular directly on, an outer surface of the insulating body.

[0013] Alternatively and / or additionally, the at least one sensor can be arranged on the inside of the insulating body, in particular directly on the surface of the insulating body.

[0014] Additional sensors may increase sensitivity and / or reliability and add other information to the measured signal, thereby enabling highly sensitive, continuous measurement over time with simple equipment of low cost and complexity to reliably detect and determine partial discharges with the advantages described previously, such as preventing damage and / or destruction of the power grid and / or electrical units.

[0015] At least one sensor can be connected to a monitoring system, in particular a continuous and / or online monitoring system. The monitoring system, in particular a continuous and / or online monitoring system, can include a computer and / or cloud-based components and / or mobile components for continuous monitoring and / or monitoring according to service intervals. Reliable monitoring of partial discharges, in particular real-time monitoring, enables rapid action to prevent damage and / or destruction of the power grid and / or electrical units. Condition-based maintenance is possible, thereby preventing higher costs and damage and reducing the effort associated with time-based maintenance, such as maintenance within predefined time periods.

[0016] Instrument transformers can be designed for voltages in the range of 1 kV up to 1200 kV, in particular in the range of 15 kV up to 1200 kV.

[0017] A method for detecting partial discharges in a high-voltage instrument transformer as described above comprises detecting a signal from at least one sensor for partial discharge measurement, in particular a transient voltage-to-ground sensor.

[0018] The method may include

[0019] - Transform the detected signal from time domain to frequency domain

[0020] - Cut off frequencies above a defined threshold

[0021] - transforming the intercepted signal from the frequency domain to the time domain, and

[0022] - Determine and compare the information content of the detected signal with the intercepted signal

[0023] Signals of the detected signal and the intercepted signal with comparable, in particular equal, information content may be identified as noise and / or signals of the intercepted signal with a lower information content compared to the detected signal information content may be identified as signals comprising partial discharge information.

[0024] The information content can be determined by calculating the Shannon entropy. Entropy is a measure of the average value of the information content of a message. The information content of a signal can be calculated. Claude Elwood Shannon defined the entropy of a discrete, memoryless information source for a certain number of characters z, corresponding to the discrete random variable H. Information content I(z) = -log2p z Assigned to event z, each probability p of the signal value corresponds to the probability p of the character z. The entropy of a character z is defined as the probability p that the character z will appear. z Information content H1 = -∑p z log2p z The expected value of . Summons with different probabilities do not add to each defined sum. The entropy of a symbol w of length n is the probability p that the symbol w will appear w H n =-∑p w log2p w By H = lim(n→∞)Hn / n, the probability H is derived as the limit (Limes)n→∞.

[0025] Noise signals have no information content because their values ​​are random. Cutting off high frequencies does not change the Shannon entropy because no information is lost. For partial discharge signals, cutting off the frequencies reduces the Shannon entropy because information is lost. Comparing the Shannon entropy of the measured signal with the Shannon entropy of the intercepted signal yields the same value for pure noise, while for signals containing partial discharge, the Shannon entropy of the intercepted signal is lower than the Shannon entropy of the measured signal. These advantages make it possible to identify the presence of partial discharge and calculate its value.

[0026] The advantages in connection with the method according to the invention for detecting partial discharges in a high-voltage instrument transformer as described above are similar to the advantages described previously in connection with the high-voltage instrument transformer.

[0027] The method according to the present invention realizes partial discharge measurement by analyzing the information content of the signal after cutting off the higher frequencies above a certain threshold of the measured signal using relatively low complexity equipment to identify and distinguish partial discharge from noise, thereby reducing noise and improving measurement results.

[0028] The relatively fast and, in particular, automatic determination and / or comparison of the information content allows, for example, monitoring of partial discharge events over time and quick action to protect the equipment, for example by disconnecting electrical lines. Maintenance can be initiated for the equipment, or for units that display a partial discharge event once and / or multiple times. Warning signals can be generated and / or transmitted, for example, on-site and / or online, via a wired Internet or mobile network, or partial discharge events can be monitored online, for example, over a period of time, via the Internet. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] The present invention is further described below with reference to illustrative embodiments shown in the accompanying drawings, in which:

[0030] Figure 1 A high-voltage instrument transformer 1 according to the invention is shown in cross section with a transient voltage-to-ground sensor 9 located on a ground shield 10 for measuring partial discharges. DETAILED DESCRIPTION

[0031] exist Figure 1 , a high-voltage instrument transformer 1 according to the present invention is shown. The high-voltage instrument transformer 1 comprises a housing 2 having an insulator 5 and a container 6, in particular a high-voltage container. The insulator 5 is hollow and cylindrical, with a slit on the outer surface to increase the leakage current length. The cylindrical insulator 5 is arranged upright on the container 6 via an overvoltage device 8, in particular a bursting disc, and a high-voltage terminal 12 located on top. High voltages ranging from 1 kV to 1200 kV can be applied to the high-voltage instrument transformer 1 via the terminal 12 to measure voltages, for example, in the transmission network and / or at electrical pipelines, and / or at electrical units such as bushings, high-voltage switches, transformers, and / or surge arresters.

[0032] The insulator 5 is made of and / or includes a material such as ceramic, silicone and / or a composite material. The container 6 is made of and / or includes a material such as a metal such as aluminum, steel and / or cast iron. The container 6 is arranged on a base 7 having a ground connection, for example, made of steel on a concrete base. A terminal box 13 with, for example, electrical terminals and / or electronic equipment is arranged on the outside of the container 6, for example to measure voltage, process signals and transmit signals / information to monitor the device. For example, a computer, a sensor box, a data receiver and / or a transmitter, particularly for online monitoring of mobile units and / or data cable units / online units used for the Internet, are arranged in the terminal box 13.

[0033] The measuring assembly for measuring the high voltage is arranged in a container 6, for example. The measuring assembly comprises in particular the main winding 3 and the voltage transformer core 4. The high voltage terminal 12 of the high voltage instrument transformer 1, located on top of the insulator 5, is electrically connected to the measuring assembly in the container 6 via a bushing 11. The bushing 11 comprises in particular a metal rod made of aluminum, steel and / or copper. The metal rod is surrounded by a control electrode, for example, embedded in an insulating paper. For the sake of simplicity, the insulating paper is not shown. Figure 1 , and is made of a metal such as copper, aluminum and / or steel, for example, is arranged at the passage from the insulator 5 to the container 6. The insulator 5 and the container 6 are in particular filled with a fluid 15 for insulation, for example an insulating gas such as SF6, clean air and / or an insulating liquid such as oil.

[0034] According to the present invention, partial discharge sensor 9, in particular a transient voltage-to-ground sensor, is arranged at, in particular directly on, and / or electrically connected to, ground shield 10. Partial discharges preferably propagate along capacitive paths. When a partial discharge initiates in or at insulator 5, it propagates through the bushing capacitance, represented by, for example, an aluminum multi-shield, to the shielded ground line, creating a closed loop. After flowing through the bushing, the signal passes through the ground shield, "closing" the circuit and enabling reliable partial discharge measurement.

[0035] Alternatively and / or additionally, for the sake of brevity not Figure 1 As shown in FIG, the outer shield of the bushing of the high voltage instrument transformer can be electrically connected to the ground shield. Figure 1 , it is shown that the further sensor can be arranged on, in particular directly on, the outer surface of the insulating body 5 and / or on the inner side of the insulating body 5 , in particular directly on the surface of the insulating body.

[0036] Partial discharge sensor 9, particularly a transient voltage-to-ground sensor, is electrically and / or optically connected to terminal box 13, for example, via connecting wires 14. The signals measured by sensor 9 are transmitted directly or after processing to terminal box 13, for example, to be further processed and transmitted to a central control room, to a mobile device, and / or displayed locally, for example, on a warning light. Sensor 9 enables continuous monitoring of the status of high-voltage instrument transformer 1, or specifically for predefined time periods, for example, via a mobile and / or cable / internet connection to a central control and / or device in the cloud.

[0037] A partial discharge is a localized dielectric breakdown of the electrical insulation at high voltage between electrodes, causing an alternating voltage and / or current in or at the insulator 5. The partial discharge signal is measured, for example, as a voltage over time. The partial discharge signal is small compared to the high voltage at terminal 12, which can range from, for example, 1 kilovolt to 1200 kilovolts, compared to the pico-coulomb signal of the partial discharge, i.e., the small voltage and current signal. Partial discharges initiate in or at the insulator 5, for example, within voids, cracks, impurities, or inclusions, particularly at the conductor-dielectric interface, and in liquids, particularly within bubbles, impurities, and / or inclusions. The partial discharge is confined to a portion of the insulation. The discharge only partially bridges the distance between the electrodes, and thus, the electrical conductors.

[0038] When a partial discharge begins, a high-frequency, transient current pulse appears and lasts for a few nanoseconds to microseconds. The current pulse then disappears and reappears repeatedly, for example, when a sine wave passes through a zero crossing. Partial discharge signals are short in duration and exhibit current rise times in the nanosecond range. High levels of electrical background noise, for example due to corona, crosstalk, and other influences, make accurate measurement, simple identification, and determination of partial discharges within high-voltage / current measurement signals difficult.

[0039] Due to the short duration and the rise times of partial discharge currents in high-voltage applications, which are in the nanosecond range, it is difficult to visualize and differentiate between noise and partial discharges in a voltage / current versus time curve. In order to identify partial discharges and / or to determine their value, the information content I of the signal S is investigated according to the invention. The signal S(t) measured over time is transformed from the time domain into the frequency domain, for example, by means of a Fourier transform and / or a discrete cosine transform. A predefined frequency limit f is cut off. lim frequencies f above, and by removing frequencies above f lim The signal component at the frequency of the intercepted signal is obtained. Frequency limit f lim The value of is defined, for example, each time at the start of a monitoring activity, respectively a measurement. lim In the following steps the signal is transformed back, correspondingly from the frequency domain to the time domain.

[0040] The partial discharge signal contains information, while the noise signal does not. The noise signal is completely uncorrelated in itself. By switching from the time domain to the frequency domain, each component has global information I i By cutting off the frequency above the limit f limIf the measured signal comprises partial discharges and not just noise, information is lost. According to the invention, the method, respectively the algorithm, extracts information from the sampled signal, for example by calculating the Shannon entropy, and compares the information content of the sampled signal with the information content of the sampled signal by cutting off the frequency above the frequency limit f lim The information content of the intercepted signal is compared with the frequency of the signal.

[0041] The information content of the measured signal, respectively the sampled signal, is calculated, in particular, by calculating the Shannon entropy, as described above, on a local computer and / or in the cloud. Similarly, the information content of the intercepted signal, respectively the frequency-clipped signal, is calculated, in particular, by calculating the Shannon entropy, as described above, on a local computer and / or in the cloud. Both calculations are performed, for example, immediately upon measurement, separately one after the other, or in a predefined order. After removing the frequency components, the time domain signal of the intercepted signal is obtained, for example, by an inverse integral transform, in particular a Fourier transform and / or a discrete cosine transform. The information content of the measured and intercepted signals is determined similarly, for example, in both cases by calculating the Shannon entropy.

[0042] Comparing the information content of the measured signal with the intercepted signal results in the identification and / or determination of a partial discharge. The comparison can be performed, for example, manually and / or automatically, by a computer and / or in the cloud. Methods for comparing the signals include, for example, division and / or subtraction of the information content of the measured and intercepted signals. If the measured signal contains a partial discharge, the result of the division is less than 1. A division result of exactly or predominantly 1 indicates the absence of a partial discharge, as the signal contains only noise and no information is lost by cutting off the frequency.

[0043] Identifying and / or determining partial discharges has the advantages described above. For example, it can trigger and / or transmit warnings and trigger further actions, such as disconnecting the voltage and / or disconnecting the high-voltage unit from the transmission grid to prevent damage and / or destruction / failure of the unit. Partial discharge measurements also provide quality assessment and diagnostic results. Partial discharges are, for example, an indicator of the condition of the high-voltage instrument transformer 1 under test. Partial discharges are performed during factory quality testing to demonstrate the actual functionality of the produced units. Online monitoring of high-voltage units, such as high-voltage switches, bushings, and / or transformers, is possible when operating in transmission grids with significant background noise.

[0044] The above-described embodiments of the present invention can also be used in combination and in conjunction with embodiments known from the prior art. For example, partial discharges can be detected by performing the steps, in particular all the steps described above, once. A higher reliability is achieved by performing this step, in particular repeating all the steps described above. The iterative method for determining partial discharges can include determining the frequency limit f lim The iterative method may comprise repeating the steps according to the invention and varying the cut-off frequency limit f lim , until the frequency limit f lim changes, the Shannon entropy changes and / or the Shannon entropy does not change.

[0045] Other sensors, in particular transient ground voltage sensors, optical sensors, acoustic sensors and / or electrical sensors can be included in the high-voltage instrument transformer 1 and / or used in combination with external sensors to increase sensitivity and / or reliability and add other information to the measured signal, thereby achieving high sensitivity and continuous measurement over time with simple equipment of low cost and complexity to reliably detect and determine partial discharges with the advantages mentioned above, such as preventing damage and / or destruction of electrical units and / or transmission networks.

[0046] Reference Signs List

[0047] 1 High-voltage instrument transformer

[0048] 2 Housing

[0049] 3. Measuring the main winding of the component

[0050] 4 Voltage transformer core of the measuring assembly

[0051] 5 Insulator

[0052] 6 containers

[0053] 7 Base with ground connection

[0054] 8 Overpressure devices, especially bursting discs

[0055] 9 Partial discharge sensor

[0056] 10 Ground shield

[0057] 11 Casing

[0058] 12 High voltage terminals

[0059] 13 Terminal box

[0060] 14 Electrical connections between terminal box and partial discharge sensor

[0061] 15 Fluids for electrical insulation, in particular insulating gases and / or oils

Claims

1. A high-voltage instrument transformer (1), comprising: Insulator (5), a container attached to the insulator, a measuring assembly (3, 4), said measuring assembly (3, 4) being enclosed in said container, a ground shield arranged to be enclosed by a passage between the insulator and the container, and At least one sensor (9) for partial discharge measurement, the at least one sensor (9) being arranged directly on the grounded shield.

2. The high-voltage instrument transformer (1) according to claim 1, characterized in that: The at least one sensor (9) is a transient ground voltage sensor.

3. The high-voltage instrument transformer (1) according to claim 1, characterized in that: The at least one sensor (9) is electrically connected to the ground shield (10).

4. The high-voltage instrument transformer (1) according to claim 1, characterized in that: The outer shield of the bushing of the high-voltage instrument transformer (1) is electrically connected to the ground shield.

5. The high-voltage instrument transformer (1) according to claim 1, characterized in that: The at least one sensor (9) is arranged on an outer surface of the insulating body (5).

6. The high-voltage instrument transformer (1) according to claim 5, characterized in that: The at least one sensor (9) is arranged directly on the outer surface of the insulating body (5).

7. The high-voltage instrument transformer (1) according to claim 1, characterized in that: The at least one sensor (9) is arranged on the inner side of the insulating body (5).

8. The high-voltage instrument transformer (1) according to claim 7, characterized in that: The at least one sensor (9) is arranged directly on the surface of the insulating body (5).

9. The high-voltage instrument transformer (1) according to claim 1, characterized in that: The at least one sensor (9) is connected to a monitoring system.

10. The high-voltage instrument transformer (1) according to claim 9, characterized in that: The at least one sensor (9) is connected to a continuous and / or online monitoring system.

11. The high-voltage instrument transformer (1) according to claim 9, characterized in that: The monitoring system includes components in a computer and / or cloud and / or mobile components for continuous monitoring and / or monitoring according to service intervals.

12. The high-voltage instrument transformer (1) according to claim 10, characterized in that: The continuous and / or online monitoring system includes components in a computer and / or cloud and / or mobile components for continuous monitoring and / or monitoring according to service intervals.

13. The high-voltage instrument transformer (1) according to any one of claims 1 to 12, characterized in that The high-voltage instrument transformer ( 1 ) is designed for voltages in the range of 1 kV up to 1200 kV.

14. The high-voltage instrument transformer (1) according to claim 13, characterized in that: The high-voltage instrument transformer (1) is designed for voltages in the range of 15 kV up to 1200 kV.

15. A method for partial discharge identification in a high-voltage instrument transformer (1) according to any one of claims 1 to 14, comprising detecting a signal from at least one sensor (9) for partial discharge measurement.

16. The method according to claim 15, characterized in that The method includes detecting a signal from a transient voltage-to-ground sensor.

17. The method according to claim 15, comprising: - Transform the detected signal from time domain to frequency domain - Cut off frequencies above a defined threshold - transform the intercepted signal from the frequency domain back to the time domain, and - Determine and compare the information content of the detected signal with the intercepted signal.

18. The method according to claim 17, characterized in that Signals of the detected signal and the intercepted signal having comparable information content are identified as noise, and / or signals of the intercepted signal having lower information content than the detected signal are identified as signals comprising partial discharge information.

19. The method according to claim 18, characterized in that Signals of the detected signal and the intercepted signal having equal information content are identified as noise.

20. The method according to any one of claims 15 to 19, characterized in that The determination of information content is performed by calculation of Shannon entropy.

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