System, having a sensor and an electronic circuit, for monitoring low currents in power substations

Abstract

The present invention relates to a system, a sensor and an electronic circuit with application in the field of devices for measuring low alternating currents, with the aim of monitoring electrical equipment in power substations and assisting in the performance of preventive maintenance, which is essential for ensuring the proper operation and safety of electrical systems. The system comprises a current transformer (1), a measurement module (2), a microprocessor unit (3) and a housing (4). The assembly in question operates in a comprehensive and self-sufficient manner in measuring low currents in power substations. Its operation, based on the magnetic principle, is robust and preserves the integrity of the network by means of contactless measurement from the current transformer (1). The housing (4) protects sensitive components from inclement weather and electromagnetic interference. The direct measurement method developed reduces uncertainties in the system and allows calibration and self-equalisation of the signal by means of simple adjustments made to the measurement module (2), without the need for post-processing to recover the information measured. The data acquired are processed and sent by the microprocessor unit (3) to the server, which provides binary-type files that can be viewed using any available source code editor.

Description

SYSTEM, WITH SENSOR AND ELECTRONIC CIRCUIT, FOR MONITORING LOW CURRENTS IN POWER SUBSTATIONS Field of invention

[0001] The present invention relates to an electronic system and circuit for measuring low alternating currents, applicable to devices for monitoring high-voltage electrical equipment in power substations. The system, adjustable for measurements in the range of tens of microamperes to tens of milliamperes, aims to diagnose faults based on the waveform, magnitude, and frequency response of the measured current, providing useful information for preventive maintenance indicators of the equipment. Fundamentals of the invention

[0002] Fault detection and sensing in power substations and transmission lines are essential to ensure the proper functioning and safety of electrical systems (Rubio-Serrano, J. et al., 2012) (Robles, G. et al., 2021). Faults in electrical equipment can result in significant economic losses, exceeding the initial acquisition and installation costs. Furthermore, these faults can cause overloads in other parts of the system, compromising the power supply in large areas (Dolník, B. et al., 2022).

[0003] For example, high-voltage insulators, which provide mechanical support and electrical insulation to transmission and distribution lines, are critical in this context (Akbar, M. et al., 2019) (Portella, KF et al., 2008) (Dolník, B. et al., 2022). Failures in these insulators can cause overloads in other lines, leaving large areas without electricity and generating considerable economic losses (Dolník, B. et al., 2022). Generally, these failures result from the accumulation of soluble salts, which, when dissolved in the presence of moisture, form alternative conductive paths, generating leakage currents (Akbar, M. et al., 2019) (Werneck, MM et al., 2014) (Oliveira, SC et al., 2009). (Fierro-Chavez, JL et al., 1996). Although the leakage current in each insulator is from hundreds of microamperes to a few milliamperes, the accumulation in several insulators can result in a significant current in the system, activating protection devices (Werneck, MM et al., 2014). Insulation performance decreases with pollution until the dielectric strength is compromised, causing the flashover phenomenon and destruction of the component.

[0004] Unplanned interruptions for corrective maintenance cause financial and operational losses for distribution companies and their customers (Werneck, MM et al., 2014) (Gençoglu, MT et al., 2008) (Jiang, Y. et al., 2014). Therefore, the prediction and prevention of such corrective occurrences is a topic of great importance in the technical and scientific literature (Gençoglu, MT et al., 2008) (Li, J. et al., 2010) (Stefeon, SF, 2022). However, the quantification of contamination in insulators is still predominantly performed after disconnection from the electrical grid. The techniques considered standard for measuring the level of contamination in isolations do not allow for real-time monitoring, which would be crucial for assessing the severity of pollution at the site (Jiang, Y. et al., 2014) (de Santos, H., 2020) (Ahmed, R., 2020).In addition to the difficulty of directly accessing these quantities due to safety and operational standards in substations, one of the main challenges of this problem is the low magnitude of currents associated with faults, such as leakage current, compromising the processing capacity of the acquired information.

[0005] Currently, real-time measurement of low currents in substations is primarily investigated using three principles: optical, resistive, or magnetic. While feasible, measurement using optical sensors faces challenges due to the influence of weather and other variables that interfere with light propagation, in addition to requiring more complex and expensive acquisition systems. The resistive approach is not feasible in the field because it requires a series measurement in the system, introducing a resistance associated with grounding, which contradicts electrical system protection standards. Despite the sensitivity to electromagnetic interference in substations, the magnetic principle, through The use of current transformers (CTs) has the potential for continuous monitoring of electrical current. While preserving the integrity of the network, contactless measurement is robust against weather, dirt, and chemicals.

[0006] Despite this, a search in the scientific field shows few studies directly related to the use of current transformers (CTs) for measuring low currents in power substations. In (Villalobos, RJ, et al., 2022), the authors present the development of a monitoring system whose sensor consists of a supermalloy alloy core, with very high magnetic permeability when compared to traditional ferrite or powdered iron cores, and a copper winding with 8000 turns. Both characteristics confer greater sensitivity to the measurement system, capable of measuring currents between 50 microamperes and 300 milliamperes, whose data are used in a simple analysis of the distortion of the acquired leakage current harmonics.However, the work found differs from that proposed in this document in factors such as the number of turns in the winding being 80 times greater, the encapsulation and insulation of the sensor being heavier and more complex to manufacture, and the core used in the winding being difficult to obtain and expensive. These characteristics directly impact the time and cost of manufacturing the device. Furthermore, the signal equalization procedure, necessary for recovering the measured information, is performed via software after acquisition, while in the proposed invention, the necessary equalization and processing are performed in the system's hardware, minimizing computational costs.

[0007] In (Gouda, OE, et al., 2022) a device for monitoring the integrity of high-voltage insulators using a current transformer (CT) is also described. The equipment works by continuously detecting the magnitudes of leakage current peaks and calculating their average value for each second or minute as the monitor software is calibrated. If the average leakage current value corresponds to a threshold related to a power outage, the device is activated. Significantly, an alarm signal and a warning message are emitted to the maintenance team. Although it also allows for continuous measurements, is low-cost, easy to handle and calibrate, and presents high precision and safety, the work found differs from that proposed in this document by only detecting leakage current peaks, without any possibility of observing the waveform of the measured signal or its frequency response. Furthermore, the alert threshold is configured for 60 mA, a value that is very high in relation to the measurement range that the proposed invention is capable of measuring, and the system suffers significantly from electromagnetic interference present in the substation environment.

[0008] Following the same pattern, the patent search reveals several records mainly related to leakage current meters for high-voltage insulators that do not use current transformers (CTs), employing different types of principles for detecting and monitoring the quantity. Examples include documents US5640154, entitled “Insulation Monitoring System For Insulated High Voltage Apparatus”, WO1996018909, named “Monitoring System For Insulated High Voltage Apparatus”, EP3130931, “Leakage Current Detection Circuit, Direct-Current High-Voltage System, And Leakage Current Detection Method And Device”, CA2987059, named “Direct Current Meter And Method Of Use”, and US20180313885, titled “Direct Current Meter Employing Waveform Separator For Detecting Leakage Current”. The US5640154 patent uses an optical sensor, which allows continuous monitoring without direct physical contact with the conductors.WO1996018909 uses a capacitive sensor to detect variations in electric fields, while EP3130931 uses piezoelectric sensors to capture variations at high frequencies. CA2987059 uses an acoustic sensor, suitable for environments with high noise interference. In turn, US20180313885 combines high-precision current sensors for real-time monitoring of electrical conditions, covering a wide range of measurements. However, leakage current is undoubtedly the most widely used quantity for the application and is considered the most important. more capable of providing a more comprehensive description of the insulators' condition (Li, J. et al., 2010).

[0009] Patents ZA1997 / 02791, entitled “Measuring Device For Measuring Electric Currents In A Stressed Conductor,” and US20180313885, named “Direct Current Meter Employing Waveform Separator For Detecting Leakage Current,” as well as CA2133047, called “System For Monitoring The Insulation Quality Of Step Graded Insulated High Voltage Apparatus,” utilize current transformers (CTs) for leakage current measurement. The ZA1997 / 02791 patent details a system for measuring eddy currents in an electrical circuit, focusing on ensuring accuracy and stability in high-voltage current measurements. The invention in document US20180313885 provides detailed eddy current measurements capable of distinguishing between DC and AC components, and is designed to provide accurate data even for high-magnitude currents and momentary transients.The current measurement in patent US20180313885 is performed indirectly through the current transformer (CT), offering a comprehensive measurement range that covers currents from low to high magnitude, improving accuracy and analysis of electrical conditions. Finally, document CA2133047 specifies a current measurement range between 4 and 20 mA, with a system that performs indirect measurement of the current of interest through the current passing through a capacitor and measured by the CT. Although the inductive measurement principle in the three patents allows for efficient decoupling of circuit operating conditions, none of the inventions is effective in measuring a current range suitable (tens of microamperes to tens of milliamperes) for the early identification of maintenance needs in electrical equipment or transmission line components.Furthermore, these inventions are not capable of directly measuring the quantity of interest, requiring artificial means to obtain the original information, which leads to greater uncertainties in the system and limits the acquisition of reliable data about the measured current.

[0010] Thus, it is possible to observe the need for the introduction of a A comprehensive and self-sufficient system for measuring low currents in power substations. It should provide a robust, safe, cost-effective product that is useful for improving preventive maintenance on electrical equipment. At the same time, the system should provide continuous and direct access to low-current signal information, enabling complete reconstruction of the measured quantity and, consequently, a greater understanding of phenomena related to the degradation of elements such as insulators. Among existing inventions, models, and works, no devices were found that simultaneously fill all the indicated gaps, as can be seen in the SYSTEM, WITH SENSOR AND ELECTRONIC CIRCUIT, FOR MONITORING LOW CURRENTS IN POWER SUBSTATIONS, described in this patent application.Thus, the development of this invention, which can be used in a self-contained manner at any point in substations where direct and complete monitoring of low currents is desired, is low-cost, easy to install and maintain, shielded against electromagnetic interference, complies with the standards established by related technical norms, and is capable of performing signal self-equalization without the need for post-processing to recover the measured information, guarantees the system's uniqueness among others. Brief description of the drawings

[0011] The invention can be better understood through the following detailed description, in accordance with the attached figures, where: Figure 1 presents the block diagram of the complete system.

[0012] Figure 2 shows cross-sections and top, front, and perspective views of the developed sensor.

[0013] Figure 3 illustrates a top view of the implemented system.

[0014] Figures 4a and 4b show flowcharts of the microprocessor unit's operation.

[0015] Figure 5 shows a schematic of the system installation in power substation.

[0016] Figure 6 illustrates an experimental setup in a high-voltage laboratory for testing insulators subjected to different degrees of pollution.

[0017] Figures 7a and 7b show graphs of leakage current measurements at high voltage in insulators with different levels of pollution. Description of the invention

[0018] The SYSTEM, WITH SENSOR AND ELECTRONIC CIRCUIT, FOR MONITORING LOW CURRENTS IN POWER SUBSTATIONS, object of this patent, comprises a Current Transformer - CT, or sensor (1), a measurement module (2), a microprocessor unit (3) and the housing (4), as shown in Figures 1 to 3.

[0019] The sensor (1), as shown in Figure 2, consists of a toroidal core (5a) surrounded by a conductive winding (6). This assembly is covered by a metallic screen (7) and sealed in a custom-made enclosure (8a). The screen (7) only covers the outer part of the toroid, concentrating the magnetic flux lines necessary for the inductive effect for sensing on the inner part of the core (5a). Finally, the ends of the winding (6) are connected via shielded cable (9) through a connector (8b) to a signal conditioning circuit – in this case, to the measurement module (2). This cable (9) is coated with a protective layer (10).

[0020] When an electric current passes through a conductor that passes through the center of the core (5a), a magnetic field is generated around it, according to Ampère's Law. The shape of the magnetic field will be circular around the conductor. The core (5a) is highly permeable to the magnetic field, concentrating and guiding the magnetic flux lines around it. According to Faraday's Law, a change in the magnetic flux passing through the core (5a) induces an electric voltage in the winding (6). This induced voltage is directly proportional to the rate of change of the current in the conductor that passes through the center of the core (5a). Thus, the induced voltage in the winding (6) can be measured with an electronic circuit, such as that of the measuring module (2). Since this voltage is proportional to the change in current in the conductor, it is possible to detect the electric current in it without having to connect it directly to the sensor (1).

[0021] The housing (4) has holes for the passage of the CT cable (9), the system power supply cable (11) and the communication antenna (12), as seen in Figure 3. In addition to providing protection to the measurement module (2) and the microprocessor unit circuit (3), due to the material from which it is made, the housing (4) contributes to the electromagnetic shielding of the system.

[0022] The measurement module (2), implemented on an integrated motherboard (13), is composed of interconnected blocks for conditioning and processing information from the sensor (1), shown in Figure 1. The Input Protection block circuit consists of fuses and biased diodes so as not to allow an impulsive current or voltage at the system input. Its purpose is to prevent partial or total damage or loss to the components.

[0023] The Equalization block circuit consists of a first-order active low-pass filter, which acts to equalize the natural frequency response of the core (5a) + winding (6) assembly, similar to that of a band-pass filter. The objective is to linearize and make constant the frequency response of the system and, at the same time, migrate it to the region of interest for current monitoring, from 50 Hz to 900 Hz. Performing the equalization in hardware minimizes both the cost of on-site processing and eliminates the need for post-processing after the information is transmitted to the Server.

[0024] The Automatic Gain Control block circuit consists of amplifiers controlled by a digital potentiometer, which receives signals from the Processing Microcontroller (14). The objective is to automate the adjustment of the gains necessary to maximize the signal resolution, optimizing the A / D (analog / digital) conversion of the information.

[0025] The Instrumentation Amplifier and Control blocks DC (direct current) level controls work together. The instrumentation amplifier reduces the common-mode voltage and, consequently, the low-frequency noise that affects the small signal coming from the sensor. The DC level control adjusts the average level of the output signal, which may eventually be modified to values ​​other than zero due to characteristics of the measurement system itself. This signal is then injected as a reference for the instrumentation amplifier. The purpose of the system is to ensure that the DC level remains stable throughout the measurement.

[0026] The Active Filter block circuit consists of a fourth-order Butterworth filter. Its objectives are to reduce noise at high frequencies and prevent signal overlap, while still preserving the harmonics of interest. This ensures higher resolution for measurements in the lower frequency ranges.

[0027] The Signal Conditioning block circuit consists of an inverting summing amplifier. Its purpose is to allow calibration of the signal excursion, respecting the voltage limits of the analog input to the Processing Microcontroller (14). The Output Protection block circuit consists of a diode array. Acting in a complementary way to the Signal Conditioning block, its purpose is to ensure that the voltage sent to the Processing Microcontroller (14) is within the acceptable limits for the safe operation of the equipment; that is, when it goes outside this range, the signal is cut off.

[0028] The microprocessor unit (3) is composed of two processing modules, implemented in the Processing Microcontroller (14) and the Communication Microcontroller (15), as illustrated in Figure 1. The Processing Microcontroller (14) performs uninterrupted sampling of the signal coming from the measurement module (2), performing its A / D conversion, storing the samples of the digitized signal in a non-volatile External Memory (16) and quantifying its magnitude to send command signals to the Automatic Gain Control block. In turn, the Communication Microcontroller Communication (15) is responsible for the control logic of the microprocessor unit (3) and for its wireless communication with the remote Server, which can send commands to the microprocessor unit (3) or receive data from it. The microcontrollers interact with each other through serial communication and a file system accessed by both in an External Memory (16). In this way, the Communication Microcontroller (15) forwards to the Processing Microcontroller (14) the sampling period Ts and sample number N settings, defined in the remote Server. The Communication Microcontroller (15) also receives firmware updates from the Server, thus being able to update itself and the Processing Microcontroller (14).

[0029] The microprocessor unit (3) implements a state machine with seven main states, detailed in Figure 4a: A - Setup, B - Sampling, C - Connection Preparation, D - Transmission, E - Sleep, F - Configuration Update, and G - Firmware Update. In state A, all initial configuration of the unit is performed, including the initialization of registers and pins. In state B, the microprocessor unit (3) samples the signal from the measurement module (2) and stores it in the External Memory (16). In state C, the unit establishes communication with the wireless network. In state D, the stored data is sent to the remote Server and, if the transmission is successful, is erased from the External Memory (16). At the end of this state, the Communication Microcontroller (15) queries the remote Server to check for new configurations and / or firmware updates. In state E, the unit enters a sleep state to save energy.

[0030] In state F, the microprocessor unit (3) updates its settings, such as the sampling period Ts, the number of samples N, and the interval between sampling windows Tj. A sampling window is defined as a period in which the unit captures N consecutive samples of the signal, spaced by Ts seconds. The start of each sampling window is separated for Tj seconds. Finally, in state G, the unit performs the firmware update of the Processing Microcontroller (14) and / or the Communication Microcontroller (15).

[0031] In standard operation, the system should start in state A, proceed sequentially to state E, return to state B, and repeat the cycle from B to E continuously. However, some special events may cause deviations in this cycle. If a failure in the communication network connection occurs, the program flow is diverted from state C directly to state E, and the data will remain stored in External Memory. All pending data will only be transmitted the next time the system enters state D.

[0032] Another event that can alter the main flow of the state machine is the remote configuration update or firmware update process. This process begins when the Communication Microcontroller (15) is in state D and receives information from the server that new configurations or new firmware are available, which directs the execution flow to state F or state G, respectively. In state F, the platform updates the sampling parameters and stores them in its non-volatile memory. Thus, even in case of power interruption, the configuration remains on the device, being restored upon restart.

[0033] In state G, the Communication Microcontroller (15) attempts to establish communication with the Server. If the connection is successful, access to the new firmware image is requested. After receiving the firmware and its information, the Communication Microcontroller (15) validates the firmware by checking the checksum. If validation is successful, the firmware update process of the Processing Microcontroller (14) or the Communication Microcontroller (15) begins, as indicated in the information transmitted along with the firmware. If the update is successful, the respective module is restarted, returning to state A.

[0034] If the firmware update process fails, whether due to network unavailability, file integrity failure, or another reason, the unit enters state E (sleep). Another event that can lead the unit from state G to state E is the exclusive update of the Processing Microcontroller firmware (14).

[0035] In state B, the Communication Microcontroller (15) sends a command to the Processing Microcontroller (14) to start sampling. This command includes information about the sampling period Ts and the number of samples N to be captured. At this point, the Processing Microcontroller (14) starts the calibration process of the conditioning circuit gain in order to maximize the signal-to-noise ratio. After the calibration step, the Processing Microcontroller (14) stores the configured gain in External Memory and starts digitizing the signal with the sampling period Ts, storing it continuously in an External Memory (16).

[0036] To ensure that N samples are captured continuously with a sampling period Ts, the system implements the strategy known as ping-pong buffering, illustrated in Figure 4b. With this architecture, the Communication Microcontroller (15) uses two internal memory regions of equal size, called Ping Buffer and Pong Buffer. When the Ping Buffer is being filled with data from the A / D converter, the data from the Pong Buffer (previously filled) is sent to the External Memory (16), as per state 1 of the switches in Figure 4b. Writing to the External Memory (16) is faster than reading from the A / D converter, so that when one buffer is completely filled, the other is already available to store new data from the A / D converter reading. At this point, the switches indicated in Figure 4b are changed to state 2, where the data from the A / D converter is sent to the Pong Buffer, and the data saved in the Ping Buffer is sent to the External Memory (16).The keys remain in state 2 until the Buffer Pong is fully filled, at which point the keys are... Changed back to state 1, and the process repeats as initially described.

[0037] This process is crucial to ensure that N samples are stored in External Memory, even if the Processing Microcontroller (14) does not have sufficient internal memory to store N samples simultaneously, or if the speed of the interface with External Memory (16) is too slow to store samples individually. When the N samples are stored in External Memory (16), the Processing Microcontroller (14) ends the sampling and informs the Communication Microcontroller (15); this, in turn, continues the state machine flow as described previously.

[0038] The complete system must be installed in the power substation near the equipment or component whose current is of interest for monitoring. A possible installation scheme is shown in Figure 5, where the system is used to monitor the leakage current in an insulator (17) connected to a high-voltage line (18). The CT (1), connected to the housing (4), is positioned to encompass the ground terminal (19) of the equipment or component. The information acquired and processed by the measurement module (2) is then handled by the microprocessor unit (3). Examples of embodiments of the invention

[0039] For the manufacture of the CT (1), the core (5a) preferably has a toroidal shape and is composed of a material with high magnetic permeability, such as an alloy formed from Fe(-Si) phase grains on a nanometric scale. In this case, a support structure, such as a fabric strip (5b), is used to maintain the integrity of the core (5a). To ensure adaptability for installation at any point in the power substations, the preferred dimensions for the core design (5a) are 41 mm outer radius, 23 mm inner radius and 35 mm height.

[0040] The winding (6) of conductive material is preferably made of enameled copper wire of AWG 36 gauge. In this configuration, 100 turns are capable of generating the desired effect. Preferably, the solution for shielding the CT (1) against the effects of electromagnetic interference and noise is to enclose the core (5) + winding (6) assembly with a thin, tightly woven M-250 copper screen (7), proving to be a cheap and effective solution. The screen (7) is grounded together with the system reference.

[0041] The coated core (5a) and the winding (6) and screen (7) are sealed with an adhesive, such as acetic silicone or similar, inside a housing (8a) made of lightweight, moldable, impact- and weather-resistant material, preferably ASA filament (acrylonitrile-styrene-acrylate). Materials with similar performance can replace it. The custom shape of the housing (8a) also accommodates the connector (8b) of the TC cable (9), connecting it to the system motherboard (13) in order to provide mechanical strength to the connections with the winding (6). A PG7 cable gland type connector (8b) is preferred, but any other that fulfills its purpose can replace it. Finally, the shielded cable (9) must be covered by a protective layer (10), such as a UV-resistant heat-shrink tubing. Due to this mounting scheme, the sensor (1) can be connected to other measuring circuits for different industrial applications related to current measurement.

[0042] The circuits of the measuring module (2) and the microprocessor unit (3) are preferably integrated onto a single motherboard (13), facilitating the manufacture, installation, and maintenance of the system. The motherboard (13) must be fixed and grounded inside the housing (4), preferably made of galvanized steel and with IP-67 certification, to guarantee electromagnetic shielding and mechanical and weather protection for the system. Furthermore, to obtain the desired performance of the measuring modules (2) and the microprocessor unit (3), the Processing Microcontroller (14) used must have a minimum processing capacity of 72 MHz and 12-bit resolution for A / D conversion, in addition to being able to save data to an External Memory (16), preferably a memory card. The Communication Microcontroller (15) must be capable of Wi-Fi communication and have a RAM memory of at least 20 kB.

[0043] For the application of interest, where the signal has the main frequency component at 60 Hz, the Equalization block needs to be adjusted for a constant frequency response up to 1 kHz, while the Active Filter is implemented for a cutoff frequency close to 3 kHz. With this configuration, the preference is that N = 8000 samples are collected with a sampling period of Ts = 125 microseconds. Despite this, these parameters are adjustable remotely using the functionalities of the microprocessor unit (3).

[0044] The data sent by the Communication Microcontroller (15) to the Server is preferably accessed via the Internet, since the External Memory (16) must be used to recover information in case of failures. The .bin type files can be viewed using any available source code editor. Preferably, a programming platform with a mathematical operations language is used to facilitate the manipulation and analysis of the data.

[0045] As a way of validating the invention, different experiments were carried out with high-voltage insulators and their leakage currents, since, in practice, these are the components most frequently monitored. The first experiment aimed to reproduce, in a laboratory environment, the electrical stress similar to that which the SYSTEM, WITH SENSOR AND ELECTRONIC CIRCUIT, FOR MONITORING LOW CURRENTS IN ENERGY SUBSTATIONS will face in the field. The sensor (1) was installed on a polymeric insulator (17) on the busbar (18) of the high-voltage laboratory, maintaining a minimum distance of 23 cm between the CT (1) and the casing (4), similarly to the scheme shown in Figure 5. The ground terminal (19) of the insulator (17), the CT (1) and the casing (4) was grounded. The same procedure should be repeated in the field installation.Table 1 shows the different levels of alternating voltage applied to the insulator and the respective currents measured by the sensor during this test. Table 1: Alternating voltages applied to the insulator and corresponding currents measured by the system.

[0046] During these tests, the measurement modules (2) and the microprocessor unit (3) operated as expected, collecting current values ​​and sending them to the Server. For each voltage level, two leakage current acquisitions were performed to verify the accuracy of the proposed device. Even under high voltage levels, the system demonstrated robustness, showing no significant variations in measured values.

[0047] Using the same experimental setup and aiming to further validate the system's robustness, a high-voltage impulse test, both positive and negative, was performed to verify the electromagnetic conditions of both the casing (4) and the CT (1). Impulsive voltages of 70 kV were applied in both positive and negative polarity. For the impulse, it was defined that the electrodes would approach a distance of 28 mm; thus, after the rupture, the impulse was injected. In both polarities, the measurement module (2) and the microprocessor unit (3) functioned as expected, with the electronic circuit withstanding the imposed electrical stresses without any failures. Even when the configuration remained de-energized, the system continued to operate without interruptions, ensuring data integrity throughout the experiment.

[0048] Finally, to verify the ability to differentiate between levels of degradation, a procedure involving the application of artificial pollution was carried out in Three insulators (17), named X, Y, and Z, as illustrated in Figure 6, according to IEC 60815-1. The insulators (17) were suspended at 150 cm and stabilized along an energized steel cable (18), together with a fourth insulator (17), named W, completely clean. A low degree of pollution was applied to insulator (17) X, while insulator (17) Y received a medium degree of pollution and insulator (17) Z, a high degree of pollution. Each insulator (17) had its ground terminal (19) connected to the grounding system so as to pass through the center of an operating CT (1). Leakage currents were monitored simultaneously with a benchtop oscilloscope, see Figure 7a, and with the proposed system, Figure 7b. For use with the oscilloscope, each of the insulators (17) was connected to a shunt resistor, enabling the use of the equipment's current probe.This test is only possible because it is a laboratory environment, since increasing resistance in the network goes against current standards. The high degree of agreement in the form and magnitude of the measurements is noticeable, as is the clear relationship between the pollution level and the magnitude of the leakage current. The phase misalignment is solely a consequence of the data chosen to plot the graphs, which were acquired at different times and have no physical significance. Non-Patent References

[0049] Ahmed, R., Kim, T., Lee, YJ, Jeon, S., Yi, J., Choi, IH, ... & Koo, JB (2020). Online condition monitoring and leakage current effect based on local area environment. Transactions in Electrical and Electronic Materials, 21, 144-149.

[0050] Akbar, M., Ullah, R., & Alam, S. J. M. R. E. (2019). Aging of silicone rubber-based composite insulators under multi-stressed conditions: an overview. Materials Research Express, 6(10), 102003.

[0051] de Santos, H., & Sanz-Bobi, M. Á. (2020). A cumulative pollution index for the estimation of the leakage current on insulator strings. IEEE Transactions on Power Delivery, 35(5), 2438-2446.

[0052] Dolník, B., Sárpataky, L., Kolcunová, I., & Havran, P. (2022). Sensing method using multiple quantities for diagnostic of insulators in different ambient conditions. Sensors, 22(4), 1376.

[0053] Fierro-Chavez, J. L, Ramirez-Vazquez, I., & Montoya-Tena, G. (1996). On-line leakage current monitoring of 400 kV insulator strings in polluted areas. IEE Proceedings-Generation, Transmission and Distribution, 143(6), 560- 564.

[0054] Gençoglu, M. T., & Cebeci, M. (2008). The pollution flashover on high voltage insulators. Electric Power Systems Research, 78(11 ), 1914-1921.

[0055] Gouda, O. E., Darwish, M. M., Mahmoud, K., Lehtonen, M., & Elkhodragy, T. M. (2022). Pollution seventy monitoring of high voltage transmission line insulators using wireless device based on leakage current bursts. IEEE Access, 10, 53713-53723.

[0056] Jiang, Y., McMeekin, S. G., Reid, A. J., Nekahi, A., Judd, M. D., & Wilson, A. (2014). Theoretical model of applying radiometry to monitor insulator contamination. In International Conf. Condition Monitoring and Diagnostics, Jeju, Korea.

[0057] Li, J., Sima, W., Sun, C., & Sebo, S. A. (2010). Use of leakage currents of insulators to determine the stage characteristics of the flashover process and contamination level prediction. IEEE Transactions on Dielectrics and Electrical Insulation, 17(2), 490-501.

[0058] Oliveira, SC, Fontana, E., & de Melo, FJDM (2009). Leakage current activity on glass-type insulators of overhead transmission lines in the northeast region of Brazil. IEEE Transactions on Energy Delivery, 24(2), 822-827.

[0059] Portella, KF, Piazza, F., Inone, PC, Ribeiro Jr, S., Cabussú, MS, Cerqueira, DP, & Chaves, CSDS (2008). Effects of atmospheric pollution (coastal and industrial) on insulators of the electrical network in the metropolitan region of Salvador. Química Nova, 31, 340-348.

[0060] Robles, G., Martínez-Tarifa, JM, Gómez-de-la-Calle, M., Barroso-de-María, G., & Izquierdo, D. (2021). Detecting series arcs in aeronautical applications using inductive sensors. IEEE Transactions in Aerospace and Electronic Systems, 58(3), 2073-2082.

[0061] Rubio-Serrano, J., Rojas-Moreno, M. V., Posada, J., Martínez- Tarifa, J. M., Robles, G., & Garcia-Souto, J. A. (2012). Electro-acoustic detection, identification and location of partial discharge sources in oil-paper insulation systems. IEEE Transactions on Dielectrics and Electrical Insulation, 19(5), 1569- 1578.

[0062] Stefenon, S. F., Seman, L. O., Neto, N. F. S., Meyer, L. H., Nied, A., & Yow, K. C. (2022). Echo state network applied for classification of medium voltage insulators. International Journal of Electrical Power & Energy Systems, 134, 107336.

[0063] Villalobos, R. J., Moran, L. A., Huenupán, F., Vallejos, F., Moncada, R. , & Pesce, C. (2022). A new current transducer for on-line monitoring of leakage current on HV insulator strings. IEEE Access, 10, 78818-78826.

[0064] Werneck, M. M., dos Santos, D. M., de Carvalho, C. C., de Nazaré, F. V. B., & Allil, R. C. D. S. B. (2014). Detection and monitoring of leakage currents in power transmission insulators. IEEE sensors journal, 15(3), 1338- 1346.

Claims

CLAIMS 1. SYSTEM, WITH SENSOR AND ELECTRONIC CIRCUIT, FOR MONITORING LOW CURRENTS IN POWER SUBSTATIONS characterized by being composed of a current transformer, sensor (1), a measurement module (2), a microprocessor unit (3) and the housing (4);and the sensor (1) is composed of a toroidal core (5a) surrounded by a conductive winding (6), covered by a metallic screen (7) and sealed in a customized enclosure (8a), and the screen (7) only covers the outer part of the toroid, concentrating the magnetic flux lines necessary for the inductive effect for sensing in the inner part of the core (5), and the ends of the winding (6) are connected via shielded cable (9), coated with a protective layer (10), by means of a connector (8b) to a signal conditioning circuit - in this case, to the measurement module (2), which is implemented on an integrated motherboard (13) and composed of interconnected blocks for conditioning and processing the information coming from the sensor (1);and by the microprocessor unit (3) being composed of two processing modules, implemented in the Processing Microcontroller (14), which performs sampling whenever requested by the Communication Microcontroller (15) of the signal coming from the measurement module (2), performing its A / D conversion, storing the samples of the digitized signal in a non-volatile External Memory (16) and quantifying its magnitude to send command signals to the Automatic Gain Control block and in the Communication Microcontroller (15), responsible for the control logic of the microprocessor unit (3) and for its wireless communication with the remote Server, which can send commands to the microprocessor unit (3) or receive data from it; and by the microcontrollers interacting with each other through serial communication and a file system accessed by both in an External Memory (16).

2. SYSTEM, WITH SENSOR AND ELECTRONIC CIRCUIT, FOR MONITORING LOW CURRENTS IN SUBSTATIONS OF ENERGY, according to claim 1, characterized by being able to measure alternating currents in the range of tens of microamperes to tens of milliamperes, with adjustment of the range of interest in both magnitude and frequency; and by being able to directly measure electric currents without interfering with the integrity of the network, minimizing the propagation of uncertainties in the system; and by acquiring the electric current signal completely and with high resolution, maintaining its integrity for subsequent analysis; and by having a dedicated communication network, enabling remote firmware configuration for updating acquisition and processing parameters and sending the acquired data via the Internet.

3. SYSTEM, WITH SENSOR AND ELECTRONIC CIRCUIT, FOR MONITORING LOW CURRENTS IN POWER SUBSTATIONS, according to claim 1, characterized by the electronic circuit of the measurement module (2) performing the equalization of the measured signal, linearizing and keeping constant its frequency response while migrating it to the region of interest for the application, typically from 50 to 900 Hz; and by the electronic circuit of the measurement module (2) enabling the manual calibration of the measurement range of interest and the DC level of the signal, making the system adaptable to different electrical equipment or transmission line components; and by the electronic circuit of the measurement module (2) enabling the automatic calibration of the gain of each harmonic of the signal, facilitating the direct reconstruction of the measured signal.

Images