Self-calibration system and program for automatic loop resistance measuring device

Abstract

The self-calibration system for an automatic loop resistance measuring device includes a processing unit (1) connected to a resistance sensor (2), having a housing (4) containing a microprocessor with memory; an auxiliary circuit (5) connected in parallel with at least two precision resistors (6) having switches (7); a communication device; and a power supply device. The automatic self-calibration procedure for the automatic loop resistance measuring device has a system similar to the previous one, including an initial stage (8) for obtaining a normalized calibration curve (8.1) of the measuring device and introducing the normalized value (8.2) into memory, and a self-calibration stage (9) including a stage for obtaining the range (10) of the loop resistance (Rb) of the measuring device, and calculating (14) the loop resistance value (15).

Description

Technical Field

[0001] This invention relates to the technical field of loop resistance measuring devices having a loop resistance sensor with a grounded conductor, wherein the calibration curve of the measuring device has at least two different value ranges, and specifically relates to a self-calibration system and procedure for these measuring devices. Background Technology

[0002] To verify the grounding system, the inspection and measurement of loop resistance are mainly applied to TN and IT distribution systems, where the protection system is based on fuses or circuit breakers.

[0003] When a certain leakage current leaves the grounding rod, a large portion of this current returns to the device through the transformer secondary rod and the faulty line conductor. Therefore, a short-circuit current flows through the faulty loop, increasing the load current in the line.

[0004] Loop resistance measurements suffer from stability issues due to a large number of variables affecting measurement uncertainty (temperature, eddy currents, microscopic geometric changes in the sensor, cable length and geometry, etc.). This is why it is difficult to make this type of sensor have a completely stable response under all conditions and environments.

[0005] Furthermore, when it is an unattended device, i.e., when it does not require continuous operation by installers, this means that under normal operating conditions, the sensing element is monitoring the conductors of the grounding system, which makes the comparison calibration process difficult because there is always a parallel loop with an unknown value.

[0006] Loop resistance sensors are commercially available, and compact, handheld measuring devices that perform this loop resistance measurement function are readily available. These devices are easy to maintain, verify, and calibrate because they are always accessible and can be connected to loops with known impedance values.

[0007] Unattended equipment will malfunction because it cannot autonomously perform the task of measuring loop resistance due to uniformity issues with the sensors used, caused by both natural factors (such as temperature and humidity) and human factors (such as the positioning and tightening of the sensors during installation). These variables affect the measurement results, thus necessitating correction for this bias. However, initial correction is insufficient because, due to the aforementioned natural factors, this bias may vary from day to day.

[0008] In the prior art, it is unknown whether any impedance measurement device or system with any self-calibration mechanism exists, and therefore, self-calibration is performed before each measurement is performed by the device, the periodicity of which is programmable. Summary of the Invention

[0009] The self-calibration system of the automatic loop resistance measuring device described herein involves a measuring device with a loop resistance sensor for a grounding conductor, and the calibration curve of the measuring device has at least two different value ranges.

[0010] The self-calibration system includes a processing unit connected to a resistance sensor and formed by a housing, which internally includes a microprocessor with storage memory, an auxiliary circuit, a communication device with a data receiving device, and a power supply.

[0011] In itself, the auxiliary circuit is connected to at least two precision resistors via switches, each with a specific value that is different from each other, such that there is at least one resistance value in each range of the calibration curve.

[0012] The system features a grounding impedance calculation algorithm, allowing it to be applied to monitor loops closed by physical grounding. This enables the measurement of grounding resistance.

[0013] This specification presents a self-calibration procedure for an automatic loop resistance measuring device, used to adjust the current injection frequency via the self-calibration system defined above.

[0014] The procedure includes an initial stage for obtaining a normalized calibration curve of the measuring device and importing the normalized value of the calibration curve into the system's memory, and a self-calibration stage with a first stage for obtaining the loop resistance range of the measuring device.

[0015] This first stage is carried out by sequentially turning on switches corresponding to at least one resistor for each range of the normalized calibration curve, such that the connection of each switch configures an equivalent circuit between the circuit of the measuring device and the auxiliary circuit of the corresponding resistor associated with the switch.

[0016] Finally, the second stage involves calculating the value of the loop resistance.

[0017] Significant improvements to the prior art have been achieved by means of a self-calibration system for automatic loop resistance measurement devices and a self-calibration procedure performed by means of the system proposed herein.

[0018] This is because a program is implemented to automatically adjust the current injection frequency before each measurement, so that the exact value of the resistance to be monitored can be obtained using the dependence on the characteristic frequency of the current transformer.

[0019] The system is also fully autonomous, allowing installers to monitor the installation continuously and unattended. Furthermore, it ensures the repeatability of measurements and reduces reliance on variables that affect measurement dispersion (temperature, vibration or shock, length and arrangement of connecting cables between sensor elements and machined parts).

[0020] Continuous communication eliminates the need for periodic verification reviews, as up-to-date information on the status of the monitoring loop is always available, thereby reducing preventative and corrective maintenance efforts.

[0021] On the other hand, the system has a specific filtering mechanism to eliminate noise caused by eddy currents with a high suppression coefficient. Eddy currents are a typical feature of electrical installation grounding systems, such as frequency converters (CTs) or substations (SEs).

[0022] The system also integrates a method for identifying current pulses in relevant conductors, a characteristic of partial discharge (DP), which is typical of systems subjected to electrical stress, such as line insulators, insulated cables used to transmit electrical energy, and transformers. This feature enables the identification of conditions such as aging, degradation, and faults, which is beneficial for preventive and corrective maintenance of power transmission and distribution network assets.

[0023] Therefore, it enables a self-calibration system and self-calibration procedure that is highly efficient, reliable, programmable, and operates continuously and completely autonomously. Attached Figure Description

[0024] To aid in a better understanding of the features of the invention, a series of accompanying drawings are provided as part of the description, according to preferred examples of its actual implementation, wherein, in an illustrative and non-limiting manner, the following have been shown:

[0025] Figure 1 A perspective view of the processing apparatus of a self-calibration system for an automatic loop resistance measuring device according to a preferred embodiment of the present invention is shown.

[0026] Figure 2 A schematic diagram of the auxiliary circuit of a self-calibration system for an automatic loop resistance measuring device according to a preferred embodiment of the present invention is shown.

[0027] Figure 3 A block diagram of the autonomous self-calibration procedure of an automatic loop resistance measuring device according to a preferred embodiment of the present invention is shown.

[0028] Figure 4.1 and 4.2 - The normalized calibration curve and characteristic calibration curve of the measuring device for the autonomous self-calibration procedure of the automatic loop resistance measuring device according to a preferred embodiment of the present invention are shown respectively. Detailed Implementation

[0029] As can be seen from the accompanying drawings, in a preferred embodiment of the invention, the self-calibration system proposed herein is used in an automatic loop resistance measuring device having a loop resistance sensor 2 for a ground conductor 3, wherein the calibration curve of the measuring device has at least two different value ranges.

[0030] In this embodiment, the calibration curve is as follows: Figure 4.2 As shown, it specifically spans three value ranges.

[0031] like Figure 1 As shown, the system includes a processing device 1 connected to a resistance sensor 2, wherein the processing device 1 is formed by a housing 4.

[0032] Inside the housing 4, the processing device 1 includes a microprocessor with storage memory, an auxiliary circuit 5 connected in parallel with at least two precision resistors 6 via switches 7, a device for communicating with a data receiving device, and a power supply device.

[0033] Each precision resistor has a specific value, which is different from each other, so that there is at least one resistance value in each range of the calibration curve.

[0034] In this preferred embodiment of the invention, such as Figure 4.2 The calibration curve shown has three different value ranges. The system includes a number of precision resistors 6 and has values ​​for at least two precision resistors 6 in each loop resistance range.

[0035] Therefore, in this specific situation, such as Figure 2 As shown, the processing device 1 consists of six precision resistors 6. Therefore, the values ​​of the first resistor R1 and the second resistor R2 are included in the first range, the values ​​of the third resistor R3 and the fourth resistor R4 are included in the second range, and the values ​​of the fifth resistor R5 and the sixth resistor R6 are included in the third range.

[0036] In this preferred embodiment of the invention, the communication device includes wireless communication, specifically GSM communication. However, in other embodiments, they can be formed via other types of wireless communication or via wired communication (e.g., via Ethernet).

[0037] On the other hand, in this preferred embodiment of the invention, the power supply device is formed by a battery connected to a solar power generation system. In other embodiments, they can be formed by connecting to a power grid or a combination of both.

[0038] The specification also proposes an autonomous self-calibration procedure for automatic loop resistance measurement devices, which adjusts the current injection frequency through a previously defined self-calibration system.

[0039] The procedure includes an initial stage 8 for obtaining the normalized calibration curve 8.1 of the measuring device, such as... Figure 4.1 As shown, the normalized value 8.2 of the calibration curve is introduced into the memory of the processing device. From this curve, the corresponding characteristic curve can be obtained through two variables K1 and K2 (gain and offset), as shown. Figure 4.2As shown.

[0040] The characteristic curve response formula is: (K1x normalized curve) + K2.

[0041] The program also has a self-calibration stage 9, which consists of a series of stages.

[0042] Therefore, the self-calibration stage 9 includes a first stage for obtaining a range 10, in which the loop resistance Rb of the device is included. The loop resistance Rb is obtained by sequentially turning on the corresponding switches 7 of two precision resistors 6 for each range of the normalized calibration curve, such that the connection between each switch 7 is configured as an equivalent circuit between the loop of the measuring device and an auxiliary loop 5 corresponding to the precision resistor 6 associated with the switch 7.

[0043] In this way, each of the six resistors (R1 to R6) is connected in sequence until the range of the loop resistance Rb of the measuring device is obtained.

[0044] In this preferred embodiment of the invention, obtaining the range 10 of the loop resistance Rb including the measuring device includes measuring 11 the value of the loop resistance Rb of the device corresponding to the equivalent circuit of at least one precision resistor 6, and comparing the obtained value with the value of the precision resistor 6, wherein the measurement 11 and the comparison 12 are performed after the switch 7 is turned on.

[0045] like Figure 3 As shown, in the general case of resistance n, this process is represented as follows, obtaining the phase of the range as follows:

[0046] First of all, Figure 3 In general, the first resistor 13(n) of the first range is connected by turning on the first switch. In the proposed embodiment using six resistors, resistor R1 is already connected.

[0047] Between the measuring circuit and auxiliary circuit 5, a circuit with two resistors connected in parallel is generated. The equivalent circuit is a circuit with resistors, the value of which is the parallel resistance of the two interconnected resistors, as shown in the following formula:

[0048]

[0049] After connecting the first resistor 13(n), the resistance of the equivalent parallel circuit (R parallel) is measured 11. In the preferred embodiment of the invention using six precision resistors, the resistor R1 of the first range is connected, and using its value and the resistance value of the equivalent parallel circuit (R parallel), we obtain the resistance value of a measurement loop resistor Rb from the previous formula, but this resistance value is unknown.

[0050] Using a deterministic algorithm, the system analyzes whether the resistance value obtained for the loop resistance Rb of the device falls within the range of the first connected resistor R1. For this purpose, a comparison 12 is made for the obtained value. If the resistance value, which is the measured loop resistance Rb corresponding to the precision resistor 6, in this embodiment is the first resistor R1, is greater than 1 / 4 of its value and less than 3 / 4 of its value, that is, if 0.25R1 < Rb < 0.75R1 (for the general case 0.25Rn < Rb < 0.75Rn).

[0051] If the comparison 12 is yes 12.1, the stage for obtaining the range ends, and the range of the loop resistance Rb of the measuring device is the same as the range of the precision resistor 6, which is the first resistor R1 in this embodiment.

[0052] In this case, knowing the range of the loop resistance Rb of the measuring device, a second calculation stage 14 of the loop resistance value 15 will be carried out.

[0053] On the other hand, if the value of the loop resistance Rb obtained through the first precision resistor is less than 1 / 4 of its value or greater than 3 / 4 of its value, the comparison 12 is no 12.2. In this case, the sequential conduction of the switches continues. In this case, the switch corresponds to the precision resistor (n + 1) consecutive to the previous one. (In this embodiment, the switch of the second resistor R2 will be conducted).

[0054] Similarly, when calculating the value of the loop resistance Rb, it is considered that the equivalent circuit corresponding to this new resistor (n + 1) is continuous with respect to the previous resistor, and the step of measuring the resistance of the equivalent parallel circuit (R parallel) is repeated to obtain the loop resistance Rb of the measuring device and check whether the loop resistance Rb corresponding to the precision resistor 6 is greater than 1 / 4 of its value and less than 3 / 4 of its value.

[0055] Once the range of the loop resistance Rb of the measuring device is obtained, for the second stage including the calculation of the loop resistance value 15, this operation is performed for each precision resistor 6 in this range. Thus, in this preferred embodiment of the present invention, if the loop resistance Rb of the measuring device has been obtained within the same range as the first resistor R1, the calculation is performed for the two resistors (R1 and R2) of the determined range.

[0056] In this preferred embodiment of the present invention, if the comparison between the loop resistance values 15 obtained for the same range is less than 1%, the value is correct 15.1, and the measurement of the loop resistance 16 is carried out at the same frequency value of the injected current and with all switches 7 off.

[0057] Therefore, the next step is to turn on switch 7 of the first resistor R1 of 13(n) and measure the resistance value of the equivalent parallel circuit (R parallel) of the first resistor (R1 or n in general) of 11(n).

[0058] Next, switch 7, which is a continuous resistor in the same range of 13(n+1), is turned on, typically R2 or (n+1) in this case, and the resistance value of the equivalent parallel circuit (R parallel) of the second resistor 11(n+1) is measured.

[0059] Using these two values, the loop resistance values ​​obtained within the same range can be compared 15. If the value is less than 1%, that is, if Rn / R(n+1)<1%, then the value is correct 15.1, and the loop resistance is measured 16 with the same frequency of the injected current and all switches 7 open.

[0060] Conversely, if a comparison of the loop resistance value 15 obtained within the same range yields a value greater than 1%, then the value is incorrect 15.2. In this case, the injected current frequency value 17 is modified to increase by 1%, and the calculation of the loop resistance value 15 is performed again 14.

[0061] The described embodiments constitute only one example of the invention. Therefore, the specific details, terms and phrases used in this specification should not be considered limiting, but should only be understood as the basis for the claims and a representative basis for providing an understandable description, and to provide sufficient information to those skilled in the art to apply the invention.

Claims

1. A self-calibration system for an automatic loop resistance measuring device, characterized in that, The measuring device has a loop resistance sensor (2) for a ground conductor (3), wherein the self-calibration system includes a processing device (1) connected to the resistance sensor (2), wherein the processing device (1) is formed by a housing (4) and includes: A microprocessor with storage memory; An auxiliary circuit (5) comprising at least two precision resistors (6) connected in parallel, the precision resistors (6) being selectively switched on by corresponding switches (7), the auxiliary circuit (5) being connected in parallel with the circuit resistance (Rb) to be measured, wherein each of the precision resistors (6) has a specific value, the values ​​being different from each other; and Power supply device; The self-calibration system also includes a device for communicating with a data receiving device; wherein The normalized calibration curve (8.1) of the measuring device has at least two different value ranges, and includes at least one resistance value in each range of the calibration curve; The self-calibration system has a grounding resistance calculation algorithm, which allows the system used to adjust the current injection frequency and calculate the resistance to be applied to unattended monitoring of loops closed by physical grounding. Furthermore, the self-calibration system is configured to implement an initial stage (8) and a self-calibration stage (9), wherein the initial stage (8) is used to obtain the normalized calibration curve (8.1) of the measuring device and input the normalized value (8.2) of the calibration curve into the memory of the processing device, and the self-calibration stage (9) includes: A range (10) including the measured loop resistance (Rb) is obtained by connecting at least one of the precision resistors (6) of each range of the normalized calibration curve (8.1) from the sequential conduction (13(n)) of the switch (7) corresponding to each precision resistor (6), such that the conduction of each switch (7) configures an equivalent circuit between the loop and the auxiliary loop (5) of the measuring device, the auxiliary loop (5) corresponding to the precision resistor (6) associated with the switch (7); and Calculate the loop resistance value (14) based on the obtained range (15).

2. The self-calibration system according to claim 1, characterized in that, The precision resistors (6) are included in a plurality of such precision resistors (6) such that for each stage of the precision resistors (6), at least two of the precision resistors (6) have values ​​within the same loop resistance range.

3. The self-calibration system according to any one of claims 1 and 2, characterized in that, The communication device consists of wired communication via Ethernet.

4. The self-calibration system according to any one of claims 1 and 2, characterized in that, The communication device is composed of wireless communication.

5. The self-calibration system according to claim 4, characterized in that, Wireless communication is formed by GSM communication.

6. The self-calibration system according to any one of claims 1, 2, and 5, characterized in that, The power supply unit is formed by batteries connected to a solar energy system.

7. The self-calibration system according to any one of claims 1, 2, and 5, characterized in that, The power supply device is formed by connecting to the power grid.

8. A self-calibration program for an automatic loop resistance measuring device, characterized in that, For adjusting the current injection frequency using the self-calibration system as described in any one of claims 1 to 7, the system includes an initial phase (8) and a self-calibration phase (9), wherein the initial phase (8) is used to obtain a normalized calibration curve (8.1) of the measuring device and to input the normalized value (8.2) of the calibration curve into the memory of the processing device, and the self-calibration phase (9) includes the following phases: A range (10) including the measured loop resistance (Rb) is obtained by connecting at least one of the precision resistors (6) of each range of the normalized calibration curve (8.1) from the sequential conduction (13(n)) of the switches (7) corresponding to each precision resistor (6), such that the conduction of each switch (7) configures an equivalent circuit between the loop of the measuring device and the auxiliary loop (5), the auxiliary loop (5) corresponding to the precision resistor (6) associated with the switch (7); and Calculate the loop resistance value (14) based on the obtained range (15).

9. The autonomous self-calibration procedure according to claim 8, characterized in that, Obtaining the range (10) of the loop resistance (Rb) including the measuring device includes measuring (11) the value of the loop resistance (Rb) of the equivalent circuit corresponding to at least one of the precision resistors (6), and comparing (12) the value obtained relative to the value of the precision resistor (6), wherein the measurement (11) and the comparison (12) are performed simultaneously with the activation of the switch (7).

10. The autonomous self-calibration procedure according to claim 9, characterized in that, If the value of the loop resistance (Rb) of the measuring device corresponding to the precision resistor (6) is greater than 1 / 4 of its value and less than 3 / 4 of its value, then comparison (12) is yes (12.1), and the stage of obtaining the range (10) ends, and the range of the loop resistance (Rb) of the measuring device is the same as that of the precision resistor (6).

11. The autonomous self-calibration procedure according to claim 9, characterized in that, If the value of the loop resistance (Rb) of the measuring device corresponding to the precision resistor (6) is less than 1 / 4 or greater than 3 / 4 of its value, then comparison (12) is negative (12.2), and the calculation of the loop resistance (Rb) of the measuring device corresponding to the equivalent circuit of the precision resistor (6) that is continuous with the previous precision resistor (6) is performed.

12. The autonomous self-calibration procedure according to any one of claims 8 to 11, characterized in that, If each range has at least two of the precision resistors (6), then the calculation (14) of the loop resistance value (15) is performed for each of the precision resistors (6) in the range.

13. The autonomous self-calibration procedure according to claim 12, characterized in that, If the comparison between loop resistance values ​​(15) obtained in the same range is less than 1%, then the value is correct (15.1), and the loop resistance is measured (16) with the same injected current frequency value and all switches (7) open.

14. The autonomous self-calibration procedure according to claim 12, characterized in that, If the comparison of loop resistance values ​​(15) obtained within the same range is greater than 1%, then the value is incorrect (15.2), and the injected current frequency value is modified (17) by increasing the injected current frequency value by 1%, and the calculation of the loop resistance value (15) is performed again (14).

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