True digital current transformer calibrator

Abstract

The invention discloses a patent technology of a true digital current transformer calibrator (hereinafter referred to as a novel CT calibrator), and relates to a major technical innovation of a calibration device of a current transformer calibrator of current metering equipment (a current transformer for measurement) which is crucial in the field of electric energy metering. According to the invention, an innovative idea of using a double-standard current transformer is smartly recommended, and a circuit principle and a structural design of a multi-range auxiliary standard current transformer CTa with an ultrahigh accuracy level are provided. In order to solve the problem that U delta is too low when CTX for SS-level wide-range metering is calibrated at the lowest measuring point, the invention discloses a CTX calibrating device for SS-level wide-range metering. And the problem that the numerical value of UN2 is too high at a measuring point with the highest current amplification multiple is solved, and the U delta and the UN2 pass through an amplification and attenuation system formed by a gain-adjustable high-accuracy in-phase proportional operational amplifier with the completely same circuit structure and a high-accuracy induction voltage divider IVD with the voltage division coefficients including 1%, 10% and 100%, and the amplification and attenuation system is composed of a high-accuracy in-phase proportional operational amplifier and an induction voltage divider IVD with the voltage division coefficients including 1%, 10% and 100%.

Description

Technical Field

[0001] The technical field of this invention, "True Digital Current Transformer Calibrator," relates to a novel precision current transformer calibration instrument with highly innovative value in ensuring the accuracy of current metering equipment (measuring current transformer), which plays a crucial role in the national power metering field. Background Technology

[0002] The accuracy and reliability of electricity metering directly affect the economic interests of both electricity suppliers and consumers, and play a significant role in the implementation of major policies such as energy conservation, emission reduction, and continuous improvement of production efficiency. The accuracy of current measurement using current transformers is a crucial guarantee for the accuracy of electricity metering.

[0003] Are there any problems with the accuracy assurance of current transformers used in the power system? Obviously, is the error value of this legally mandated metering instrument, the current transformer, accurate? It is naturally worth prioritizing whether there are any loopholes. Among the various methods to plug this loophole, strictly controlling the "calibration instrument for metering current transformers" becomes extremely important.

[0005] From a purely technical perspective, I have found some problems with the traditional current transformer calibrators that my country has used for more than half a century and the digital display electronic transformer calibrators that have been used for more than forty years, as well as the calibration methods, calibration devices, and calibration procedures of these instruments. Summary of the Invention

[0006] The purpose of this invention is to provide a true digital current transformer calibrator, which solves the problem of large error values ​​in traditional current transformer calibrators that have been used in my country for more than half a century and digital display electronic current transformer calibrators that have been used for more than forty years.

[0007] To achieve the above objectives, the present invention provides the following technical solution:

[0008] The self-balancing current comparator CC used in this patented invention, "True Digital Current Transformer Calibrator," features ultra-low noise (Barkhausen noise). Besides accurately amplifying the differential current IΔ between the tested current transformer CTX and the main standard current transformer CTN at various measurement points from 0.1% to 200% of the rated current by a factor of 10, it ensures that the differential voltage UΔ = IΔRF, converted by the differential current / differential voltage conversion resistor RF, is consistently amplified to greater than 0.35V through a six-channel amplification and attenuation system, meeting the effective voltage level requirements of the A / D converter. It converts the analog quantity UΔ into a digital quantity with virtually no accuracy loss during transmission and conversion, sending it to a PC for high-precision digital processing. Another important function of CC is that, due to its three input windings, it can use any high-accuracy standard current transformer, including ultra-high accuracy "two-stage current transformers," as a standard. It can also be directly used to calibrate "two-stage current transformers" below the 0.01 class. It can also perform comparison work between two-stage current transformers with any higher accuracy level.

[0009] Furthermore, to ensure the accuracy requirements for the verification and traceability of high-accuracy standard current transformers with a precision better than 0.01%, and especially to completely solve the long-term inaccuracy problem of the phase difference value of current transformers, the "True Digital Current Transformer Verifier" invented in this patented technology adopts the design concept and corresponding technical measures of main and auxiliary dual standard current transformers.

[0010] The accuracy of the primary standard current transformer (CTN) required depends on the user's intended use and is unrelated to the calibration instrument; the user must provide their own. However, this is not shown in the appendix. Figure 1 The appendix Figure 5 The ultra-high accuracy auxiliary standard current transformer CTa shown here employs a completely new design concept for the commonly used compensation resistor RC. In addition to a precision, high-power, high-stability, low-temperature-coefficient metal film resistor element with the exact same resistance value as its load resistor R, it also features a high-quality, high-strength enameled wire cut from a coaxial product of the same specifications (length and diameter) as the secondary winding of the CTa's main transformer, connected in series at each different transformation ratio. This enameled wire is manufactured by the same company as the main transformer and is cut from the same coaxial product. Figure 6 , 7 The technical requirements described after each view are for the fabrication of constant resistance micro-inductance precision compensation resistors.

[0011] Furthermore, for the calibration instrument used to verify Class S "measuring current transformers", attached Figure 1The system comprises two voltage signal processing systems: a six-channel in-phase precision operational amplifier A with amplification and attenuation ratios of 100, 20, 5, 1, 0.83333, and 0.66666 respectively; a calibration instrument for calibrating SS-grade "wide-range current transformers for metering" with six-channel in-phase precision operational amplifier A with amplification and attenuation ratios of 1000, 200, 100, 20, 5, 1, 0.83333, and 0.5 respectively; and two high-accuracy low-voltage power frequency inductive voltage dividers (IVDs) with voltage division coefficients of 1%, 10%, and 100%. Only the transmission coefficients need to be finely adjusted so that the difference does not exceed 0.00002%, without requiring extremely high absolute accuracy. This design concept, utilizing relevant measurement theory to achieve ultra-high precision measurement, is a highly distinctive innovation in the field of transformer calibration instruments.

[0012] Furthermore, the invention recommended in this patent is as follows (see appendix). Figure 9 Appendix Figure 10 The current source shown is a 2000VA (volt-ampere) apparent power source that is strictly synchronized with the 50 / 60Hz frequency of the mains power, has extremely low waveform distortion, and can achieve manual or automatic fine adjustment of the output current with the help of a stepper motor by adjusting the fineness of better than 1 / 1800 or even 1 / 3600 through a ten-turn precision potentiometer.

[0013] Furthermore, the self-balancing current comparator CC with ultra-low noise (Barkhausen noise) used in this patented invention, "True Digital Current Transformer Tester," can measure the current transformer CT under test at various measurement points from 0.1% to 200% of the rated current. X With the main standard current transformer CT N The differential current IΔ is precisely amplified by 10 times to ensure that the differential current / differential voltage conversion resistor R... F The converted differential pressure is UΔ=IΔR F The voltage is then amplified to greater than 0.35V through a six-channel amplification and attenuation system, meeting the effective voltage level requirements of the A / D converter. The analog quantity UΔ is converted into a digital quantity with almost no accuracy loss during transmission and conversion, which is then sent to a PC for high-precision digital processing. Another important function is that, because the CC has three input windings, it can use any high-accuracy standard current transformer, including ultra-high accuracy "two-stage current transformers," as a standard. It can also be directly used to calibrate "two-stage current transformers" with an accuracy class of 0.01 or lower. Furthermore, it can perform comparisons between two-stage current transformers with any higher accuracy class. Therefore, this patented invention represents a significant technological innovation.

[0014] Furthermore, to ensure the accuracy requirements for the verification and traceability of high-accuracy standard current transformers with a precision better than 0.01%, and especially to completely solve the long-term inaccuracy problem of the phase difference value of current transformers, the "True Digital Current Transformer Verifier" invented in this patented technology adopts the design concept and corresponding technical measures of main and auxiliary dual standard current transformers.

[0015] The main standard current transformer (CT) required to be used is among them. N The accuracy depends on the user's intended use and is unrelated to the calibrator; the user must provide their own. However, it is not shown in the attached document. Figure 1 The appendix Figure 5 The ultra-high accuracy auxiliary standard current transformer CTa shown here employs a completely new design concept for the commonly used compensation resistor RC. In addition to a precision high-power, high-stability, low-temperature-coefficient metal film resistor element with the exact same resistance value as its load resistor R, it also features a high-quality, high-strength enameled wire cut from a coaxial product of the same specifications (length and diameter) as the secondary winding of the CTa's main transformer, connected in series at each different transformation ratio. This enameled wire is manufactured by the same company as the main transformer and is cut from the same coaxial product. Figure 6 , 7 The technical requirements described after each view are for the fabrication of constant resistance micro-inductance precision compensation resistors.

[0016] Furthermore, for the calibration instrument used to verify Class S "measuring current transformers", attached Figure 1 The system comprises two voltage signal processing systems: a six-channel in-phase precision operational amplifier A with amplification and attenuation ratios of 100, 20, 5, 1, 0.83333, and 0.66666 respectively; a calibration instrument for calibrating SS-grade "wide-range current transformers for metering" with six-channel in-phase precision operational amplifier A with amplification and attenuation ratios of 1000, 200, 100, 20, 5, 1, 0.83333, and 0.5 respectively; and two high-accuracy low-voltage power frequency inductive voltage dividers (IVDs) with voltage division coefficients of 1%, 10%, and 100%. Only the transmission coefficients need to be finely adjusted so that the difference does not exceed 0.00002%, without requiring extremely high absolute accuracy. This design concept, utilizing relevant measurement theory to achieve ultra-high precision measurement, is a highly distinctive innovation in the field of transformer calibration instruments.

[0017] Furthermore, the invention recommended in this patent is as follows (see appendix). Figure 9 Appendix Figure 10 The current source shown is a 2000VA (volt-ampere) apparent power source that is strictly synchronized with the 50 / 60Hz frequency of the mains power, has extremely low waveform distortion, and can achieve manual or automatic fine adjustment of the output current with the help of a stepper motor by adjusting the fineness of better than 1 / 1800 or even 1 / 3600 through a ten-turn precision potentiometer.

[0018] The beneficial effects of this invention are:

[0019] (1) This patented technology enables the value transfer agencies of current transformers at the provincial, municipal, autonomous region, and prefecture-level (measuring system) levels and above, as well as the value traceability and verification agencies of power systems of the same level, to complete a large number of verification tasks for various standard current transformers of 0.01 class and below, quickly and accurately, by using the new CT calibrator provided by this patented technology. It can even provide the highest national metrology authority with a calibration instrument for current transformers with an accuracy of several × 10⁻⁶. -6 This testing equipment allows for comparison with ultra-high accuracy standard current transformers of the order of magnitude. It completely solves the long-standing problem of inaccurate phase difference (angle difference) values ​​in current transformers in my country's transformer industry, providing technical support for ensuring the accuracy of power metering under low power factor conditions.

[0020] (2) It can also provide a new type of calibration instrument for the heavy periodic calibration work of the grassroots units of the product research and development, production and use departments of current transformers, a legal measuring instrument, which can save time and effort, quickly and accurately complete a large number of calibration work for various measuring current transformers, including two-stage current transformers and miniature current transformers, of the 0.1 class and below (mainly 0.5S, 0.2S and 0.5SS, 0.2SS classes).

[0021] Eliminating the arduous operation of passive current comparators that require complex switching of primary and secondary connecting wires will bring significant benefits to reducing the mental and physical workload of technicians at all levels, including senior technicians, and greatly reducing the time they spend on their work.

[0022] (3) It can provide value transfer agencies for current transformers at the provincial, municipal, autonomous region, and prefecture-level (measuring system) levels and above, as well as value traceability and verification agencies for power systems of the same level, with the new CT calibrator provided by this patented technology. This allows for time-saving, labor-saving, rapid, and accurate completion of a large number of verification tasks for various standard current transformers of 0.01 class and below, even down to 0.005 class. It can even provide the highest national metrology authority with a calibration instrument for current transformers with an accuracy of several × 10⁻⁶. -6 This testing equipment allows for comparison with ultra-high accuracy standard current transformers of the order of magnitude. It completely solves the long-standing problem of inaccurate phase difference (angle difference) values ​​in current transformers in my country's transformer industry, providing technical support for ensuring the accuracy of power metering under low power factor conditions.

[0023] (4) It can also provide a new type of calibration instrument for the heavy periodic calibration work of grassroots units in the product research and development, production and use departments of current transformers, a legal measuring instrument, which can save time and effort, quickly and accurately complete a large number of calibration work for various measuring current transformers, including two-stage current transformers and miniature current transformers, of the 0.1 class and below (mainly 0.5S, 0.2S and 0.5SS, 0.2SS classes).

[0024] Eliminating the arduous operation of passive current comparators that require complex switching of primary and secondary connecting wires will bring significant benefits to reducing the mental and physical workload of technicians at all levels, including senior technicians, and greatly reducing the time they spend on their work.

[0025] The above description is merely an overview of the technical solution of the present invention. In order to better understand the technical means of the present invention and to implement it in accordance with the contents of the specification, the preferred embodiments of the present invention are described in detail below with reference to the accompanying drawings. Attached Figure Description

[0026] Figure 1 This is a schematic diagram of a true digital current transformer according to an embodiment of the present invention.

[0027] Figure 2 This is the schematic diagram of the high-accuracy self-balancing current comparator CC according to the present invention.

[0028] Figure 3 This is a detailed structural layout diagram of a CC zero-detection core coil system according to an embodiment of the present invention.

[0029] Figure 4.1 This is a view of the BNC socket and resistor assembly mounted on a large circular copper plate according to the present invention.

[0030] Figure 4.2 The coaxial non-inductive resistive shunt R shown in this invention F The view and the enlarged sectional view.

[0031] Figure 5 This is a schematic diagram of the ultra-high accuracy auxiliary standard current transformer CTa as shown in this invention.

[0032] Figure 6 This is a cross-sectional view of the hollow skeleton coil structure of Rij in the compensation resistor Rci shown in this invention.

[0033] Figure 7 This is a diagram showing the soldering arrangement of 50 high-power precision metal film resistors on a soldering plate, as illustrated in this invention.

[0034] Figure 8This is a circuit diagram of a high-precision amplification and attenuation system consisting of a six-channel operational amplifier and an IVD as shown in this invention.

[0035] Figure 9 This is a block diagram illustrating the principle of a power supply that is synchronized with the mains frequency and has a distortion rate of less than 1%, as shown in this invention.

[0036] Figure 10 This is a circuit diagram of a precision voltage regulator that can be adjusted manually or numerically controlled by a stepper motor, as shown in this invention. Detailed Implementation

[0037] The technical solution of the present invention will now be clearly and completely described with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0038] Furthermore, the technical features involved in the different embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0039] According to the appendix Figure 1 The schematic diagram shown demonstrates the ability to precisely amplify any type of circuit in a design and manufacturing process.

[0040] Appendix Figure 1 :

[0041] Symbols: CC – Self-balancing high-accuracy current comparator; R – Load resistor of ultra-high accuracy auxiliary standard current transformer CTa (precision non-inductive coaxial resistor shunt); Two (I-I – VI-VI) – Six-channel in-phase variable gain high-accuracy proportional operational amplifier attenuator system from 1000 to 0.5; IVD – Single-core high-accuracy inductive voltage divider with three voltage division coefficients of 1%, 10%, and 100% via winding taps; A / D – 16-bit high-speed analog-to-digital converter; PC – 32-bit desktop computer.

[0042] Appendix Figure 2 CTs of various accuracy levels of current transformers under test X With the main standard current transformer CT N The product of the difference current IΔ and the feedback resistance is UΔ = IΔR. F The CC-type self-balancing current comparator boasts ultra-low noise and high accuracy up to 100 times. In this comparator, RF is a non-inductive resistive shunt with an accuracy better than 0.01%. F — Flowing through R F Feed W F Feedback current;

[0043] According to the appendix Figure 2The schematic diagram of CC shown is used to design and manufacture each of its components.

[0044] Symbol: WⅠ – Main standard current transformer CT N The secondary winding is an input winding where the polarity terminals are connected to each other and the non-polarity terminals are connected to each other; WⅡ—connected to the current transformer CT under test. X The secondary winding is an input winding in which the polarity terminals are connected to each other and the non-polarity terminals are connected to each other; WΔ─CT N With CT X When used in a two-stage current transformer, the secondary winding of the compensating transformer is connected to the polarity-to-polarity input winding, and the non-polarity end is connected to the non-polarity end; Wcd—the zero-detection winding wound on the zero-detection core T2 for detecting residual magnetic flux; W F —The feedback winding of the CC closed-loop negative feedback system; R F —A non-inductive resistive shunt with an accuracy better than 0.01% connected in series in the feedback winding circuit of a CC closed-loop negative feedback system; I F — Flowing through R F Feed W F The feedback current.

[0045] Appendix Figure 3 According to the appendix Figure 3 The diagram shows the structure of the CC zero-detection core winding and its shielding system, along with the attached technical requirements. It includes the winding of a 2000-turn non-directional zero-detection winding Wcd, and the design and manufacture of magnetic and electromagnetic shielding.

[0046] Symbols: Ⅰ—A hollow copper electromagnetic shielding shell with a bracelet-like ring and a wall thickness of 2.5mm; Ⅱ—A 0.8mm discontinuous gap on the outer cylindrical surface; Ⅲ—The upper shielding core constituting core T1; Ⅳ—The zero-detection winding Wcd, wrapped with a plastic film shock-absorbing insulating strip with sufficient mechanical strength and insulation resistance; Ⅴ—The T2 core protection box made of PT material; Ⅵ—The outer shielding core constituting core T1; Ⅶ—Effective cross-section SC ≥ 3.8cm 2 A 1-permeability μ0 > 60000 purifying alloy zero-detection core T2 is installed in an insulating protective box; VIII-forming the lower shielding core of core T1; IX-forming the inner shielding core of core T1.

[0047] Technical requirements: Each lead-out wire at the beginning and end of the zero winding shall be fitted with a 1mm outer diameter Teflon sleeve, and two layers of insulating tape shall be half-overlapped and pressed tightly to secure the beginning and end. The polarity end shall be marked before leading out.

[0048] A black multi-strand rubber-sheathed flexible wire is welded firmly to the copper shield as a grounding wire. Sufficient insulation and mechanical strength tape is wrapped around the wire for winding the comparison and feedback windings of the self-balancing current comparator. The input coil WΔ of the secondary current of the auxiliary current transformer, which serves as both the standard and tested current transformers, is wound with multiple thicker enameled wires (e.g., five φ1 wires) to ensure its copper resistance is less than 20 mΩ. Therefore, the inner diameter of the copper shield should be no less than 100mm. The 7×φ0.12 tin-plated rubber-sheathed grounding electromagnetic flexible wire connected to the electromagnetic shield should be no less than 200mm in length. The gap between the four iron cores of T2 should be <0.5mm.

[0049] Figure 4: Figure 4.1 A view of a BNC socket and resistor assembly mounted on a large circular copper plate.

[0050] Appendix Figure 4.2 : R is a coaxial non-inductive resistive shunt F The view and the enlarged sectional view.

[0051] Symbols: Ⅰ—M6 H63 brass screw nickel-plated terminal at the high potential current end of the shunt; Ⅱ—M12 H63 brass nickel-plated external thread sleeve terminal at the low potential current end of the shunt; Ⅲ—High potential current collector board of the shunt; Ⅳ—High potential current collector board at the high potential end of the shunt; Ⅴ—Ten symmetrically distributed parallel resistors of the shunt; Ⅵ—Long cylindrical thin-walled nickel-plated copper tube for current return path; Ⅶ—Low potential current collector board of the shunt; Ⅷ—Annular epoxy resin fixing cap; Ⅸ—High-quality BNC socket for shunt potential output; Ⅹ—Highly conductive spring washer; Ⅺ—Hexagonal BNC socket fastening nut; Ⅻ—Long straight potential lead in zero magnetic field space.

[0052] Technical requirements: It is emphasized here that the large round copper solder plate and the thin-walled copper tube must be continuously and evenly welded together to ensure that the current returning along the thin-walled copper tube is evenly distributed on the circumference, thereby ensuring that the long straight potential lead located at the center is under zero magnetic field conditions, so that the shunt resistor can obtain a near-ideal non-inductive state.

[0053] The structural requirement for strictly symmetrically welding ten 1000Ω parallel resistors is to ensure that the accuracy of this 100Ω coaxial resistor shunt, after fine adjustment of the resistance value and time constant, is better than 5×10⁻⁶. -5 The fundamental guarantee.

[0054] Purchased power of 1W, resistance of 1000Ω, and adjustment accuracy of 1×10 -4 High-quality precision metal film resistors from reputable brands, after several rounds of manual aging and fine-tuning, are not difficult to manufacture with an accuracy of several × 10⁻⁶. -5 A non-inductive resistive shunt of the order of magnitude.

[0055] Appendix Figure 5 According to the appendix Figure 5 The schematic diagram shows the principle circuit of an auxiliary standard current transformer CTa with ultra-high accuracy, which uses an auxiliary current transformer for compensation (using CTa2 to compensate CTa1), and the components contained therein are designed and manufactured one by one.

[0056] Symbols: P0 – Low-potential terminal of the CTa primary winding wound on two iron cores; P1 – Input terminal for CTa 150A-250A primary current; P2 – Input terminal for CTa 75A-100A primary current; The winding shown by the dashed line is a 1-5 turn through-type primary winding; S2', S3', S4', S5' – Current output terminals of the secondary winding of the auxiliary transformer CTa2 wound on the right iron core T2; Rci – Compensation resistors for different ranges composed of Rc1, Rc2, Rc3, Rc4, Rc5 respectively; R – External load resistor of CTa, usually a coaxial non-inductive resistive shunt; Rci = R + Rij, Rij – Usually equivalent metal film resistors of the copper resistance of each secondary tap winding of the main transformer CTa1 wound on the left iron core T1; Here, a highly innovative constant resistance low inductance copper wire resistor is used.

[0057] Appendix Figure 6 According to the appendix Figure 6 The diagram shows the numerical correspondence between the additional compensation resistor Rcji used for different turns ratios with innovative value and the copper wire resistance Rcui of the secondary winding of the main transformer CTa1, and designs and manufactures the constant resistance micro-inductance additional resistor element Rcji required for each turns ratio.

[0058] Symbols: Ⅰ—A bracelet-shaped skeleton on one side of the flat spiral coil; Ⅱ—A rigid, annular, sheet-like film separator with adjustable thickness between the two flat spiral coils; Ⅲ—A bracelet-shaped skeleton on the other side of the flat spiral coil; [Cross-section AA, marked in red]—A specific implementation of a flat, tightly wound single coil resembling two mosquito repellent incense coils.

[0059] Appendix Figure 7 : Figure 7 For the appendix Figure 1 The welding view of the load resistor R of the auxiliary standard current transformer CTa, which actually exists but is not shown for the sake of simplifying the drawing.

[0060] Symbols: Ⅰ—Double-sided thick copper-clad epoxy resin printed circuit board (rectangular frame painted orange) connected to the high-potential input terminal; Ⅱ—Large round copper resistance soldering board; Ⅲ—50 low-lead tin alloy solder joints on the large copper soldering board; Ⅳ—One of 50 high-power precision metal film resistors; Ⅴ—Double-sided thick copper strip with high-quality metallized holes connected to the low-potential output terminal; Ⅵ—Double-sided thick copper strip with high-quality metallized holes connected to the high-potential output terminal; Ⅶ—In the context of electrical... The uniform distribution of 50 solder joints with a circumference of 600mm on the circular large copper resistance welding plate connected to the low potential input terminal; ΦⅠ─The uniform distribution of 50 solder joints with a circumference of 600mm on the circular large copper resistance welding plate (the diameter of the circular large copper resistance welding plate is 0.1mm smaller than the diameter of the thin-walled copper tube from which the shunt current returns); ΦⅡ─The diameter of the circle containing the 50 solder joints on the circular large copper resistance welding plate; ΦⅢ─The mounting hole diameter is 0.1mm larger than the mounting hole of the high-quality BNC socket of the current potential output terminal.

[0061] Technical requirements: The high-potential, high-power resistor leads carrying large currents must be laser-soldered securely to the two metallized vias. The two thick copper printed circuit boards, except for the area 2mm from the outer edge where the surrounding copper is etched away, are plated with a sufficiently thick lead-tin alloy on both sides to increase conductivity.

[0062] Appendix Figure 8 Design and fabricate two sets of high-accuracy combined amplification and attenuation systems according to the schematic diagram shown. Each set consists of six selectable non-inverting operational amplifiers with closed-loop gain accuracy better than 0.005% and inductive voltage dividers (IVDs) with voltage division factors including 1%, 10%, and 100%. Select the amplification factor of this combined amplification and attenuation system to ensure that its output voltage always remains ≥0.35V RMS.

[0063] To verify the current transformers used for S-class measurement, the amplification and attenuation factors of the six-channel combined in-phase operational amplifiers were set to 100.00, 20.000, 5.000, 1.0000, 0.83333, and 0.6666, respectively.

[0064] To calibrate the current transformers used in SS-class measurements, the amplification and attenuation factors of the six-channel combined in-phase amplifiers are set to 1000.0, 200.0, 100.0, 20.00, 5.0000, 1.0000, 0.83333, and 0.5000, respectively. Only the first two and last channels of the combined amplifier attenuator used in the S-class configuration need to be replaced with combined amplifiers with dual amplification factors (1000.0 and 100.00, 200.0 and 20.00, 0.83333 and 0.5000).

[0065] Appendix Figure 8 The inductive voltage divider (IVD) shown in the figure uses a permalloy core with a cross-sectional area of ​​Sc = η2 × 2 cm², produced by the Beijing Functional Materials Research Institute. It contains 5% copper and has an initial permeability of μ0 ≥ 60000. The primary winding is wound with 1000 turns of high-strength, high-quality enameled wire of φ0.5 mm, and the secondary winding is wound with 1000 turns of high-strength, high-quality enameled wire of φ0.25 mm using a non-directional winding method, with 10 turns and 100 turns of center taps.

[0066] Appendix Figure 8 :

[0067] Technical requirements: (1) When used as a current transformer for calibrating Class S measurement, the amplification and attenuation factors of the two-stage combined operational amplifiers from the first to the sixth channel are respectively: 100.00, 20.00, 5.000, 1.0000, 0.83333, 0.66666; when used as a wide-range current transformer for calibrating Class SS measurement, the amplification and attenuation factors of the two-stage combined operational amplifiers from the first to the sixth channel are respectively: 1000.0 / 100.00, 200.0 / 20.00, 5.000, 1.0000, 0.66666, 0.83333 / 0.5000 (i.e., the first, second, and sixth channel combined amplifiers are made to have two selectable amplification factors). The input and output terminals are isolated by potential followers. (2) The inductive voltage divider (IVD) can achieve a gain better than 1×10 when made according to the above requirements. -5 The accuracy mentioned above can also eliminate the influence of DC bias that is usually unavoidable in the preceding electronic amplifier attenuators.

[0068] When each has Figure 7 The copper wire compensation resistor Rij, which is of constant resistance and low inductance, is installed together with the load resistor R. Figure 5 After the auxiliary standard current transformer CTa shown is installed, its error under different turns ratios is checked using a self-calibration method. The total inductance is adjusted by finely adjusting the number of rigid plastic film laminations of the two flat helical spacers to minimize its error. Finally, after firmly solidifying the structure of each Rij, it is installed into the CTa, thus obtaining a current transformer with an inductance better than 1×10⁻⁶. -5 Even several times 10 -6 A multi-range auxiliary standard current transformer with ultra-high accuracy.

[0069] Appendix Figure 1 The design and fabrication of the load resistor R for the 10Ω coaxial non-inductive resistive shunt, which serves as the auxiliary standard current transformer CTa: To prevent excessive power consumption at the highest current amplification factor, the secondary rated current of CTa is set to 1A. Only when occasionally verifying the error of an SS-class metering wide-range current transformer at 200%In measurement points, the power consumption of R will reach as high as 40W within a short period of 5 seconds. Its coaxial structure principle is the same as that of R.F The structure is similar, but it requires 50 precision metal film resistors of 500Ω and 3W connected in parallel symmetrically. Besides the larger structural size and more solder pads and holes, it is similar to R... F The manufacturing process requirements are exactly the same.

[0070] Appendix Figure 9 : Figure 9 This is a block diagram of a power supply that is synchronized with the mains frequency and has a distortion of less than 1%.

[0071] Depend on Figure 9 It is evident that the 10V voltage waveform applied to a 12-bit analog-to-digital converter (A / D) via an isolation transformer typically exhibits approximately 5% distortion. Since narrowband digital filters are far more effective than analog filters at filtering frequencies of 50 or 60Hz, the harmonic digital components contained in the digital data output by the A / D converter can be largely filtered out. Therefore, the approximately 10V analog voltage output by the 12-bit D / A converter will possess a very satisfactory sine wave.

[0072] Appendix Figure 10 It can be adjusted manually or with the help of tools such as those mentioned below. Figure 10 The stepper motor shown features a 10-turn precision potentiometer for numerical control adjustment, allowing for adjustments of 1 / 1800 or 1 / 3600. This provides a continuously and monotonically adjustable input voltage for a commercially available magnetic power amplifier with a total harmonic distortion (THD) of <1% and a high power output of 2000 VA. This completely solves the problem of misinterpretation of calibration results caused by differences in test current settings at the lowest measurement points.

[0073] Symbol: V IN ─Taken from Figure 9 Input voltage of the D / A converter; V0—output voltage of the electronic voltage regulator; R W —Precision 10-turn potentiometer; M —Controlled stepper motor.

[0074] Figure 9 The output of the D / A digital-to-analog converter is an analog voltage with an effective value of 10V, a frequency synchronized with the mains frequency, a near-pure sine wave, and extremely stable amplitude and phase at 50 / 60Hz. This voltage is used as the input voltage V of the voltage regulator. IN A precision 10-turn potentiometer R with a resistance of 5.1kΩ is applied. W Up. R W The knob can be adjusted manually or precisely via command control of the rigidly connected stepper motor M's shaft. The voltage regulator's output voltage V0 can be finely adjusted monotonically upwards and downwards within the range of 0-10V according to a set operating program. V0 will be sent to the attached... Figure 9A 2000VA power frequency magnetometer amplifier with high input impedance is used to apply sufficient output voltage and current to the current booster of the device to be tested, supplying the required test current.

[0075] The benefits that can be brought:

[0076] In summary, this invention provides a true digital current transformer calibrator, the benefits of which include:

[0077] (1) This patented technology enables the value transfer agencies of current transformers at the provincial, municipal, autonomous region, and prefecture-level (measuring system) levels and above, as well as the value traceability and verification agencies of power systems of the same level, to complete a large number of verification tasks for various standard current transformers of 0.01 class and below, quickly and accurately, by using the new CT calibrator provided by this patented technology. It can even provide the highest national metrology authority with a calibration instrument for current transformers with an accuracy of several × 10⁻⁶. -6 This testing equipment allows for comparison with ultra-high accuracy standard current transformers of the order of magnitude. It completely solves the long-standing problem of inaccurate phase difference (angle difference) values ​​in current transformers in my country's transformer industry, providing technical support for ensuring the accuracy of power metering under low power factor conditions.

[0078] (2) It can also provide a new type of calibration instrument for the heavy periodic calibration work of the grassroots units of the product research and development, production and use departments of current transformers, a legal measuring instrument, which can save time and effort, quickly and accurately complete a large number of calibration work for various measuring current transformers, including two-stage current transformers and miniature current transformers, of the 0.1 class and below (mainly 0.5S, 0.2S and 0.5SS, 0.2SS classes).

[0079] Eliminating the arduous operation of passive current comparators that require complex switching of primary and secondary connecting wires will bring significant benefits to reducing the mental and physical workload of technicians at all levels, including senior technicians, and greatly reducing the time they spend on their work.

[0080] (3) It can provide value transfer agencies for current transformers at the provincial, municipal, autonomous region, and prefecture-level (measuring system) levels and above, as well as value traceability and verification agencies for power systems of the same level, with the new CT calibrator provided by this patented technology. This allows for time-saving, labor-saving, rapid, and accurate completion of a large number of verification tasks for various standard current transformers of 0.01 class and below, even down to 0.005 class. It can even provide the highest national metrology authority with a calibration instrument for current transformers with an accuracy of several × 10⁻⁶. -6 This testing equipment allows for comparison with ultra-high accuracy standard current transformers of the order of magnitude. It completely solves the long-standing problem of inaccurate phase difference (angle difference) values ​​in current transformers in my country's transformer industry, providing technical support for ensuring the accuracy of power metering under low power factor conditions.

[0081] (4) It can also provide a new type of calibration instrument for the heavy periodic calibration work of grassroots units in the product research and development, production and use departments of current transformers, a legal measuring instrument, which can save time and effort, quickly and accurately complete a large number of calibration work for various measuring current transformers, including two-stage current transformers and miniature current transformers, of the 0.1 class and below (mainly 0.5S, 0.2S and 0.5SS, 0.2SS classes).

[0082] Eliminating the arduous operation of passive current comparators that require complex switching of primary and secondary connecting wires will bring significant benefits to reducing the mental and physical workload of technicians at all levels, including senior technicians, and greatly reducing the time they spend on their work.

[0083] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0084] The embodiments described above are merely illustrative of implementation methods of the present invention, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this invention patent should be determined by the appended claims.

[0085] illustrate

[0086] Because of the power dissipation limit of the auxiliary standard current transformer CTa with a load resistance of R = 10Ω at the maximum current amplification measurement point, the secondary rated current of CTa can only be selected as 1A. Clearly, this calibrator is perfectly suitable for calibrating current transformers with a secondary rated current of 1A; however, when calibrating current transformers with a secondary rated current of 5A, the calibration result will increase by a factor of 5. This is not difficult to handle; simply adding a division by 5 step to the simple calculation program installed on the PC will solve the problem.

Claims

1. A true digital current transformer calibrator, characterized in that, The self-balancing current comparator CC, featuring ultra-low noise (Barkhausen noise), can precisely amplify the differential current IΔ between the tested current transformer CTX and the main standard current transformer CTN at various measurement points from 0.1% to 200% of the rated current by 10 times. This ensures that the differential voltage UΔ = IΔRF, converted by the differential current / differential voltage conversion resistor RF, is consistently amplified to greater than 0.35V through a six-channel amplification and attenuation system, meeting the effective level requirements of the A / D converter. It transforms the analog quantity UΔ into a voltage with virtually no precision during transmission and conversion. The digital quantity with degree loss is sent to the PC for high-precision digital calculation processing; another important function is that because the CC has three input windings, it can use any high-accuracy standard current transformer, including ultra-high accuracy "two-stage current transformers", as a standard. It can also be used directly to verify "two-stage current transformers" with an accuracy class of less than 0.

01. It can also perform comparison work between two-stage current transformers with any higher accuracy class. Therefore, this patented invention is a major technological innovation and requires the protection of the invention rights.

2. The true digital current transformer calibrator as described in claim 1, characterized in that, To ensure the accuracy requirements for the verification and traceability of high-accuracy standard current transformers with a precision better than 0.01%, and especially to completely solve the long-term inaccuracy problem of the phase difference value of current transformers, the design concept and corresponding technical measures of the main and auxiliary dual standard current transformers adopted in the "True Digital Current Transformer Verifier" of this patented technology also require the protection of the invention rights. The accuracy of the main standard current transformer CTN required depends on the user's purpose and is unrelated to the calibration instrument; the user must provide it themselves. However, the ultra-high accuracy auxiliary standard current transformer CTa shown in Figure 5 (not included in Figure 1) employs a completely new design concept for the commonly used compensation resistor RC. In addition to a precision high-power, high-stability, low-temperature-coefficient metal film resistor element with the same resistance value as its load resistor R, it also has a high-strength enameled wire cut from a coaxial product with the same specifications (length and diameter) and manufacturer as the secondary winding of the main transformer CTa, connected in series at each different ratio range. This high-strength enameled wire is made according to the technical requirements described in the following views of Figures 6 and 7 and is subject to the same rights protection.

3. The true digital current transformer calibrator as described in claim 1, characterized in that, For the calibration instrument used to verify S-class "measuring current transformers", the six-channel in-phase precision operational amplifier A in Figure 1 with amplification and attenuation ratios of 100, 20, 5, 1, 0.83333, and 0.66666 respectively, and the calibration instrument used to verify SS-class "measuring wide-range current transformers", with six-channel in-phase precision operational amplifier A with amplification and attenuation ratios of 1000, 200, 100, 20, 5, 1, 0.83333, and 0.5 respectively; and two high-accuracy low-voltage power frequency inductive liquid separators (IVD) with voltage division coefficients of 1%, 10%, and 100%, forming two voltage signal processing systems; it is only necessary to finely adjust their transmission coefficients so that their differences do not exceed 0.00002%, and extremely high absolute accuracy is not required. This design concept of achieving ultra-high precision measurement using relevant measurement theory is also a highly distinctive innovation in the field of transformer calibration instrument technology, and therefore, rights protection is also required.

4. The true digital current transformer calibrator as described in claim 1, characterized in that, The 2000VA (volt-ampere) apparent power current source recommended in this patent invention, as shown in Figures 9 and 10, is strictly synchronized with the 50 / 60Hz frequency of the mains power, has extremely low waveform distortion, and can achieve manual or automatic fine adjustment of the output current with the aid of a stepper motor through a 1 / 1800 to 1 / 3600 adjustment fineness via a ten-turn precision potentiometer. This invention also claims protection.

5. A true digital current transformer calibrator as described in claim 1, characterized in that, The self-balancing current comparator CC used in this patented invention, "True Digital Current Transformer Tester," features ultra-low noise (Barkhausen noise). This comparator can measure the current transformer CT under test at various measurement points from 0.1% to 200% of its rated current. X With the main standard current transformer CT N The differential current IΔ is precisely amplified by 10 times to ensure that the differential current / differential voltage conversion resistor R... F The converted differential pressure is UΔ=IΔR F The voltage is then amplified to greater than 0.35V through a six-channel amplification and attenuation system, meeting the effective voltage level requirements of the A / D converter. The analog quantity UΔ is converted into a digital quantity with almost no accuracy loss during transmission and conversion, which is then sent to a PC for high-precision digital processing. Another important function is that, because the CC has three input windings, it can use any high-accuracy standard current transformer, including ultra-high accuracy "two-stage current transformers," as a standard. It can also be directly used to calibrate "two-stage current transformers" below 0.01 accuracy. Furthermore, it can perform comparisons between two-stage current transformers of any higher accuracy level. Therefore, this patented invention is a significant technological innovation, and its invention rights should be protected.

6. The true digital current transformer calibrator as described in claim 1, characterized in that, To ensure the accuracy requirements for the verification and traceability of high-accuracy standard current transformers with a precision better than 0.01%, and especially to completely solve the long-term inaccuracy problem of the phase difference value of current transformers, the design concept and corresponding technical measures of the main and auxiliary dual standard current transformers adopted in the "True Digital Current Transformer Verifier" of this patented technology also require the protection of the invention rights. The main standard current transformer (CT) required to be used is among them. N The accuracy depends on the user's intended use and is unrelated to the calibrator, which the user must provide. However, the ultra-high accuracy auxiliary standard current transformer CTa shown in Figure 5 (not included in Figure 1) employs a completely new design concept for the commonly used compensation resistor RC. In addition to a precision high-power, high-stability, low-temperature coefficient metal film resistor element with the same resistance value as its load resistor R, it also has a high-strength enameled wire cut from a coaxial product with the same specifications (length and diameter) and manufacturer as the enameled wire used in the secondary winding of the CTa's main transformer for the corresponding strain ratio. This high-strength enameled wire is manufactured according to the technical requirements described in the following views of Figures 6 and 7 and is also subject to rights protection.

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