Precision compensation method suitable for circuit breaker protection mutual inductor

Abstract

The invention discloses a precision compensation method suitable for a circuit breaker protection transformer, and the method comprises the following steps: measuring the actual on-load output of a current transformer under the condition of 1-15 times of rated current, and obtaining the RMS effective value data corresponding to the output current under each current multiple; constructing a polynomial fitting equation not exceeding quintic based on the RMS effective value data so as to compensate the output characteristics of the current transformer; and based on the measurement results of at least 30 current transformer samples, performing normal distribution statistical analysis on the parameters of the polynomial fitting equation obtained by each sample to obtain a mean value of each fitting coefficient, and taking the mean value as a general compensation parameter. According to the method, the universal polynomial compensation model is constructed, so that the measurement precision of the current transformer under high-power current is effectively improved, the tripping error of the circuit breaker is remarkably reduced, and the production calibration cost is reduced.

Description

Technical Field

[0001] The present invention relates to the field of circuit breakers, and in particular to a precision compensation method applicable to a circuit breaker protection mutual inductor. Background Art

[0002] With the development of intelligent electrical equipment, circuit breaker products have gradually evolved from traditional thermal-magnetic tripping circuit breakers to electronic tripping circuit breakers. Electronic circuit breakers generally use current transformers (CTs) as the primary current sensing element. A microcontroller (MCU) analyzes the CT output signal to make tripping decisions. Compared to traditional structures, these electronic circuit breakers offer significant advantages in protection accuracy, response speed, and functional scalability.

[0003] In electronic circuit breakers, the measurement accuracy of current transformers (CTs) is directly related to the overall protection performance of the device. Typically, CTs maintain good linear output at low overload currents (e.g., 1 to 2 times the rated current), ensuring accurate current detection. However, as the current multiple increases, the CT core saturates, and the output characteristic exhibits significant nonlinear distortion. Within the range of 7 to 10 times the rated current, the CT output error can reach 10% to 25% or more, severely impacting the trip unit's response to overload and short-circuit faults, posing the risk of false tripping or failure to operate.

[0004] To address the above issues, the existing technology attempts to improve the high current measurement accuracy of the transformer through the following two methods: By increasing the core cross-sectional area and raising the upper limit of magnetic flux density, saturation can be mitigated. However, this solution increases the size of the transformer, hindering the overall miniaturization of the circuit breaker design and contradicting the current trend of miniaturization and modularization of circuit breaker products.

[0005] The use of low-loss, high-inductance materials with better performance can improve the linear range of the transformer. However, high-performance magnetic materials are expensive and complex to process, increasing the overall manufacturing cost of the circuit breaker and hindering the product's market competitiveness.

[0006] In addition, some literature proposes to compensate for transformers through hardware linearization circuits. However, such hardware compensation solutions generally have problems such as complex circuits, large space occupation, and high debugging difficulty, making them difficult to apply on a large scale in compact electronic circuit breakers. Summary of the Invention

[0007] In order to solve the above problems, the present invention provides an accuracy compensation method suitable for circuit breaker protection transformers, which improves the measurement accuracy of the transformer under high overload current without increasing the volume of the transformer and significantly increasing the material cost.

[0008] The present invention is achieved through the following technical solution: a precision compensation method for a circuit breaker protection transformer, comprising the following steps: Step 1: measuring the actual load output of the current transformer under conditions of 1 to 15 times the rated current, and obtaining RMS effective value data of the output current corresponding to each current multiple; Step 2: constructing a polynomial fitting equation of no more than five degrees based on the RMS effective value data to compensate for the output characteristics of the current transformer; Step 3: Based on the measurement results of at least 30 current transformer samples, perform normal distribution statistical analysis on the parameters of the polynomial fitting equation obtained for each sample, obtain the mean of each fitting coefficient and use it as a universal compensation parameter; Step 4: Execute the compensation method in the micro control unit of the electronic circuit breaker to compensate and correct the output of the current transformer to improve measurement accuracy.

[0009] As a preferred technical solution, in step 1: The actual on-load output refers to the output current of the current transformer when connected to a rated load, and a true effective value calculation is performed on the output current to obtain the RMS effective value data.

[0010] As a preferred technical solution, in step 2: The polynomial fitting equation is used to characterize the relationship between the output measurement value of the current transformer and the actual current value, and the polynomial order does not exceed fifth order.

[0011] As a preferred technical solution, in step three: Based on the measurement results of at least 30 current transformer samples, a normal distribution statistical analysis is performed on the fitting coefficients of the polynomial fitting equation, and the mean of each fitting coefficient is determined as a universal compensation parameter of the compensation method.

[0012] As a preferred technical solution, in step 4: The compensation method is applied to a microcontroller unit of an electronic circuit breaker to compensate and correct the measurement output of the current transformer, thereby improving the current measurement accuracy of the circuit breaker.

[0013] As a preferred technical solution, the compensation method reduces the measurement error of the current transformer and controls it within 5% under high current conditions of 7 to 10 times the rated current.

[0014] The beneficial effects of the present invention are as follows: 1. By measuring the output of the current transformer in the range of 1 to 15 times the rated current and establishing a polynomial fitting compensation model based on the collected data, the present invention can effectively correct the nonlinear output distortion of the transformer under high-multiple overload current conditions, thereby significantly improving the current measurement accuracy of the circuit breaker electronic release; Second, the present invention adopts a polynomial fitting method of no higher than fifth order, taking into account both compensation accuracy and computational complexity. The microcontroller unit (MCU) can quickly complete compensation calculations while ensuring real-time performance, making it suitable for miniaturized and embedded applications of circuit breakers. 3. By statistically analyzing the fitting parameters of no less than 30 sets of transformer samples, the mean value of each order coefficient is extracted as the universal compensation parameter. This eliminates the need for separate calibration of each set of transformers, simplifies the production process, reduces batch manufacturing and calibration costs, and has good economic benefits. Fourth, after applying the method of the present invention during the operation of the circuit breaker, the measurement error of the transformer under conditions of 7 to 10 times the rated current was reduced from more than 25% to less than 5%, effectively improving the operation accuracy and reliability of the circuit breaker in overload protection and short-circuit protection scenarios; 5. The present invention does not require increasing the size of the mutual inductor or replacing high-cost magnetic materials, thus avoiding the product design limitations and increased manufacturing costs caused by the expansion of structural size or material upgrades in the prior art, and has better engineering applicability and promotion value. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0016] Figure 1 It is the workflow diagram of the present invention. DETAILED DESCRIPTION

[0017] All features disclosed in this specification, or all steps in the disclosed methods or processes, except mutually exclusive features and / or steps, can be combined in any manner.

[0018] Any feature disclosed in this specification (including any appended claims, abstract, and drawings), unless otherwise stated, may be replaced by other equivalent or similar features. In other words, unless otherwise stated, each feature is only an example of a series of equivalent or similar features.

[0019] like Figure 1The present invention relates to an accuracy compensation method for circuit breaker protection transformers. The primary purpose is to improve the measurement accuracy of current transformers in electronic circuit breaker systems at high currents through standardized output characteristic measurement, mathematical modeling and fitting, and statistical parameter optimization. A specific embodiment is described below.

[0020] First, the output characteristics of the transformer are systematically measured. A current transformer sample of the target specification and model is selected, and a load test circuit is constructed on the experimental platform. The load used is the same as that used in actual circuit breaker applications, such as a power relay coil or a corresponding equivalent impedance load, to ensure that the test conditions are consistent with actual use.

[0021] During the test, inputs of 1 times, 2 times, 3 times, 5 times, 7 times, 10 times and 15 times the rated current were gradually applied according to the standard, and the output signals on the secondary side of the transformer were recorded respectively.

[0022] The output signal is collected using a high-precision sampling module. After low-pass filtering to eliminate high-frequency interference, the signal is calculated as true RMS to ensure that the obtained data accurately reflects the actual output level of the transformer under different current loads.

[0023] Based on the above collected current input and output RMS effective value data, the output characteristic curve of the transformer is mathematically fitted.

[0024] The present invention adopts polynomial curve fitting technology and processes data points using the least square method to fit a polynomial equation that can describe the nonlinear relationship between the input current and the output effective value of the mutual inductor.

[0025] Considering the limited internal MCU resources of the circuit breaker electronic trip unit and the need for real-time response, the order of the control polynomial is not higher than fifth order when fitting the equation modeling.

[0026] By tuning the fitting models of various orders and calculating the residual sum of squares, the equation with the best fitting effect and acceptable computational complexity is selected as the final compensation model.

[0027] The compensation model can better cover the output characteristics of the transformer in the entire range of 1 to 15 times the rated current, especially for the nonlinear distortion area of the high overload current segment.

[0028] In order to obtain universal compensation parameters, repeated measurements and modeling are further performed on multiple mutual inductor samples.

[0029] Specifically, at least thirty sets of transformers of the same model are selected, and each set of transformers is individually subjected to the above-mentioned output characteristic test and fitting modeling, and the corresponding polynomial coefficient data are extracted respectively.

[0030] Then, a statistical analysis was performed on all fitting coefficients of the same order. The statistical method was based on the normal distribution assumption and used the maximum likelihood estimation method to obtain the mathematical mean of the fitting coefficients of each order as a universal compensation parameter, and the standard deviation was calculated as a reference indicator of model stability.

[0031] Through this large sample size statistics, the slight deviations of individual transformers caused by process differences can be effectively eliminated, ensuring that the final compensation model has good applicability and consistency in batch transformers.

[0032] The standard polynomial compensation model determined above is solidified into the microcontroller unit (MCU) of the circuit breaker electronic trip unit control module in the form of program code.

[0033] During the specific implementation process, a compensation operation module is added to the MCU software design. When the secondary signal output by the transformer in real time is collected, the RMS effective value is first calculated and then input into the compensation operation module. The calculation is performed based on the universal compensation polynomial and the corrected current value is output.

[0034] The MCU compares the corrected current value with the set trip current threshold to determine whether to issue a trip signal. To ensure responsiveness, the compensation module uses a table lookup plus linear interpolation or directly invokes a simplified polynomial formula to ensure real-time system response even under high-load conditions.

[0035] By applying the precision compensation method provided by the present invention, the output error of the current transformer is reduced from more than 25% to less than 5% under high overload conditions of 7 to 10 times the rated current of the circuit breaker, greatly improving the accuracy and reliability of tripping judgment and effectively avoiding the risk of false operation or refusal to operate due to measurement errors.

[0036] At the same time, the method of the present invention adopts pure software compensation technology, which does not require increasing the volume of the mutual inductor or replacing the core material. It not only meets the overall miniaturization design requirements of the circuit breaker, but also controls the manufacturing cost. It has good engineering promotion value and market application prospects.

[0037] The design of the present invention can effectively improve the accuracy of circuit breaker opening, reducing the overload protection error from more than 25% to less than 5%. By analyzing the distribution characteristics of the polynomial parameters, a common set of compensation parameters can be used for all mutual inductors, which can greatly reduce the production and calibration costs. The invention has good economic and application benefits.

[0038] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or substitutions that are not conceived through creative work should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be based on the scope of protection defined in the claims.

Claims

1. A precision compensation method for a circuit breaker protection transformer, characterized in that: The steps include: Step 1: measuring the actual load output of the current transformer under conditions of 1 to 15 times the rated current, and obtaining RMS effective value data of the output current corresponding to each current multiple; Step 2: constructing a polynomial fitting equation of no more than five degrees based on the RMS effective value data to compensate for the output characteristics of the current transformer; Step 3: Based on the measurement results of at least 30 current transformer samples, perform normal distribution statistical analysis on the parameters of the polynomial fitting equation obtained for each sample, obtain the mean of each fitting coefficient and use it as a universal compensation parameter; Step 4: Execute the compensation method in the micro control unit of the electronic circuit breaker to compensate and correct the output of the current transformer to improve measurement accuracy.

2. The accuracy compensation method for circuit breaker protection transformer according to claim 1, characterized in that: In step one: The actual on-load output refers to the output current of the current transformer when connected to a rated load, and a true effective value calculation is performed on the output current to obtain the RMS effective value data.

3. The accuracy compensation method for circuit breaker protection transformer according to claim 1, characterized in that: In step 2: The polynomial fitting equation is used to characterize the relationship between the output measurement value of the current transformer and the actual current value, and the polynomial order does not exceed fifth order.

4. The accuracy compensation method for circuit breaker protection transformer according to claim 1, characterized in that: In step three: Based on the measurement results of at least 30 current transformer samples, a normal distribution statistical analysis is performed on the fitting coefficients of the polynomial fitting equation, and the mean of each fitting coefficient is determined as a universal compensation parameter of the compensation method.

5. The accuracy compensation method for circuit breaker protection transformer according to claim 1, characterized in that: In step four: The compensation method is applied to a microcontroller unit of an electronic circuit breaker to compensate and correct the measurement output of the current transformer, thereby improving the current measurement accuracy of the circuit breaker.

6. The accuracy compensation method for circuit breaker protection transformer according to claim 5, characterized in that: The compensation method reduces the measurement error of the current transformer and controls it within 5% under the condition of a high current of 7 to 10 times the rated current.

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