Two-stage separation type current transformer with air gap
By designing a two-stage split current transformer with an air gap, and utilizing the difference in permeability between the first and second iron cores and the compensation winding current, the problem of low accuracy of open-type current transformers is solved, and high-accuracy conversion of current transformers is achieved.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Utility models(China)
- Current Assignee / Owner
- Filing Date
- 2025-04-22
- Publication Date
- 2026-03-27
AI Technical Summary
Open-type current transformers have low accuracy, which affects the accuracy of converting large currents into small currents. They also have problems such as large size of the standard, inconvenience of disassembling and assembling the primary busbar of the equipment under test, and the inability to shut down the power supply during operation.
Design a two-stage split current transformer with air gap, using a first iron core and a second iron core. The permeability of the first iron core is less than that of the second iron core. The winding structure is designed as a primary winding, a compensation winding, and a secondary winding, which are connected in parallel to form the first-stage and second-stage current transformers. The current generated by the compensation winding is used to compensate for errors and improve accuracy.
The accuracy of the current transformer has been significantly improved. The error of the improved current transformer is one order of magnitude better than that of the existing products, meeting the 0.05S level technical specification.
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Figure CN224052996U_ABST
Abstract
Description
TECHNICAL FIELD
[0001] The utility model relates to the technical field of current transformer, especially a kind of air gap two-stage separation type current transformer. BACKGROUND
[0002] In the international Electromagnetic Consultative Committee (Consultative Committee on Electromagnetism, CCEM) "electromagnetic calibration and measurement ability classification", "high voltage and large current (>100A)" is one of the key projects. The principle of measuring large current is mainly to convert large current into small current for general instrument measurement. Therefore, the accuracy of conversion ratio is crucial.
[0003] Power frequency large current on-line measurement usually needs to convert the measured large current into small current by high-accuracy current ratio standard according to the expected ratio. However, due to the factors such as large size of standard device, inconvenience of disassembling primary bus of the tested equipment, and unavailability of power-off during operation of the tested equipment, as well as the measurement uncertainty introduced by repeated disassembly, all of which affect the traceability of the value.
[0004] The principle of converting large current into small current mainly includes mutual inductance type, Hall type and shunt type. From the structure of the core, there are open type and closed type. The open type current transformer usually includes a core with air gap, primary winding and secondary winding. The existence of air gap reduces the magnetic permeability of the core, resulting in that the accuracy grade of the open type current transformer is significantly lower than that of the closed type device. However, the open type current transformer is widely used due to its convenient use. How to improve the accuracy of the open type current transformer is a problem to be solved. CONTENT OF THE UTILITY MODEL
[0005] The utility model provides a kind of air gap two-stage separation type current transformer to solve the technical problem of the accuracy of open type current transformer is lower.
[0006] To solve the above technical problems, the utility model provides an air gap two-stage separation type current transformer, comprising a first core, a second core, a primary winding, a secondary winding and a compensation winding.
[0007] The first core and the second core both have air gap, and the magnetic permeability of the first core is less than that of the second core.
[0008] The primary winding is wound on one side of the first core and the second core, the secondary winding is wound on the other side of the first core and the second core, and the compensation winding and the secondary winding are connected in parallel.
[0009] The primary winding, the first iron core, and the secondary winding constitute a first-stage current transformer, and the primary winding, the second iron core, the secondary winding, and the compensation winding constitute a second-stage current transformer.
[0010] Preferably, the number of turns in the primary winding is 1 turn.
[0011] Preferably, the secondary winding and the compensation winding have the same number of turns.
[0012] Preferably, the secondary winding and the compensation winding have the same impedance.
[0013] Preferably, the first iron core and the second iron core are of the same size.
[0014] Preferably, the air gap width of the first iron core and the second iron core ranges from (0 to 1 mm).
[0015] Preferably, the average magnetic circuit length of the first iron core and the second iron core is in the range of [20cm, 60cm].
[0016] Preferably, the cross-sectional areas of the first iron core and the second iron core are in the range of [0.5cm]. 2 2.5cm 2 ].
[0017] Preferably, the permeability of the first iron core is [5000×4π×10]. -4 mH / m, 10000×4π×10 -4 [mH / m], the permeability of the second iron core ranges from (10000×4π×10 mH / m) to (mH / m). -4 mH / m, 50000×4π×10 -4 mH / m).
[0018] This utility model provides a two-stage separated current transformer with an air gap, comprising a first iron core, a second iron core, a compensation winding, a first-stage current transformer, and a second-stage current transformer. The first iron core is an auxiliary iron core, which bears the main magnetic flux and the induced electromotive force of the secondary circuit; it has a high magnetic induction intensity and a large excitation current. The second iron core is the main iron core, with extremely low magnetic induction intensity, operating in a near-zero magnetic flux state, effectively reducing the excitation current; however, its permeability is greater than that of the first iron core. The second-stage secondary current generated on the compensation winding is the compensation current I. B It merges with the first-stage secondary current I2 to form the compensated secondary current I. 2B By compensating current I B It can compensate for the error of the current transformer and improve the accuracy of the current transformer. Attached Figure Description
[0019] Figure 1 is a structure diagram of a two-stage separated current transformer with air gap according to an embodiment of the present application.
[0020] Figure 2 is a characteristic curve of the air gap width and average magnetic path length of the iron core and the ratio error of the current transformer according to an embodiment of the present application.
[0021] Figure 3 is a characteristic curve of the air gap width and average magnetic path length of the iron core and the phase error of the current transformer according to an embodiment of the present application.
[0022] Figure 4 is a characteristic curve of the air gap width and cross-sectional area of the iron core and the ratio error of the current transformer according to an embodiment of the present application.
[0023] Figure 5 is a characteristic curve of the air gap width and cross-sectional area of the iron core and the phase error of the current transformer according to an embodiment of the present application.
[0024] Figure 6 is a characteristic curve of the air gap width and permeability of the iron core and the ratio error of the current transformer according to an embodiment of the present application.
[0025] Figure 7 is a characteristic curve of the air gap width and permeability of the iron core and the phase error of the current transformer according to an embodiment of the present application.
[0026] The reference signs are as follows:
[0027] First iron core-1, second iron core-2, primary current of the current transformer-I1; secondary current of the current transformer before compensation-I2; compensation current of the current transformer-I B , number of turns of the primary winding of the current transformer-N1, number of turns of the secondary winding of the current transformer-N2, number of turns of the compensation winding of the current transformer-N B , secondary winding impedance-Z2, compensation winding impedance-Z B . DETAILED DESCRIPTION
[0028] In order to make the purpose, advantages and characteristics of the present application more clear, the following will make further detailed description on the current transformer with air gap according to the present application in combination with the drawings. It should be noted that the drawings are very simplified and use non-precise scale, and are only used to conveniently and clearly assist the purpose of explaining the embodiments of the present application.
[0029] In the description of the utility model, the terms "first", "second" and the like qualifiers are added for the convenience of description and reference, and cannot be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features qualified with "first", "second" and the like can explicitly or implicitly include one or more of the features.
[0030] As shown in Figure 1 , the embodiment provides a dual-stage separated current transformer with air gap, which comprises a first core 1, a second core 2, a primary winding, a secondary winding and a compensation winding; the first core 1 and the second core 2 both have air gaps, and the magnetic permeability of the first core 1 is smaller than that of the second core 2; the primary winding is wound on one side of the first core 1 and the second core 2, the secondary winding is wound on the other side of the first core 1 and the second core 2, and the compensation winding is connected in parallel with the secondary winding; the primary winding, the first core 1 and the secondary winding constitute a first-stage current transformer, and the primary winding, the second core 2, the secondary winding and the compensation winding constitute a second-stage current transformer. Figure 1 The asterisk in the formula indicates the polarity end of the inductor.
[0031] The embodiment provides a dual-stage separated current transformer with air gap, which comprises a first core 1, a second core 2, a compensation winding, a first-stage current transformer and a second-stage current transformer. The first core 1 is an auxiliary core, which bears the main magnetic flux and the induced electromotive force of the secondary circuit, has a high magnetic induction intensity and a large excitation current. The second core 2 is a main core, which has a very low magnetic induction intensity, is in a nearly zero magnetic flux state, effectively reduces the excitation current, but has a larger magnetic permeability than the first core 1. The second-stage secondary current, i.e. compensation current I B , generated on the compensation winding is combined with the first-stage secondary current I2 to form the compensated secondary current I 2B . The compensation current I B can compensate the error of the current transformer and improve the accuracy of the current transformer.
[0032] Preferably, the number of turns of the primary winding is 1. In order to facilitate the use of the dual-stage separated current transformer with air gap, the working state of the measured circuit is not affected, so the primary winding of the current transformer is designed as a through-type, i.e. the number of turns of the primary winding is 1.
[0033] Preferably, the number of turns of the secondary winding and the compensation winding is the same, which can simplify the structure of the current transformer.
[0034] Preferably, the impedance of the secondary winding and the compensation winding is the same, which can simplify the structure of the current transformer.
[0035] Preferably, referring to Figure 1 As shown in the drawings, the first core 1 and the second core 2 have the same size, which can simplify the structure of the current transformer and facilitate winding.
[0036] Preferably, referring to Figure 1 As shown in the drawings, the air gap width of the first core 1 and the second core 2 ranges from (0, 1mm), which is verified by experiments, and thus can improve the accuracy of the current transformer.
[0037] Preferably, referring to Figure 1 As shown in the drawings, the average magnetic path length of the first core 1 and the second core 2 ranges from [20cm, 60cm], which is verified by experiments, and thus can improve the accuracy of the current transformer.
[0038] Preferably, referring to Figure 1 As shown in the drawings, the cross-sectional area of the first core 1 and the second core 2 ranges from [0.5cm 2 ,2.5cm 2 ], which is verified by experiments, and thus can improve the accuracy of the current transformer.
[0039] Preferably, referring to Figure 1 As shown in the drawings, the permeability of the first core 1 ranges from [5000×4π×10 -4 mH / m, 10000×4π×10 -4 mH / m], and the permeability of the second core 2 ranges from (10000×4π×10 -4 mH / m, 50000×4π×10 - 4 mH / m), which is verified by experiments, and thus can improve the accuracy of the current transformer.
[0040] Referring to Figure 1 As shown in the drawings, the derivation process of the calculation formula of the theoretical error of the current transformer is as follows:
[0041] The magnetic motive force balance equation of the first core 1 and the second core 2 is:
[0042] I1N1+I2N2=I 01 N1 (1)
[0043] I1N1+I2N2+I B N B =I 02 N1 (2)
[0044] Wherein, I1 represents the primary current of the current transformer; I2 represents the secondary current of the current transformer before compensation; I Brepresents the compensation current of the current transformer; N1 represents the number of turns of the primary winding of the current transformer; N2 represents the number of turns of the secondary winding of the current transformer; N B represents the number of turns of the compensation winding of the current transformer; I 01 represents the excitation current of the first core 1; I 02 represents the excitation current of the second core 2.
[0045] According to Faraday's law of electromagnetic induction, the electromotive force balance equation of the secondary winding and the compensation winding loop is:
[0046]
[0047] wherein, Φ1 represents the magnetic flux of the first core 1; Φ2 represents the magnetic flux of the second core 2; R2 represents the resistance component of the secondary winding impedance Z2; L2 represents the inductance component of the secondary winding impedance Z2, Z2 = R2 + jωL2; R B represents the resistance component of the compensation winding impedance Z B ; L B represents the inductance component of the compensation winding impedance Z B ; Z B = R B + jωL B .
[0048] The equivalent total magnetic resistance is the algebraic sum of the core magnetic resistance and the air gap magnetic resistance. According to the Ohm's law of the magnetic circuit, the equation can be obtained:
[0049]
[0050] wherein, l represents the average magnetic circuit length of the first core 1 and the second core 2; μ1 represents the magnetic permeability of the first core 1; μ2 represents the magnetic permeability of the second core 2; S represents the cross-sectional area of the first core 1 and the second core 2; x represents the air gap width of the first core 1 and the second core 2; μ0 represents the magnetic permeability in vacuum, which is equivalent to the magnetic permeability of air here.
[0051] The error of the two-stage split current transformer is the negative value of the product of the first-stage current transformer error and the second-stage current transformer error, and is determined by the excitation current of the second-stage current transformer core. Combining the above formulas, and letting N2 = N B = N, R2 = R B = R, L2 = L B = L, the complex expression of the error of the current transformer is obtained as:
[0052]
[0053] wherein, ε represents the theoretical error of the current transformer; f represents the ratio error of the current transformer; δ represents the phase error of the current transformer; ω represents the angular frequency of the primary current; j represents the imaginary unit; a1, a2, and b represent simplified parameters; the black dot above the current indicates that the current is a phasor.
[0054] The theoretical error of the current transformer can be calculated according to formula (7), providing a basis for product design. As can be seen from formula (7), the ratio error and phase error of the current transformer are closely related to the number of turns of the secondary winding, the number of turns of the compensation winding, the resistance value of the secondary winding, the resistance value of the compensation winding, the inductance value of the secondary winding, the inductance value of the compensation winding, the angular frequency of the power supply, the average magnetic circuit length of the core, the cross-sectional area of the core, the permeability of the core, and the width of the air gap. Once the expected indicators of the current transformer are determined, the values of the first seven parameters can be obtained through actual measurement or formula calculation. The reasonable design of the core geometry and the effective utilization of magnetic properties are crucial to the performance improvement of the current transformer; in addition, the problem of increased excitation current caused by the air gap leading to increased leakage flux and significant decrease in magnetic properties cannot be ignored, and exploring its width limit has important practical significance. Therefore, the influence of the average magnetic circuit length, cross-sectional area, permeability, and air gap width on the ratio error and phase error is analyzed quantitatively.
[0055] To visually display the characteristic curves of ratio error and phase error, a mathematical model was established in the software. Specific parameter settings are shown in Table 1. Using the air gap width as the basic variable, the average magnetic circuit length, cross-sectional area, and permeability of the iron core were sequentially superimposed in pairs to form the functional relationships f(x,l), δ(x,l), f(x,S), δ(x,S), f(x,μ2), and δ(x,μ2). The error characteristic curves are shown below. Figures 2 to 7 As shown, Figures 2 to 7 The first iron core 1 and the second iron core 2 have the same dimensions. Figure 6 and Figure 7 In this context, u2 represents the permeability μ2 of the second iron core 2.
[0056] Table 1 Current Transformer Parameter Settings
[0057]
[0058]
[0059] Based on theoretical research, this utility model developed a prototype of a two-stage split current transformer with an air gap. The design parameters are shown in Table 2.
[0060] Table 2. Parameter Design of Two-Stage Separated Current Transformer with Air Gap
[0061]
[0062] The first iron core 1 and the second iron core 2 are in the same shape and are both openable and closable circular rings, D1 represents the inner diameter of the iron core, and D2 represents the outer diameter of the iron core. h represents the height of the iron core. According to the measurement, the actual error of the air-gap double-stage separated current transformer in Table 2 meets the technical index requirement of 0.05S level, while the actual error of the existing open-type current transformer is only 0.2S level. The error of the improved current transformer is more than one order of magnitude better than the existing product.
[0063] In summary, the air-gap double-stage separated current transformer provided by the utility model comprises a first iron core 1, a second iron core 2, a compensation winding, a first-stage current transformer and a second-stage current transformer. The first iron core 1 is an auxiliary iron core, which bears the main magnetic flux and the induced electromotive force of the secondary circuit, has a higher magnetic induction intensity and a larger excitation current. The second iron core 2 is a main iron core, which has a very low magnetic induction intensity and is in an approximate zero magnetic flux state, effectively reduces the excitation current, but has a larger magnetic permeability than the first iron core 1. The second-stage secondary current, i.e. compensation current I B , generated on the compensation winding is combined with the first-stage secondary current I2 to form the compensated secondary current I 2B . The compensation current I B can compensate the error of the current transformer and improve the accuracy of the current transformer.
[0064] The above description is only the description of the preferred embodiments of the utility model, and does not limit the scope of the utility model. Any modification and change made by the ordinary skilled in the art according to the above disclosure is within the protection scope of the utility model.
Claims
1. A two-stage split-core current transformer with air gap, characterized in that, The first core, the second core, the primary winding, the secondary winding and the compensation winding are included; The first core and the second core both have air gaps, and the permeability of the first core is less than that of the second core; The primary winding is wound on one side of the first core and the second core, the secondary winding is wound on the other side of the first core and the second core, and the compensation winding is connected in parallel with the secondary winding; The primary winding, the first core and the secondary winding constitute a first-stage current transformer, and the primary winding, the second core, the secondary winding and the compensation winding constitute a second-stage current transformer.
2. A dual stage split current transformer with air gap as claimed in claim 1 characterized by, The number of turns of the primary winding is 1.
3. A dual stage split current transformer with air gap as claimed in claim 1 characterized by, The number of turns of the secondary winding and the compensation winding is the same.
4. A dual stage split current transformer with air gap as claimed in claim 3 wherein, The impedance of the secondary winding and the compensation winding is the same.
5. A dual stage split current transformer with air gap as claimed in claim 1 characterized by, The sizes of the first core and the second core are the same.
6. A dual stage split current transformer with air gap as claimed in claim 5 wherein, The air gap width of the first core and the second core ranges from 0 to 1mm.
7. A dual stage split current transformer with air gap as claimed in claim 5 wherein, The average magnetic path length of the first core and the second core ranges from 20cm to 60cm.
8. A dual stage split current transformer with air gap as claimed in claim 5 wherein, The cross-sectional area of the first core and the second core ranges from [0.5 cm 2 ,2.5 cm 2 ].
9. A dual stage split current transformer with air gap as claimed in claim 1 characterized by, The permeability of the first core is [5000 x 4π x 10 -4 mH / m, 10000 x 4π x 10 -4 mH / m], and the permeability of the second core is in the range of (10000 x 4π x 10 -4 mH / m, 50000 x 4π x 10 -4 mH / m).