A transformer overvoltage sensor based on the principle of dual-core complementarity

Abstract

A transformer overvoltage sensor based on the principle of dual-core complementarity comprises a primary winding on the primary side and a secondary winding comprising a high-frequency core, a low-frequency core, a secondary winding, and a compensation winding on the secondary side. The secondary winding comprises a high-frequency side second winding and a high-frequency-low-frequency coupling winding. The high-frequency core is a magnetic ring made of high-frequency material, and the low-frequency core is a magnetic ring made of low-frequency material. The compensation winding is wound on the low-frequency core, and the high-frequency side second winding is wound on the high-frequency core. After the high-frequency core and the low-frequency core are coaxially arranged in parallel, a high-frequency-low-frequency coupling winding is wound on both the high-frequency core and the low-frequency core. The secondary winding is formed by the high-frequency side second winding and the high-frequency-low-frequency coupling winding. The present invention maintains the through-core structure of the mutual inductor and expands the equivalent frequency band of the through-core sensor by passively complementing the magnetic cores. This not only takes into account the reliability and accuracy of bushing end screen overvoltage monitoring, but also solves the problem of accurate transmission of signals of different frequencies.

Description

Technical Field

[0001] The present invention relates to the technical field of online monitoring of electrical equipment, and in particular to a transformer overvoltage sensor based on a dual-core complementary principle. Background Art

[0002] Power transformers are essential components of power grids, and their safe operation is the cornerstone of grid reliability. High-slope overvoltages, after being attenuated by busbars or lines, are injected into the transformer at varying frequency bands. Winding insulation damage caused by high voltage amplitudes is generally irreversible, necessitating overvoltage monitoring to provide early warning of potential accidents such as winding insulation failures. The primary parameter for overvoltage monitoring is voltage amplitude. The frequency range of overvoltage signals encompasses all frequencies between upper and lower frequency limits. Overvoltage sensors must ensure stable signal transmission within the frequency band to detect overvoltages of varying amplitudes.

[0003] Since using independent equipment to obtain overvoltage signals from the high-voltage end will increase the floor space and the amount of equipment maintenance, the existing technology generally obtains signals from the end screen of the capacitor bushing for transformer overvoltage monitoring, and calculates the overvoltage amplitude through the end screen signal. The end screen of the capacitor bushing needs to be reliably grounded, and series connection of acquisition components is generally not allowed. The end screen grounding structure also has certain requirements for the flow rate. The through-type sensor can ensure that the grounding characteristics of the bushing are not changed, thereby ensuring the safety of the primary equipment to the greatest extent. Therefore, a through-type wide-band sensor is required for transformer overvoltage monitoring, which can ensure the safe operation of the capacitor bushing while accurately monitoring the voltage signal.

[0004] Conventional capacitive sensors require ungrounded conductors, making them suitable only for bushings with both terminal and secondary terminals. While measuring the series impedance of the transformer terminal terminal offers advantages such as good frequency characteristics and ease of acquisition and measurement, this method's safety is widely questioned. Grounding the transformer terminal terminal impairs the current-carrying capacity of the transformer bushing, compromising the safe operation of the primary equipment. Conventional through-hole transformers, whether made of silicon steel, manganese zinc, or nickel zinc, fail to cover the entire monitoring frequency band, resulting in inaccurate overvoltage transmission at certain frequencies and failure to identify damage to the transformer caused by these overvoltages. Rogowski coils have a wide operating frequency band, covering the transformer overvoltage band. However, their use of air as a magnetic conductor results in low electromagnetic conversion efficiency. The induced potential of the Rogowski coil is differentially related to the measured current, requiring a wide-band integration circuit to recover the measured current signal. Because the upper and lower limits of the transformer overvoltage band differ by a factor of 100,000, the current rate of change fluctuates significantly, making the Rogowski coil integration circuit difficult and expensive to implement, and requiring high component quality. Summary of the Invention

[0005] In order to address the deficiencies in the prior art, the present invention provides a transformer overvoltage sensor based on the dual-core complementary principle, which maintains the through-type structure of the transformer, expands the equivalent frequency band of the through-type sensor by means of passive complementarity of the magnetic cores, and achieves stable transmission of overvoltage amplitudes of different frequencies; it not only takes into account the reliability and accuracy of overvoltage monitoring of the bushing end screen, but also fundamentally solves the accurate transmission of signals of different frequencies.

[0006] The present invention adopts the following technical solutions.

[0007] The present invention proposes a transformer overvoltage sensor based on the dual-core complementary principle. The sensor includes a primary side and a secondary side. The primary side includes a primary winding with N1 turns. The sensor is characterized by:

[0008] The secondary side includes: a high-frequency magnetic core, a low-frequency magnetic core, a secondary winding, and a compensation winding; wherein the secondary winding includes a high-frequency side second winding and a high-frequency and low-frequency coupling winding;

[0009] Among them, the high-frequency magnetic core is a magnetic ring made of high-frequency materials, and the low-frequency magnetic core is a magnetic ring made of low-frequency materials;

[0010] A compensation winding is wound on the low-frequency core, and the compensation winding is hinged only to the low-frequency core; a high-frequency side second winding is wound on the high-frequency core, and the high-frequency side second winding is hinged only to the high-frequency core; after the high-frequency core and the low-frequency core are coaxially arranged in parallel, a high-frequency and low-frequency coupling winding is wound on both the high-frequency core and the low-frequency core, and the high-frequency and low-frequency coupling winding is hinged to both the high-frequency core and the low-frequency core;

[0011] The secondary winding is formed by the high-frequency side second winding and the high-frequency and low-frequency coupling winding.

[0012] The primary windings of the high-frequency magnetic core and the low-frequency magnetic core are a common one-turn through-core structure.

[0013] The inner diameter and outer diameter of the magnetic rings used in the high-frequency magnetic core and the low-frequency magnetic core are the same, but the heights of the magnetic rings used in the high-frequency magnetic core and the low-frequency magnetic core are different. The height difference of the two magnetic rings is used to adjust the ratio of the cross-sectional area of ​​the high-frequency magnetic core to the cross-sectional area of ​​the low-frequency magnetic core.

[0014] The number of turns of the compensation winding is N b2 The number of turns of the second winding on the high-frequency side is N b The number of turns of the high-frequency and low-frequency coupling winding is N2-N b The number of turns of the secondary winding is N2 turns.

[0015] The winding directions of all windings are the same, including clockwise and counterclockwise.

[0016] One end of the compensation winding is connected to one end of the compensation impedance, and the other end of the compensation winding is connected to the other end of the compensation impedance; one end of the secondary winding is connected to one end of the secondary impedance, and the other end of the secondary winding is connected to the other end of the secondary impedance.

[0017] The compensation impedance is composed of RLC passive components and has frequency selection characteristics.

[0018] The high-frequency core induced current satisfies the following relationship:

[0019]

[0020] The low-frequency core induced current satisfies the following relationship:

[0021]

[0022] In the formula

[0023] I1 is the primary current,

[0024] is the high frequency core induced current,

[0025] is the low-frequency core induced current,

[0026] N1 is the number of turns of the primary winding,

[0027] N2 is the number of turns of the secondary winding,

[0028] N b is the number of turns of the second winding on the high-frequency side;

[0029] High frequency core induced current and low frequency core induced current They are in series relationship and unequal in size, and are shunted by the excitation impedance of the high-frequency magnetic core and the low-frequency magnetic core.

[0030] In the low frequency case, the excitation impedance of the high frequency core is smaller than that of the low frequency core, and the current is shunted from the excitation impedance of the high frequency core. The current flowing through the secondary impedance is determined by the transformation ratio of the low frequency core.

[0031] In the case of high frequency, the excitation impedance of the high frequency core is greater than the excitation impedance of the low frequency core, the current is shunted from the excitation impedance of the low frequency core, and the current flowing through the secondary impedance is determined by the transformation ratio of the high frequency core;

[0032] In the case of medium frequency, the equivalent value of the compensation impedance converted to the secondary side has a frequency-selective characteristic, which shunts the current on the excitation impedance of the high-frequency magnetic core and the excitation impedance of the low-frequency magnetic core.

[0033] The beneficial effect of the present invention is that, compared with the prior art, the performance of the transformer overvoltage sensor proposed by the present invention is greatly improved while ensuring the through-hole reliable grounding of the transformer bushing end screen.

[0034] The present invention is based on the magnetic permeability characteristics of magnetic materials and has the characteristics of high signal transmission efficiency. It balances the characteristics of different magnetic permeability materials through the number of coil turns and secondary load, achieving higher transmission efficiency while realizing relatively flat transmission characteristics, making it convenient for subsequent circuits to use digital acquisition methods to restore overvoltage signals. The system is easy to implement and the performance of overvoltage monitoring can be greatly improved.

[0035] The present invention uses magnetic media as the transmission material, and the signal transmission efficiency is greatly improved compared with the Rogowski coil.

[0036] The present invention balances the difference in magnetic permeability through winding circuit design, connects different secondary output windings in series, and realizes signal energy complementarity in different frequency bands, thereby achieving relatively flat transmission characteristics in a wider frequency band and maintaining high signal conversion efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 This is a schematic diagram of the appearance of a transformer overvoltage sensor based on the dual-core complementary principle proposed by the present invention;

[0038] Figure 2 This is a schematic diagram of a transformer overvoltage sensor based on the dual-core complementary principle proposed by the present invention;

[0039] Figure 3 This is an equivalent circuit diagram of a transformer overvoltage sensor based on the dual-core complementary principle proposed by the present invention;

[0040] Figures 1 to 3 The reference numerals in the figures are described as follows:

[0041] T1-high frequency magnetic core, T2-low frequency magnetic core, 1-secondary winding, 2-compensation winding, 3-second winding on high frequency side, 4-high frequency and low frequency coupling winding; DETAILED DESCRIPTION

[0042] To make the objectives, technical solutions, and advantages of the present invention more clear, the technical solutions of the present invention will be clearly and completely described below in conjunction with the accompanying drawings in the embodiments of the present invention. The embodiments described in this application are only part of the embodiments of the present invention, not all of them. Based on the spirit of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0043] The present invention proposes a transformer overvoltage sensor based on the dual-core complementary principle. The sensor includes a primary side and a secondary side. The primary side includes a primary winding with N1 turns. Figure 1 As shown, the secondary side includes: a high-frequency magnetic core T1, a low-frequency magnetic core T2, a secondary winding 1, and a compensation winding 2; wherein the secondary winding 1 includes a high-frequency side second winding 3 and a high-frequency and low-frequency coupling winding 4.

[0044] The high-frequency core is a magnetic ring made of high-frequency material, while the low-frequency core is a magnetic ring made of low-frequency material. The high-frequency and low-frequency cores are coaxially arranged in parallel. The transformer overvoltage sensor proposed in this invention utilizes a through-hole structure, which maintains the current flow characteristics of the grounded end shield, ensuring the reliability of the bushing insulation while detecting overvoltage.

[0045] The magnetic core used in the transformer overvoltage sensor is generally a magnetic ring structure. Depending on the operating frequency of the magnetic material, magnetic rings with different characteristics can be used, including but not limited to: silicon steel strip magnetic rings, manganese zinc ferrite magnetic rings, nickel zinc ferrite magnetic rings. The present invention selects a magnetic ring made of low-frequency material and a magnetic ring made of high-frequency material, and forms a wide-band through-the-core sensor with cross-material frequency characteristics through compensation. Although materials such as silicon steel, manganese zinc, and nickel zinc cannot cover the overvoltage operating frequency band, the overvoltage sensor proposed in the present invention adopts a dual-core complementary method to achieve stable transmission of the electrical signal amplitude within a wide frequency band, providing conditions for monitoring overvoltage signals in different frequency bands.

[0046] The inner diameter and outer diameter of the magnetic rings used for the high-frequency magnetic core and the low-frequency magnetic core are the same, but the heights of the magnetic rings are different. The height difference of the two magnetic rings is used to adjust the proportional relationship between the cross-sectional area of ​​the high-frequency magnetic core and the cross-sectional area of ​​the low-frequency magnetic core.

[0047] Among them, N is wound on the low-frequency core T2. b2 Compensation winding 2 is only connected to the low-frequency core T2; N turns are wound on the high-frequency core T1. b The high-frequency side second winding 3 is only hinged with the high-frequency core T1; after the high-frequency core T1 and the low-frequency core T2 are arranged coaxially in parallel, N2-N is wound on the high-frequency core T1 and the low-frequency core T2. b The high-frequency side second winding 3 and the high-frequency low-frequency coupling winding 4 form a secondary winding 1 with a total number of turns N2.

[0048] The winding directions of all windings are the same, including clockwise and counterclockwise.

[0049] like Figure 2 As shown, one end of the compensation winding 2 is connected to the compensation impedance Z bOne end of the compensation winding 2 is connected to the compensation impedance Z b one end of the secondary winding 1 is connected to one end of the secondary impedance Z2, and the other end of the secondary winding 1 is connected to the other end of the secondary impedance Z2.

[0050] The general rule of magnetic materials is that the magnetic permeability of low-frequency cores is high, and the magnetic permeability of high-frequency cores is low. The primary windings of high-frequency cores and low-frequency cores are a common one-turn through-core structure. Since the number of turns of the secondary winding coupled on the low-frequency core is N2-N b The number of turns is smaller than the number of turns N2 coupled to the high-frequency core. By adopting this unequal turns method, the gain of the low-frequency signal is proportionally compressed, which effectively reduces the magnetic permeability of the low-frequency material and effectively expands the frequency band of the through-hole sensor.

[0051] The frequency characteristic curve of magnetic materials is not an ideal straight line. The curve of magnetic permeability changing with frequency often shows an arc-shaped attenuation characteristic. The ideal transmission characteristic cannot be obtained by proportionally superimposing the magnetic permeability characteristics of two different materials. A "bump" will appear in the frequency band where high frequency and low frequency meet. That is, in the mid-frequency band, the characteristics of the two magnetic materials can play a certain role. After superposition, the gain characteristic of the sensor is increased. Therefore, the use of compensation winding and compensation impedance Z b Reduce sensor gain.

[0052] Compensation impedance Z b Rather than being a single passive component, the compensation impedance is composed of RLC passive components. Through appropriate RLC combinations, specific mid-frequency impedance characteristics can be achieved, exhibiting frequency-selective properties. The compensation impedance has higher impedance in the high- and low-frequency bands, which does not affect the sensor's transmission characteristics. The compensation impedance has lower impedance in the mid-frequency band, allowing the mid-frequency magnetic flux of the low-frequency core to pass through the second compensation winding demagnetization circuit, reducing the gain of the low-frequency core in the mid-frequency band and attenuating the sensor's transmission characteristics. This results in a relatively flat gain across the entire frequency band, achieving a relatively flat transmission characteristic across the entire frequency band. Therefore, the compensation impedance and compensation windings are used to provide targeted compensation for the curves of different magnetic materials, correcting the sensor's overall transmission characteristics.

[0053] The transformer overvoltage sensor provided by the present invention can balance the core characteristics of two different operating frequencies and different magnetic permeabilities by adjusting the compensation impedance and the secondary winding, thereby achieving linear transmission in a wide bandwidth range. While isolating the overvoltage, it can relatively accurately transmit the overvoltage waveform, thereby realizing accurate monitoring of overvoltages with different incoming wave steepness.

[0054] The equivalent circuit diagram of the dual-core complementary transformer overvoltage sensor is as follows: Figure 3 shown.

[0055] A dual-core sensor with one turn through the core is equivalent to two transformers with different ratios connected in series. The high-frequency core T1 corresponds to a larger ratio, while the low-frequency core T2 corresponds to a smaller ratio. Because the primary winding is a through-core structure, the impedance of the transformer's primary portion is very small and does not affect the magnitude of the primary current. The primary current can be considered a current source. The two transformers induce currents in the secondary coil according to their respective turns ratios. The induced current in the high-frequency core satisfies the following relationship:

[0056]

[0057] The low-frequency core induced current satisfies the following relationship:

[0058]

[0059] In the formula

[0060] I1 is the primary current,

[0061] is the high frequency core induced current,

[0062] is the low-frequency core induced current,

[0063] N1 is the number of turns of the primary winding,

[0064] N2 is the number of turns of the secondary winding,

[0065] N b is the number of turns of the second winding on the high-frequency side.

[0066] Due to the high frequency magnetic core induced current and low frequency core induced current Since they are in series relationship and of unequal magnitude, the current in the equivalent circuit must be divided by the excitation impedance.

[0067] In the low frequency case, the excitation impedance Z of the high frequency core m1 Small, the shunt current mainly flows from Z m1 Flow, due to the low frequency core excitation impedance Z m2 The current flowing through the secondary impedance Z2 is basically determined by the transformation ratio of the low-frequency magnetic core.

[0068] At high frequencies, Z m2 Smaller and Z m1 The current flowing through the secondary impedance Z2 is basically determined by the transformation ratio of the high-frequency magnetic core.

[0069] Therefore, the frequency characteristics of the cores determine the main source of signal energy in each frequency band when connected in series. In the mid-frequency band, since the magnetic permeability of the two cores cannot be ignored, part of the induced current must flow through the Z with larger impedance. m1 and Z m2, thus generating a larger voltage on the secondary impedance Z2, increasing the gain of the mid-frequency signal. The equivalent value of the compensation impedance converted to the secondary side is Z b ', Z b 'It has frequency selection characteristics, low impedance in the mid-frequency band, and can shunt Z m1 and Z m2 The intermediate frequency current on the Z side ensures the gain is stable in the intermediate frequency band. b 'The impedance is larger in the low and high frequency bands, which does not affect the transmission characteristics of these two parts.

[0070] The secondary impedance is connected to the secondary winding. The secondary impedance is the load impedance of the back-end acquisition system. Resistive load and capacitive load can be selected according to the overvoltage calculation principle.

[0071] The overvoltage sensor proposed in the present invention uses two types of magnetic conductive materials with different frequency characteristics as the magnetic core of the through-type mutual inductor. By adjusting the number of turns and the secondary load, the difference in magnetic permeability of different magnetic materials is balanced, and a proportional output signal of the primary current is obtained, achieving a relatively flat transmission characteristic, thereby creating favorable conditions for the back-end digital acquisition and digital integration, and realizing the acquisition of wide-band overvoltage signals while ensuring the safe operation of the transformer bushing.

[0072] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the above embodiments, ordinary technicians in the field should understand that the specific implementation methods of the present invention can still be modified or replaced by equivalents. Any modification or equivalent replacement that does not depart from the spirit and scope of the present invention should be covered by the scope of protection of the claims of the present invention.

Claims

1. A transformer overvoltage sensor based on the dual-core complementary principle, comprising a primary side and a secondary side, wherein the primary side comprises a primary winding with N1 turns, and wherein: The secondary side includes: a high-frequency magnetic core, a low-frequency magnetic core, a secondary winding, and a compensation winding; wherein the secondary winding includes a high-frequency side second winding and a high-frequency and low-frequency coupling winding; Among them, the high-frequency magnetic core is a magnetic ring made of high-frequency materials, and the low-frequency magnetic core is a magnetic ring made of low-frequency materials; A compensation winding is wound on the low-frequency core, and the compensation winding is hinged only to the low-frequency core; a high-frequency side second winding is wound on the high-frequency core, and the high-frequency side second winding is hinged only to the high-frequency core; after the high-frequency core and the low-frequency core are coaxially arranged in parallel, a high-frequency and low-frequency coupling winding is wound on both the high-frequency core and the low-frequency core, and the high-frequency and low-frequency coupling winding is hinged to both the high-frequency core and the low-frequency core; The secondary winding is formed by the high-frequency side second winding and the high-frequency and low-frequency coupling winding.

2. The transformer overvoltage sensor based on the dual-core complementary principle according to claim 1 is characterized in that: The primary windings of the high-frequency magnetic core and the low-frequency magnetic core are a common one-turn through-core structure.

3. The transformer overvoltage sensor based on the dual-core complementary principle according to claim 1 is characterized in that: The inner diameter and outer diameter of the magnetic rings used in the high-frequency magnetic core and the low-frequency magnetic core are the same, but the heights of the magnetic rings used in the high-frequency magnetic core and the low-frequency magnetic core are different. The height difference of the two magnetic rings is used to adjust the ratio of the cross-sectional area of ​​the high-frequency magnetic core to the cross-sectional area of ​​the low-frequency magnetic core.

4. The transformer overvoltage sensor based on the dual-core complementary principle according to claim 1, characterized in that: The number of turns of the compensation winding is N b2 The number of turns of the second winding on the high-frequency side is N b The number of turns of the high-frequency and low-frequency coupling winding is N2-N b The number of turns of the secondary winding is N2 turns.

5. The transformer overvoltage sensor based on the dual-core complementary principle according to claim 1, characterized in that: The winding directions of all windings are the same, including clockwise and counterclockwise.

6. The transformer overvoltage sensor based on the dual-core complementary principle according to claim 1, characterized in that: One end of the secondary winding is connected to one end of the secondary impedance, and the other end of the secondary winding is connected to the other end of the secondary impedance.

7. The transformer overvoltage sensor based on the dual-core complementary principle according to claim 1, characterized in that: One end of the compensation winding is connected to one end of the compensation impedance, and the other end of the compensation winding is connected to the other end of the compensation impedance.

8. The transformer overvoltage sensor based on the dual-core complementary principle according to claim 7, characterized in that: The compensation impedance is composed of RLC passive components and has frequency selection characteristics.

9. The transformer overvoltage sensor based on the dual-core complementary principle according to claim 8, characterized in that: The high-frequency core induced current satisfies the following relationship: The low-frequency core induced current satisfies the following relationship: In the formula I1 is the primary current, is the high frequency core induced current, is the low-frequency core induced current, N1 is the number of turns of the primary winding, N2 is the number of turns of the secondary winding, N b is the number of turns of the second winding on the high-frequency side; High frequency core induced current and low frequency core induced current They are in series relationship and unequal in size, and are shunted by the excitation impedance of the high-frequency magnetic core and the low-frequency magnetic core.

10. The transformer overvoltage sensor based on the dual-core complementary principle according to claim 9, characterized in that: In the low frequency case, the excitation impedance of the high frequency core is smaller than that of the low frequency core, and the current is shunted from the excitation impedance of the high frequency core. The current flowing through the secondary impedance is determined by the transformation ratio of the low frequency core. In the case of high frequency, the excitation impedance of the high frequency core is greater than the excitation impedance of the low frequency core, the current is shunted from the excitation impedance of the low frequency core, and the current flowing through the secondary impedance is determined by the transformation ratio of the high frequency core; In the case of medium frequency, the equivalent value of the compensation impedance converted to the secondary side has a frequency-selective characteristic, which shunts the current on the excitation impedance of the high-frequency magnetic core and the excitation impedance of the low-frequency magnetic core.

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