Current transformer with harmonic measurement function

Abstract

The invention discloses a current transformer with a harmonic measurement function. The current transformer comprises an oil tank; the lower end of the outer insulating sleeve is connected to the top of the oil tank and vertically penetrates through the oil tank to form an accommodating space; the expander is connected to the top of the outer insulation sleeve; the transformer body is arranged in the containing space and comprises a primary winding, a main insulator and a secondary winding, the main insulator wraps the periphery of the primary winding, and the secondary winding is arranged on the periphery of the main insulator in a sleeving mode and located in the oil tank; wherein the main insulator is provided with a plurality of capacitive screens, the plurality of capacitive screens are sequentially wound to form a capacitive screen loop layer, the outermost layer of the capacitive screen loop layer is a ground screen, the main insulator is of a U-shaped structure, and a first voltage-dividing capacitive screen and a second voltage-dividing capacitive screen are arranged on a semi-circular ring part of the U-shaped structure. And the first voltage-dividing capacitive screen and the second voltage-dividing capacitive screen are adjacently attached to the inner peripheral wall and the outer wall of the ground screen respectively. According to the mutual inductor, the harmonic signals are accurately measured according to the capacitance voltage dividing principle, the voltage dividing ratio is controllable, the structure is simple, the influence on the service life of a product is small, and economical efficiency is good.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of mutual inductor, more particularly, to a current transformer with harmonic measurement function. BACKGROUND

[0002] Harmonic voltage measurement, analysis and treatment are the focus of power quality research, and harmonic voltage signal extraction is the basis of all harmonic research work.

[0003] At present, the data source of high-voltage power grid harmonic analysis mainly comes from the capacitive voltage transformer (CVT), and existing research shows that CVT cannot accurately and timely reflect harmonic, fluctuation and flicker and other indicators, so it is not suitable for measuring various power quality indicators.

[0004] Therefore, it is necessary to carry out innovative research on this technical problem and propose a simpler, more reliable and economical way. SUMMARY

[0005] Therefore, the purpose of the present application is to provide a current transformer with harmonic measurement function, which aims to solve the problems existing in the prior art.

[0006] According to the present application, a current transformer with harmonic measurement function is provided, comprising:

[0007] an oil tank;

[0008] an outer insulation sleeve, the lower end of which is connected to the top of the oil tank, and the oil tank is vertically through to form a containing space;

[0009] an expander connected to the upper end of the outer insulation sleeve;

[0010] a body provided in the containing space, comprising a primary winding, a main insulation and a secondary winding, the main insulation is wrapped around the outer periphery of the primary winding, and the secondary winding is sleeved on the outer periphery of the main insulation and located in the oil tank;

[0011] wherein, a plurality of capacitor screens are provided on the main insulation, and the plurality of capacitor screens are sequentially wrapped to form a capacitor screen ring sleeve layer, the outermost layer of the capacitor screen ring sleeve layer is a ground screen, the main insulation is a U-shaped structure, the semicircular ring part of the U-shaped structure is provided with a first voltage dividing capacitor screen and a second voltage dividing capacitor screen, and the first voltage dividing capacitor screen and the second voltage dividing capacitor screen are respectively arranged adjacent to the inner wall and the outer wall of the ground screen.

[0012] Preferably, an insulation layer is provided between every two adjacent capacitor screens, and the insulation layers corresponding to the adjacent two capacitor screens form a capacitor;

[0013] The first and second voltage dividing capacitor screens form a voltage dividing capacitor with the ground screen.

[0014] Preferably, the size of the voltage dividing capacitor is adjusted by adjusting the length of the first and second voltage dividing capacitor screens and the thickness of the insulating layer between the voltage dividing capacitor screens and the ground screen.

[0015] Preferably, the lead-out wires of the first and second voltage dividing capacitor screens are connected inside the oil tank to form a harmonic measurement terminal.

[0016] The harmonic measurement terminal is led out through a harmonic measurement terminal lead-out sleeve provided on the oil tank.

[0017] Preferably, the lower part of the U-shaped structure is located inside the oil tank.

[0018] Preferably, the innermost layer of the capacitor screen ring sleeve layer is a zero screen, which is adjacent to the primary winding and is electrically connected to the high voltage of the primary winding.

[0019] Preferably, the lead-out of the secondary winding and the lead-out of the ground screen are led out through a secondary lead-out box on the side of the oil tank.

[0020] Preferably, it further comprises a harmonic measurement terminal box, and the harmonic measurement terminal is connected to the harmonic measurement terminal box after being led out through a harmonic measurement terminal lead-out sleeve provided on the oil tank.

[0021] Preferably, the harmonic measurement terminal box comprises a grounding knife switch, a protection circuit module and a data acquisition module.

[0022] The grounding knife switch is used for normal operation, and the grounding knife switch is closed, and the first and second voltage dividing capacitor screens are grounded. When harmonic measurement is needed, the grounding knife switch is opened, and the first and second voltage dividing capacitor screens form a voltage dividing capacitor with the main insulating capacitor screen.

[0023] The data acquisition module acquires the output signal of the harmonic measurement terminal, outputs the signal through an optical fiber, and supplies a power quality detection terminal.

[0024] The data acquisition module acquires the output signal of the harmonic measurement terminal, outputs the signal through an optical fiber, and supplies a power quality detection terminal.

[0025] Preferably, the harmonic measurement terminal is connected to the harmonic measurement terminal box through a shielded cable after being led out through a harmonic measurement terminal lead-out sleeve provided on the oil tank.

[0026] Beneficial effects:

[0027] The current transformer with harmonic voltage measurement function provided by the application realizes accurate measurement of harmonic signals by using the principle of capacitive voltage division, and the voltage division ratio is controllable. The design only needs to increase two capacitive screens in the existing main insulation structure, has no influence on the main insulation of the product, has the advantages of simple structure, small influence on product life, good economy, and the like, and is beneficial to popularization and application. BRIEF DESCRIPTION OF DRAWINGS

[0028] The above and other objects, features and advantages of the present application will become more apparent from the following description of embodiments of the present application with reference to the accompanying drawings.

[0029] Figure 1 A structure schematic diagram of the current transformer with harmonic measurement function according to the embodiment of the application is shown.

[0030] Figure 2 A capacitive screen setting structure schematic diagram of the main insulation according to the embodiment of the application is shown.

[0031] Figure 3 A harmonic measurement principle diagram according to the embodiment of the application is shown.

[0032] Figure 4 A structure schematic diagram of the main insulation according to the embodiment of the application is shown.

[0033] Figure 5 A connection diagram of the main insulation and the harmonic measurement junction box according to the embodiment of the application is shown.

[0034] In the figure: expander 1, outer insulation sleeve 2, primary winding 3, main insulation 4, secondary winding 5, oil tank 6, harmonic measurement outgoing line bushing 7, high-voltage screen outgoing line 8, zero screen 9, first main screen 11, second main screen 12, first voltage division capacitive screen 13, ground screen 14, second voltage division capacitive screen 15, newly added capacitive screen outgoing line 16, ground screen outgoing line 17, harmonic measurement junction box 18. DETAILED DESCRIPTION

[0035] Various embodiments of the present application will be described in detail below with reference to the accompanying drawings. In each of the drawings, the same elements are denoted by the same or similar reference numerals to indicate the same elements. Each part in the drawings is not drawn to scale for the sake of clarity.

[0036] As Figures 1-2As shown, the current transformer with harmonic measurement function provided by the application comprises an oil tank 6, an outer insulation sleeve 2, the outer insulation sleeve 2 and an expander 1. The lower end of the outer insulation sleeve 2 is connected to the top of the oil tank 6, and a containing space is formed through the oil tank 6 from top to bottom. The expander 1 is connected to the upper end of the outer insulation sleeve 2. A body is arranged in the containing space and comprises a primary winding 3, a main insulation 4 and a secondary winding 5. The main insulation 4 is wrapped around the outer periphery of the primary winding 3, and the secondary winding 5 is wrapped around the outer periphery of the main insulation 4 and located in the oil tank 6. A plurality of capacitor screens are arranged on the main insulation 4, and the plurality of capacitor screens are sequentially wrapped to form a capacitor screen ring sleeve layer. The outermost layer of the capacitor screen ring sleeve layer is a ground screen 14. The main insulation 4 has a U-shaped structure. The semicircular ring part of the U-shaped structure is provided with a first voltage dividing capacitor screen 13 and a second voltage dividing capacitor screen 15. The first voltage dividing capacitor screen 13 and the second voltage dividing capacitor screen 15 are respectively arranged adjacent to the inner wall and the outer wall of the ground screen.

[0037] The bottom of the oil tank 6 is provided with a supporting leg, and the lower part of the oil tank 6 is provided with an arc-shaped protruding structure which is matched with the U-shaped structure of the bottom of the body. The lower part of the U-shaped structure is located in the oil tank 6, thereby saving the assembly space. The oil tank 6 is welded by a steel plate. A secondary outlet box is arranged on the side surface of the oil tank 6. An oil drain valve is arranged on the bottom of the oil tank 6, and a harmonic measurement outlet sleeve 7 is arranged on the upper part of the oil tank 6.

[0038] The expander 1 has a stacked ripple structure and is connected to the upper flange of the outer insulation sleeve 2 through a pressing ring. The outer insulation sleeve 2 is a silicon rubber glass steel composite sleeve or a high-strength electric porcelain sleeve, which is stacked on the upper part of the oil tank 6 and connected to the oil tank 6 through a lower flange.

[0039] The expander 1 is filled with oil. When the temperature of the oil changes, the oil expands and shrinks to adjust the internal pressure balance of the containing space.

[0040] The primary winding 3 is a U-shaped aluminum pipe, and the main insulation 4 is wrapped around the primary winding 3. The secondary winding 5 is fixed on the support at the lower part of the primary winding 3. A primary terminal is arranged on the upper part of the insulation sleeve and connected to the two U-shaped end heads of the primary winding 3, so that the current transformer with harmonic measurement function is connected to the power grid.

[0041] The outlet of the secondary winding 5 and the outlet of the ground screen 14 are led out through the secondary outlet box on the side surface of the oil tank 6. The current transformer with harmonic measurement function further comprises a harmonic measurement terminal box 18. The harmonic measurement terminal is led out through the harmonic measurement terminal outlet sleeve arranged on the oil tank 6 and connected to the harmonic measurement terminal box 18.

[0042] Referring to Figure 5The harmonic measurement terminal is led out through the harmonic measurement terminal outlet sleeve pipe arranged on the oil tank 6 and connected with the harmonic measurement terminal box 18 through the shielded cable.

[0043] The harmonic measurement terminal is led out through the harmonic measurement terminal outlet sleeve pipe arranged on the oil tank 6 and connected with the harmonic measurement terminal box 18 through the shielded cable.

[0044] Referring to Figure 4 The insulating layer between every two adjacent capacitor screens forms a capacitor with the corresponding insulating layer between the adjacent capacitor screens. The first voltage dividing capacitor screen 13 and the second voltage dividing capacitor screen 15 form a voltage dividing capacitor with the ground screen 14, and form a capacitor voltage divider with the main insulation 4.

[0045] The size of the voltage dividing capacitor is adjusted by adjusting the length of the first voltage dividing capacitor screen 13 and the second voltage dividing capacitor screen 15 and the thickness of the insulating layer between the first voltage dividing capacitor screen 13 and the second voltage dividing capacitor screen 15 and the ground screen 14, so as to control the harmonic voltage dividing ratio.

[0046] The first voltage dividing capacitor screen 13 and the second voltage dividing capacitor screen 15 are connected in the oil tank 6 to form a harmonic measurement terminal, and the harmonic measurement terminal is led out through the harmonic measurement terminal outlet sleeve pipe arranged on the oil tank 6.

[0047] The innermost layer of the capacitor screen ring sleeve layer is the zero screen 9, the zero screen 9 is adjacent to the primary winding 3, and the zero screen 9 is electrically connected with the high voltage of the primary winding 3.

[0048] The secondary winding 5 is sleeved on the primary winding 3 and fixed on the support at the lower part of the primary winding 3, and the outgoing line is led into the secondary terminal box on the side of the oil tank 6, and the number of the secondary winding 5 is multiple. The main insulation 4 is the capacitor type oil paper insulation, and the high-voltage cable paper is wrapped on the U-shaped primary winding 3, and a plurality of capacitor screens are arranged therebetween. Each two capacitor screens and the insulation layer therebetween constitute a capacitor. The capacitor screen close to the primary winding 3 is the zero screen 9, and the capacitor screen at the outermost layer of the main insulation 4 is the ground screen 14, which must be reliably grounded in operation. Meanwhile, a section of the capacitor screen is wrapped on the inner and outer sides of the ring part of the main insulation 4 close to the ground screen 14, that is, the ground screen 14 is wrapped on the outside of the first voltage-dividing capacitor screen 13, the second voltage-dividing capacitor screen 15 is wrapped on the outside of the ground screen 14, and the outgoing lines of the first voltage-dividing capacitor screen 13 and the second voltage-dividing capacitor screen 15 are connected in the oil tank 6 as the harmonic measurement terminals. The harmonic measurement terminals are led out through the harmonic measurement outgoing line sleeve 7 on the upper part of the oil tank 6, and then connected with the harmonic measurement terminal box 18 through the shielded cable.

[0049] Referring to Figure 2 and 3 Compared with the main insulation of the existing vertical current transformer, the two sections of capacitor screens close to the ground screen 14 are added, the capacitances between the two sections of newly added capacitor screens and the ground screen 14 are used as the voltage-dividing capacitor, and the capacitances of the main insulation 4 constitute the capacitor voltage divider, so that the accurate measurement of the harmonic voltage signal is realized. The size of the voltage-dividing capacitor C h is adjusted by controlling the length of the newly added capacitor screen and the insulation thickness between the newly added capacitor screen and the ground screen 14, so that the control of the harmonic voltage-dividing ratio is realized.

[0050] The capacitance of the main insulation of the vertical current transformer can be divided into the ring part capacitance and the straight line part capacitance, the ring part is the semicircular ring of the lower part of the U shape, and the straight line part is the two straight line segments of the U shape. i is the total number of the main screens excluding the zero screen, m is the first voltage-dividing capacitor screen, which is located between the i-1th main screen and the ground screen (i-th main screen), n is the second voltage-dividing capacitor screen, which is located outside the ground screen, C1 is the capacitance between the zero screen and the i-1th capacitor screen, C2 is the straight line part capacitance between the i-1th main screen and the ground screen, since the first voltage-dividing capacitor screen and the second voltage-dividing capacitor screen are both located in the ring part, the capacitances between the main screens of the straight line part and the newly added section of the main screen in the ring part capacitance are not affected, and are only related to the arrangement of the main screens in the main insulation structure. C3 is the capacitance between the i-1th main screen and the ground screen without the newly added capacitor screen, C4 is the capacitance of the first voltage-dividing capacitor screen to the i-1th main screen, and C h1 is the capacitance of the first voltage-dividing capacitor screen to the ground screen. C h2 is the capacitance of the second voltage-dividing capacitor screen to the ground screen.

[0051] The output potentials of the newly added capacitor screens 1 and 2 are:

[0052]

[0053] Currently, the number of main screens of 220kV and below vertical current transformers is usually 4-6, the voltage between screens is usually tens of kilovolts, and the rated output voltage of the newly added capacitor screen can be set between 50-100V, so the newly added capacitor screen is required to be close to the ground screen, i.e. C h1 and C h2 are much greater than C4. Then the expression of U h can be simplified as:

[0054]

[0055] In the formula, is the main insulation capacitance; C5=C2+C3+C4 is the capacitance between the i-1th main screen and the ground screen; C h =C h1 +C h2 is the voltage dividing capacitance; is the harmonic voltage dividing ratio. Among them, C and C5 mainly depend on the arrangement of the main screen in the main insulation structure, and are fixed values. C h and C4 are related to the arrangement of the newly added capacitor screen, and by adjusting the length of the newly added capacitor screen and the insulation thickness between the newly added capacitor screen and the ground screen, the corresponding size can be changed, so as to realize the control of the harmonic voltage dividing ratio K h .

[0056] By wrapping the ground screen outside the first voltage dividing capacitor screen, wrapping the second voltage dividing capacitor screen outside the ground screen, and connecting the two sections of the newly added capacitor screen lead-out lines in the oil tank, the voltage dividing capacitance C h is increased, so that the harmonic measurement terminal outputs a smaller voltage. The first is that the subsequent signal processing does not need to be reduced again but directly processed or only needs to be reduced by a small amplitude, so that the subsequent sampling data processing value is more accurate.

[0057] Referring to Figure 4, the main insulation is a capacitive oil paper insulation structure, a plurality of capacitor screens are arranged therebetween, the number of capacitor screens adopted by different manufacturers is different, and taking four main screens as an example, from inside to outside, they are zero screen 9, end screen, first main screen 11, second main screen 12, first voltage division capacitor screen 13, ground screen 14 and second voltage division capacitor screen 15. The zero screen 9 is the innermost main screen, and is electrically connected with the high-voltage winding through the high-voltage screen lead-out wire 8. The ground screen 14 is the outermost main screen, and is led out to the side of the oil tank 6 through the ground screen lead-out wire 18 and needs to be grounded during operation. The end screen is arranged between the two main screen end portions, so as to improve the electric field distribution of the end portion. The first voltage division capacitor screen 13 and the second voltage division capacitor screen 15 are both located in the ring portion of the main insulation, wherein the first voltage division capacitor screen 13 is wrapped between the second main screen 12 and the ground screen 14 and is close to the ground screen 14. The second voltage division capacitor screen 15 is wrapped outside the ground screen 14 and is insulated by cable paper in the middle. By adjusting the length of the first voltage division capacitor screen 13 and the second voltage division capacitor screen 15 and the thickness of the cable paper between the first voltage division capacitor screen 13 and the second voltage division capacitor screen 15 and the ground screen, the capacitance C h1 of the first voltage division capacitor screen to the ground screen and the capacitance C h2 of the second voltage division capacitor screen to the ground screen are changed, so that the control of the harmonic voltage division ratio is realized. The first voltage division capacitor screen and the second voltage division capacitor screen are respectively led out through lead-out wires and are connected in the oil tank, and the lead-out wire 16 of the new capacitor screen is led out through the harmonic measurement end lead-out sleeve 7.

[0058] During normal operation, the grounding knife switch is closed, and the new capacitor screen is grounded. When harmonic measurement is needed, the grounding knife switch is opened, and the new capacitor screen and the main insulation capacitor screen form a capacitor voltage division. The data acquisition module collects the output signal of the harmonic measurement end, and outputs the signal through an optical fiber for use by a power quality detection terminal. The protection circuit module prevents damage to the data acquisition module caused by overvoltage.

[0059] The protection point of the application at least includes:

[0060] (1) By adding two segments of capacitor screens to the ring portion of the main insulation of the upright current transformer, the capacitance between the two segments of new capacitor screens and the ground screen and the main insulation capacitor form a capacitor voltage division, so that accurate measurement of the harmonic signal is realized;

[0061] (2) The ground screen is wrapped outside the first voltage division capacitor screen, the second voltage division capacitor screen is wrapped outside the ground screen, and the lead-out wires of the two segments of new capacitor screens are connected in the oil tank, so that the size of the voltage division capacitor C h is increased.

[0062] (3) By adjusting the length of the new capacitor screen and the insulation thickness between the new capacitor screen and the ground screen, the size of the voltage division capacitor C h is adjusted, so that the control of the harmonic voltage division ratio is realized.

[0063] (4) The harmonic measurement terminal output signal acquisition is realized through the harmonic measurement junction box, the signal acquisition is output through the optical fiber, and the power quality detection terminal is used.

[0064] The current transformer with harmonic voltage measurement function provided by the application realizes accurate measurement of harmonic signals by using the principle of capacitive voltage division, and the voltage division ratio is controllable. The design only needs to increase two capacitive screens in the existing main insulation structure, has no influence on the main insulation of the product, has the advantages of simple structure, small influence on product life, good economy, etc., and is beneficial to popularization and application.

[0065] It should be noted that in this text, relational terms such as first and second are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between such entities or operations. Moreover, the terms "comprises", "comprising", or any other variations thereof are intended to cover non-exclusive inclusions, so that a process, method, article, or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or inherent to such a process, method, article, or device. Without more limitations, the element defined by the statement "comprises a" does not exclude the presence of additional identical elements in the process, method, article, or device including the element.

[0066] Finally, it should be noted that: obviously, the above embodiments are only examples for clearly illustrating the application, and are not limitations on the embodiments. Based on the above description, other different forms of changes or variations can be made by those skilled in the art. Here, all the embodiments need not and cannot be exhausted. The obvious changes or variations derived therefrom are still within the protection scope of the application.

Claims

1. A current transformer with a harmonic measurement function, characterized by comprising: The utility model relates to a kind of harmonic measurement terminal and harmonic measurement terminal connection structure, including: Oil tank; Outer insulation cover, its lower end is connected to the top of the oil tank, with the oil tank upper and lower through and form accommodating space; Expander, connected to the upper end of the outer insulation cover; Body, it is equipped in the accommodating space, it includes primary winding, main insulation and secondary winding, the main insulation is wrapped in the outer periphery of the primary winding, the secondary winding is wrapped in the outer periphery of the main insulation and located in the oil tank; Wherein, the main insulation is equipped with multiple capacitive screens, multiple capacitive screens are sequentially wrapped to form capacitive screen ring cover layer, the outermost layer of capacitive screen ring cover layer is ground screen, the main insulation is U-shaped structure, the semicircular ring part of the U-shaped structure is equipped with first voltage divider capacitive screen and second voltage divider capacitive screen, the first voltage divider capacitive screen and second voltage divider capacitive screen are respectively adjacent to the inner wall and outer wall of the ground screen.

2. The current transformer with a harmonic measurement function according to claim 1, characterized by, Insulating layer is provided between every two adjacent capacitive screens, and the insulating layer corresponding to the two adjacent capacitive screens forms a capacitor. Wherein, the first voltage divider capacitive screen and second voltage divider capacitive screen form voltage divider capacitors with the ground screen, and form a capacitive voltage divider with the main insulation.

3. The current transformer with a harmonic measurement function according to claim 2, characterized by, The size of the voltage divider capacitors is adjusted by adjusting the length of the first voltage divider capacitive screen and second voltage divider capacitive screen and the thickness of the insulating layer between the first voltage divider capacitive screen and second voltage divider capacitive screen and the ground screen.

4. The current transformer with a harmonic measurement function according to claim 3, characterized by The lead-out wires of the first voltage divider capacitive screen and second voltage divider capacitive screen are connected in the oil tank to form harmonic measurement terminals. The harmonic measurement terminals are led out through harmonic measurement terminal lead-out sleeve pipes arranged on the oil tank.

5. The current transformer with a harmonic measurement function according to claim 1, characterized by, The lower part of the U-shaped structure is located in the oil tank.

6. The current transformer with a harmonic measurement function according to claim 1, characterized by, The innermost layer of the capacitive screen ring cover layer is zero screen, the zero screen is adjacent to the primary winding, and the zero screen is electrically connected to the high voltage of the primary winding.

7. The current transformer with a harmonic measurement function according to claim 1, characterized by, The lead-out head of the secondary winding and the lead-out head of the ground screen are led out through a secondary lead-out box on the side of the oil tank.

8. The current transformer with a harmonic measurement function according to claim 4, characterized by, The harmonic measurement terminal is connected to a harmonic measurement terminal connection box after being led out through the harmonic measurement terminal lead-out sleeve pipes arranged on the oil tank.

9. The current transformer with a harmonic measurement function according to claim 8, characterized by, The harmonic measurement terminal connection box includes a grounding knife switch, a protection circuit module and a data acquisition module. The grounding knife switch is used for grounding when the harmonic measurement terminal is in normal operation, and the first voltage divider capacitive screen and second voltage divider capacitive screen are grounded. The data acquisition module acquires the output signal of the harmonic measurement terminal and outputs the signal through an optical fiber for use by a power quality detection terminal. The harmonic measurement terminal is connected to the harmonic measurement terminal connection box through a shielded cable after being led out through the harmonic measurement terminal lead-out sleeve pipes arranged on the oil tank.

10. The current transformer with a harmonic measurement function according to claim 9, characterized by, ​

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