A high voltage low pass filter and its design method

Abstract

The present invention provides a high-voltage low-pass filter, comprising: a reactor and a capacitor, wherein the high-voltage low-pass filter is a low-pass filter of a voltage level of 100 kV or above. The high-voltage low-pass filter also includes a voltage grading ring, which is located at the top of the high-voltage low-pass filter and between the reactor and the capacitor of the high-voltage low-pass filter to reduce the electric field strength on the surface of the high-voltage electrode. The present invention also provides a method for designing a high-voltage low-pass filter.

Description

Technical Field

[0001] The present invention relates to the field of low-pass filters, and more specifically, to a high-voltage low-pass filter and a design method thereof. Background Art

[0002] The partial discharge test is a routine test in the production and design process of power transformers with voltage levels of 110kV and above, as well as most dry-type power transformers. The test power supply mostly uses a generator set. Since the equipment conditions of each manufacturer are different, the test conditions are very different. Most transformer manufacturers have outdated equipment such as generator sets and intermediate transformers, and the power supply of the test station is mixed with the power supply of the workshop production. Therefore, the background noise is very large during partial discharge measurement, which affects the accuracy of the test measurement, and even many power supply interferences make the test difficult to conduct.

[0003] At present, for power transformers with a voltage level of 110kV and above, the voltage on the input side of the voltage meter under test is 6kV, 10kV or 35kV, and there is no filter that can filter out interference. Instead, it is filtered out through an intermediate transformer or an isolation transformer. The filtering effect is limited. One transformer can usually only filter out about 10dB. When multiple transformers are connected in series, the short-circuit impedance increases significantly due to the test power supply frequency of 150-200Hz. At high voltage levels, the loss during the test is very large.

[0004] Therefore, it is necessary to provide a high-voltage low-pass filter and a design method that can effectively filter out power supply and environmental interference in a partial discharge test of a high-voltage and large-capacity power transformer. Summary of the invention

[0005] The object of the present invention is to provide a high voltage low pass filter and a design method thereof which can effectively filter out power supply and environmental interference in a partial discharge test of a high voltage and large capacity power transformer.

[0006] In order to achieve the above object, the present invention adopts the following technical solutions:

[0007] A high-voltage low-pass filter comprises a reactor and a capacitor. The high-voltage low-pass filter is a low-pass filter with a voltage level of 100 kV and above.

[0008] Preferably, the capacitance value of the high-voltage low-pass filter is KL / Z 0 The fitting relationship between the actual offset parameters is obtained as follows:

[0009]

[0010] Where Ω represents KL / Z 0 , K = 2π, L is the inductance value of the reactor of the high voltage low pass filter, Z 0is the interference source impedance, and A is a constant parameter of 5.32.

[0011] Preferably, the high voltage low pass filter comprises one or more single body structures, each single body structure comprising a capacitor and a reactor.

[0012] Preferably, the attenuation characteristic of the high-voltage low-pass filter is:

[0013] Attenuation capability of more than 20dB from 40kHz to 100kHz; and

[0014] Under the conditions of 100kHz to 400kHz, the attenuation capability is above 40dB.

[0015] Preferably, the high-voltage low-pass filter further comprises a voltage-equalizing ring, which is located at the top of the high-voltage low-pass filter and between the reactor and the capacitor of the high-voltage low-pass filter.

[0016] Another aspect of the present application provides a design method for a high voltage low pass filter.

[0017] Determine the design specifications of the high voltage low pass filter;

[0018] Determine the filter impedance according to the rated voltage and rated current in the design indicators of the high-voltage low-pass filter;

[0019] Determine the inductance value of the high voltage low pass filter; and

[0020] Determine the capacitance value of the high voltage low pass filter. The capacitance value is based on KL / Z 0 The fitting relationship between the actual offset parameters is obtained as follows:

[0021]

[0022] Where Ω represents KL / Z 0 , K = 2π, L is the inductance value of the reactor of the high voltage low pass filter, Z 0 is the interference source impedance, A is a constant parameter 5.32,

[0023] Among them, the high-voltage low-pass filter is a high-voltage low-pass filter with a voltage level of 100kV and above.

[0024] The beneficial effects of the present invention are as follows:

[0025] The technical solution of the present invention provides a high-voltage low-pass filter and a design method that can effectively filter out power supply and environmental interference in a partial discharge test of a high-voltage and large-capacity power transformer. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] The specific embodiments of the present invention are further described in detail below in conjunction with the accompanying drawings;

[0027] Figure 1 is a monomer structure diagram of a high-voltage low-pass filter according to the present disclosure;

[0028] Figure 2 is a circuit schematic diagram of a monomer structure of a high-voltage low-pass filter according to the present disclosure;

[0029] Figure 3 is a circuit schematic diagram of an exemplary high-voltage low-pass filter structure composed of monomers of the high-voltage low-pass filter according to the present disclosure;

[0030] Figure 4 is a circuit schematic diagram of an exemplary high-voltage low-pass filter structure composed of monomers of the high-voltage low-pass filter according to the present disclosure;

[0031] Figure 5 is a flow chart of an exemplary design method of a high voltage low pass filter according to the present disclosure; and

[0032] Figure 6 The circuit schematic diagram is a circuit schematic diagram for testing the attenuation characteristics of the high-voltage low-pass filter according to the present disclosure, taking a single-body structure as an example. DETAILED DESCRIPTION

[0033] In order to more clearly illustrate the present invention, the present invention is further described below in conjunction with preferred embodiments and accompanying drawings. Similar components in the accompanying drawings are represented by the same reference numerals. It should be understood by those skilled in the art that the content specifically described below is illustrative rather than restrictive, and should not be used to limit the scope of protection of the present invention.

[0034] Figure 1 1 is a single body structure diagram of the high voltage low pass filter 10 according to the present disclosure.

[0035] like Figure 1 As shown, the monomer structure of the high voltage low pass filter 10 of the present disclosure includes a reactor 101 and a capacitor 103, and further includes voltage grading rings 105-1 and 105-2. Each monomer structure is a half filter structure, that is, including a reactor 101 and a capacitor 103 connected in series.

[0036] like Figure 1 , which is a monomer structure diagram of the high-voltage low-pass filter 10 disclosed in the present invention.

[0037] As shown in the figure, the reactor 101 is located above the capacitor 103, and the grading rings 105-1 and 105-2 are located on the top of the high-voltage low-pass filter 10 to reduce the electric field strength on the surface of the high-voltage electrode and avoid corona discharge caused by the tip of the wire in the reactor coil, which affects the measurement of partial discharge. The grading rings 105-1 and 105-2 can be made of metal plates, preferably 2mm thick aluminum plates that are spun and welded, with a polished surface. The electrode shape is also annular. The exemplary dimensions of the grading rings 105-1 and 105-2 are shown in Figure 2 , the inner diameter of the ring D = 40 cm, the cross-sectional diameter of the ring d = 8 cm, under this exemplary size, the highest voltage without generating corona discharge is:

[0038] U=41.5×8 0.72 ×(40 / 5+1) 0.32 =329kV (1)

[0039] The exemplary grading ring can be used in any filter with an operating voltage lower than this value by a certain margin. It should be understood that, similarly, when a filter with an operating voltage higher than this value is required, the size can be appropriately adjusted based on the exemplary grading ring.

[0040] like Figure 1 As shown in , due to the large size and high weight of the high-voltage low-pass filter, casters are installed under the package of each single structure for easy movement during use.

[0041] The specific parameters and combined topology of the reactor 101 and the capacitor 103 in the high-voltage low-pass filter 10 will be described below in combination with Figure 2 , Figure 3 and Figure 4 Detailed description. Figure 2 is a circuit schematic diagram of a monomer structure of a high-voltage low-pass filter 10 according to the present disclosure; Figure 3 is a circuit schematic diagram of an exemplary high-voltage low-pass filter structure composed of monomers of the high-voltage low-pass filter 10 according to the present disclosure; and Figure 4 is a circuit schematic diagram of an exemplary high-voltage low-pass filter structure composed of monomers of the high-voltage low-pass filter 10 according to the present disclosure.

[0042] like Figure 2 The circuit diagram of the reactor 101 (indicated by L in the figure) and the capacitor 103 (indicated by C in the figure) connected in series is shown. If necessary, they can be combined when used. When combined, the capacitors 103 in the two monomer structures are directly connected in parallel to form the following Figure 3The "T" type filter shown in the figure connects the ends of the reactors 101 in the two monomer structures that are not connected to the capacitor 103 in series, thus forming a "π" type filter. When applied to filtering applications of power transformers, such as partial discharge testing, when each phase needs to be filtered in the form of a combination of monomer structures, a partial discharge test of the power transformer requires 6 monomer structures to be used simultaneously.

[0043] In order to describe the high-voltage low-pass filter 10 of the present application in more detail, Figure 5 An exemplary design method of the high voltage low pass filter 10 according to the present disclosure is described.

[0044] In step 201, in order to enable the high-voltage low-pass filter 10 to be applied to power transformers with a voltage level of 110 kV or above, in this embodiment, the indicators achieved by the designed high-voltage low-pass filter 10 are:

[0045] Rated voltage: 80kV to ground (effective value)

[0046] Attenuation characteristics: 100kHz-400kHz filter frequency attenuation ≥40dB

[0047] Self partial discharge: ≤5pC.

[0048] In this embodiment, in order to meet the partial discharge test requirements of most transformers, the rated current is increased to 100A.

[0049] In this embodiment, the rated frequency is 150 Hz, which can meet the situation that the output power frequency of the generator set is between 100 Hz and 200 Hz.

[0050] In this embodiment, the high-voltage low-pass filter 10 disclosed in the present invention can meet the following requirements: under the condition of 40kHz to 100kHz, the attenuation capability is more than 20dB; and under the condition of 100kHz to 400kHz, the attenuation capability is more than 40dB. Since the background noise of partial discharge test in general test sites exceeds 1000pC, and the attenuation is 40dB in the range of 100-400kHz, the high-voltage low-pass filter 10 disclosed in the present invention can reduce the background noise in this range to 10pC in partial discharge test.

[0051] In step 203, the impedance of the high-voltage low-pass filter 10 is determined. In order to meet the rated voltage of 80 kV and the rated current of 100 A, that is, the excitation impedance of the measured power transformer satisfies: Z = 80 kV / 100 A = 800 Ω, and the impedance of the filter is as low as possible to avoid insertion loss, usually its impedance is about 1% of the excitation impedance of the measured power transformer. In this embodiment, the impedance (represented by X) of the reactor 101 of the high-voltage low-pass filter 10 can be set to 10 Ω.

[0052] In step 205, according to the determined impedance value, the inductance of the high-voltage low-pass filter 10 is determined as:

[0053]

[0054] In step 207, the capacitance of capacitor 103 is determined. Specifically, if it is assumed that the load impedance Z 2 and the interference source impedance Z 0 Equal, that is, the offset parameter V=Z2 / Z=1. When the voltage level is less than 1kV, the internal impedance of the interference source and the transmission line is usually 50Ω or 75Ω. In this embodiment, the rated voltage is 80kV, and the interference source impedance is assumed to be 4000Ω.

[0055] In actual testing, the offset parameter Z2 / Z 0 =1 does not exist. In the power system, the offset parameters of the filter with different loads are quite different. In the high-voltage power transformer, it is even more difficult to accurately determine the offset parameters.

[0056] In the present disclosure, KL / Z is determined 0 The fitting relationship between the actual offset parameter is used to calculate the capacitance value. Specifically, the fitting relationship is:

[0057]

[0058] Where Ω represents KL / Z 0 , K = 2π, L is the inductance value of the reactor of the high voltage low pass filter, Z 0 is the interference source impedance, and A is a constant parameter of 5.32.

[0059] In this embodiment, when a 40% margin is left, when the high-voltage low-pass filter 10 reaches 40 dB from 100 kHz, the corner frequency fs = 100 × 60% = 60 kHz. Then KL / Z 0 =2×π×60000Hz×0.01H / (4000)=0.94, KL / Z 0 Substituting the value of into formula (2), we can calculate V=5.6.

[0060] Then we can get C = L × (V / Z 0 )≈20nF.

[0061] Therefore, in the single structure of the high-voltage low-pass filter 10 of this embodiment, the value of the reactor 101 is 5 mH, and the value of the capacitor 103 is 10 nF.

[0062] Determine KL / Z by the above 0The fitting relationship between the actual offset parameters can obtain the capacitor value of the low-pass filter at the high voltage level at one time, so that the production design at the high voltage level does not need to use a large number of simulation and debugging processes under low voltage conditions, thus overcoming the problem of not being able to design and produce at the high voltage level. In other words, the design process of the capacitor in the filter is simplified, so that the high-voltage low-pass filter can be industrialized.

[0063] Conventional tests were performed on the monomer structure assembled by the above method, and the experimental results shown in Table 3 were obtained:

[0064] Table 3

[0065]

[0066]

[0067] according to Figure 6 The circuit schematic diagram shown in the figure measures the attenuation characteristics of the monomer structure of the high-voltage low-pass filter 10 obtained in this embodiment, where G represents the signal generator, R1 is equivalent to the interference source impedance, R2 is equivalent to the load impedance, and V1 and V2 represent AC millivoltmeters. The insertion loss is defined as The experimental results are shown in Table 4:

[0068] Table 4

[0069]

[0070] It can be seen from the test results of Table 3 and Table 4 that when the high-voltage low-pass filter 10 of this embodiment is connected to the power transformer for partial discharge measurement, when the test voltage is 80kV, the partial discharge amount is 2pC, not more than 5pC, and the insertion loss is not more than 50dB. Using the high-voltage low-pass filter 10 disclosed in the present invention can provide an ideal test condition for partial discharge test.

[0071] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not limitations on the implementation methods of the present invention. For ordinary technicians in the relevant field, other different forms of changes or modifications can be made based on the above description. It is impossible to list all the implementation methods here. All obvious changes or modifications derived from the technical solution of the present invention are still within the protection scope of the present invention.

Claims

1. A design method for a high voltage low pass filter, characterized in that: include: Determining design parameters of the high-voltage low-pass filter; Determine the filter impedance according to the rated voltage and rated current in the design indicators of the high-voltage low-pass filter; Determining the inductance value of the reactor of the high voltage low pass filter; as well as, Determine the capacitance value of the high-voltage low-pass filter, the capacitance value is obtained according to the fitting relationship between KL / Z0 and the actual offset parameter, the fitting relationship is: Wherein, Ω=KL / Z0, K=2π, L is the inductance of the reactor, Z0 is the impedance of the interference source, and A is a constant parameter of 5.32; Wherein, the high-voltage low-pass filter is a high-voltage low-pass filter with a voltage level of 100kV and above; The high-voltage low-pass filter also includes a voltage grading ring, which is located at the top of the high-voltage low-pass filter and between the reactor and the capacitor of the high-voltage low-pass filter; The pressure equalizing ring is made of a 2 mm thick aluminum plate that is spun and then welded, with a polished surface and an annular electrode shape.

2. A high-voltage low-pass filter designed by the design method of a high-voltage low-pass filter according to claim 1, comprising a reactor and a capacitor, characterized in that: The high voltage low pass filter is a low pass filter with a voltage level of 100 kV or above; The capacitance value of the high-voltage low-pass filter is obtained according to the fitting relationship between KL / Z0 and the actual offset parameter, and the fitting relationship is: Wherein, Ω=KL / Z0, K=2π, L is the inductance of the reactor, Z0 is the impedance of the interference source, and A is a constant parameter of 5.32; The high-voltage low-pass filter also includes a voltage grading ring, which is located at the top of the high-voltage low-pass filter and between the reactor and the capacitor of the high-voltage low-pass filter; The pressure equalizing ring is made of a 2 mm thick aluminum plate that is spun and then welded, with a polished surface and an annular electrode shape.

3. The high voltage low pass filter according to claim 2, characterized in that: It comprises one or more single structures, each of which comprises one capacitor and one reactor.

4. The high voltage low pass filter according to claim 2, characterized in that: The attenuation characteristics of the high-voltage low-pass filter are: Attenuation capability of more than 20dB from 40kHz to 100kHz; and Under the condition of 100kHz to 400kHz, the attenuation capability is above 40dB.

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