Methods and apparatus for measuring the electromagnetic shielding effectiveness of high-voltage shielded cables

Abstract

This invention discloses a method for measuring the electromagnetic shielding effectiveness of high-voltage shielded cables. In the 30MHz-1GHz frequency band, the measurement is performed according to the following steps: S1: Connect a coaxial cable with known insertion loss to the cable segment to replace the shielded cable under test. Measure the power value at the measured frequency point where the first current probe is located, and then measure the power value at the measured frequency point where the second current probe is located, eliminating system measurement errors; S2: Connect the shielded cable under test to the cable segment and measure the power value at the measured frequency point where the second current probe is located to obtain P1; S3: Simultaneously move the power absorption clamp and the auxiliary absorption clamp to find the maximum value P2 at the measured frequency point; S4: The shielding effectiveness value of the shielded cable at this frequency point is SE = P1 - P2. An alternative measurement procedure is used in the 9kHz-30MHz frequency band. This method can accurately measure the electromagnetic shielding effectiveness of high-voltage shielded cables.

Description

Technical Field

[0001] This invention relates to electromagnetic shielding effectiveness testing technology for high-voltage shielded cables, and particularly to a method and apparatus for measuring the electromagnetic shielding effectiveness of high-voltage shielded cables. Background Technology

[0002] High-voltage cables are used for transmitting high currents such as DC voltage and power frequency voltage. During transmission switching, they generate a large amount of radio frequency interference signals, causing serious electromagnetic pollution to the operating environment. To suppress electromagnetic interference, a shielding layer is added to the outside of the high-voltage cable, forming a high-voltage shielded cable. This cable is widely used in electric vehicles, power communications, aerospace, shipbuilding, and military industries. The shielding effect of high-voltage shielded cables and how to evaluate its shielding effectiveness has been a hotly debated issue. Some researchers use the line injection method or the triaxial method to measure the surface transfer impedance of high-voltage shielded cables to represent the cable's shielding effectiveness. However, many problems and difficulties have been encountered in implementation.

[0003] Based on the measured port impedance, shielded cables can be divided into two types: fixed impedance shielded cables (such as 50Ω coaxial cables, whose impedance remains constant at 50Ω within a frequency range) and non-fixed impedance shielded cables (such as various shielded wires). Fixed impedance shielded cables are generally used for radio frequency signal transmission, while non-fixed impedance shielded cables are generally used for high-voltage power transmission.

[0004] The electromagnetic shielding effectiveness measurement method for fixed impedance shielded cables, such as the "power absorption clamp method," utilizes the characteristic that the impedance of the shielded cable under test remains constant (the entire measurement system is a 50Ω system) to obtain a baseline measurement value P1. The maximum value of the leakage radio frequency signal of the shielded cable under test, P2, is then found using the power absorption clamp on a 6000mm test rail. The shielding effectiveness value SE of the shielded cable at the measurement frequency is calculated as SE = P1 - P2. The measurable frequency range is 30MHz-1GHz.

[0005] The electromagnetic shielding effectiveness of non-fixed impedance shielded cables cannot be measured using the same methods as fixed impedance shielded cables. This is because the port impedance of a non-fixed impedance shielded cable varies with frequency, length, thickness, and manufacturing process. Radio frequency (RF) signals will be reflected at the junctions where impedance is discontinuous. If the extent of RF signal reflection is unclear, an accurate reference measurement value P1 cannot be obtained, and without P1, the electromagnetic shielding effectiveness cannot be measured. This is why, to date, there is no internationally recognized method for measuring the electromagnetic shielding effectiveness of non-fixed impedance shielded cables. Summary of the Invention

[0006] The purpose of this invention is to provide a method and apparatus for measuring the electromagnetic shielding effectiveness of high-voltage shielded cables, which can be used to accurately measure the electromagnetic shielding effectiveness of non-fixed impedance shielded cables.

[0007] To achieve the above objectives, in a first aspect, the present invention provides a method for measuring the electromagnetic shielding effectiveness of high-voltage shielded cables, wherein a measuring device is established in the 30MHz-1GHz frequency band as follows:

[0008] A signal generator and a terminal load are set at both ends. From the signal generator to the terminal load, a first current probe, a wall mount, a cable segment, and a second current probe are connected in sequence. A movable auxiliary absorption clamp and a power absorption clamp are connected to the cable segment. The power absorption clamp is connected to the receiver. A reflective ground plane is set at the wall mount.

[0009] Perform the measurement according to the following steps:

[0010] S1: Connect a coaxial cable with known insertion loss to the cable segment to replace the shielded cable under test. Measure the power value at the frequency point under test where the first current probe is located, and measure the power value at the frequency point under test where the second current probe is located to eliminate system measurement errors.

[0011] S2: Connect the shielded cable under test to the cable segment and measure the power value at the frequency point where the second current probe is located to obtain P1;

[0012] S3: Simultaneously move the power absorption clamp and the auxiliary absorption clamp to find the maximum value P2 of the measured frequency point;

[0013] S4: The shielding effectiveness value of the shielded cable at this frequency is SE = P1 - P2.

[0014] Furthermore, a current probe calibration device is also provided at the first current probe and the second current probe.

[0015] Furthermore, an electric measuring rail is also provided next to the cable section.

[0016] Furthermore, in the 9kHz-30MHz frequency band, the measurement device is established as follows:

[0017] The signal generator and the terminal load are set at both ends. From the signal generator to the terminal load, the wall-penetrating base, the third current probe, the cable segment, and the fourth current probe are connected in sequence. A reflective grounding plate is set at the wall-penetrating base.

[0018] Perform the measurement according to the following steps:

[0019] S1: Connect a coaxial cable with known insertion loss to the cable segment to replace the shielded cable under test. Measure the power value at the frequency point under test where the third current probe is located, and measure the power value at the frequency point under test where the fourth current probe is located to eliminate system measurement errors.

[0020] S2: Connect the cable segment to the shielded cable under test, measure the power value at the frequency point under test where the third current probe is located, measure the power value at the frequency point under test where the fourth current probe is located, and obtain P1;

[0021] S3: Move the position of the third or fourth current probe and measure at three positions on the shielded cable under test. Take the average value to obtain P2 or find the maximum leakage value as P2.

[0022] S4: The shielding effectiveness value of the shielded cable at this frequency is SE = P1 - P2.

[0023] Furthermore, a current probe calibration device is also provided at the third and fourth current probes.

[0024] Secondly, the present invention also provides a measuring device for the electromagnetic shielding effectiveness of a high-voltage shielded cable applicable to the above-mentioned measurement method, in the 30MHz-1GHz frequency band, comprising: a signal generator and a terminal load located at both ends, a first current probe, a wall-penetrating base, a cable segment, and a second current probe sequentially connected from the signal generator to the terminal load, a movable auxiliary absorption clamp and a power absorption clamp connected to the cable segment, the power absorption clamp being connected to a receiver; and a reflective ground plane provided at the wall-penetrating base.

[0025] Furthermore, in the 9KHz-30MHz frequency band, the measuring device also includes a signal generator and a terminal load at both ends, with a wall-penetrating base, a third current probe, a cable segment, and a fourth current probe connected sequentially from the signal generator to the terminal load; a reflective ground plane is provided at the wall-penetrating base.

[0026] Compared with existing technologies, this invention, through a rationally constructed measurement system and an innovative measurement method, can accurately measure the reference value P1 of a non-fixed impedance shielded cable, and on this basis, ultimately obtain the electromagnetic shielding effectiveness of the non-fixed impedance shielded cable. Attached Figure Description

[0027] Figure 1 This is a test connection diagram for a vector network analyzer.

[0028] Figure 2 The graph shows the test results of the impedance value of a 0.6m thin cable.

[0029] Figure 3 The graph shows the test results of attenuation value of a 0.6m thin cable;

[0030] Figure 4 The graph shows the test results of the impedance value of a 1.2m thin cable.

[0031] Figure 5 The graph shows the test results of attenuation value of a 1.2m thin cable;

[0032] Figure 6 The graph shows the test results of the impedance value of a 6m thin wire cable.

[0033] Figure 7 The graph shows the test results of attenuation value of a 6m thin wire cable.

[0034] Figure 8 The graph shows the test results of the impedance value of a 0.6m thick cable.

[0035] Figure 9 The graph shows the test results of attenuation value for a 0.6m thick cable.

[0036] Figure 10 The graph shows the test results of the impedance value of a 1.2m thick cable.

[0037] Figure 11 The graph shows the test results of attenuation value of a 1.2m thick cable;

[0038] Figure 12 The graph shows the test results of the impedance value of a 6m thick cable.

[0039] Figure 13 The graph shows the test results of attenuation value of a 6m thick cable;

[0040] Figure 14 A measuring device (30MHz-1GHz band) for measuring the electromagnetic shielding effectiveness of high-voltage shielded cables provided in an embodiment of the present invention;

[0041] Figure 15 A measuring device (9kHz-30MHz frequency band) for measuring the electromagnetic shielding effectiveness of high-voltage shielded cables provided in an embodiment of the present invention;

[0042] Figure 16 A test curve of the shielding effectiveness of a 6m thin-wire cable (9kHz-30MHz);

[0043] Figure 17 The effective value test curve of a 6m thin cable shield (30MHz-300MHz). Detailed Implementation

[0044] The principles and spirit of the invention will now be described with reference to several exemplary embodiments illustrated in the accompanying drawings. It should be understood that these embodiments are described merely to enable those skilled in the art to better understand and implement the invention, and are not intended to limit the scope of the invention in any way.

[0045] Before introducing the technical solutions of the embodiments of the present invention, the explorations and analyses made when the present invention was proposed will be introduced first. These explorations and analyses played an important role in the proposal of the present invention, and the inventors made creative efforts for this.

[0046] When considering how to obtain the reference measurement P1 required for the shielding effect measurement of a non-fixed impedance shielded cable, this invention first studied its characteristics and variation law using a vector network analyzer. Figure 1 For testing connection diagrams. Figures 2 to 7 These are the impedance and attenuation test results for different lengths of the same type of shielded cable. Figures 8 to 13 The following are the impedance and attenuation test results for different lengths of another type of shielded cable. Relevant test data are shown in Tables 1-6.

[0047] Table 1 Impedance and Attenuation Values ​​of 0.6m Thin Wire

[0048] frequency impedance Attenuation value 30kHz 49Ω 0dB 50kHz 49Ω 0dB 494kHz 50Ω 0dB 1MHz 50Ω -1dB 10MHz 44Ω 0dB 57MHz 14Ω -2dB 140MHz 49Ω 0dB 226MHz 23Ω -3dB 286MHz 49Ω -2dB 363MHz 30Ω -3dB 400MHz 49Ω -2dB

[0049] Table 2 Impedance and Attenuation Values ​​of 1.2m Thin Wire

[0050] frequency impedance Attenuation value 30kHz 49Ω 0dB 1MHz 49Ω 0dB 10MHz 33Ω 0dB 37MHz 13Ω -3dB 69MHz 44Ω -1dB 110MHz 17Ω -3dB 147MHz 37Ω -1dB 187MHz 24Ω -3dB 215MHz 44Ω -2dB 248MHz 21Ω -4dB 286MHz 46Ω -2dB 330MHz 30Ω -4dB 363MHz 44Ω -3dB 400MHz 31Ω -4dB

[0051] Table 3 Impedance and Attenuation Values ​​of 6m Thin Wire

[0052]

[0053]

[0054] Table 4 Impedance and Attenuation Values ​​of 0.6m Thick Wire

[0055]

[0056] Table 5 Impedance and Attenuation Values ​​of 1.2m Thick Wire

[0057] frequency impedance Attenuation value 30kHz 50Ω 0dB 1MHz 50Ω 0dB 9MHz 24Ω -2dB 39MHz 4Ω -7dB 75MHz 44Ω -1dB 116MHz 6Ω -7dB 154MHz 36Ω -1dB 196MHz 11Ω -6dB 226MHz 42Ω -2dB 273MHz 13Ω -7dB 300MHz 42Ω -2dB 346MHz 14Ω -7dB 381MHz 37Ω -2dB 400MHz 8Ω -5dB

[0058] Table 6 Impedance and Attenuation Values ​​of 6m Thick Wire

[0059] frequency impedance Attenuation value 30kHz 49Ω 0dB 518kHz 45Ω 0dB 1MHz 35Ω -1dB 7MHz 4Ω -6dB 14MHz 38Ω -1dB 22MHz 5Ω -7dB 27MHz 36Ω -2dB 35MHz 4Ω -7dB 42MHz 32Ω -2dB 49MHz 5Ω -7dB 57MHz 30Ω -2dB 62MHz 5Ω -7dB 72MHz 26Ω -3dB 49MHz 7Ω -7dB 87MHz 21Ω -4dB 237MHz 10Ω -9dB 273MHz 21Ω -7dB 381MHz 14Ω -10dB

[0060] from Figure 2-13 It can be seen that different cables, or cables of the same length but different lengths, will have the following characteristics:

[0061] ① The impedance of shielded cables changes significantly with frequency.

[0062] ② Even with the same shielded cable, different lengths will result in different impedances, and these impedances can vary greatly.

[0063] ③ For the same shielded cable, once the geometric dimensions are fixed, the change in impedance is only a function of frequency (a single variable).

[0064] ④ Once the cable's geometry, structure, measurement frequency, and other factors are determined, the impedance is a constant, and the attenuation is also a constant.

[0065] ⑤ For the same shielded cable, there is no linear relationship between length and attenuation (at certain frequencies, longer cables do not necessarily have higher insertion loss).

[0066] ⑥ The impedance varies greatly with frequency, but is always less than 50Ω.

[0067] ⑦ The impedance of cables below 1MHz remains basically unchanged.

[0068] In other words, when a shielded cable of a fixed length but with non-fixed impedance is placed in a 50Ω measurement system, the required reference measurement value P1 can be accurately obtained by measuring the attenuation. The shielded cable under test in the 50Ω measurement system can be regarded as an RF attenuator that changes with frequency. The change in the value of S21 truly reflects the change in the reference measurement value P1 caused by the change in frequency, impedance, and reflection of the RF signal within the shielded cable under test. The biggest difference from the shielding effect measurement method for fixed impedance shielded cables is that the reference value P1 in the shielding effect measurement of non-fixed impedance shielded cables changes with the type, length, frequency, etc. of the cable, and needs to be measured in real time (this reference value changes greatly, which will bring twice the measurement error).

[0069] Accordingly, in this embodiment of the invention, the shielded cable is placed in a 50Ω measurement system. By measuring the attenuation, the reference value P1 for the shielding effect measurement can be obtained. The measurement frequency of 9kHz-1GHz is divided into two parts: 30MHz-1GHz and 9kHz-30MHz. Two sets of devices are designed to measure the shielding effect separately, and the attenuation value P2 can be obtained.

[0070] 30MHz-1GHz Cable Sheathing Effectiveness Measurement Device and Method:

[0071] 30MHz-1GHz frequency band, using Figure 14 The measurement device was used for the measurement. Based on the original measurement device for the shielding effect of 50Ω coaxial cable, two current probe calibration devices were connected in series. While ensuring that the entire measurement system (except for the shielded cable under test) is a 50Ω system in the measurement frequency band, the reference value P1 of the measurement signal was obtained by using the current probe. By using the power absorption clamp and coupling clamp on the 600mm measurement rail, the attenuation measurement value P2 was obtained by finding the maximum value of the leakage signal. Thus, the shielding effect measurement value SE = P1 - P2 of the shielded cable was obtained.

[0072] Specifically, a signal generator 11 and a terminal load 17 are positioned at opposite ends. From the signal generator 11 to the terminal load 17, a first current probe 13a, an NN through-wall mount 18, a cable segment, and a second current probe 13b are connected sequentially. A movable auxiliary absorption clamp 14 and a power absorption clamp 15 are connected to the cable segment, with the power absorption clamp 15 connected to a receiver 110. A 2m×2m×2mm grounding reflective copper plate 19 is installed at the through-wall mount 18. A 6m long motorized measuring rail 16 is also provided beside the cable segment. Current probe calibration devices 12 are also installed at the first current probe 13a and the second current probe 13b. The cable segment is used to mount the shielded cable 111 under test or to eliminate system measurement errors.

[0073] The measurement method is as follows:

[0074] S1: Replace the shielded cable 111 under test with a 50Ω coaxial cable with known insertion loss, and measure the power values ​​at points A and D at the frequency to be measured to eliminate system measurement errors.

[0075] S2: Connect the shielded cable 111 under test, and measure the power value at point D at the frequency to be measured to obtain P1.

[0076] S3: Simultaneously move the power absorption clamp and the auxiliary absorption clamp to find the maximum value P2 of the measured frequency point.

[0077] S4: The shielding effectiveness value of the shielded cable at this frequency is SE = P1 - P2;

[0078] The shielding effectiveness value obtained by this method for shielded cables is independent of the length of the shielded cable in the 30MHz-1GHz frequency band, and this method is recommended to be performed in a shielded room.

[0079] Test apparatus and methods for cable shielding effectiveness in the 9kHz-30MHz range:

[0080] Measuring the shielding effectiveness of shielded cables in the 9kHz-30MHz frequency band. In principle, a similar method can be applied, but in practice, it's quite difficult. At a wavelength of 10 meters for 30MHz, finding the reference value and maximum leakage value for shielded cables above 30MHz within half the wavelength is not a problem. However, at 30 meters for 10MHz, 100 meters for 3MHz, 300 meters for 1MHz, and so on, up to 30,000 meters for 10kHz. Finding P1 and P2 within half the wavelength becomes very difficult.

[0081] As discussed earlier, the characteristic impedance of shielded cables changes very little in the frequency band below 1MHz, basically 50Ω (when the termination load is 50Ω). In other words, the measurement uncertainty caused by reflection of shielded cables below 1MHz is very small and can be ignored. If you really want to find the maximum leakage value of shielded cables by half the wavelength, you can take half of the 1MHz wavelength. There is no need to find the maximum leakage value in the frequency band below 1MHz.

[0082] Because shielded cables of the same type have different lengths, impedances, and reflections, the measured shielding effectiveness values ​​will also differ. Therefore, we recommend measuring the shielding effectiveness of shielded cables within the frequency range of 9kHz-30MHz, using the actual length of the shielded cable in use as the standard. If the shielded cable manufacturer has the necessary facilities (able to set up a half-wavelength measurement environment), they can also use the same measurement method to measure the shielding effectiveness of the cable.

[0083] It should be noted that this measurement method is the most accurate for measuring the shielding effectiveness of half-wavelength shielded cables (for the shielded cable as a whole). Measuring the shielding effectiveness of shielded cables of the actual length in use is the most consistent with actual usage (for the users of shielded cables).

[0084] Connection for shielding effectiveness measurement of shielded cables in the 9kHz-30MHz frequency range, as follows: Figure 15 As shown, a signal generator 21 and a terminal load 26 are positioned at both ends. From the signal generator 21 to the terminal load 26, an NN through-wall mount 22, a third current probe 25a, a cable segment, and a second current probe 25b are connected sequentially. A 2m × 2m grounding reflective copper plate 23 is installed at the through-wall mount. Current probe calibration devices 24 are also installed at the third current probe 25a and the fourth current probe 25b, and are connected to a grounding copper plate 28. In addition, the device is equipped with a 0.8m high non-metallic test frame 27.

[0085] Perform the measurement according to the following steps:

[0086] S1: Replace the shielded cable under test with a 50Ω coaxial cable with known insertion loss, and measure the power values ​​at points A and E at the frequency to be measured to eliminate system measurement errors.

[0087] S2: Connect the shielded cable under test, and measure the power values ​​at points E and E on the frequency to be tested to obtain P1.

[0088] S3: Move the measuring current probe 25 (the measuring current probe 25 can be either the third current probe 25a or the fourth current probe 25b) to the position, measure at positions B, C, and D, and take the average value to obtain P2 (or find the maximum leakage value P2).

[0089] S4: The shielding effectiveness value of the shielded cable at this frequency point is SE = P1 - P2

[0090] Test Results

[0091] Tables 7 and 8 show the shielding effectiveness values ​​measured for different lengths of the same type of shielded cable.

[0092] Tables 9 and 10 show the shielding effectiveness values ​​measured for different lengths of the same type of shielded cable.

[0093] Table 11 shows the shielding effectiveness values ​​obtained from the measurement of another type of shielded cable.

[0094] Screen effect value SE = E point value - (the maximum value among B point value, C point value, and D point value).

[0095] Table 7 Test results of 0.6m thick wire

[0096] Date: Cable Length: 0.6m Model: Thick Cable Output Amplitude: 110dBuV

[0097] frequency Point A value Point E value Point B value Point C value Point D value Screen performance value 10kHz 110 108 81 81 82 26 50kHz 112 104 71 71 71 33 100kHz 110 106 67 67 67 39 500kHz 107 105 55 55 55 50 1MHz 105.7 103.6 50.6 50.6 50.6 53 5MHz 106.4 104.2 57.4 56.4 56.4 46.8 10MHz 109 103.2 52.3 52.3 52.3 50.9 20MHz 111 100.7 52.8 52.8 52.8 47.9 30MHz 111.4 99 51.3 50.3 51.3 47.7

[0098] Table 8 Test results of 1.2m thick wire

[0099] Date: Cable Length: 1.2m Model: Thick Cable Output Amplitude: 110dBuV

[0100] frequency Point A value Point E value Point B value Point C value Point D value Screen performance value 10kHz 107 107 79 79 79 28 50kHz 109 106 65 66 66 40 100kHz 108 102 62 62 62 40 500kHz 104 100 51 51 51 49 1MHz 100.7 97.6 45.6 40.6 46.6 51 5MHz 95.2 90.4 54.4 51.4 54.4 40.8 10MHz 106.2 91 46.3 46.3 46.3 59.9 20MHz 95.7 92 48.8 53.8 47.8 41.9 30MHz 107.2 96.7 54.3 54.3 54.3 42.4

[0101] Table 9 Test results of 0.6m fine thread

[0102] Date: Cable Length: 0.6m Model: Fine Cable Output Amplitude: 110dBuV

[0103] frequency Point A value Point E value Point B value Point C value Point D value Screen performance value 10kHz 108 108 86 86 86 22 50kHz 110 106 75 75 75 31 100kHz 110 106 72 72 72 34 500kHz 107 105 61 61 61 44 1MHz 105.7 103.6 56.6 56.6 56.6 47 5MHz 106.4 104.2 60.4 60.4 60.4 43.8 10MHz 108 104.2 57.3 58.3 58.3 45.9 20MHz 110 102.7 55.8 57.8 56.8 44.9 30MHz 110.4 101 54.3 53.3 54.3 46.7

[0104] Table 10 Test results of 1.2m thin thread

[0105] Date: Cable Length: 1.2m Model: Fine Cable Output Amplitude: 110dBuV

[0106] frequency Point A value Point E value Point B value Point C value Point D value Screen performance value 10kHz 109 107 90 90 90 19 50kHz 110 106 78 78 78 28 100kHz 110 106 74 74 74 32 500kHz 107 104 61 61 61 43 1MHz 105.7 103.6 55.6 55.6 55.6 48 5MHz 107.4 104.2 57.4 57.4 57.4 46.8 10MHz 109 103.2 55.3 55.3 55.3 47.9 20MHz 111 100.7 55.8 54.8 55.8 44.9 30MHz 110.4 100 53.3 51.3 54.3 45.7

[0107] Table 11 Test Results of 6m Fine Wire

[0108] Date: December 2nd; Cable Length: 6m; Model: Fine Cable; Output Amplitude: 110dBuV

[0109] frequency Point A value Point E value Point C value Screen performance value 30MHz 109.3 101 61 40 50MHz 101.7 100.6 68.1 32.5 100MHz 107.1 98.3 66.4 31.9 120MHz 108.2 97.5 65.1 32.4 150MHz 106 98.2 77.8 20.4 200MHz 105.3 90.3 71.1 19.2 250MHz 105 90 71.5 18.5 300MHz 100 87 64.5 22.5 400MHz 99 86 75.9 10.1

[0110] Figure 16 The test curve for the shielding effectiveness of a 6m thin-wire cable (9kHz-30MHz) is shown. Figure 17Test curve of shielding effectiveness for 6m thin cable (30MHz-300MHz).

[0111] It is important to note that the joints of the shielded cable being tested must be subjected to strict shielding measures. The shielding effectiveness value of this section must be higher than that of the shielded cable being tested.

[0112] The current probe method for measuring the electromagnetic shielding effectiveness of high-voltage shielded cables provided in this invention has been tested and verified over several months, demonstrating accurate test data and good repeatability. It essentially solves the problem of measuring the electromagnetic shielding effectiveness of high-voltage shielded cables in the 9kHz-400MHz frequency range, and the measurement frequency range can be extended to 9kHz-1GHz. This method is also applicable to the shielding effectiveness testing of coaxial cables.

[0113] This embodiment presents a novel method for measuring the electromagnetic shielding effectiveness of high-voltage shielded cables—the current probe method. The method is based on the fundamental principles of electromagnetic shielding effectiveness measurement. The high-voltage shielded cable under test is placed in a specially designed 50Ω measurement system. Using a current probe and its calibration device, the baseline measurement value P1 required for measuring the electromagnetic shielding effectiveness of the high-voltage shielded cable is accurately obtained in the frequency range of 9kHz-1GHz. The attenuation measurement value P2 after shielding is obtained using the current probe in the 9kHz-30MHz frequency band, and the attenuation measurement value P2 after shielding is obtained using a power absorption clamp in the 30MHz-1GHz frequency band, thereby measuring the shielding effectiveness value SE of the high-voltage shielded cable (SE = P1 - P2).

[0114] This method provides quantitative indicators of shielding effectiveness for the further application of high-voltage shielded cables in fields such as power communication, electric vehicles, aerospace, and shipbuilding, and offers useful assistance in solving system-level electromagnetic compatibility problems.

[0115] This article uses specific examples to illustrate the inventive concept in detail. The description of the above embodiments is only for the purpose of helping to understand the core idea of ​​the present invention. It should be noted that any obvious modifications, equivalent substitutions or other improvements made by those skilled in the art without departing from the inventive concept should be included within the protection scope of the present invention.

Claims

1. A method for measuring the electromagnetic shielding effectiveness of high-voltage shielded cables, characterized in that, In the 30MHz-1GHz frequency band, the measurement device should be established as follows: A signal generator and a terminal load are set at both ends. From the signal generator to the terminal load, a first current probe, a wall mount, a cable segment, and a second current probe are connected in sequence. A movable auxiliary absorption clamp and a power absorption clamp are connected to the cable segment. The power absorption clamp is connected to the receiver. A reflective ground plane is set at the wall mount. Perform the measurement according to the following steps: S1: Connect a coaxial cable with known insertion loss to the cable segment to replace the shielded cable under test. Measure the power value at the frequency point under test where the first current probe is located, and measure the power value at the frequency point under test where the second current probe is located to eliminate system measurement errors. S2: Connect the shielded cable under test to the cable segment and measure the power value at the frequency point where the second current probe is located to obtain P1; S3: Simultaneously move the power absorption clamp and the auxiliary absorption clamp to find the maximum value P2 of the measured frequency point; S4: The shielding effectiveness value of the shielded cable at this frequency is SE = P1 - P2; In the 9kHz-30MHz frequency band, the measurement device should be set up as follows: The signal generator and the terminal load are set at both ends. From the signal generator to the terminal load, the wall-penetrating base, the third current probe, the cable segment, and the fourth current probe are connected in sequence. A reflective grounding plate is set at the wall-penetrating base. Perform the measurement according to the following steps: S1: Connect a coaxial cable with known insertion loss to the cable segment to replace the shielded cable under test. Measure the power value at the frequency point under test where the third current probe is located, and measure the power value at the frequency point under test where the fourth current probe is located to eliminate system measurement error. S2: Connect the cable segment to the shielded cable under test, measure the power value at the frequency point under test where the third current probe is located, measure the power value at the frequency point under test where the fourth current probe is located, and obtain P1; S3: Move the position of the third or fourth current probe and measure at three positions on the shielded cable under test. Take the average value to obtain P2 or find the maximum leakage value as P2. If you are looking for the maximum leakage value of the shielded cable at half wavelength below 1MHz, take half of the 1MHz wavelength. S4: The shielding effectiveness value of the shielded cable at this frequency is SE = P1 - P 2- .

2. The method for measuring the electromagnetic shielding effectiveness of a high-voltage shielded cable according to claim 1, characterized in that, A current probe calibration device is also provided at the first current probe and the second current probe.

3. The method for measuring the electromagnetic shielding effectiveness of a high-voltage shielded cable according to claim 1, characterized in that, An electric measuring rail is also installed next to the cable section.

4. The method for measuring the electromagnetic shielding effectiveness of a high-voltage shielded cable according to claim 1, characterized in that, The third and fourth current probes are also equipped with current probe calibration devices.

5. A measuring device for the electromagnetic shielding effectiveness of a high-voltage shielded cable, applicable to the measurement method described in claim 1, characterized in that, In the 30MHz-1GHz frequency band, it includes: a signal generator and a terminal load located at both ends; a first current probe, a wall mount, a cable segment, and a second current probe are connected sequentially from the signal generator to the terminal load; a movable auxiliary absorption clamp and a power absorption clamp are connected to the cable segment; the power absorption clamp is connected to the receiver; and a reflective ground plane is provided at the wall mount. The measuring device is characterized in that, in the 9KHz-30MHz frequency band, it further includes a signal generator and a terminal load at both ends, and a wall-penetrating base, a third current probe, a cable segment, and a fourth current probe are sequentially connected from the signal generator to the terminal load; a reflective grounding plate is provided at the wall-penetrating base; and the measuring device is also equipped with a 0.8m high non-metallic test frame.

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