CN107656226A - HFCT electrical parameter test devices and method of testing based on transmission coefficient - Google Patents

Abstract

The invention discloses a transmission coefficient-based HFCT electrical parameter test device and a test method. The test device includes a network analyzer and a tester; Connected input interface and output interface, the input interface is connected to the output end of the network analyzer through the first coaxial cable, the output interface is connected with a matching resistor, the HFCT to be tested is placed in a metal shell, and the metal wire passes through its center, And connect to the input end of the network analyzer through the second coaxial cable. The present invention just can obtain the transmission coefficient of HFCT through one test, obtains transfer function and transmission impedance according to its transfer function and the relation of transmission impedance and transmission coefficient again, further obtains its electric parameter (comprising bandwidth, lower limit frequency, upper limit frequency, sensitivity etc. ), so as to realize the rapid and stable measurement of HFCT electrical parameters, and provide data support for HFCT performance evaluation.

Description

HFCT electrical parameter testing device and testing method based on transmission coefficient

technical field

The invention belongs to the technical field of power system detection, and relates to a transmission coefficient-based HFCT electrical parameter testing device and a testing method.

Background technique

Discharge, electromagnetic force, thermal stress, hot and humid environment, harmful active gas, oil, dust, etc. during the operation of power equipment will cause the gradual deterioration of the performance of insulating materials, so that some insulation weak links in power equipment (power transmission lines) Partial discharge occurs. With the development of power system and the increase of voltage level, partial discharge has become one of the main reasons for the insulation degradation of power equipment.

At present, the partial discharge detection method is mainly used to detect and evaluate the insulation status of high-voltage AC equipment in power systems. The partial discharge detection method is based on various phenomena generated by partial discharge, and characterizes partial discharge by describing the physical quantities of various phenomena; according to different detection principles, partial discharge detection methods can be divided into two categories: (1) current-based The principle of electromagnetic induction, including electromagnetic coupling method, directional coupling method, ultra-high frequency inductive coupling method, etc.; (2) The principle of capacitive coupling based on voltage, including capacitive coupling method, differential method, transient ground voltage method, etc. Among them, the electromagnetic coupling method mainly uses a high-frequency current sensor (High Frequency Current Transformer) to couple high-frequency current pulses on the ground line to realize the detection of partial discharge signals of power equipment. Before using the electromagnetic coupling method to detect partial discharge signals of power equipment, it is necessary to test the electrical performance parameters of HFCT (including bandwidth, upper and lower limit frequencies, sensitivity, etc.) to select an HFCT suitable for partial discharge detection of power equipment.

At present, there are two main ways to test the electrical performance parameters of HFCT at home and abroad: (1) Using the test equipment composed of signal source, three high-frequency capacitors and an oscilloscope, using the signal source to generate sine waves of various frequencies, through two identical The high-frequency capacitor is used to divide the voltage, and then the same high-frequency capacitor is used to pass through the geometric center of the sensor and connected in parallel with one of the voltage-dividing capacitors. The HFCT output port signal is measured with an oscilloscope, and finally the amplitude-frequency characteristic curve of the HFCT is obtained. See [Shanghai Jiaotong University Sun Jing's master's thesis "Research on Partial Discharge Detection Technology for High-Voltage Power Cables", "Design of Partial Discharge High-Performance Current Sensor" published by Dai Xuyi and others in the "Journal of Shanghai Electric Power Institute" in 2014];( 2) The test equipment composed of signal source and non-inductive resistor is used. The signal source is externally connected to a non-inductive resistor and passes through the HFCT. The signal source is used to generate sine waves of various frequencies, and the signals at both ends of the non-inductive resistor and the output of the HFCT are measured. Make the amplitude-frequency characteristic curve or transmission impedance of HFCT [Research on Partial Discharge Detection System under Oscillating Impulse Voltage published by Zhao Xuefeng et al. in "Instrument and Apparatus" in 2010]. Both of the above two methods need to measure multiple frequency points one by one, use an arbitrary waveform generator to generate a signal, and pass the obtained current signal line through the test circuit as vertically as possible through the geometric center of the HFCT, and use an oscilloscope to measure the signal. Since the arbitrary waveform generator can only generate one waveform at each frequency point, it is necessary to adjust each frequency point to measure one by one, which takes a long time; the test effect is better at low frequencies, but at higher frequencies, due to The inductive reactance of various connecting wires at high frequencies and the different positions of the test wires passing through the HFCT during each test will cause different magnitudes of the induced electromotive force, which will have a greater impact on the measurement results, resulting in high-frequency test results. large error.

From the above analysis, it can be seen that the current HFCT electrical performance test methods all have test limitations, in particular, there is a lack of a solution to effectively reduce the HFCT electrical performance test error at high frequencies. Therefore, it is of great significance to develop a HFCT electrical performance test method with simple operation and high measurement accuracy for the development of partial discharge detection technology.

Contents of the invention

Aiming at the problems of time-consuming and errors in the current HFCT electrical parameter testing method, the present invention provides a transmission coefficient-based HFCT electrical parameter testing device and testing method, which can not only shorten the testing time, improve the measurement efficiency, but also reduce the Small test error, improve measurement accuracy.

The invention provides a transmission coefficient-based HFCT electrical parameter testing device, including a network analyzer and a tester; the tester consists of a metal shell, and input interfaces respectively arranged at both ends of the metal shell and connected by metal wires and the output interface, the input interface is connected to the output end of the network analyzer through the first coaxial cable, the output interface is connected with a matching resistor, the HFCT to be tested is placed in a metal shell, and the metal wire connecting the input interface and the output interface is connected from the center of the HFCT Through it, HFCT is connected to the input end of the network analyzer through the second coaxial cable through its BNC connector (Bayonet Nut Connector).

In the above-mentioned HFCT electrical parameter testing device based on the transmission coefficient, the inside of the metal housing forms a space for accommodating the HFCT. In order to avoid the influence of the external electromagnetic field on the HFCT test, at least the upper side and the left and right sides of the metal housing are made of metal; HFCT, and ensure that the metal wire passes through the center of the HFCT, and the bottom of the HFCT can be fixed in the metal shell through an insulating support.

The above-mentioned HFCT electrical parameter testing device based on the transmission coefficient adopts a network analyzer to test the HFCT transmission coefficient, utilizes the calibration function of the network analyzer, and uses the test line for the network analyzer (model: E5061B) and the tester before the test. Connect, test the transmission coefficient of the test device itself, and perform self-calibration to eliminate the influence of the test device's own transfer characteristics on the HFCT transfer characteristic test, thereby reducing test errors; when the test device is performing self-calibration, the network analyzer , tester, etc. The implementation of the specific circuit loop is as follows: the input interface of the tester is connected to the output end of the network analyzer through the first coaxial cable, and the output interface is connected to the input end of the network analyzer through the second coaxial cable .

The above-mentioned HFCT electrical parameter testing device based on the transmission coefficient is connected with a matching resistor at the output interface of the tester, so that the testing device forms a circuit loop, and the current generated is the same as the current generated by the circuit loop formed when the testing device is self-calibrating.

The present invention further provides a kind of HFCT electric parameter test method based on transmission coefficient, adopts above-mentioned HFCT electric parameter test device based on transmission coefficient, and its test procedure is as follows:

(1) Carry out self-calibration to the test device, to eliminate the influence of the transmission coefficient of the test device itself on the measurement results;

(2) Test the HFCT to obtain its transmission coefficient S ₁₂ :

Connect the input interface of the tester to the output end of the network analyzer through the first coaxial cable, the output interface is connected with a matching resistor, the HFCT to be tested is placed in a metal shell, and the metal wire connecting the input interface and the output interface is connected from the center of the HFCT Through, the HFCT is connected to the input end of the network analyzer through the second coaxial cable through its BNC connector; the HFCT is tested by the network analyzer to obtain the transmission coefficient S ₁₂ of the HFCT;

(3) Calculate the transfer function of HFCT according to the following formula (i):

|H(ω)|＝S ₁₂ +20log ₁₀ (R _t ) (i)

Among them, |H(ω)| is the transfer function of HFCT, S ₁₂ is the transmission coefficient, and R _t is the resistance value of the matching resistor;

The corresponding frequency of |H(ω)| obtained after taking the |H(ω)| transfer function amplitude and setting the reference value is the lower limit frequency and the upper limit frequency, and the difference between the upper limit frequency and the lower limit frequency is the bandwidth;

(4) Obtain the transmission impedance of HFCT according to the following formula (ii), and use it as the sensitivity of HFCT:

where Z(f) is the transfer impedance.

The above-mentioned HFCT electrical parameter test method based on the transmission coefficient, the specific circuit circuit implementation method of self-calibration of the test device is: the input interface of the tester is connected to the output end of the network analyzer through the first coaxial cable, and the output interface is connected through the first coaxial cable. The two coaxial cables are connected to the input end of the network analyzer, and then the tester, the first coaxial cable and the second coaxial cable are tested for transmission coefficient, and self-calibration is performed to eliminate the transmission coefficient of the test device itself.

The above-mentioned HFCT electrical parameter test method based on transmission coefficient, from |H(ω)|=S ₁₂ +20log ₁₀ (R _t ), it can be seen that the transfer function |H(ω)| of HFCT is linearly related to its transmission coefficient S ₁₂ , when the transmission coefficient of HFCT is obtained, the transfer function of HFCT can be obtained, and then the bandwidth and upper and lower limit frequencies of HFCT can be further obtained according to the obtained transfer function |H(ω)|; further, when the transmission coefficient of HFCT is obtained , available by The transmission impedance Z(f) is obtained. Since the transmission impedance and sensitivity are equivalent, the obtained transmission impedance Z(f) can be used as the sensitivity parameter of HFCT, and its peak value is the maximum sensitivity.

In the traditional HFCT electrical parameter test method, when testing the amplitude-frequency characteristics of HFCT, it is necessary to measure multiple frequency points one by one. Each test requires a long test time, and because the test device itself will generate interference at high frequencies, Certain test errors will be generated, which will have a negative impact on the test results of the HFCT amplitude-frequency characteristics.

Compared with the prior art, the HFCT electrical parameter testing device and testing method based on transmission coefficient provided by the present invention have the following beneficial effects:

1, HFCT electrical parameter testing device of the present invention utilizes network analyzer to carry out self-calibration to testing device, eliminates the influence of testing device self transmission coefficient on testing HFCT transmission coefficient;

2. The HFCT electrical parameter testing device of the present invention seals the HFCT in a metal casing, and the metal casing has a shielding effect, thereby avoiding the interference of electromagnetic fields in some spaces;

3. The internal height of the metal shell of the HFCT electrical parameter testing device of the present invention matches the height of the HFCT, so that the HFCT is fixed in the metal shell to prevent the movement of the HFCT, thereby avoiding measurement errors caused by the movement of the HFCT;

4, HFCT electrical parameter testing method of the present invention, just can obtain the transmission coefficient of HFCT by a test, then obtain the transfer function and transmission impedance of HFCT according to the relation of HFCT transfer function and transmission impedance and HFCT transmission coefficient, further obtain the electrical parameter of HFCT (including bandwidth, lower limit frequency, upper limit frequency, sensitivity, etc.), so as to realize fast and stable measurement of HFCT electrical parameters, greatly reducing the workload.

Description of drawings

FIG. 1 is a schematic diagram of the self-calibration of the transmission coefficient-based HFCT electrical parameter testing device of the present invention.

Fig. 2 is a schematic diagram during testing of the transmission coefficient-based HFCT electrical parameter testing device of the present invention.

Fig. 3 is an equivalent circuit diagram during testing of the HFCT electrical parameter testing device based on the transmission coefficient of the present invention.

Fig. 4 is a curve of transmission coefficient versus frequency obtained before calibration of the test device in Example 1 of the present invention.

FIG. 5 is a curve of transmission coefficient versus frequency obtained after calibration of the test device in Example 1 of the present invention.

FIG. 6 is a curve of the HFCT transmission coefficient varying with frequency obtained through testing in Example 2 of the present invention.

FIG. 7 is a curve of HFCT transmission impedance varying with frequency obtained through testing in Example 2 of the present invention.

FIG. 8 is a curve of the HFCT transmission coefficient varying with frequency obtained through testing in Example 3 of the present invention.

FIG. 9 is a curve of HFCT transmission impedance varying with frequency obtained through testing in Example 3 of the present invention.

1. Network analyzer, 2. Tester, 21. Metal shell, 22. Input interface, 23. Output interface, 3. Matching resistance, 4. First coaxial cable, 5. Metal wire, 6. Second coaxial cable Shaft cable, 7, HFCT.

Detailed ways

Embodiments of the present invention will be given below in conjunction with the accompanying drawings, and the technical solutions of the present invention will be further clearly and completely described through the embodiments. Apparently, the embodiments described are only some of the embodiments of the present invention, but not all of them. Based on the content of the present invention, all other embodiments obtained by persons of ordinary skill in the art without making creative efforts fall within the protection scope of the present invention.

Example 1

The HFCT electrical parameter testing device based on the transmission coefficient provided in this embodiment is mainly composed of a network analyzer 1 , a tester 2 , a matching resistor 3 , a first coaxial cable 4 , a metal wire 5 , and a second coaxial cable 6 . The network analyzer model is Agilent E5061B. The composition of the tester 2 includes a rectangular metal shell 21, an input interface 22 and an output interface 23 respectively arranged at both ends of the metal shell and connected by metal wires 5; when facing the tester, the rectangular metal shell 21 includes upper and lower , left and right four sides, all four sides are made of aluminum, the metal shell is 319mm long, 220mm wide and 166mm high. The interior of the metal shell 21 constitutes a space for accommodating the HFCT, and the interior height of the metal shell 21 is greater than the outer diameter of the HFCT. The above-mentioned HFCT electrical parameter testing device circuit connection mode based on the transmission coefficient is divided into two states: the test device self-calibration state (as shown in Figure 1) and the test state (as shown in Figure 2):

(1) Self-calibration state, the input interface 22 of tester is connected with the output end of network analyzer 1 through the first coaxial cable 4, and output interface 23 is connected with the input end of network analyzer 1 through the second coaxial cable 6;

(2) Test state, the input interface 22 of tester is connected with the output terminal of network analyzer 1 through the first coaxial cable 4, and output interface 23 is connected with matching resistor 3, and the HFCT to be tested passes through insulating support (such as foam) Placed in a metal shell, the metal wire 5 connecting the input interface and the output interface passes through the center of the HFCT, and the HFCT is connected to the input end of the network analyzer 1 through the second coaxial cable 6 through its BNC connector.

Example 2

This embodiment adopts the HFCT electrical parameter testing device based on transmission coefficient provided in embodiment 1 to test, and the test steps are as follows:

(1) Carry out self-calibration to the test device to eliminate the influence of the tester's own transmission coefficient on the test results:

The input interface 22 of the tester is connected with the output end of the network analyzer 1 through the first coaxial cable 4, and the output interface 23 is connected with the input end of the network analyzer 1 through the second coaxial cable 6, and then the tester 2 and The first coaxial cable 4 and the second coaxial cable 6 carry out the transmission coefficient test, and its test result is as shown in Figure 4, shows that the test device itself has a transmission coefficient, if the test device itself is not calibrated, the transmission coefficient of the HFCT will be Tests have an impact. Operate the network analyzer according to the test results, so that the transmission coefficient of the test device itself is basically 0 (as shown in Figure 5), complete the self-calibration of the test device, and eliminate the influence of the transmission coefficient of the test device itself on the HFCT transmission coefficient.

(2) Test the HFCT to obtain its transmission coefficient S ₁₂ :

The input interface 22 of tester is connected with the output terminal of network analyzer 1 through the first coaxial cable 4, and output interface 23 is connected with matching resistance 3 (R _t =50Ω in the present embodiment), and the HFCT to be tested passes through insulating support Parts (such as foam) are placed in the metal shell, and the metal wire 5 connecting the input interface and the output interface passes through the center of the HFCT, and the HFCT is connected to the input end of the network analyzer 1 through the second coaxial cable 6 through its BNC connector; The network analyzer 1 tests the HFCT to obtain the transmission coefficient S ₁₂ of the HFCT; the variation curve of the transmission coefficient S ₁₂ with frequency is shown in FIG. 6 .

(3) Obtain the transfer function of HFCT, and further obtain the lower limit frequency, upper limit frequency and bandwidth of HFCT:

The above-mentioned equivalent circuit diagram based on transmission coefficient HFCT electrical parameter testing device when carrying out transmission coefficient test to HFCT as shown in Figure 3, above-mentioned HFCT transmission coefficient S ₁₂ and the input signal u ₁ (ω) and network of the input end of network analyzer The output signal u ₂ (ω) at the output of the analyzer satisfies the following relation:

Due to the transfer function of HFCT Substituting the above formulas (iii) and (iv) into formula (v), we get |H(ω)|=S ₁₂ +20log ₁₀ (R _t ) (i), where |H(ω)| is the HFCT Transfer function, S ₁₂ is the transmission coefficient, R _t is the resistance value of the matching resistor.

Take |H(ω)| the transfer function amplitude drops to set the reference value and the corresponding frequency of |H(ω)| is the lower limit frequency and the upper limit frequency, and the difference between the upper limit frequency and the lower limit frequency is the bandwidth; in this embodiment, the reference value is set The value is -6dB; because the transfer function |H(ω)| is linearly correlated with the transmission coefficient _S12 in the present embodiment, and the correlation coefficient is 1, therefore, according to the variation curve of the transmission coefficient _S12 with frequency, according to the transmission coefficient After the amplitude of S ₁₂ is reduced and the reference value is set, the corresponding frequency of S ₁₂ is the lower limit frequency and the upper limit frequency. The lower limit frequency of the HFCT obtained in this embodiment is 0.1 MHz, the upper limit frequency is 100 MHz, and the bandwidth is 99.9 MHz.

(4) Obtain the sensitivity of HFCT:

Due to the transfer impedance of the HFCT Substituting the above formulas (iii) and (iv) into formula (vi), we get where Z(f) is the transfer impedance.

Substituting the transmission coefficient _S12 obtained in step (2) into formula (ii) to obtain the transmission impedance of HFCT, the curve of the obtained transmission impedance Z(f) with frequency is shown in Figure 7, because the transmission impedance and sensitivity are equivalent , so the transmission impedance is regarded as the sensitivity of HFCT, and its peak value is the maximum sensitivity. It can be seen from Figure 7 that the maximum sensitivity is 4.75V/A.

The HFCT model tested in this embodiment is HFCT5861. According to its test report, the upper and lower limit frequencies converted to -6dB in this embodiment are 0.1-99MHz, and the maximum sensitivity is 5.01V/A.

It can be seen that the electrical parameters of the HFCT measured in this embodiment are basically consistent with those given by the manufacturer, and the HFCT electrical parameter testing method based on the transmission coefficient provided in this embodiment can quickly and stably obtain the electrical parameters of the HFCT, which is an important factor for the performance of the HFCT. Evaluation provides data support.

Example 3

The HFCT model tested in this embodiment is HFCT21970.

The HFCT electrical parameter test method adopted in this embodiment is the same as that in Embodiment 2. The transmission coefficient S ₁₂ obtained through the test varies with frequency as shown in Figure 8, and the transmission coefficient S ₁₂ is substituted into |H(ω)|=S ₁₂ + 20log ₁₀ (R _t ), the bandwidth at -6dB (set reference value) of HFCT is 18.43MHz, the upper limit frequency is 18.53MHz, and the lower limit frequency is 0.1MHz. Substitute the obtained transmission coefficient S ₁₂ into The transmission impedance of the HFCT is obtained, and the curve of the obtained transmission impedance Z(f) as a function of frequency is shown in Figure 9. It can be seen from the figure that its maximum sensitivity is 4.09V/A.

Claims (5)

1. a kind of HFCT electrical parameter test devices based on transmission coefficient, it is characterised in that including Network Analyzer (1) and survey Try instrument (2)；The composition of the tester includes metal shell (21), is separately positioned on metal shell both ends and passes through plain conductor (5) input interface (22) and output interface (23) of connection, input interface is through the first coaxial cable (4) and Network Analyzer (1) Output end connection, output interface is connected with build-out resistor (3), and HFCT to be tested is placed in metal shell, and connection input connects Mouthful passed through with the plain conductor (5) of output interface from HFCT centers, HFCT by its BNC connector through the second coaxial cable (6) and The input connection of Network Analyzer.

2. the HFCT electrical parameter test devices according to claim 1 based on transmission coefficient, it is characterised in that the gold It is metal material to belong to housing at least top and the left and right sides.

3. the HFCT electrical parameter test devices according to claim 1 or 2 based on transmission coefficient, it is characterised in that described HFCT is placed in metal shell by dielectric support.

4. utilize the method for the test device test HFCT electric parameters described in claim 1 or 2 or 3, it is characterised in that including Following testing procedure：

(1) self calibration is carried out to test device, to eliminate influence of the transmission coefficient of test device itself to measurement result；

(2) HFCT is tested, obtains its transmission coefficient S₁₂：

The input interface (22) of tester is connected through the first coaxial cable (4) with the output end of Network Analyzer (1), output connects Mouth (23) matching connection resistance (3), HFCT to be tested are placed in metal shell, connect the metal of input interface and output interface Wire (5) passes through from HFCT centers, and HFCT passes through input of its BNC connector through the second coaxial cable (6) Yu Network Analyzer Connection, is tested HFCT by Network Analyzer (1), obtains HFCT transmission coefficient S₁₂；

(3) HFCT transmission function is calculated according to below equation (i)：

| H (ω) |=S₁₂+20log₁₀(R_t) (i)

Wherein, | H (ω) | for HFCT transmission function, S₁₂For transmission coefficient, R_tFor build-out resistor resistance；

Take | H (ω) | transmission function amplitude, which declines, to be set obtained by after reference value | H (ω) | respective frequencies is lower frequency limits and the upper limit The difference of frequency, upper limiting frequency and lower frequency limit is bandwidth；

(4) HFCT transfer impedance is obtained according to below equation (ii), and as HFCT sensitivity：

<mrow> <mi>Z</mi> <mrow> <mo>(</mo> <mi>f</mi> <mo>)</mo> </mrow> <mo>=</mo> <msub> <mi>R</mi> <mi>t</mi> </msub> <mo>&amp;times;</mo> <msup> <mn>10</mn> <mrow> <msub> <mi>S</mi> <mn>12</mn> </msub> <mo>/</mo> <mn>20</mn> </mrow> </msup> <mo>-</mo> <mo>-</mo> <mo>-</mo> <mrow> <mo>(</mo> <mi>i</mi> <mi>i</mi> <mo>)</mo> </mrow> </mrow>

Wherein, Z (f) is transfer impedance.

5. the method for test HFCT electric parameters according to claim 4, it is characterised in that self-correcting is carried out to test device Accurate physical circuit loop implementation is：By the input interface (22) of tester through the first coaxial cable (4) and network analysis The output end connection of instrument (1), output interface (23) are connected through the second coaxial cable (6) with the input of Network Analyzer (1), so The transmission coefficient of test device itself is tested afterwards, and carries out self calibration, to eliminate the transmission characteristic of test device itself.