Method for testing stray magnetic field interference resistance of ultra-large current transformer

Abstract

The invention discloses a method for testing the anti-magnetic field interference performance of an extra-large current transformer (ELCT) matched with a nuclear power and thermal power large generator set. The method comprises the following steps: firstly, carrying out field magnetic field environment simulation to obtain a field flux density condition, then carrying out equivalence on a magnetic field interference influence in an ELCT field state on a built ultra-large current test device, carrying out error and temperature rise test on the ELCT by adopting a single-turn eccentric method in the equivalent state, subtracting a measured value in a middle state from a measured value at the moment, and finally, carrying out error and temperature rise test on the ELCT. And the anti-magnetic field interference performance index of the ELCT is further obtained. According to the method, the defect of a method for testing the magnetic shielding protection performance of the ELCT is overcome, the field magnetic field environment is simulated, the main technical indexes of the ELCT are tested in the state of the field magnetic field environment, the requirements for design, manufacturing and operation maintenance of the ELCT are met, and particularly, the technical support is achieved for safe and reliable operation of a nuclear power unit.

Description

Technical Field

[0001] The present invention relates to a method for testing the anti-magnetic field interference performance of an extra large current transformer (ELCT) supporting large-scale nuclear power and thermal power generating sets, belonging to the technical field of design, manufacture and operation and maintenance of large-scale generator bushing current transformers. The present invention can be used not only for testing the main technical indicators of the ELCT, but also for testing the magnetic shielding protection performance of a large current transformer (LCT). Background Art

[0002] The ELCT installed on the outgoing line side and the neutral point side of a large generator is an important device that reflects the true current value of the generator. Whether the ELCT can accurately and reliably reflect the primary current during operation plays a very important role in the safe and stable operation of the generator set and the power grid. The ELCT used in large units is generally installed in a three-phase or six-phase arrangement. Due to the close distance between the phases of the conductors and the distance between the current-carrying conductor and the ELCT, the magnetic field interference between them is serious under ultra-large currents (25kA~55kA). Therefore, effective magnetic shielding protection measures must be taken to reduce stray magnetic field interference. Today's large nuclear power and thermal power units all use balanced windings as shielding protection measures on ELCT. Therefore, an accurate and reliable test method is urgently needed for the testing and index evaluation of the ELCT shielding performance, so that its various performance indicators can be guaranteed to meet the requirements in design, manufacturing, operation and maintenance.

[0003] With the rapid development of my country's economy and the increasing demand for new energy, especially in nuclear power generation, the rated current of a single unit has reached 45kA. On the other hand, with the compactness of the generator structure, the phase spacing is further reduced. As a result, the conductors on the generator's outgoing line side and the neutral point side of the bus conductor generate a strong interference magnetic field on the ELCT, which may cause the ELCT core magnetic flux to be partially saturated, and the current of the ELCT balance winding to rise, resulting in an increase in its temperature and an increase in error, affecting the safe operation of the generator, such as causing the unit to shut down. The impact of such a huge loss of power generation capacity on the safe and stable operation of the power grid and the social impact it brings is unimaginable.

[0004] The impact of strong magnetic field on ELCT performance is mainly reflected in the impact on the magnetic density of its iron core. Therefore, the industry often uses the eccentricity method to cause the performance changes caused by the local saturation of the iron core to simulate the impact of the interference magnetic field. However, looking at the experimental research on ELCT conducted at home and abroad, the eccentricity method is an indirect measurement method based on the equal ampere-turn principle. This method has the following disadvantages when testing under ultra-large current:

[0005] 1. For the interference of simulated stray magnetic field, whether the primary current reaches the rated value and the layout direction of the primary conductor will affect the intensity and direction of the interference magnetic field. The core of the equal ampere-turn method is to replace the increase of current with the increase of turns to meet the principle of ampere-turn balance. Therefore, if the primary current does not reach the rated value, the interference amount of the stray magnetic field cannot be clearly stated.

[0006] 2. The test results of the equal ampere-turn method are affected by the distribution of the number of turns on the toroidal core, the tightness of the winding, etc., which makes the stability and repeatability of the test results very poor (especially in the TPY type air-gap core structure).

[0007] 3. At the operation site of ELCT, the stray magnetic field interference is very strong, so the state conditions during the test should be as close as possible to the on-site conditions during installation and operation, so as to assess whether the product can meet the actual needs. However, the principle of equal ampere-turns determines that the test state is different from the actual operation state, which brings uncertainty to the accuracy and reliability of the test results under ultra-large current.

[0008] Since the rated current value of ELCT increases with the increase of generator capacity, and it is different from the special characteristics of traditional current transformers, so far, there are no relevant standards, technical requirements and test methods at home and abroad for its magnetic shielding protection performance. In addition, the test work is restricted by the test equipment and capabilities, and the test method for ELCT's anti-magnetic field interference has been missing. Summary of the invention

[0009] In this context, the present invention proposes a test method for equivalent stray magnetic field interference, which is to first simulate and calculate the on-site interference magnetic field to obtain the on-site magnetic density, and then use the single-turn eccentricity method on an ultra-large current test device to equivalently simulate the magnetic flux density obtained by the on-site simulation, and then perform ELCT error and temperature rise tests in a simulated equivalent environment, so as to obtain true, reasonable and effective test results.

[0010] The technical solution adopted by the present invention is a method for testing the anti-stray magnetic field interference performance of an ultra-large current transformer, comprising the following steps:

[0011] Step 1: On-site stray magnetic field environment simulation

[0012] The stray magnetic field of the generator on site is simulated around the installation arrangement of ELCT. The typical state affecting the magnetic flux density is selected, and the distance between the generator outgoing conductor and the neutral point bus conductor and the ELCT is attributed to three states affecting the magnetic flux density. The maximum value of the magnetic flux density is obtained by simulation calculation, which is used as the interference magnetic field environment of the ELCT of the large generator set.

[0013] Step 2: Magnetic field interference environment under equivalent ELCT operation state

[0014] Place the ELCT in an ultra-large current test device, let the primary conductor pass through the center of the inner cavity of the ELCT, and the return conductor of the primary current is divided into eight parallel branches, evenly distributed around the test object. In this centered state, the error test and temperature rise test of the ELCT are carried out according to the IEC standard or GB standard to obtain an error value and temperature rise value that are close to those without stray magnetic field interference;

[0015] Step 3: Single-turn eccentricity method under ultra-high current

[0016] The influence value of the change of the eccentric distance of the single-turn primary conductor on the ELCT magnetic density is used on the ultra-large current test device to be equivalent to the ELCT magnetic density obtained in the on-site simulation, specifically as follows: the maximum magnetic flux density value on-site is obtained from step 1, and then the eccentric distance of the single-turn primary conductor is adjusted in step 3 to reproduce the magnetic flux density value obtained by the simulation in step 1 on the tested ELCT. Furthermore, the ELCT is subjected to error and temperature rise tests according to the IEC standard or the GB standard under the above-mentioned equivalent magnetic density state, thereby obtaining the error value and temperature rise value under the interference of the on-site stray magnetic field;

[0017] Step 4: Assessment of anti-interference capability

[0018] The error value and temperature rise value obtained in step 2 are respectively subtracted from the error value and temperature rise value obtained in step 3. In the tests conducted under the conditions of simulating no stray magnetic field interference and simulating stray magnetic field interference in the field operation state, the above data of the two are subtracted. The difference can be used as the basis for evaluating the ELCT's ability to resist stray magnetic field interference.

[0019] Preferably, in step 3, a stray magnetic field environment equivalent to that of the field is simulated on the ultra-large current device. Therefore, an enameled copper wire is used on the outer surface of the ELCT, starting from the secondary outlet position, and 10 turns are wound at every 45° position in the circumferential direction to form a full-angle induced potential test winding, and then a transformer tester is used for measurement to obtain the omnidirectional induced potential value of the iron core. At this time, an excitation current I1 is passed through the ELCT, and according to the principle of measuring the vector ΔU / I, the vector E2 / I2 is measured to obtain the impedance Z of the induced potential winding, and the impedance values ​​of the points shown are measured, and then the magnetic flux density Bm of the ELCT is calculated by bringing it into the formula of the law of electromagnetic induction.

[0020]

[0021] Where: S is the core cross section (cm 2 ), f is the frequency (Hz), K is the core lamination coefficient, N2 is the number of turns of the induction winding, Bm is the magnetic flux density (Gs), Z=R+jx, and I2 is the secondary current.

[0022] The beneficial effects of the present invention are: 1. It meets the supporting needs of the rapid development of the capacity of large-scale generator sets, especially nuclear power generator sets, with a rated current of up to 45kA. Such a huge current, coupled with the compact structure of the generator, causes the conductor on the generator outlet side and the neutral point bus conductor to generate a strong interference magnetic field on the ELCT, which increases the temperature of the ELCT and increases the error, affecting the safe and reliable operation of the ELCT. Therefore, from the design and manufacture of the ELCT to the operation and maintenance, there is an urgent need for a test method for its magnetic shielding protection capability. 2. It makes up for the lack of relevant test methods for ELCT and promotes the process of forming relevant technical standards. 3. It proposes to use the single-turn eccentricity method to remove the stray interference magnetic field of the equivalent field and directly measure the error and temperature rise of the ELCT, which is closer to the field operation than the traditional equal ampere-turn indirect measurement method, and is accurate and reliable. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 The single turn primary conductor of the test device is located at the physical center of the ELCT.

[0024] Figure 2 The single turn primary conductor of the test device is in a physically eccentric position of the ELCT.

[0025] Figure 3 It is a schematic diagram of the six-phase arrangement and two distance values ​​of the generator outgoing conductors and the neutral point outgoing conductors.

[0026] Figure 4 Schematic diagram of the distance from the neutral point bus conductor to the ELCT and the aluminum cover shielding.

[0027] Figure 5 This is a top view of the eight branches of the primary return conductor of the test device.

[0028] Figure 6 Schematic diagram of the distribution of the full-angle induced potential winding of the iron core.

[0029] Markings in the figure: 1-iron core, 2-primary conductor, 3-neutral point bushing conductor, 4-super large current transformer, 5-neutral point aluminum cover, 6-return conductor branch, 7-neutral point bus conductor, 8-secondary winding, 9-induced potential winding. DETAILED DESCRIPTION

[0030] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Generally, the components of the embodiments of the present invention described and shown in the drawings here can be arranged and designed in various different configurations.

[0031] like Figure 1 to Figure 2As shown, the single-turn eccentricity method adopted in the present invention belongs to a direct measurement method. It is on a large current test device, a large current conductor is passed through the inner cavity of the ELCT, and when its physical center is eccentric, the influence of the bias magnetic field conditions on the ELCT is simulated and tested. At this time, the magnetic flux of the core 1 will change, and even local saturation of the magnetic density will occur, causing the error and temperature rise value of the ELCT to exceed the standard.

[0032] The ELCT is physically eccentric on the large current test device (the ELCT is eccentric to the single-turn primary conductor 2 of the test device) to simulate and equate the external magnetic field interference that the ELCT is subjected to during operation. Based on this, an ELCT that meets various technical performance requirements is designed and manufactured. Therefore, a “test method for the anti-stray magnetic field interference performance of ultra-large current transformers” is proposed to solve the existing technical problems.

[0033] Taking a 1300MW nuclear power unit with a rated current of 45kA as an example, the stray interference magnetic field of the ELCT installed on the generator outlet and neutral point outlet bushings during operation is analyzed. The traditional and conventional method is to consider the stray magnetic flux interference when the three-phase conductors of the generator are arranged. At this time, the main focus is on the phase spacing between the three-phase conductors.

[0034] In the environmental assessment of on-site stray magnetic fields, the main thing is to find the source of stray magnetic field interference and analyze its value. The key to measuring the size of the interference is the distance, that is, the distance between the interference source and the ELCT. According to the inverse square law, when the current is constant, the magnetic field strength decays linearly with the square of the distance. That is:

[0035]

[0036] Where: r-distance; μ0-vacuum magnetic permeability

[0037] That is, the magnetic flux density is inversely proportional to the square of the distance.

[0038] In fact, the commonly used method for analyzing the operating magnetic field of ELCT is too rough and too simple, resulting in low accuracy in the assessment of the impact of stray magnetic fields on site, which affects the design and manufacture of ELCT shielding performance and the assessment of its anti-magnetic field interference performance.

[0039] The present invention proposes a "test method for the anti-stray magnetic field interference performance of ultra-large current transformer", the steps are as follows:

[0040] Step 1, see Figure 3 and Figure 4 As shown in the figure, this is the difference between the current traditional method and the simulation calculation method used in this method to evaluate the on-site magnetic field interference. First, the on-site stray magnetic field of the generator is analyzed based on the installation layout of the ELCT. According to the typical states and distances that affect the magnetic flux density, three states of distance affecting the magnetic flux density are summarized:

[0041] 1. Two distance values ​​between the six-phase arrangement of the generator outgoing conductor and the neutral point outgoing conductor and the ELCT.

[0042] 2. Distance from neutral point bus conductor 7 to ELCT and aluminum cover shielding.

[0043] 3. Phase distance between conductors with very large current.

[0044] The maximum value of magnetic flux density is obtained through simulation calculation and used as the interference magnetic field environment of ELCT of large generator sets.

[0045] Step 2, see attached Figure 3 , place the ELCT in the ultra-large current test device, let the primary current conductor pass through the center of the inner cavity of the ELCT, and the return conductor of the primary current is divided into eight parallel branches evenly distributed around the test object, and then carry out the error test and temperature rise test of the ELCT according to the IEC standard or GB standard in this centered state, and obtain an error value and temperature rise value that are approximately free of stray magnetic field interference.

[0046] The first condition for implementing this method is to establish an ultra-large current test device, let the primary current conductor pass through the center of the inner cavity of the ELCT, that is, the primary main circuit conductor is placed in the center of the ELCT, and the magnetic field generated acts evenly on the iron core 1. The primary return conductor of the device is divided into eight parallel branches, and the current of each branch only accounts for 1 / 8 of the rated current of the primary main circuit. The distance between each branch and the ELCT test product is about 3 meters and is evenly distributed along the circumference of the device. See attached Figure 5 Compared with the single-turn conductor of the primary main circuit, which is eccentrically arranged in the ELCT inner cavity under the rated current, the influence on the magnetic density of the core 1 at this time is relatively negligible, thereby simplifying the difficulty of analyzing the simulated magnetic field of the device. Therefore, this method is based on the platform of the ultra-large current test device, and uses the eccentricity of the primary main circuit conductor in the ELCT inner cavity to equivalent the size of the interference magnetic field on site. At this time, the change in the eccentric distance of the single-turn conductor brings about the change in the magnetic field intensity, which in turn affects the magnetic properties of the core 1, and finally reflects in the error and temperature rise index of the ELCT.

[0047] Step 3, see attached Figure 6 , simulate the interference magnetic field state of step 1 on the test device through the equivalent of magnetic density, and measure the magnetic density of the core 1 by full-angle induced potential measurement method. Specifically, first, use enameled copper wire on the outer surface of the ELCT test piece starting from the secondary outlet position, and wind 10 turns every 45° along the circumferential direction to form a full-range induced potential test winding, and then use a transformer tester to measure, pass the excitation current I1 into the ELCT, and measure the vector E2 / I2 according to the principle of measuring vector ΔU / I. The impedance Z of the induced potential winding 9 can be obtained, according to Figure 6 Measure the impedance value of each point shown, then substitute it into the formula of electromagnetic induction law to calculate the magnetic flux density Bm of ELCT.

[0048]

[0049] Where: S is the core cross section (cm 2 ), f is the frequency (Hz), K is the core lamination coefficient, N2 is the number of turns of the induction winding, Bm is the magnetic flux density (Gs), Z=R+jx, and I2 is the secondary current.

[0050] Step 4, using the influence value of the change of the eccentric distance of the single-turn primary conductor 2 on the ELCT magnetic density on the ultra-large current test device to be equivalent to the ELCT magnetic density obtained in the field simulation. Specifically as follows: the field magnetic density value is obtained from step 1, and then step 3 is performed to adjust the eccentric distance of the single-turn primary conductor 2, and the magnetic density value obtained by the simulation of step 1 is approximately reproduced on the ELCT, and finally the error and temperature rise test is performed according to the IEC standard or GB standard under the state of the above-mentioned equivalent magnetic density value, so as to obtain the error value and temperature rise value under the interference of an equivalent field stray magnetic field.

[0051] Furthermore, the error value and temperature rise value obtained in step 2 are respectively subtracted from the error value and temperature rise value obtained in step 4, thereby making a technical assessment of the ELCT's anti-stray magnetic field interference performance.

[0052] In summary, the present invention can be used to perform equivalent tests on the anti-interference performance of the generator ELCT to stray magnetic fields and the magnetic shielding protection performance of the ELCT in large-scale nuclear power and thermal power projects, so that the design and manufacture of ELCTs with excellent performance have a reliable guarantee. So far, the traditional current transformer test method cannot test the shielding protection performance of ELCT under the interference of stray magnetic fields on site. At the same time, there are no relevant standards and methods for testing the shielding protection performance of ELCT at home and abroad. Therefore, the present invention provides technical support for the design and manufacture of ELCT, and also provides a strong guarantee for the safe and stable operation of ELCT of generator sets in large-scale nuclear power and thermal power projects.

[0053] The above shows and describes the basic principles and main features of the present invention and the advantages of the present invention. It should be understood by those skilled in the art that the present invention is not limited to the above embodiments. The above embodiments and descriptions are only for explaining the principles of the present invention. Without departing from the spirit and scope of the present invention, the present invention may have various changes and improvements, which fall within the scope of the present invention to be protected. The scope of protection of the present invention is defined by the attached claims and their equivalents.

Claims

1. A test method for the anti-stray magnetic field interference performance of ultra-large current transformers, characterized in that: The following steps are involved: Step 1: On-site stray magnetic field environment simulation The stray magnetic field of the generator on site is simulated around the installation arrangement of ELCT. The typical state affecting the magnetic flux density is selected, and the distance between the generator outgoing conductor and the neutral point bus conductor and the ELCT is attributed to three states affecting the magnetic flux density. The maximum value of the magnetic flux density is obtained by simulation calculation, which is used as the interference magnetic field environment of the ELCT of the large generator set. Step 2: Magnetic field interference environment under equivalent ELCT operation state Place the ELCT in an ultra-large current test device, let the primary conductor pass through the center of the inner cavity of the ELCT, and the return conductor of the primary current is divided into eight parallel branches, evenly distributed around the test object. In this centered state, the error test and temperature rise test of the ELCT are carried out according to the IEC standard or GB standard to obtain an error value and temperature rise value that are close to those without stray magnetic field interference; Step 3: Single-turn eccentricity method under ultra-high current The influence value of the change of the eccentric distance of the single-turn primary conductor on the ELCT magnetic density is used on the ultra-large current test device to be equivalent to the ELCT magnetic density obtained in the on-site simulation, specifically as follows: the maximum magnetic flux density value on-site is obtained from step 1, and then the eccentric distance of the single-turn primary conductor is adjusted in step 3 to reproduce the magnetic flux density value obtained by the simulation in step 1 on the tested ELCT. Furthermore, the ELCT is subjected to error and temperature rise tests according to the IEC standard or the GB standard under the above-mentioned equivalent magnetic density state, thereby obtaining the error value and temperature rise value under the interference of the on-site stray magnetic field; Step 4: Assessment of anti-interference capability The error value and temperature rise value obtained in step 2 are respectively subtracted from the error value and temperature rise value obtained in step 3. In the tests conducted under the conditions of simulating no stray magnetic field interference and simulating stray magnetic field interference in the field operation state, the above data of the two are subtracted. The difference can be used as the basis for evaluating the ELCT's ability to resist stray magnetic field interference.

2. The method for testing the anti-stray magnetic field interference performance of the ultra-large current transformer according to claim 1 is characterized in that: In step 3, a stray magnetic field environment equivalent to that of the field is simulated on the ultra-high current device. Therefore, an enameled copper wire is used on the outer surface of the ELCT. Starting from the secondary outlet position, 10 turns are wound at every 45° position in the circumferential direction to form a full-angle induced potential test winding. Then, a transformer tester is used for measurement to obtain the omnidirectional induced potential value of the iron core. At this time, an excitation current I1 is passed through the ELCT. According to the principle of measuring the vector ΔU / I, the vector E2 / I2 is measured to obtain the impedance Z of the induced potential winding, measure the impedance values ​​of the points shown, and then bring it into the formula of the law of electromagnetic induction to calculate the magnetic flux density Bm of the ELCT. Where: S is the core cross section (cm 2 ), f is the frequency (Hz), K is the core lamination coefficient, N2 is the number of turns of the induction winding, Bm is the magnetic flux density (Gs), Z=R+jx, and I2 is the secondary current.

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