Method and system for measuring low-voltage resistance of transformer

Abstract

The invention provides a method and system for measuring low-voltage resistance of a transformer, and the method comprises the steps: 1, judging the structure of the transformer, and selecting two symmetrical low-voltage windings on the same main transformer iron core of the transformer as test points if the structure of the transformer belongs to a preset structure type; step 2, injecting same-direction direct current into the two test points through two independent current channels at the same time, and collecting voltage data and current data of the two low-voltage windings in real time; and 3, calculating the direct-current resistance values of the two low-voltage windings according to the voltage data and the current data, and calculating the direct-current resistance value of the transformer based on the direct-current resistance values.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of transformers, in particular to a transformer low-voltage resistance measurement method and system. BACKGROUND

[0002] With the rapid development of economy, the structure of transformers is increasingly complex, and many transformer windings have large inductance and small resistance. In particular, the larger the capacity, the greater the inductance of the winding, and the smaller the resistance, so the time constant is large.

[0003] When measuring the DC resistance of the winding, after the DC power supply is turned on, the charging current needs to go through a transient process to reach a stable value. The duration of the transient process is generally several minutes for small transformers, and can be up to ten minutes or more for high-voltage large transformers. Even for a 500kV three-phase transformer, it takes 6 hours to measure. Therefore, it is of great significance to shorten the transient process time and speed up the measurement. Especially when doing transformer temperature rise test, the average temperature rise of the winding should be calculated by measuring the electric resistance, which should be measured within 1 minute after the load is cut off, and measured every 30s-60s within 10-12 minutes. Moreover, the measured resistance should be accurate. Therefore, it is very important to quickly and accurately measure the DC resistance. SUMMARY

[0004] The embodiments of the present application provide a transformer low-voltage resistance measurement method and system to at least solve the problems in the related art.

[0005] In a first aspect, the embodiments of the present application provide a transformer low-voltage resistance measurement method, including the following steps:

[0006] Step one: judging the structure of the transformer, if the structure of the transformer belongs to a preset structure type, then selecting two symmetrical low-voltage windings on the same main transformer core as test points;

[0007] Step two: injecting the same direction DC current to the two test points through two independent current channels, and collecting the voltage data and current data of the two low-voltage windings in real time;

[0008] Step three: calculating the DC resistance values of the two low-voltage windings according to the voltage data and the current data, and calculating the DC resistance value of the transformer based on the DC resistance values.

[0009] Further, the preset structure type includes a multi-core conjugate structure, and the transformer with the multi-core conjugate structure includes at least one voltage regulating transformer core and two main transformer cores with a conjugate structure.

[0010] Further, in the step two, the same direction direct current is applied in the same direction, and the magnetic fields generated by the two low-voltage windings are superposed in the main transformer core, so as to accelerate the magnetic saturation of the main transformer core and reduce the inductance.

[0011] Further, the low-voltage windings are connected in any one of the same-core double-star connection, the same-core double-angle connection, and the same-core star and angle connection.

[0012] Further, the value of the direct current is 2-3 times of the transformer no-load current, so as to force the core into the saturation state.

[0013] In the second aspect, the application further provides a transformer low-voltage resistance measurement system, comprising:

[0014] The test point selection module is configured to judge the structure of the transformer, and if the structure of the transformer belongs to a preset structure type, select two symmetrical low-voltage windings on the same main transformer core of the transformer as test points.

[0015] The data acquisition module is configured to simultaneously inject same direction direct currents into the two test points through two independent current channels, and acquire voltage data and current data of the two low-voltage windings in real time.

[0016] The measurement module is configured to calculate direct current resistance values of the two low-voltage windings according to the voltage data and the current data, and calculate a direct current resistance value of the transformer based on the direct current resistance values.

[0017] Further, the preset structure type includes a multi-core conjugate structure, and the transformer with the multi-core conjugate structure comprises at least one voltage regulating transformer core and two main transformer cores with a conjugate structure.

[0018] Further, in the data acquisition module, the same direction direct current is applied in the same direction, and the magnetic fields generated by the two low-voltage windings are superposed in the main transformer core, so as to accelerate the magnetic saturation of the main transformer core and reduce the inductance.

[0019] Further, the low-voltage windings are connected in any one of the same-core double-star connection, the same-core double-angle connection, and the same-core star and angle connection.

[0020] Further, the value of the direct current is 2-3 times of the transformer no-load current, so as to force the core into the saturation state.

[0021] Compared with the related art, the transformer low-voltage resistance measurement method and system provided by the embodiment of the application measures the low-voltage DC resistance by using a special wiring mode, measures the DC resistance of two symmetrical windings on the same conjugate core at the same time, and keeps the current direction consistent, so that double current acts on the transformer main core, thereby improving the measurement time of the low-voltage resistance.

[0022] The details of one or more embodiments of the application are presented in the following drawings and description to make other features, objects and advantages of the application more clear and easy to understand. BRIEF DESCRIPTION OF DRAWINGS

[0023] The drawings described herein are used to provide further understanding of the application, and form a part of the application. The illustrative embodiments of the application and their description serve to explain the application, and do not constitute an improper limitation on the application. In the drawings:

[0024] Figure 1 Flow chart of the transformer low-voltage resistance measurement method in the first embodiment of the application;

[0025] Figure 2 Measurement wiring schematic diagram of the transformer low-voltage resistance measurement method in the first embodiment of the application;

[0026] Figure 3 Current growth time curve diagram of the transformer low-voltage resistance measurement method in the first embodiment of the application;

[0027] Figure 4 Structure block diagram of the transformer low-voltage resistance measurement system in the second embodiment of the application.

[0028] The following specific implementation will further illustrate the application in combination with the above drawings. DETAILED DESCRIPTION

[0029] In order to make the purpose, technical solutions and advantages of the application more clear and easy to understand, the application is described and explained below in combination with the drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the application, and do not limit the application. Based on the embodiments provided by the application, all other embodiments obtained by those of ordinary skill in the art without creative labor fall within the scope of protection of the application.

[0030] Obviously, the accompanying drawings described below are merely some examples or embodiments of this application. Those skilled in the art can apply this application to other similar scenarios based on these drawings without any inventive effort. Furthermore, it is understood that although the efforts made in this development process may be complex and lengthy, for those skilled in the art related to the content disclosed in this application, any changes to design, manufacturing, or production based on the technical content disclosed in this application are merely conventional technical means and should not be construed as insufficient disclosure of the content of this application.

[0031] In this application, the reference to "embodiment" means that a specific feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of this application. The appearance of this phrase in various places in the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment that is mutually exclusive with other embodiments. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described in this application may be combined with other embodiments without conflict.

[0032] Unless otherwise defined, the technical or scientific terms used in this application shall have the ordinary meaning understood by one of ordinary skill in the art to which this application pertains. The terms “a,” “an,” “an,” “the,” and similar words used in this application do not indicate quantity limitation and may represent singular or plural. The terms “comprising,” “including,” “having,” and any variations thereof used in this application are intended to cover non-exclusive inclusion; for example, a process, method, system, product, or device that includes a series of steps or modules (units) is not limited to the listed steps or units, but may also include steps or units not listed, or may include other steps or units inherent to these processes, methods, products, or devices. The terms “connected,” “linked,” “coupled,” and similar words used in this application are not limited to physical or mechanical connections, but may include electrical connections, whether direct or indirect.

[0033] Example 1

[0034] Please see Figure 1 The figure shows a method for measuring the low-voltage resistance of a transformer according to the first embodiment of the present invention. The method specifically includes steps S101 to S103:

[0035] S101, the structure of the transformer is judged. If the structure of the transformer belongs to the preset structure type, two symmetrical low-voltage windings are selected as test points on the same main transformer core of the transformer.

[0036] S102, injects DC current in the same direction into the two test points simultaneously through two independent current channels, and collects the voltage and current data of the two low-voltage windings in real time;

[0037] S103, calculate the DC resistance value of the two low-voltage windings based on the voltage data and the current data, and calculate the DC resistance value of the transformer based on the DC resistance value.

[0038] In step S102, the direction of the applied DC current in the same direction satisfies the same polarity of the inlet and outlet, so that the magnetic fields generated by the two low-voltage windings are superimposed in the main transformer core, accelerating the magnetic saturation of the main transformer core to reduce the inductance.

[0039] Specifically, the low-voltage winding is connected in any one of the following ways: double-star connection with the same core, double-delta connection with the same core, and star and delta connection with the same core; the value of the DC current is 2 to 3 times the transformer no-load current, so as to force the core into saturation.

[0040] In practical implementation, the equivalent circuit principle of transformer winding resistance measurement (such as...) is used. Figure 2 As shown), where L x R x For the charging inductor and the resistor being measured, the current equation is as follows:

[0041]

[0042] In the formula, T represents the time constant. Changes in the charging circuit, such as Figure 3 As shown;

[0043] When t = T

[0044] When t = ∞

[0045] When t = 5T R x′ Compared to the actual R x There is an error of +0.67%, therefore, in this embodiment, the charging time is greater than 5T.

[0046] The relationship between T and current is shown in Table 1 below:

[0047] Table 1

[0048] t 0 0.5T T 2T 3T 4T 5T 6T i 0 0.394I 0.632I 0.865I 0.95I 0.98I 0.993I 0.998I

[0049] For example: a large transformer high-voltage winding L1 month tail 115H, resistance 0.484Ω, then T = 115 / 0.484 = 238s, 5T = 1,190s = 19.8min, therefore, the charging current needs to pass 20min can be stable.

[0050] From the time constant T-L / R can be obtained, reduce T, by reducing the inductance l or increasing the loop resistance R can shorten the charging time t, the inductance of transformer winding l depends on the number of turns of the winding, the geometric size of the core and the silicon steel sheet. For the subject transformer, the number of turns n, the core interface S, and the core loop length l are known, and only the μ permeability coefficient can be changed.

[0051] When the magnetic field strength H is greater, the core magnetic flux density tends to saturation, which decreases significantly, and the inductance L of the transformer also decreases, therefore, to increase the magnetic field strength, the current needs to be increased to 2-3 times the no-load current, and the inductance L can be effectively reduced. A resistance R is connected in the loop, which increases the loop resistance, and also reduces the time constant T.

[0052] Therefore, whether to increase the loop current I to reduce the influence of inductance L or to increase the loop resistance is to reduce the time constant T, but it needs to increase the voltage and capacity of the DC power supply.

[0053] In the embodiment, the preset structure type includes a multi-core conjugate structure, and the transformer of the multi-core conjugate structure comprises at least one voltage regulating transformer core and two main transformer cores with a conjugate structure; based on the complexity of the circuit branch of the transformer, measuring the direct current resistance of any point will form a transient process on the three cores. Especially when measuring the low-voltage direct current resistance, the transient process is longer. If it is a batch product, the long measurement time will cause great waste of human resources. Many attempts have been made, and the test data are described in detail as follows:

[0054] According to the working principle of the direct current resistance tester and the shortening of the transient time, a special wiring mode (i.e. double channel) is used to measure the low-voltage direct current resistance. That is, when measuring the low-voltage resistance, the direct current resistances of two symmetrical windings on the same conjugate core are measured at the same time. The measurement mode is to measure two channels at the same time, and the current direction remains consistent. This test method is equivalent to twice the current acting on the transformer main transformer, which realizes the effect of 1+1>2. And according to the current equipment, the low-voltage resistances of two points can be measured at the same time, so the time required for measuring the low-voltage resistance will be faster than that of the ordinary measurement method.

[0055] The measurement results are as follows:

[0056] Table 2

[0057]

[0058]

[0059] Table 3

[0060]

[0061]

[0062] Table 4

[0063]

[0064] As shown in Table 2 to Table 4, the double-channel measurement method is faster than the conventional test method (i.e. single channel) to obtain stable resistance values, and the test results are basically consistent, proving that the test results of the double channel are effective. Among various double-channel test methods, the double-channel simultaneous measurement of the upper and lower cores of the main transformer is the fastest.

[0065] As per the conventional test method (i.e. single channel), the time for testing one point of the low-voltage resistance of the transformer is about 12 minutes. Taking the product as an example, there are a total of 24 low-voltage test points for each transformer in this series of products, so the total test time is about 12x24=288 minutes, which basically requires more than four hours.

[0066] As per the double-channel test method, the time for testing one point of the low-voltage resistance of the transformer is about 5 minutes, and the double channel can simultaneously measure 2 low-voltage test points, so the total test time is about 5x12=60 minutes, which can be basically completed in 1 hour.

[0067] In summary, the measurement method of the low-voltage resistance of the transformer in the above embodiments adopts a special wiring method to measure the low-voltage DC resistance, simultaneously measures the DC resistance of two symmetrical windings on the same conjugate core, keeps the current direction consistent in and out, and makes twice the current act on the main transformer core, so as to improve the measurement time of the low-voltage resistance.

[0068] Example Two

[0069] Another aspect of the present application also proposes a measurement system of the low-voltage resistance of the transformer. Please refer to Figure 4 , which is a measurement system of the low-voltage resistance of the transformer in the second embodiment of the present application, comprising:

[0070] The test point selection module 11 is used for judging the structure of the transformer, and if the structure of the transformer belongs to a preset structure type, then two symmetrical low-voltage windings on the same main core of the transformer are selected as test points.

[0071] The data acquisition module 12 is configured to inject same-direction direct current to the two test points through two independent current channels and acquire voltage data and current data of the two low-voltage windings in real time.

[0072] The measurement module 13 is configured to calculate direct current resistance values of the two low-voltage windings according to the voltage data and the current data and calculate a direct current resistance value of the transformer based on the direct current resistance values.

[0073] Further, the preset structure type includes a multi-core conjugate structure, and the transformer of the multi-core conjugate structure comprises at least one voltage regulating transformer core and two main transformer cores with a conjugate structure.

[0074] Further, in the data acquisition module 12, the same-direction direct current is applied in the same direction, so that the magnetic fields generated by the two low-voltage windings are superposed in the main transformer core, and the magnetic saturation of the main transformer core is accelerated to reduce the inductance.

[0075] Further, the connection mode of the low-voltage windings is any one of the following modes: same-core double-star connection, same-core double-angle connection, and same-core star and angle connection.

[0076] Further, the value of the direct current is 2-3 times of the no-load current of the transformer, so as to force the core to enter the saturation state.

[0077] The functions or operation steps realized when the above modules are executed are basically the same as those of the above method embodiments, and thus will not be described here.

[0078] The implementation principle and the technical effects of the measurement system of the low-voltage resistance of the transformer provided in the embodiment of the application are the same as those of the above method embodiments, and for brief description, the part not mentioned in the system embodiment can be referred to the corresponding content in the above method embodiments.

[0079] The technical features of the above embodiments can be combined in any manner, and for the sake of brevity, not all possible combinations of the technical features in the above embodiments are described, however, as long as the combinations of the technical features do not exist contradictory, they should be considered as the scope of the description.

[0080] The above embodiments only express several implementation manners of the application, the description is more specific and detailed, but it should not be understood as the limitation of the patent scope of the application. It should be pointed out that, for ordinary skilled in the art, without departing from the concept of the application, several modifications and improvements can be made, which all belong to the protection scope of the application. Therefore, the patent protection scope of the application should be subject to the appended claims.

Claims

1. A method of measuring the low voltage resistance of a transformer, characterized in that, The method comprises the following steps: Step 1: judging the structure of the transformer, if the structure of the transformer belongs to a preset structure type, then selecting two symmetrical low-voltage windings on the same main transformer core of the transformer as test points; Step 2: injecting same-direction direct current through two independent current channels to the two test points at the same time, and collecting voltage data and current data of the two low-voltage windings in real time; Step 3: calculating direct current resistance values of the two low-voltage windings according to the voltage data and the current data, and calculating a direct current resistance value of the transformer based on the direct current resistance values.

2. The method of claim 1, wherein, The preset structure type comprises a multi-core conjugate structure, and the transformer with the multi-core conjugate structure comprises at least one voltage regulating transformer core and two main transformer cores with a conjugate structure.

3. The method of claim 1, wherein, In the step 2, the application direction of the same-direction direct current satisfies consistent in-out polarity, so that magnetic fields generated by the two low-voltage windings are superposed in the main transformer core, and the magnetic saturation of the main transformer core is accelerated to reduce inductance.

4. The method of claim 1, wherein, The connection mode of the low-voltage windings is any one of same-core double-star connection, same-core double-angle connection, and same-core star and angle connection.

5. The method of claim 1, wherein, The value of the direct current is 2-3 times of the no-load current of the transformer, so as to force the core into a saturated state.

6. A system for measuring the low voltage resistance of a transformer, characterized in that, The method comprises: a test point selection module configured to judge the structure of the transformer, if the structure of the transformer belongs to a preset structure type, then selecting two symmetrical low-voltage windings on the same main transformer core of the transformer as test points; a data collection module configured to inject same-direction direct current through two independent current channels to the two test points at the same time, and collect voltage data and current data of the two low-voltage windings in real time; a measurement module configured to calculate direct current resistance values of the two low-voltage windings according to the voltage data and the current data, and calculate a direct current resistance value of the transformer based on the direct current resistance values.

7. The system of claim 6, wherein, The preset structure type comprises a multi-core conjugate structure, and the transformer with the multi-core conjugate structure comprises at least one voltage regulating transformer core and two main transformer cores with a conjugate structure.

8. The system of claim 6, wherein, In the data collection module, the application direction of the same-direction direct current satisfies consistent in-out polarity, so that magnetic fields generated by the two low-voltage windings are superposed in the main transformer core, and the magnetic saturation of the main transformer core is accelerated to reduce inductance.

9. The system of claim 6, wherein, The connection mode of the low-voltage windings is any one of same-core double-star connection, same-core double-angle connection, and same-core star and angle connection.

10. The system of claim 6, wherein, The value of the direct current is 2-3 times of the no-load current of the transformer, so as to force the core into a saturated state.

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