Power transformer short circuit bearing capability test protection method and test device

Abstract

The invention provides a power transformer short circuit bearing capability test protection method and a test device, and relates to the technical field of transformer protection, and the method comprises the steps: obtaining a test voltage and a test current of a power transformer; inputting a protection starting signal; and monitoring the test voltage and the test current in response to the protection starting signal so as to output a tripping signal to terminate the test of the power transformer when the test current exceeds a preset current threshold and / or the impedance value of the power transformer exceeds a preset impedance threshold. Therefore, current, voltage and impedance can be comprehensively judged, abnormities in the test process can be quickly found, and a tripping power-off signal can be sent out before the fault is further deteriorated to terminate the test instead of tripping and power-off after the preset test time is up all the time. The economic loss caused by test failure can be reduced, and the test safety is greatly improved.

Description

Technical Field

[0001] The present invention relates to the technical field of transformer protection, and more specifically, to a short-circuit withstand capability test protection method for a power transformer and a short-circuit withstand capability test device for a power transformer. Background Art

[0002] During operation, power transformers will inevitably be subject to short-circuit accidents caused by line faults. When an accident occurs, the transformer will have to withstand short-circuit fault currents that are several to dozens of times the rated current. The huge mechanical force and thermal effects caused by the fault current are a severe test for the power transformer. If the transformer cannot withstand the short-circuit fault current and is damaged or explodes and catches fire, the direct and indirect economic losses will be enormous. Since the transformer's ability to withstand short circuits is directly related to the safe and stable operation of the power grid, major international and domestic large-capacity test laboratories are currently conducting short-circuit withstand tests for power transformers to verify the short-circuit withstand capacity of power transformers.

[0003] The common test method currently used is to short-circuit the secondary side of the transformer and apply the rated voltage on the primary side. The voltage application time is mainly 250ms and 500ms depending on the capacity of the transformer, and some also have a requirement of 1000ms. Due to the different short-circuit impedances of various transformers, the transformer winding flows through a current several to dozens of times larger than the rated current during the test. At this time, the transformer is subjected to huge energy. Once the transformer cannot withstand it and is damaged, it is easy to cause the transformer to burn and explode, which not only causes huge economic losses to transformer manufacturers and laboratories, but also poses serious safety hazards. Since the commonly used test method currently used is to apply voltage for a fixed time, even if the transformer is severely damaged halfway through the test process, the voltage application will not stop, resulting in further damage and destruction.

[0004] At present, the short-circuit test process of power transformers only uses the current of the tested transformer as the protection parameter. This single-parameter protection cannot detect the impedance change caused by winding deformation during the test, and cannot trip and terminate the test in the early stage of a serious fault.

[0005] Therefore, a new technical solution is urgently needed to solve the above technical problems. Summary of the invention

[0006] A series of simplified concepts are introduced in the Summary of the Invention, which will be further described in detail in the Detailed Description of the Invention. The Summary of the Invention does not mean to attempt to define the key features and essential technical features of the claimed technical solution, nor does it mean to attempt to determine the scope of protection of the claimed technical solution.

[0007] In a first aspect, the present invention provides a short-circuit capability test protection method for a power transformer, comprising:

[0008] Obtain the test voltage and test current of the power transformer;

[0009] Input protection start signal;

[0010] In response to the protection start signal, calculations are performed for the test voltage and the test current so that when the test current exceeds a preset current threshold and / or the impedance value of the power transformer exceeds a preset impedance threshold, a trip signal is output to terminate the test on the power transformer, wherein the impedance value of the power transformer is obtained based on the test current and the test voltage.

[0011] Optionally, monitoring of the test voltage and test current is performed, including:

[0012] Remove the asymmetric components in the test current.

[0013] Optionally, remove the asymmetric components in the test current, including:

[0014] Calculate the average value of two peaks in the same direction among three adjacent positive and negative peaks of the test current;

[0015] The difference between another peak value other than the two peak values ​​in the same direction among three adjacent positive and negative peak values ​​and the average value is calculated to obtain the effective value of the current.

[0016] Optionally, monitoring of the test voltage and test current is performed, including:

[0017] Calculate the voltage effective value based on the two adjacent positive and negative peak values ​​of the test voltage;

[0018] The impedance value of the power transformer is obtained in the following way:

[0019] Divide the rms voltage by the rms current to obtain the impedance value.

[0020] Optionally, the method further comprises:

[0021] A user interface is displayed, wherein the user interface is used to display a preset current threshold and a preset impedance threshold, and is also used to display a test condition of the power transformer.

[0022] Optionally, monitoring of the test voltage and test current is performed, including:

[0023] The effective current and impedance are calculated every half cycle.

[0024] Optionally, the method further comprises:

[0025] A 32-bit high-speed microprocessor is used to calculate the test voltage and test current.

[0026] In the second aspect, a short-circuit test device for a power transformer is also proposed, comprising:

[0027] Power transformer short-circuit withstand test circuit;

[0028] A test circuit protection device electrically connected to a short-circuit withstand capability test circuit of a power transformer;

[0029] The test circuit protection device is used to obtain the test voltage and test current of the power transformer, and in response to the protection start signal output by the power transformer short-circuit capacity test circuit, monitor the test voltage and test current, so as to output a trip signal to terminate the test of the power transformer when the test current exceeds a preset current threshold and / or the impedance value of the power transformer exceeds a preset impedance threshold, wherein the impedance value of the power transformer is obtained based on the test current and the test voltage.

[0030] Optionally, the power transformer short-circuit withstand capability test circuit includes:

[0031] a current transformer, electrically connected to the power transformer under test, the current transformer being used to transmit a test current to the test circuit protection device;

[0032] A voltage transformer, electrically connected to the power transformer under test, the voltage transformer being used to transmit the test voltage to the test circuit protection device;

[0033] The circuit breaker is electrically connected to the test circuit protection device, and the circuit breaker is used to open in response to a trip signal from the test circuit protection device.

[0034] Optionally, test circuit protection devices, including:

[0035] microprocessor;

[0036] A signal conditioning circuit, one end of which is electrically connected to the current transformer and the voltage transformer, and the other end of which is electrically connected to the microprocessor, and the signal conditioning circuit is used to convert analog signals corresponding to the test current and the test voltage into digital signals and transmit them to the microprocessor;

[0037] A switch input circuit, one end of which is electrically connected to a short-circuit capability test circuit of a power transformer, and the other end of which is electrically connected to a microprocessor. The switch input circuit is used to input a protection start signal to the microprocessor to start the microprocessor so that the microprocessor calculates and processes the test voltage and the test current.

[0038] A switch output circuit, one end of which is electrically connected to the power transformer short-circuit capacity test circuit, and the other end of which is electrically connected to the microprocessor. The switch output circuit is used to transmit the trip signal output by the microprocessor to the circuit breaker to control the short-circuit capacity test circuit of the power transformer to be disconnected;

[0039] A communication interface circuit is electrically connected to the microprocessor, and the communication interface circuit is used to realize the communication connection between the microprocessor and the computer device, wherein the computer device is used to input control parameters to the microprocessor;

[0040] The display and keyboard input circuit is electrically connected to the microprocessor. The display and keyboard input circuit is used to input a preset current threshold value and a preset impedance threshold value into the microprocessor in response to a user's operation instruction, and is also used to display the test status of the power transformer.

[0041] According to the above technical scheme, the test voltage and test current of the power transformer are first obtained, and a protection start signal is input at the same time. In response to the protection start signal, the test voltage and test current are monitored, so that when the test current exceeds the preset current threshold and / or the impedance value of the power transformer exceeds the preset impedance threshold, a trip signal is output to terminate the test of the power transformer. Thus, the collected test current and voltage can be quickly calculated and processed in real time, the impedance value of the tested transformer is calculated based on the current and voltage, and the current, voltage, and impedance are comprehensively judged to quickly find abnormalities in the test process, and a trip power-off signal can be issued to terminate the test before the fault further deteriorates, rather than waiting until the preset test time before tripping and powering off. The present invention can not only reduce the economic losses caused by test failures, but also greatly improve the safety of the test.

[0042] The power transformer short-circuit capacity test protection method of the present invention, other advantages, objectives and features of the present invention will be reflected in part through the following description, and in part will be understood by technicians in this field through research and practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments consistent with the present application and, together with the description, serve to explain the principles of the present application.

[0044] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, for ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative labor.

[0045] Various other advantages and benefits will become apparent to those of ordinary skill in the art by reading the detailed description of the exemplary embodiments below. The accompanying drawings are only for the purpose of illustrating exemplary embodiments and are not to be considered as limiting the present application. Also, the same reference symbols are used throughout the accompanying drawings to represent the same components. In the accompanying drawings:

[0046] Figure 1 A schematic flow chart of a power transformer short-circuit capability test protection method according to an embodiment of the present invention is shown;

[0047] Figure 2 A circuit schematic diagram of a single-phase power transformer short-circuit withstand capability test according to an embodiment of the present invention is shown;

[0048] Figure 3 A schematic diagram of fast calculation for removing asymmetric components in a test current according to an embodiment of the present invention is shown;

[0049] Figure 4 A schematic block diagram of a power transformer short-circuit withstand capability test device according to an embodiment of the present invention is shown;

[0050] Figure 5 A schematic block diagram of a test circuit protection device according to an embodiment of the present invention is shown. DETAILED DESCRIPTION

[0051] In order to more clearly understand the above-mentioned purposes, features and advantages of the present application, the scheme of the present application will be further described below. It should be noted that the embodiments of the present application and the features in the embodiments can be combined with each other without conflict.

[0052] The terms "first", "second", "third", "fourth", etc. (if any) in the specification and claims of the present application and the above-mentioned drawings are used to distinguish similar objects, and are not necessarily used to describe a specific order or sequence. It should be understood that the data used in this way can be interchangeable where appropriate, so that the embodiments described herein can be implemented in an order other than that illustrated or described herein. In addition, the terms "including" and "having" and any of their variations are intended to cover non-exclusive inclusions, for example, a process, method, system, product or device that includes a series of steps or units is not necessarily limited to those steps or units that are clearly listed, but may include other steps or units that are not clearly listed or inherent to these processes, methods, products or devices. The technical solutions in the embodiments of the present application will be clearly and completely described below in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all of the embodiments.

[0053] In the following description, many specific details are set forth to facilitate a full understanding of the present application, but the present application may also be implemented in other ways different from those described herein; obviously, the embodiments in the specification are only part of the embodiments of the present application, rather than all of the embodiments.

[0054] In order to solve the above technical problems, according to the first aspect of the present application, a short-circuit capability test protection method for a power transformer is proposed. Figure 1 FIG. 1 is a schematic flow chart of a power transformer short-circuit capability test protection method 100 according to an embodiment of the present invention. Figure 1 As shown, method 100 may include the following steps.

[0055] Step S110, obtaining the test voltage and test current of the power transformer.

[0056] Figure 2 The circuit schematic diagram of the short-circuit capability test of a single-phase power transformer according to an embodiment of the present invention is shown. For ease of understanding and description, the following description only takes the short-circuit capability test of a single-phase power transformer as an example. The principle of the three-phase test is the same, and only three single-phase circuits need to be combined. The phase difference of the power supply of each single-phase circuit is 120°. The specific process of the three-phase test can be understood by reading the following single-phase test, which will not be elaborated in detail here.

[0057] like Figure 2 As shown, before the test, all DS disconnectors and CB circuit breakers can be closed. At the zero crossing point of the power supply voltage, the SCB synchronous switch is closed. Figure 2 The circuit is a closed loop, and the test voltage and test current can be obtained from the test transformer IT. It can be understood that the test transformer can adjust the power supply voltage to the expected voltage value to provide it to the transformer under test. For details, see Figure 2 , OTT is the transformer under test; P represents the power supply, which can be network power or generator; XL represents the adjustment reactor, which can be used to adjust the test current.

[0058] Step S120: input a protection start signal.

[0059] For example, after the SCB synchronous switch is closed, the closing signal can be used as a protection start signal to input the protection device to start the protection device. Figure 2 Not shown in the figure, it can be connected to the CB circuit breaker to control the opening and closing of the CB circuit breaker.

[0060] Step S130, in response to the protection start signal, monitor the test voltage and the test current to output a trip signal to terminate the test on the power transformer when the test current exceeds a preset current threshold and / or the impedance value of the power transformer exceeds a preset impedance threshold, wherein the impedance value of the power transformer is obtained based on the test current and the test voltage.

[0061] Preferably, a 32-bit high-speed microprocessor can be used to calculate and process the test voltage and test current, which can meet various high-speed data processing requirements and greatly improve the calculation and processing efficiency. For example, the current transformer CT can transmit the current signal to the protection device, and the voltage transformer VT can transmit the voltage signal to the protection device. Specifically, the high voltage and high current can be converted into low voltage and low current signals, and provided to the protection device to achieve protection of the protection device and facilitate subsequent calculations. Then the effective value of the test voltage and the test current can be calculated, and the effective value can be obtained by any existing or future calculation method. After the effective value is calculated, the current effective value can be compared with the preset current threshold. If the current effective value exceeds the preset current threshold, a trip signal can be output to the protection device. The protection device controls the CB circuit breaker to disconnect based on the trip signal to achieve power outage of the tested transformer, thereby terminating the test of the power transformer. Similarly, after calculating the effective value of voltage and the effective value of current, the effective value of voltage can be divided by the effective value of current to obtain the current impedance value, and then the calculated current impedance value can be compared with the preset impedance threshold value. If the current impedance value exceeds the preset impedance threshold value, a trip signal can be output to cut off the power. The power-off method is consistent with the previous text and will not be repeated here. It should be noted that there are many abnormal phenomena in the short-circuit capacity test of power transformers. Sometimes, the current suddenly increases or decreases, and the impedance suddenly increases or decreases. A more serious situation is that serious internal damage causes breakdown discharge, which may cause the transformer oil tank to rupture and the transformer oil to leak out, and may also cause an explosion or fire. Before this serious situation occurs, a sudden change in current or impedance often occurs. The above-mentioned technical solution of the present application can monitor the test current and transformer impedance in real time, and can adopt current and impedance combined parameter monitoring to protect the transformer, thereby improving the sensitivity of protection.

[0062] According to the above technical scheme, the test voltage and test current of the power transformer are first obtained, and a protection start signal is input at the same time. In response to the protection start signal, the test voltage and test current are monitored, so that when the test current exceeds the preset current threshold and / or the impedance value of the power transformer exceeds the preset impedance threshold, a trip signal is output to terminate the test of the power transformer. Thus, the collected test current and voltage can be quickly calculated and processed in real time, the impedance value of the tested transformer is calculated based on the current and voltage, and the current, voltage, and impedance are comprehensively judged to quickly find abnormalities in the test process, and a trip power-off signal can be issued to terminate the test before the fault further deteriorates, rather than waiting until the preset test time before tripping and powering off. The present invention can not only reduce the economic losses caused by test failures, but also greatly improve the safety of the test.

[0063] It should be noted that, since the short-circuit capacity test of the power transformer is closed at the moment when the voltage passes through zero, the nature of the inductance determines that the test current will contain a large asymmetric component. In order to ensure that the test can be carried out normally without accidental power failure, the protection value must be set relatively large, resulting in insensitive protection. Only when a very serious overcurrent occurs will the protection trip, but it is often too late at this time. In this regard, the present application uses the following method to remove the asymmetric component in the test current to further protect the transformer.

[0064] Specifically, removing the asymmetric component in the test current may include: calculating the average value of two same-direction peaks among three adjacent positive and negative peaks of the test current; calculating the difference between another peak other than the two same-direction peaks among the three adjacent positive and negative peaks and the average value to obtain the effective value of the current.

[0065] Figure 3 FIG. 2 shows a schematic diagram of a fast calculation for removing asymmetric components in a test current according to an embodiment of the present invention. Figure 3 As shown, the average value of the positive peak 1 and the peak 3 can be taken as A. The difference between A and the negative peak 2 is approximately equal to the peak value of the equivalent symmetrical component at this time, divided by The effective value of the symmetrical component of the current can be obtained.

[0066] Optionally, step S130 of monitoring the test voltage and the test current may further include: calculating the effective value of the voltage based on two adjacent positive and negative peak values ​​of the test voltage.

[0067] Unlike current, voltage signals do not have asymmetric components and can only have amplitude changes, which makes calculations relatively easy. For example, collecting two adjacent positive and negative peaks and dividing them by The effective value of voltage can be quickly calculated. Therefore, the effective value of voltage can be divided by the effective value of current to quickly find the impedance value of the transformer at that time. Preferably, the effective value of current and impedance value can be calculated once every half cycle. Specifically, after the calculation of peak values ​​1, 2, and 3, the effective value of the symmetrical component of current corresponding to peak values ​​2, 3, and 4 can be calculated, and so on. The voltage signal can also be recursively calculated in a similar manner. In this way, in addition to the first three peak values ​​of the current, a set of current and impedance values ​​for protection judgment can be calculated every half cycle (10ms at a frequency of 50Hz), realizing real-time monitoring of the test current and transformer impedance, while avoiding the occurrence of current and voltage fluctuations, which affect the calculation results, and further improve the accuracy of the calculation results, providing more reliable protection for transformer protection.

[0068] Optionally, the method may further include: displaying a user interface, wherein the user interface is used to display a preset current threshold and a preset impedance threshold, and is also used to display a test condition of the power transformer.

[0069] Exemplarily, the user can input the preset current threshold and the preset impedance threshold using an input device such as a mouse and keyboard according to actual needs or experience, and the input values ​​can be displayed through the user interface for the user to consult. In addition, the user interface can also display the status of the test on the power transformer, such as "testing", "testing ended" or "testing terminated", so that the user can grasp the progress of the test in real time. Thus, the preset current threshold, the preset impedance threshold and the test status of the power transformer are displayed to the user in a visual manner, so that the user can more intuitively understand the test-related parameters and specific progress, which facilitates the smooth progress of the test process.

[0070] According to the second aspect of the present invention, a device for testing the short-circuit capability of a power transformer is also provided. Figure 4 FIG. 4 is a schematic block diagram of a power transformer short-circuit withstand capability test device 400 according to an embodiment of the present invention. Figure 4 As shown, the device 400 may include: a power transformer short-circuit withstand capability test circuit 410 and a test circuit protection device 420 .

[0071] Power transformer short circuit withstand capability test circuit 410;

[0072] A test circuit protection device 420 is electrically connected to a power transformer short-circuit withstand capability test circuit 410;

[0073] The test circuit protection device 420 is used to obtain the test voltage and test current of the power transformer, and in response to the protection start signal output by the power transformer short-circuit capacity test circuit, monitor the test voltage and test current, so as to output a trip signal to terminate the test of the power transformer when the test current exceeds a preset current threshold and / or the impedance value of the power transformer exceeds a preset impedance threshold, wherein the impedance value of the power transformer is obtained based on the test current and the test voltage.

[0074] Optionally, the power transformer short-circuit withstand capability test circuit 410 may include:

[0075] a current transformer, electrically connected to the power transformer under test, the current transformer being used to transmit a test current to the test circuit protection device;

[0076] A voltage transformer, electrically connected to the power transformer under test, the voltage transformer being used to transmit the test voltage to the test circuit protection device;

[0077] The circuit breaker is electrically connected to the test circuit protection device, and the circuit breaker is used to open in response to a trip signal from the test circuit protection device.

[0078] Figure 5 FIG. 5 shows a schematic block diagram of a test circuit protection device 500 according to an embodiment of the present invention. Figure 5 As shown, the device 500 may include: a microprocessor, a signal conditioning circuit, a switch input circuit, a switch output circuit, a communication interface circuit, and a display and keyboard input circuit.

[0079] The signal conditioning circuit has one end electrically connected to the current transformer and the voltage transformer, and the other end electrically connected to the microprocessor. The signal conditioning circuit is used to convert the analog signals corresponding to the test current and the test voltage into digital signals and transmit them to the microprocessor. The test current is Figure 5 The CT current signal shown is Figure 5 The VT voltage signal shown;

[0080] A switch input circuit, one end of which is electrically connected to a short-circuit capability test circuit of a power transformer, and the other end of which is electrically connected to a microprocessor. The switch input circuit is used to input a protection start signal to the microprocessor to start the microprocessor so that the microprocessor calculates and processes the test voltage and the test current.

[0081] A switch output circuit, one end of which is electrically connected to the power transformer short-circuit capacity test circuit, and the other end of which is electrically connected to the microprocessor. The switch output circuit is used to transmit the trip signal output by the microprocessor to the circuit breaker to control the short-circuit capacity test circuit of the power transformer to be disconnected;

[0082] A communication interface circuit is electrically connected to the microprocessor, and the communication interface circuit is used to realize the communication connection between the microprocessor and the computer device, wherein the computer device is used to input control parameters to the microprocessor;

[0083] The display and keyboard input circuit is electrically connected to the microprocessor. The display and keyboard input circuit is used to input a preset current threshold value and a preset impedance threshold value into the microprocessor in response to a user's operating instruction, and is also used to display the test conditions of the power transformer. Specifically, the test conditions of the power transformer can be displayed using a display, and the preset current threshold value and the preset impedance threshold value can be input into the microprocessor using input devices such as a keyboard, and the input values ​​can be displayed using a display for the user to view.

[0084] A person skilled in the art may understand the specific details and beneficial effects of the short-circuit capability test device for a power transformer by reading the above description of the short-circuit capability test protection method for a power transformer, which will not be described in detail here for the sake of brevity.

[0085] In the several embodiments provided in the present application, it should be understood that the disclosed devices and / or equipment can be implemented in other ways. For example, the device embodiments described above are only schematic, for example, the division of units is only a logical function division, and there may be other division methods in actual implementation, such as multiple units or components can be combined or integrated into another system, or some features can be ignored or not executed. Another point is that the mutual coupling or direct coupling or communication connection shown or discussed can be through some interfaces, indirect coupling or communication connection of devices or units, which can be electrical, mechanical or other forms.

[0086] The units described as separate components may or may not be physically separated, and the components shown as units may or may not be physical units, that is, they may be located in one place or distributed on multiple network units. Some or all of the units may be selected according to actual needs to achieve the purpose of the solution of this embodiment.

[0087] In addition, each functional unit in each embodiment of the present application may be integrated into one processing unit, or each unit may exist physically separately, or two or more units may be integrated into one unit. The above-mentioned integrated unit may be implemented in the form of hardware or in the form of software functional units.

[0088] If the integrated unit is implemented in the form of a software functional unit and sold or used as an independent product, it can be stored in a computer-readable storage medium. Based on this understanding, the technical solution of the present application is essentially or the part that contributes to the prior art or all or part of the technical solution can be embodied in the form of a software product, and the computer software product is stored in a storage medium, including a number of instructions to enable a computer device (which can be a personal computer, a server, or a network device, etc.) to perform all or part of the steps of the various embodiments of the present application. The aforementioned storage medium includes: U disk, mobile hard disk, read-only memory (Read-Only Memory, ROM), random access memory (Random Access Memory, RAM), disk or optical disk and other media that can store program codes.

[0089] The above embodiments are only used to illustrate the technical solutions of the present application, rather than to limit them. Although the present application has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some of the technical features therein by equivalents. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present application.

Claims

1. A short-circuit protection test method for a power transformer, characterized in that: include: Obtaining a test voltage and a test current of the power transformer; Input protection start signal; In response to the protection start signal, the test voltage and the test current are monitored to output a trip signal to terminate the test of the power transformer when the test current exceeds a preset current threshold and / or the impedance value of the power transformer exceeds a preset impedance threshold, wherein the impedance value of the power transformer is obtained based on the test current and the test voltage.

2. The short-circuit capability test protection method for power transformer according to claim 1, characterized in that: The monitoring of the test voltage and the test current includes: The asymmetrical components in the test current are removed.

3. The short-circuit capability test protection method for power transformer according to claim 2, characterized in that: The removing of the asymmetric component in the test current comprises: Calculate the average value of two peak values ​​in the same direction among three adjacent positive and negative peak values ​​of the test current; The difference between another peak value of the three adjacent positive and negative peak values ​​except the two peak values ​​in the same direction and the average value is calculated to obtain the effective value of the current.

4. The short-circuit capability test protection method for power transformer according to claim 3, characterized in that: The monitoring of the test voltage and the test current includes: Calculate the voltage effective value based on two adjacent positive and negative peak values ​​of the test voltage; The impedance value of the power transformer is obtained by: The impedance value is obtained by dividing the voltage effective value by the current effective value.

5. The short-circuit capability test protection method for power transformer according to claim 1, characterized in that: The method further comprises: A user interface is displayed, wherein the user interface is used to display the preset current threshold and the preset impedance threshold, and is also used to display the test status of the power transformer.

6. The short-circuit capability test protection method for power transformer according to claim 4, characterized in that: The monitoring of the test voltage and the test current includes: The effective current value and the impedance value are calculated once every half cycle.

7. The short-circuit capability test protection method for a power transformer according to any one of claims 1 to 6, characterized in that: The method further comprises: A 32-bit high-speed microprocessor is used to calculate and process the test voltage and the test current.

8. A short-circuit test device for a power transformer, characterized in that: include: Power transformer short-circuit withstand test circuit; A test circuit protection device electrically connected to the short-circuit capability test circuit of the power transformer; The test circuit protection device is used to obtain the test voltage and test current of the power transformer, and in response to the protection start signal output by the short-circuit capacity test circuit of the power transformer, monitor the test voltage and the test current, so as to output a trip signal to terminate the test of the power transformer when the test current exceeds a preset current threshold and / or the impedance value of the power transformer exceeds a preset impedance threshold, wherein the impedance value of the power transformer is obtained based on the test current and the test voltage.

9. The short-circuit withstand capability test device for power transformers according to claim 8, characterized in that: The short-circuit capability test circuit of the power transformer comprises: a current transformer, electrically connected to the power transformer under test, the current transformer being used to transmit the test current to the test circuit protection device; a voltage transformer, electrically connected to the power transformer under test, the voltage transformer being used to transmit the test voltage to the test circuit protection device; A circuit breaker is electrically connected to the test circuit protection device, and the circuit breaker is used to open in response to the trip signal from the test circuit protection device.

10. The short-circuit withstand capability test device of a power transformer according to claim 9, characterized in that: The test circuit protection device comprises: microprocessor; a signal conditioning circuit, one end of which is electrically connected to the current transformer and the voltage transformer, and the other end of which is electrically connected to the microprocessor, wherein the signal conditioning circuit is used to convert analog signals corresponding to the test current and the test voltage into digital signals and transmit the digital signals to the microprocessor; a switch input circuit, one end of which is electrically connected to the short-circuit capability test circuit of the power transformer, and the other end of which is electrically connected to the microprocessor, wherein the switch input circuit is used to input the protection start signal to the microprocessor to start the microprocessor so that the microprocessor calculates and processes the test voltage and the test current; a switch output circuit, one end of which is electrically connected to the power transformer short-circuit capacity test circuit, and the other end of which is electrically connected to the microprocessor, wherein the switch output circuit is used to transmit the trip signal output by the microprocessor to the circuit breaker to control the short-circuit capacity test circuit of the power transformer to be disconnected; A communication interface circuit is electrically connected to the microprocessor, and the communication interface circuit is used to realize the communication connection between the microprocessor and a computer device, wherein the computer device is used to input control parameters to the microprocessor; The display and keyboard input circuit is electrically connected to the microprocessor. The display and keyboard input circuit is used to input the preset current threshold and the preset impedance threshold into the microprocessor in response to the user's operation instructions, and is also used to display the test status of the power transformer.

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