Static short circuit test method for verifying differential protection polarity of generator and transformer

Abstract

The invention relates to the technical field of electrical tests, and particularly discloses a static short circuit test method for verifying the differential protection polarity of a generator and a transformer, and the method comprises the steps: S1, obtaining a first technical parameter and a second technical parameter of a to-be-verified generator and a to-be-verified transformer respectively; s2, first short-circuit impedance and second short-circuit impedance of the generator to be verified and the transformer to be verified are calculated according to S1; s3, respectively calculating a first short-circuit power supply capacity and a second short-circuit power supply capacity of a generator and a transformer required by differential protection polarity verification according to the S2; s4, selecting an adaptive target frequency converter according to the first short-circuit power supply capacity and the second short-circuit power supply capacity; and S5, respectively setting a generator verification short circuit point and a transformer verification short circuit point on the generator to be verified and the transformer to be verified, and carrying out differential protection polarity verification on the generator-transformer group protection device according to a static short circuit test method. According to the invention, the safety and economy of the test can be improved.

Description

Technical Field

[0001] The present invention relates to the technical field of electrical testing, and in particular to a static short-circuit test method for verifying the polarity of differential protection of a generator and a transformer. Background Art

[0002] Currently, when power plants install or renovate generator and transformer protection devices and their secondary circuits, they typically use load verification and dynamic short-circuit testing to verify the correct polarity of the differential circuit. This is because differential protection is one of the key protective measures in power systems, used to detect internal transformer faults. If the polarity of the differential circuit is incorrectly configured, the protection device will be unable to accurately identify the direction and magnitude of the fault current, potentially causing false or non-operation of the protection device. This not only threatens the safe operation of the equipment but can also lead to serious power grid accidents. By verifying the correct polarity of the differential circuit, the protection device can reliably detect the fault area, minimize equipment damage and power outage duration, and ensure the safety and stability of the power system. Therefore, this verification step is crucial for preventing potential risks and ensuring the normal operation of equipment.

[0003] When using the load verification method to verify the polarity of the differential circuit, first, the polarity configuration is typically used when the generator and transformer are started and connected to the grid. Whether to activate differential protection is determined based on the polarity configuration. Normally, differential protection is activated after the polarity is correctly configured, and the overcurrent protection operating time of the transformer's high-voltage grid-connected circuit breaker is reduced. This method requires that the polarity verification be performed for a period of time after the generator is connected to the grid under a low load. Correct polarity is quick, but incorrect polarity requires on-site modification and continuous polarity adjustment until the polarity is correct, which is time-consuming. There is also the risk of malfunctioning of the high-voltage transformer differential protection during auxiliary power transfer and of malfunctioning of the transformer's high-voltage grid-connected circuit breaker overcurrent protection in the event of a short-circuit fault in the power generation system. Second, when the generator and transformer are started and connected to the grid, the generator-transformer differential protection is deactivated. Simultaneously, the overcurrent protection operating time of the transformer's high-voltage grid-connected circuit breaker is reduced. This allows for polarity verification during the normal load ramp-up process after the generator is started and connected to the grid. This method has the risk of malfunction of the overcurrent protection of the grid-connected circuit breaker on the high-voltage side of the transformer and the risk of the generator and transformer losing their main protection when a short-circuit fault occurs in the system.

[0004] When using the dynamic short-circuit test method to verify the polarity correctness of the differential circuit, the test power source is primarily the generator. This test is carried out before the generator is started and connected to the grid, and the verification task is completed by adding short-circuit points. However, due to the need to conduct multiple short-circuit point tests, it is time-consuming and consumes a lot of fuel. The short-circuit current is difficult to control, and the test is relatively costly. Therefore, this method is more accurate in polarity verification and is currently the most commonly used test method. Summary of the Invention

[0005] The present invention provides a static short-circuit test method for verifying the polarity of generator and transformer differential protection. By employing a frequency converter and following a static test method, this method not only avoids the high current impact on the 380V plant power system during static short-circuit testing, but also improves test safety by eliminating the need to directly use the 380V plant power system as a power source during the differential protection polarity verification of the modified power plant generator-transformer unit. Furthermore, the method allows verification of the polarity of the differential protection to be performed immediately after the power plant generator-transformer unit protection device has been modified, eliminating the need for excessive fuel consumption during the test. This reduces verification costs and is economical and environmentally friendly.

[0006] In order to achieve the above object, the present invention adopts the following technical solutions: A static short-circuit test method for verifying the polarity of differential protection of generators and transformers includes: S1, respectively obtaining first technical parameters and second technical parameters of the generator and transformer to be verified; S2, respectively calculating first short-circuit impedance and second short-circuit impedance of the generator and transformer to be verified based on the first technical parameters and the second technical parameters; S3, respectively calculating first short-circuit power supply capacity and second short-circuit power supply capacity of the generator and transformer required for differential protection polarity verification based on the first short-circuit impedance and the second short-circuit impedance; S4, selecting a corresponding target inverter based on the first short-circuit power supply capacity and the second short-circuit power supply capacity; S5, respectively setting a generator verification short-circuit point and a transformer verification short-circuit point on the generator and transformer to be verified, and the target inverter performs a differential protection polarity test based on the generator verification short-circuit point and the transformer verification short-circuit point, and carries out differential protection polarity verification of the generator-transformer group protection device according to the static short-circuit test method.

[0007] Beneficial effects: Compared with the existing technology, first of all, the safety of the test is improved. The existing load verification method and dynamic short-circuit test method have many safety hazards. For example, the load verification method needs to be carried out after the generator is connected to the grid. There is a risk of false operation of the high-voltage plant transformer differential protection when the plant power is switched, and the risk of false operation of the overcurrent protection of the transformer high-voltage side grid-connected circuit breaker when the system is short-circuited; the dynamic short-circuit test method consumes a lot of fuel, and the test process is complicated, time-consuming and high-risk. The present invention adopts a static short-circuit test method and combines it with a frequency converter for testing. There is no need to connect the generator to the grid, which avoids the impact on the power grid and the potential risk of false operation, and significantly improves the safety of the test.

[0008] Secondly, it improves test efficiency. By accurately calculating the short-circuit impedance and power supply capacity and selecting the appropriate inverter, this method can complete the calibration in a short time, greatly improving test efficiency.

[0009] At the same time, the test cost is reduced. The existing static short-circuit test method, such as using an AC 380V voltage regulator, requires a large-capacity AC three-phase 380V voltage regulator when conducting polarity verification of differential protection of large generators and transformers. The size and weight of the voltage regulator are very large, which not only increases the equipment cost but also makes it difficult to carry and operate. Therefore, it is generally not adopted. The present invention uses a frequency converter to replace the existing voltage regulator. The size and weight of the frequency converter are significantly reduced, and the output voltage can be flexibly controlled by adjusting the frequency. There is no need to customize large-capacity equipment, which greatly reduces the cost and operation difficulty of the test equipment.

[0010] This method improves test flexibility and adaptability, making it applicable to common generator-transformer groups for verifying differential circuit polarity. By calculating short-circuit impedance and power supply capacity and selecting the appropriate inverter based on actual needs, this method can adapt to the calibration needs of generators and transformers of varying capacities and parameters. The inverter's V / F control method allows for flexible adjustment of test voltage based on actual needs, further enhancing test flexibility and adaptability.

[0011] Furthermore, the safety of the generator-transformer set was ensured. During the test, precise calculation and control of the test current and voltage avoided the high current shock to the 380V plant power system during the static short-circuit test, which would have occurred during the polarity verification of the differential protection of the modified power plant's generator-transformer set. Furthermore, the inverter's overcurrent protection function effectively prevented damage to the generator-transformer set due to excessive current during the test, further ensuring equipment safety.

[0012] Finally, early verification prevents risks. This method can verify the polarity of differential protection after the generator-transformer protection device is modified and before the unit is started. This method can detect and correct polarity errors in advance, avoiding false or non-operational protection caused by polarity errors, thereby minimizing equipment damage and power outage duration, and ensuring the safety and stability of the power system.

[0013] Preferably, the second technical parameter includes the transformer high-voltage side rated voltage Un, the transformer high-voltage side rated current In and the transformer short-circuit (half-through) impedance voltage U k ; The calculation formula for the second short-circuit impedance to be verified is: Z k1 =U k *Un / (100*In); where Z k1 is the second short-circuit impedance.

[0014] Beneficial Effects: By clarifying the second technical parameters, including the transformer's high-voltage side rated voltage, rated current, and short-circuit impedance voltage, and providing a calculation formula for the second short-circuit impedance, a clear parameter basis can be provided for subsequent accurate calculation of the short-circuit impedance. This allows the precise determination of the transformer's electrical characteristics in the short-circuit state during differential protection polarity verification, laying the foundation for subsequent steps such as selecting the appropriate short-circuit power supply capacity and inverter. This improves the scientific nature and accuracy of the entire verification method, ensuring that the verification process is tailored to the transformer's actual characteristics and avoiding verification errors or risks caused by inaccurate parameters.

[0015] Preferably, when performing the differential protection polarity test, the primary current I 极 Not less than 4% of the rated current In on the high-voltage side of the transformer; the primary current I of the differential protection polarity of the transformer to be tested 极 In the calibration state, U 高侧 =Z k1* I 极 , where U 高侧 The high voltage side voltage of the high power transformer, desulfurization transformer and excitation transformer is U 高侧 , check the primary current I of the differential protection polarity 极 Calculate the capacity of the second short-circuit power supply according to the high-voltage side voltage U of the high-voltage transformer, desulfurization transformer and excitation transformer 高侧 , check the primary current I of the differential protection polarity 极 , and the second short-circuit power supply capacity selects the target inverter.

[0016] Beneficial Effects: When conducting a differential protection polarity test, the current required to verify the differential protection polarity of the transformer to be verified should be no less than 4% of the rated current on the high-voltage side of the transformer. The relationship between the high-voltage side voltage of the high-voltage transformer, desulfurization transformer, and excitation transformer, as well as the short-circuit impedance and polarity current, is also provided. This technical detail ensures that sufficient current flows through the transformer during polarity verification, placing it in a state close to actual operating conditions, thereby more accurately verifying the correctness of the differential protection polarity. Furthermore, by calculating the high-voltage side voltage of the high-voltage transformer, desulfurization transformer, and excitation transformer to determine the short-circuit power supply capacity, it can provide an accurate basis for selecting the appropriate target inverter, further ensuring the safety and reliability of the verification process and avoiding problems such as inaccurate verification or equipment damage due to insufficient current or voltage.

[0017] Preferably, a transformer verification short-circuit point is set outside the current transformer of the circuit breaker on the low-voltage side of the transformer, and the transformer verification short-circuit point is set to verify the correctness of the differential protection polarity of the high-voltage side of the transformer, desulfurization transformer and excitation transformer.

[0018] Beneficial Effects: A transformer verification short-circuit point is specified after the current transformer on the transformer's low-voltage side circuit breaker. This is used to verify the polarity of differential protection on the high-voltage side of the transformer's high-voltage transformer, desulfurization transformer, and excitation transformer. This short-circuit point configuration allows for direct verification of key transformer components, ensuring accurate differential protection polarity in these areas. This ensures that verification results more accurately reflect the actual differential protection polarity during operation, improving the pertinence and effectiveness of verification and providing reliable assurance for the safe operation of power plants.

[0019] Preferably, the first technical parameter includes the direct-axis ultra-transient reactance saturation value X ’’ d , Generator rated voltage U ’ 额 , stator rated current I ’ 额 , rated capacity S; the first technical parameter of the transformer to be tested includes the short-circuit impedance voltage U ’ k. Rated voltage U on high voltage side ’ n. Rated current I on high voltage side ’ n; the calculation formula for the first short-circuit impedance to be checked is: Z k2 =X ’’ d / 100*(U ’ 额 )² / S; where Z k2 is the first short-circuit impedance to be verified; when the high-voltage side of the transformer to be verified is short-circuited, the impedance calculation formula on the low-voltage side is: Z k3 =U ’ k%*U ’ n / (100*I ’ n); where Z k3 is the impedance of the low-voltage side of the transformer to be tested when the high-voltage side is short-circuited; the first short-circuit impedance of the generator is the first short-circuit impedance Z to be tested k2 The impedance Z of the low-voltage side when the high-voltage side of the transformer to be tested is short-circuited k3 sum.

[0020] Beneficial effects: By listing the first technical parameters, including the direct-axis ultra-transient reactance saturation value, rated voltage, motor stator rated current, and rated capacity; the first technical parameters of the transformer to be verified, including the short-circuit impedance voltage, high-voltage side rated voltage, and high-voltage side rated current, and providing the calculation formula for the first short-circuit impedance and the impedance of the low-voltage side when the high-voltage side of the main transformer is short-circuited. The clarification of these parameters and the provision of calculation formulas make it possible to accurately calculate the impedance characteristics of the generator and transformer under the short-circuit state when the differential protection polarity of the generator and transformer is verified. This provides an accurate basis for the subsequent determination of the short-circuit power supply capacity of the generator and transformer and the selection of a suitable inverter, ensuring that the verification process can be carried out according to the actual characteristics of the generator, improving the accuracy and reliability of the verification, avoiding the risk of verification errors or equipment damage due to inaccurate parameters, and ensuring the effectiveness of the differential protection polarity verification of the generator and transformer.

[0021] Preferably, when performing the differential protection polarity test, the primary current I ’ 极 Not less than the generator stator rated current I ’ 额 4%; in the calibration of the generator to be calibrated, the primary current I ’ 极 In the calibration state, the current I ’ 中 Not less than the generator stator rated current I ’ 额 4%; the voltage at the neutral point of the generator is U ’ 中 =(Z k2 +Z k3 )*I ’ 中 According to the voltage U at the neutral point of the generator ’ 中 , the primary current I of the differential protection polarity of the generator to be verified ’ 极 Calculate the first short-circuit power supply capacity according to the primary current I of the differential protection polarity of the generator to be tested ’ 极 , the voltage U at the neutral point of the generator ’ 中 , and the first short-circuit power supply capacity selects the target inverter.

[0022] Beneficial Effects: During differential protection polarity testing, the primary current and neutral point current of the generator to be tested must be no less than 4% of the rated stator current of the generator. A calculation formula for the neutral point voltage is also provided. This technical detail ensures that when verifying the polarity of the generator differential protection, the verification results are closer to actual operating conditions, allowing for more accurate verification of the correctness of the differential protection polarity. Furthermore, by calculating the voltage at the generator neutral point to determine the short-circuit power supply capacity and selecting the target inverter accordingly, the safety and reliability of the verification process can be guaranteed, avoiding problems such as inaccurate verification or equipment damage due to insufficient current or voltage, further improving the effectiveness and safety of generator differential protection polarity verification.

[0023] Preferably, a generator verification short-circuit point is set outside the current transformer of the high-voltage side circuit breaker of the generator or transformer to be verified.

[0024] Beneficial effects: It is clarified that the generator verification short-circuit point is set outside the current transformer of the high-voltage side circuit breaker of the generator and transformer to be verified. The setting position of this short-circuit point can directly calibrate the key connection parts between the generator and the main transformer, ensuring the accuracy of the differential protection polarity of this part. Setting the short-circuit point outside the current transformer of the high-voltage side circuit breaker of the transformer can avoid unnecessary impact on other equipment or systems, and also make the verification process safer and more reliable. In addition, this setting method can more directly reflect the differential protection polarity relationship between the generator and the main transformer, provide a more accurate verification basis for the protection device of the power plant generator-transformer group, ensure that the power plant generator-transformer group can accurately judge the differential protection polarity before starting, avoid protection misoperation or refusal to operate due to polarity errors, and improve the safety and stability of power plant operation.

[0025] Preferably, in S5, a first power injection point and a second power injection point are respectively set at the generator and transformer to be checked; the differential protection polarity check is performed at the first power injection point and the second power injection point respectively; wherein, the first power injection point includes the neutral point of the generator, and the second power injection point includes the high-voltage side of the high-voltage plant transformer, the desulfurization transformer and the excitation transformer.

[0026] Beneficial effects: The first power injection point and the second power injection point are respectively set on the generator and transformer to be calibrated. This setting enables the test power to be more accurately injected into the key parts of the equipment to be calibrated when performing differential protection polarity calibration. By setting the power injection points separately, it is possible to avoid interference from other factors during the transmission process of the test power supply, ensuring that the test power supply can accurately act on the specific parts of the transformer and generator, thereby improving the accuracy of the calibration results. At the same time, this setting method also provides a more flexible operating space for the calibration process, which is convenient for adjustment and optimization according to different calibration requirements and equipment characteristics, further enhancing the applicability and reliability of the calibration method, and providing more effective technical support for the differential protection polarity calibration of the generator-transformer group protection device of the power plant.

[0027] Preferably, the first short-circuit power supply capacity and the second short-circuit power supply capacity are compared. If the second short-circuit power supply capacity is higher than the first short-circuit power supply capacity, the second short-circuit power supply capacity is selected as the target inverter; conversely, if the second short-circuit power supply capacity is not higher than the first short-circuit power supply capacity, the first short-circuit power supply capacity is selected as the target inverter.

[0028] Beneficial effects: By comparing the first short-circuit power supply capacity and the second short-circuit power supply capacity and selecting a suitable target inverter based on the comparison results, it is possible to ensure that the selected inverter can meet the power supply capacity requirements during the verification process. This selection method avoids the risk of verification failure or equipment damage due to insufficient inverter capacity, and also prevents the waste of resources and increased costs caused by the selection of an inverter with too large a capacity. Accurately selecting the target inverter based on the actual required short-circuit power supply capacity can ensure the safety, reliability and economy of the verification process, making the verification method more feasible and practical in actual applications, and providing a more reasonable and efficient equipment selection basis for the differential protection polarity verification of the generator-transformer group protection device of the power plant, which helps to reduce verification costs and improve verification efficiency.

[0029] Preferably, the target inverter is set to V / F control mode, and the output voltage U is controlled at the power frequency of 50Hz by modifying the upper limit frequency of the inverter. 输出 , carry out polarity verification of the generator-transformer group protection device; U 输出 =Un / f 上限 *f 交流 , where U n is the rated operating voltage of the inverter, f 交流 The standard frequency of alternating current is 50Hz, f 上限 To set the upper limit frequency of the voltage regulator in real time.

[0030] Beneficial effects: By setting the target inverter to V / F control mode and using the adjustment of the inverter's operating upper limit frequency to control the output voltage at a frequency of 50Hz, flexible and controllable operation of the differential protection polarity calibration of the generator-transformer group protection device is achieved. This control method not only can accurately adjust the test voltage as needed, avoiding the problems of existing voltage regulators that are difficult to control the adjustment range and speed, and other static test methods that are prone to shock to the equipment, but also improves the safety and reliability of the test. At the same time, because the size and weight of the inverter are significantly reduced compared to existing voltage regulators, the equipment is more convenient to carry and operate, further improving the calibration efficiency and reducing the calibration cost, providing an efficient, economical and safe test method for the differential protection polarity calibration of the generator-transformer group protection device in power plants. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 Schematic diagram of a static short-circuit test method for verifying the polarity of differential protection of a generator and a transformer according to an embodiment. DETAILED DESCRIPTION

[0032] The following embodiments of the technical solution of the present invention will be described in detail with reference to the accompanying drawings. The following embodiments are only used to more clearly illustrate the technical solution of the present invention and are therefore only examples and are not intended to limit the scope of protection of the present invention. It should be noted that, unless otherwise specified, the technical or scientific terms used in this application should have the common meanings understood by those skilled in the art to which the present invention belongs.

[0033] The embodiment is further described: Voltage regulators are primarily used to stabilize output voltage, ensuring a stable voltage supply to loads and preventing voltage fluctuations from damaging electrical equipment. They are also commonly used calibration equipment in power plants.

[0034] Specifically, when using the existing static short-circuit test method to verify the polarity correctness of the differential circuit, the test power source is primarily an AC three-phase 380V low-voltage distribution system, input at the generator neutral point or at the high-voltage side terminals of the high-voltage transformer, desulfurization transformer, and excitation transformer. This verification task is completed by adding short-circuit points. Although economical and accurate in polarity verification, this existing method cannot be used on large generators and transformers. Therefore, existing technicians generally use a single low-voltage distribution system to perform the static short-circuit test method to verify the polarity correctness of the differential circuits of large generators and transformers.

[0035] In addition, existing technologies exist to address the uncontrollable test current issue of a single low-voltage distribution system. To address the aforementioned issues with the static short-circuit method for verifying differential protection polarity, existing methods employ AC three-phase 380V voltage regulators with a capacity sufficient to verify the polarity of generator and transformer differential protection. However, in practice, it has been found that while using voltage regulators to verify the polarity of differential protection for high-voltage transformers, desulfurization transformers, and excitation transformers is feasible, it is not feasible for verifying large generators and transformers. Large generators refer to steam turbine generators with a single unit capacity of 300MW or greater, and large transformers generally refer to power transformers with a rated power of 300 megavolt-amperes (MVA) or greater. At the same time, in theory, for example, Ding Xin, Xu Tianle, Jiang Weimin and Mo Fei jointly published a document in Hunan Electric Power Journal in 2022, "Automatic Polarity Verification Method for Current Transformer of Zero-Sequence Differential Protection of Generator Transformer Group", with the specific reference number being Ding Xin, Xu Tianle, Jiang Weimin, et al. Automatic Polarity Verification Method for Current Transformer of Zero-Sequence Differential Protection of Generator Transformer Group [J]. Hunan Electric Power, 2022(003):042.DOI:10.3969 / j.issn.1008-0198.2022.03.011. This document clearly mentions the use of a three-phase voltage regulator to perform polarity verification of the current transformer of the differential protection of the generator transformer group, and also states that the input voltage of the voltage regulator needs to be stable and that the test needs to be carried out during the continuous operation period of the generator transformer group. In addition, during the test, attention should be paid to the adjustment range and speed of the voltage regulator to avoid excessive impact on the equipment. It can be seen from this that when using a voltage regulator to check the correctness of the polarity of the differential circuit, it is easy to have incorrect adjustment range and speed, causing excessive impact on the equipment and causing unnecessary calibration accidents.

[0036] Example like Figure 1 As shown, this embodiment provides a static short-circuit test method for verifying the polarity of differential protection of generators and transformers, including: S1, respectively obtaining first technical parameters and second technical parameters of the generator and transformer to be checked.

[0037] Specifically, the second technical parameters include the transformer high-voltage side rated voltage Un, the transformer high-voltage side rated current In and the transformer short-circuit (or half-through) impedance voltage U k The first technical parameter includes the direct-axis super transient reactance saturation value X ’’ d , Generator rated voltage U ’ 额 , stator rated current I ’ 额 , rated capacity S; the first technical parameter of the transformer to be tested includes the short-circuit impedance voltage U ’ k. Rated voltage U on high voltage side ’ n. Rated current I on high voltage side’ n 。

[0038] S2, respectively calculating the first short-circuit impedance and the second short-circuit impedance of the generator and the transformer to be checked according to the first technical parameters and the second technical parameters.

[0039] Specifically, the calculation formula for the second short-circuit impedance to be verified is: Z k1 =U k *Un / (100*In); where the second short-circuit impedance is Z k1 The calculation formula for the first short-circuit impedance to be verified is: Z k2 =X ’’ d / 100*(U ’ 额 )² / S, the calculation formula for the low-voltage side impedance when the high-voltage side of the transformer to be tested is: Z k3 =U ’ k*U ’ n / (100*I ’ n); where Z k2 is the first short-circuit impedance to be checked, Z k3 The low-voltage side resistance when the high-voltage side of the transformer is short-circuited. The combined first short-circuit impedance of the generator and transformer is the first short-circuit impedance to be verified Z k2 The low-voltage side impedance Z when the high-voltage side of the main transformer to be verified is short-circuited k3 sum.

[0040] S3, respectively calculating a first short-circuit power supply capacity and a second short-circuit power supply capacity of the generator and the transformer required for protection polarity verification according to the first short-circuit impedance and the second short-circuit impedance.

[0041] Specifically, when the transformer to be tested is undergoing a differential protection polarity test, the primary current I 极 Not less than 4% of the rated current In on the high voltage side of the transformer. 极 In the calibration state, U 高侧 =Z k1* I 极 , where U 高侧 The high voltage side voltage of the high power transformer, desulfurization transformer and excitation transformer is U 高侧 , check the differential protection polarity current I 极 Calculate the capacity of the second short-circuit power supply according to the high-voltage side voltage U of the high-voltage transformer, desulfurization transformer and excitation transformer 高侧 , check the primary current I of the differential protection polarity 极 , and the second short-circuit power supply capacity selects the target inverter.

[0042] When the generator and transformer to be checked are undergoing differential protection polarity test, the primary current I ’ 极 Not less than the generator stator rated current I ’ 额 4%. When checking the differential protection polarity of the generator to be checked, the primary current I ’ 极 In the calibration state, the current I ’ 中 Not less than the generator stator rated current I ’ 额 4%; the voltage at the neutral point of the generator is U ’ 中 =(Z k2 +Z k3 )*I ’ 中。 According to the voltage U at the neutral point of the generator ’ 中 , the primary current I of the differential protection polarity of the generator to be verified ’ 极 Calculate the first short-circuit power supply capacity according to the primary current I of the differential protection polarity of the generator to be tested ’ 极 , the voltage U at the neutral point of the generator ’ 中 , and the first short-circuit power supply capacity selects the target inverter.

[0043] Whether it is the second short-circuit power supply capacity or the first short-circuit power supply capacity, the power supply capacity formula can be used: S= *I 极 *U, when calculating the second short-circuit power supply capacity S1= * I 极* U 高侧。 When calculating the first short-circuit power supply capacity, S2= * I ’ 极* U ’ 中。

[0044] S4, selecting a target inverter that matches the first short-circuit power supply capacity and the second short-circuit power supply capacity.

[0045] Specifically, the second short-circuit power supply capacity S1 is compared with the first short-circuit power supply capacity S2. If the second short-circuit power supply capacity is higher than the first short-circuit power supply capacity, the second short-circuit power supply capacity is selected as the target inverter. Conversely, if the second short-circuit power supply capacity is not higher than the first short-circuit power supply capacity, the first short-circuit power supply capacity is selected as the target inverter.

[0046] S5. Set the generator verification short-circuit point and transformer verification short-circuit point on the generator and transformer to be verified respectively. The target inverter performs differential protection polarity test according to the generator verification short-circuit point and transformer verification short-circuit point respectively, and carries out polarity verification of the generator-transformer group protection device according to the static short-circuit test method.

[0047] Specifically, a transformer verification short-circuit point is set outside the current transformer of the circuit breaker on the low-voltage side of the transformer. This short-circuit point is used to verify the correct polarity of differential protection on the high-voltage side of the transformer's high-voltage transformer, desulfurization transformer, and excitation transformer. A second power injection point is set on the transformer to be verified, including the high-voltage side of the transformer's high-voltage transformer, desulfurization transformer, and excitation transformer.

[0048] A generator verification short-circuit point is set at the high-voltage side circuit breaker of the generator and transformer to be verified. A first power injection point is set at the generator to be verified, and the first power injection point is outside the generator neutral point current transformer.

[0049] Set the target inverter to V / F control mode, and control the output voltage U at 50Hz by modifying the upper limit frequency of the inverter. 输出 , carry out polarity verification of the generator-transformer group protection device; U 输出 =Un / f 上限 *f 交流 , where U n is the rated operating voltage of the inverter, f 交流 The standard frequency of alternating current is 50Hz, f 上限 To set the upper limit frequency of the voltage regulator in real time.

[0050] Beneficial effects of this embodiment Compared with the existing technology, the load verification method and dynamic short-circuit test method are usually used to check the correctness of the differential circuit polarity, or the static short-circuit test method is used to check the correctness of the differential circuit polarity of the generator and transformer using a single output current AC three-phase 380V low-voltage distribution system.

[0051] This embodiment uses a frequency regulator in conjunction with a static circuit test method to verify the polarity correctness of the differential circuits of generators and transformers. This not only avoids the impact of static short-circuit testing on the protection of the modified power plant's generator-transformer units, improving test safety, but also offers universal applicability. It addresses the inability of existing static circuit test methods to verify the polarity correctness of the differential circuits of large generators (steam turbine generators with a single unit capacity of 300 MW and above) or transformers (power transformers with a rated power of 300 megavolt-amperes (MVA) and above). Furthermore, it eliminates the need to consume excessive fuel to conduct the test, resulting in low verification costs and an economical and environmentally friendly approach. Furthermore, the polarity correctness of the differential protection can be verified before the power plant's generator-transformer units are started, reducing verification costs. Furthermore, compared to testing using a voltage regulator, the device is significantly smaller.

[0052] Specifically, first of all, the voltage regulator and the frequency converter are different devices with different working principles. It is difficult for technicians to think of using the frequency converter to perform static short-circuit tests.

[0053] Specifically, first, based on commonly accepted verification methods and equipment, power plants primarily use the on-load verification method, dynamic short-circuit test method, and static short-circuit test method using an AC three-phase 380V voltage regulator to verify the polarity of generator and transformer differential protection. These methods have established relatively fixed operating modes and technical understanding within the industry. For example, the on-load verification method is performed while the equipment is operating, the dynamic short-circuit test method relies on the start-up and operation of the generator itself, and the use of the voltage regulator is based on its ability to provide stable voltage output. The long-term use of these existing methods has led technicians to prioritize the corresponding verification methods and equipment when faced with verification tasks.

[0054] Second, the technical problems solved by voltage regulators and frequency converters differ. Frequency converters are commonly used in power plants to control motor speed and power. Their primary function is to adjust the motor's operating state by varying the frequency, achieving energy savings and precise control. Technicians often limit their understanding of frequency converters to this function, rarely linking them to static short-circuit testing. While the frequency converter's V / F control method can regulate voltage, in practice, this function is primarily used for motor soft-starting and speed regulation, rather than providing a stable test voltage. Therefore, when considering calibration equipment, technicians often struggle to align the frequency converter's functionality with the requirements of static short-circuit testing.

[0055] Third, there are differences in the technical parameters of voltage regulators and frequency converters. Voltage regulators are primarily designed to provide stable voltage output, with an output voltage adjustment range and accuracy that meet the requirements of static short-circuit testing. Frequency converters, on the other hand, are primarily designed to control motor speed and power by varying frequency. Their output voltage adjustment is primarily designed to accommodate motor operation at different frequencies. While frequency converters can adjust voltage through V / F control, their output voltage stability and adjustment accuracy lag behind those of voltage regulators. When considering static short-circuit testing, technicians are more likely to choose a voltage regulator specifically designed for voltage regulation, rather than using a frequency converter as an alternative.

[0056] Fourth, differences in application scenarios. Voltage regulators are typically used for voltage regulation in the laboratory or on-site, making them highly compatible with static short-circuit testing. Frequency converters, on the other hand, are primarily used for motor control, primarily driving motors in industrial production processes. When conducting static short-circuit tests, technicians typically select appropriate equipment based on the specific requirements of the test. However, the application scenarios of frequency converters differ from those required for static short-circuit testing, making it difficult for technicians to consider frequency converters when selecting equipment.

[0057] Fifth, the specific nature of the test requirements. Static short-circuit tests must be conducted with the equipment not in operation and require stable test voltage and current to ensure accuracy and safety. Voltage regulators are well suited to this requirement. While frequency converters can adjust voltage through V / F control, in practice, their output voltage stability and regulation accuracy require rigorous testing and verification to ensure they meet the requirements of static short-circuit tests. When faced with such complex testing requirements, technicians prefer proven and stable equipment.

[0058] Sixth, voltage regulators are a commonly used calibration device. Since voltage regulators are a common and widely used device in power plants, they provide a highly stable voltage output for regular calibration of generators and transformers, ensuring they operate within their rated parameters. Furthermore, voltage in power systems fluctuates with load changes. Using a voltage regulator, these fluctuations can be simulated in a laboratory or field environment to verify the performance of generators and transformers under varying load conditions. Furthermore, beyond the normal operating range, voltage regulators can be used to simulate extreme voltage conditions, assessing the stability and safety of equipment under abnormal circumstances. Therefore, voltage regulators are a common and widely used device in power plants.

[0059] Seventh, and crucially, due to the VFD's inherent output characteristics, its output voltage waveform is not a standard sine wave. Conventional technology typically requires a sine wave test signal conforming to the standard AC frequency (50Hz) when verifying the polarity of the differential protection of a generator-transformer unit. Because the VFD's output waveform contains harmonic components, which can easily lead to deviations in the verification results, VFDs are not considered for this type of verification. Instead, voltage regulators that output stable sine waves are preferred as verification equipment. After all, verification of these modified power plant generator-transformer units is a crucial acceptance step, requiring stringent accuracy. However, generators and transformers typically have internal or external capacitors of a certain capacity, particularly within the circuit loops formed by the corresponding primary and secondary power injection points, as well as the generator and transformer verification short-circuit points. These capacitors absorb and filter harmonics. When a VFD outputs a non-sinusoidal voltage and is connected to a generator-transformer unit, the capacitors within the unit effectively absorb higher-order harmonics, resulting in a voltage waveform closely resembling a standard sine wave. Experimental examples have demonstrated that when verifying the polarity of the generator-transformer unit's differential protection, using a VFD in conjunction with the unit's own capacitors can produce a relatively ideal sinusoidal waveform at the output. Therefore, using a VFD for verification is not only feasible but also ensures accuracy and reliability, expanding the application of VFDs in verification scenarios.

[0060] In summary, this embodiment uses a frequency converter in conjunction with a static short-circuit test method to verify the polarity correctness of the differential circuits of generators and transformers, which is difficult for ordinary technicians to conceive of. This overcomes the technical prejudice in the industry against verifying the polarity correctness of the differential circuits of generators and transformers.

[0061] Secondly, after an overcurrent condition, the VFD's stable output current can reach up to 300 amperes, sufficient for verifying the polarity of the differential circuits of various current-spec generator-transformer sets. Furthermore, the VFD weighs approximately 50 kg, requiring only two people to perform this verification. Currently, however, a typical voltage regulator weighs 200 kg when operating at a maximum current of 40 A. Increasing the maximum operating current also increases the weight proportionally, reaching 1-2 tons when the maximum operating current reaches 400 A. Furthermore, there are currently no voltage regulators on the market with a maximum operating current exceeding several hundred amperes. This would require specialized customization, which is extremely costly and inconvenient for verification workers due to its weight. Furthermore, the test current required for steam turbine generators with a unit capacity of 300 MW or above, or power transformers with a rated power of 300 megavolt-amperes (MVA) or above, is typically over a hundred amperes. Currently available voltage regulators are not sufficient for verifying the polarity of the differential circuits of large generators and transformers.

[0062] Finally, this method utilizes the V / F control mode of the frequency converter to modify the upper operating limit of the frequency converter to control the output voltage at a 50Hz power frequency, ensuring current stability. The static short-circuit test method ensures stable short-circuit current output and verifies the correct polarity of the differential protection before the power plant generator-transformer set is started. This ensures safety and stability without impacting the 380V plant power system, resulting in low testing costs and meeting practical needs. Currently, whether it is the on-load verification method, the dynamic short-circuit test method, or the static short-circuit test method using a single current and low-voltage system, the test is typically performed using an excitation regulator. If an automatic excitation regulation system is used, a high-voltage power supply must be connected to provide excitation power. The resulting short-circuit current is difficult to control and can easily impact the generator-transformer set. This often requires the generator set to operate continuously at 3000 rpm for several hours to verify the correct polarity of the differential protection. This is not only time-consuming and fuel-intensive, but also leads to high testing costs.

[0063] Test example In the embodiment, a static short-circuit test method for verifying the polarity of the generator and transformer differential protection is used. The specific process of practical testing is as follows: The No. 4 high-voltage transformer of a certain factory is a three-winding double-split power transformer with a rated capacity of 31500 / 20000-20000kVA, a high-voltage side rated voltage Un of 20kV, a high-voltage side rated current In of 909.3A, a low-voltage side rated voltage of 6.3kV, a low-voltage side rated current of 1832.9A, a splitting coefficient of 5.37, a no-load loss of 21.2kW, a load loss of 113.8kW, a no-load current of 0.33%, and a half-through impedance voltage (high-voltage-low-voltage) U kThe current transformer ratio on the high-voltage side is 1500 / 5, and the current transformer ratio at the low-voltage side circuit breaker is 3000 / 5. k1 =U k *Un / (100*In), when the low voltage side of No. 4 high-voltage transformer is short-circuited, the second short-circuit impedance is Z k1 =13.9%*20*1000 / (100*909.3)=3.057Ω.

[0064] According to the verification of the polarity of the differential protection, the primary current I 极 It should not be less than 4%In, so the current on the high-voltage side of the differential protection polarity of the No. 4 high-voltage transformer in the plant should be no less than I 极= 4%In=36.36A, at this current the high-voltage side voltage of the high-voltage transformer is U 高侧 is the short-circuit impedance Z k With the high-voltage side current I 极 The product is: U 高侧 =Z k1* I 极= 3.057*36.36=111.15V.

[0065] Based on this, you can choose AC power frequency three-phase U 三相 =380 V input, 0-380 V output, rated current is 36.36A or more, that is, the power supply capacity S is greater than 24kVA voltage regulator, the power supply capacity is S= *I 极 *U 三相 .

[0066] To this end, the plant used a voltage regulator with an AC three-phase 380V input, 0-380V output, a rated current of 40A, a capacity of 30kVA, and a weight of 200 kg. The static short-circuit test method was used to pass the output voltage of the voltage regulator on the high-voltage side of the No. 4 high-voltage transformer, desulfurization transformer, and excitation transformer. A transformer verification short-circuit point was set outside the current transformer of the circuit breaker on the low-voltage side of the transformer to ensure current circulation on the high and low voltage sides.

[0067] After verifying the polarity of the differential protection by regulating the voltage with a voltage regulator and safely and smoothly completing the modification of the protection device for the No. 4 generator-transformer group, the polarity of the differential protection was verified for the high-voltage side of the high-voltage transformer, desulfurization transformer, and excitation transformer of the above-mentioned transformer. However, when attempting to use this AC power frequency three-phase 380V voltage regulator for the polarity verification of the differential protection of the generator and transformer, the calculated capacity did not meet the requirements, and a larger capacity AC power frequency three-phase voltage regulator was required. The calculation is as follows: Table 1 Main parameters of the plant's No. 4 generator

[0068] As shown in Table 1, the first short-circuit impedance is: Z k2 =X ’’ d / 100*(U ’ 额 )² / S=15.58% / 100*(20*20) / 353=0.1765Ω. The No. 4 main transformer of the plant is a double-winding power transformer with a rated capacity of S ’ =370000kVA, rated voltage on high voltage side U ’ n is 500kV, and the rated current on the high-voltage side is I ’ n is 388A, the rated voltage on the low-voltage side is 20kV, the rated current on the low-voltage side is 10680A, the no-load loss is 199.2kW, the no-load current is 0.12%, and the impedance voltage U ’ k is 14.04%. The current transformer ratio of the high-voltage side circuit breaker is 2500 / 1, and the current transformer ratio of the low-voltage side is 15000 / 5. The short-circuit impedance calculation formula Z on the high-voltage side of the main transformer is: k3 =U ’ k*U ’ n / (100*I ’ n) It can be obtained that the high-voltage side of No. 4 main transformer is short-circuited, and the low-voltage side short-circuit impedance Z k3 It is 0.263Ω.

[0069] According to the verification of the polarity of the differential protection primary current I' 极 Not less than 4%I ’ 额 If a generator short-circuit point is set at the high-voltage side circuit breaker of the main transformer, and power is added to the neutral point of the generator to perform differential protection polarity verification, then the current I at the neutral point of the generator No. 4, i.e. the main transformer differential protection polarity generator, will be ’ 中 Should be no less than 4%I ’ 额 =4%*10189=407.4A, the phase voltage at the neutral point of the generator is U ’ 中 =(Z k2 +Z k3 )*I ’ 中 * =(0.1765+0.263)*407.4* ≈310.1V. Therefore, a voltage regulator with a three-phase AC input of 380V, a 0-380V output, and a rated current of 407.4A or higher, or a capacity greater than 303.4kVA, should be selected. Such a large-capacity AC three-phase voltage regulator would be very heavy and bulky, requiring custom fabrication, resulting in high testing costs and difficulty in transportation.

[0070] Whether using the load verification method, the dynamic short-circuit test method or the common and existing static short-circuit test method to test the correctness of the differential circuit polarity, the voltage regulator is used to adjust the output voltage by changing the winding tap, so that the current transformer in the secondary circuit generates a corresponding current, which is used to test the polarity of the differential circuit.

[0071] From the above analysis and calculations, it can be seen that if a device with functions similar to that of an AC three-phase power frequency voltage regulator could be found, which could gradually increase the voltage from zero to the required value while also being controllable in real time, then when using the static short-circuit test method to verify the polarity of the generator and main transformer differential protection, there would be no impact on the AC three-phase 380V low-voltage power plant's power system.

[0072] Because power plants utilize a large number of AC three-phase 380V low-voltage inverters of various power ratings, engineers and technicians have a thorough understanding of their performance parameters and control methods. They've learned from their use that some inverters have a maximum operating frequency of up to 500Hz. By configuring the inverter to use V / F control, the maximum operating frequency can be adjusted to varying output voltages at 50Hz, much like the functionality of an AC three-phase power-frequency voltage regulator.

[0073] For example, if the maximum operating frequency of the inverter is set to 500Hz, then its output voltage at 50Hz (which meets the output frequency of AC power, that is, the standard output frequency of AC power) is = 380 / 500*50 = 38V; if the upper limit operating frequency of the inverter is set to 400Hz, then its output voltage at 50Hz is = 380 / 400*50 = 47.5V; if the upper limit operating frequency of the inverter is set to 300Hz, then its output voltage at 50Hz is = 380 / 300*50 = 63.3V; if the upper limit operating frequency of the inverter is set to 200Hz, then its output voltage at 50Hz is = 380 / 200*50 = 95V; if the upper limit operating frequency of the inverter is set to 100Hz, then its output voltage at 50Hz is = 380 / 100*50 = 190V. Similarly, by changing the upper operating frequency limit of the inverter, the output voltage can be adjusted from 38V to 380V at 50 Hz, effectively functioning as a voltage regulator. Compared to voltage regulators, AC three-phase 380V low-voltage inverters of the same power are significantly smaller and lighter. A 110kW AC three-phase 380V low-voltage inverter weighs approximately 50 kg and can be carried by two people.

[0074] To this end, the plant's engineering and technical personnel decided to use a 110kW AC three-phase 380V low-voltage inverter (with the overcurrent value set to 1.5 times) to conduct a polarity check on the generator and main transformer differential protection according to the static short-circuit test method. By setting a short-circuit point at the high-voltage side circuit breaker of the No. 4 main transformer and inserting power at the neutral point of the No. 4 generator using the inverter, the polarity of the generator and main transformer differential protection was verified. The verification results fully met expectations, indicating that the polarity verification was correct. The verification process did not impact the plant's AC three-phase 380V low-voltage distribution system, and was safe and controllable.

[0075] In order to verify the effect of the inverter in checking the polarity of differential protection of other transformers, the plant used the inverter to re-check the correctness of the differential protection polarity of No. 4 high-voltage transformer, desulfurization transformer and excitation transformer according to the static short-circuit test method. The effect was consistent with that of using an AC industrial frequency three-phase voltage regulator.

[0076] Beneficial effects of this test example After retrofitting the protection system for power plant generator-transformer units, the polarity of differential protection can be verified before unit startup, significantly reducing verification costs. Furthermore, by utilizing a three-phase 380V AC low-voltage inverter and employing the static short-circuit method, the polarity of differential protection for large generators and transformers can be verified without impacting the three-phase 380V AC low-voltage distribution system or causing uncontrollable test current.

[0077] In this specification, a large number of specific details are described. However, it is understood that embodiments of the present invention can be put into practice without these specific details. In some instances, known methods, systems, and techniques are not shown in detail so as not to obscure the understanding of this specification. In the description of this specification, the description of reference terms "one embodiment", "some embodiments", "example", "specific example" or "some examples" etc. means that the specific features, methods, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of this specification.

[0078] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the above embodiments, or make equivalent replacements for some or all of the technical features therein. These modifications or replacements do not deviate the essence of the corresponding technical solutions from the scope of the technical solutions of the embodiments of the present invention, and they should all be included in the scope of the claims and description of the present invention.

Claims

1. A static short-circuit test method for verifying the polarity of generator and transformer differential protection, characterized in that: include: S1, respectively obtaining first technical parameters and second technical parameters of the generator and transformer to be verified; S2, calculating the first short-circuit impedance and the second short-circuit impedance of the generator and the transformer to be checked respectively according to the first technical parameters and the second technical parameters; S3, respectively calculating a first short-circuit power supply capacity and a second short-circuit power supply capacity of the generator and the transformer required for protection polarity verification according to the first short-circuit impedance and the second short-circuit impedance; S4, selecting a target inverter that matches the first short-circuit power supply capacity and the second short-circuit power supply capacity; S5. Set the generator verification short-circuit point and transformer verification short-circuit point on the generator and transformer to be verified respectively. The target inverter performs differential protection polarity test according to the generator verification short-circuit point and transformer verification short-circuit point respectively, and carries out differential protection polarity verification of the generator-transformer group protection device according to the static short-circuit test method.

2. The static short-circuit test method for verifying the polarity of differential protection of generators and transformers according to claim 1 is characterized in that: The second technical parameters include the transformer high-voltage side rated voltage Un, the transformer high-voltage side rated current In and the second short-circuit impedance voltage U k ; The calculation formula for the second short-circuit impedance to be verified is: Z k1 =U k *Un / (100*In); where Z k1 is the second short-circuit impedance.

3. The static short-circuit test method for verifying the polarity of differential protection of generators and transformers according to claim 2 is characterized in that: When conducting differential protection polarity test, the primary current I of the transformer to be tested is 极 Not less than 4% of the rated current In on the high-voltage side of the transformer; The primary current I of the differential protection polarity of the transformer to be tested 极 In the calibration state, U 高侧 =Z k1* I 极 , where U 高侧 The high voltage side voltage of the high-voltage plant transformer, high voltage desulfurization transformer, and excitation transformer; According to the high voltage side voltage U of the high power transformer, desulfurization transformer and excitation transformer 高侧 , check the primary current I of the differential protection polarity 极 Calculate the capacity of the second short-circuit power supply according to the high-voltage side voltage U of the high-voltage transformer, desulfurization transformer and excitation transformer 高侧 , check the primary current I of the differential protection polarity 极 , and the second short-circuit power supply capacity selects the target inverter.

4. The static short-circuit test method for verifying the polarity of differential protection of generators and transformers according to claim 2 is characterized in that: A transformer verification short-circuit point is set outside the current transformer of the circuit breaker on the low-voltage side of the transformer. The transformer verification short-circuit point is used to inject a primary current outside the current transformer on the high-voltage side of the high-voltage transformer, desulfurization transformer and excitation transformer to verify the correctness of the differential protection polarity.

5. The static short-circuit test method for verifying the polarity of differential protection of generators and transformers according to claim 1 is characterized in that: The first technical parameter includes the direct-axis super transient reactance saturation value X ’’ d , Generator rated voltage U ’ 额 , stator rated current I ’ 额 , rated capacity S; The first technical parameter of the transformer to be tested includes the short-circuit impedance voltage U ’ k. Rated voltage U on high voltage side ’ n. Rated current I on high voltage side ’ n; The calculation formula for the first short-circuit impedance to be verified is: Z k2 =X ’’ d / 100*(U ’ 额 )² / S; where Z k2 is the first short-circuit impedance to be verified; When the high-voltage side of the transformer to be tested is short-circuited, the impedance calculation formula for the low-voltage side is: Z k3 =U ’ k*U ’ n / (100*I ’ n); where Z k3 The impedance of the low-voltage side of the transformer to be tested when the high-voltage side is short-circuited; The combined first short-circuit impedance of the generator and transformer is the first short-circuit impedance to be verified Z k2 The impedance Z of the low-voltage side when the high-voltage side of the generator or transformer to be tested is short-circuited k3 sum.

6. The static short-circuit test method for verifying the polarity of differential protection of generators and transformers according to claim 5, characterized in that: When conducting differential protection polarity test, the primary current I of the generator to be tested is ’ 极 Not less than the generator stator rated current I ’ 额 , rated current of transformer high voltage side I ’ 4% of n; When checking the polarity of the differential protection of the generator to be checked, the primary current I ’ 极 In the calibration state, the primary current I injected into the neutral point of the generator to be calibrated is ’ 中 Not less than the generator stator rated current I ’ 额 4%; Generator neutral point voltage U ’ 中 =(Z k2 +Z k3 )*I ’ 中 According to the voltage U at the neutral point of the generator ’ 中 , the primary current I required for the polarity of the differential protection of the generator to be verified ’ 极 Calculate the first short-circuit power supply capacity according to the primary current I required for the polarity of the differential protection of the generator to be verified. ’ 极 , the voltage U at the neutral point of the generator ’ 中 , determine the first short-circuit power supply capacity and select the target inverter.

7. The static short-circuit test method for verifying the polarity of differential protection of generators and transformers according to claim 4 is characterized in that: A generator verification short-circuit point is set outside the current transformer of the high-voltage side circuit breaker of the generator or transformer to be verified.

8. The static short-circuit test method for verifying the polarity of differential protection of generators and transformers according to claim 7, characterized in that: In S5, a first power injection point and a second power injection point are respectively set on the generator to be checked and the transformer to be checked; The differential protection polarity is checked at the first power injection point and the second power injection point respectively; the first power injection point includes the neutral point of the generator, and the second power injection point includes the high-voltage side of the high-voltage plant transformer, desulfurization transformer and excitation transformer.

9. The static short-circuit test method for verifying the polarity of differential protection of generators and transformers according to claim 1, characterized in that: comparing the first short-circuit power supply capacity and the second short-circuit power supply capacity, and selecting the second short-circuit power supply capacity as the target inverter if the second short-circuit power supply capacity is higher than the first short-circuit power supply capacity; On the contrary, if the second short-circuit power supply capacity is not higher than the first short-circuit power supply capacity, the first short-circuit power supply capacity is selected as the target inverter.

10. The static short-circuit test method for verifying the polarity of differential protection of generators and transformers according to claim 1, characterized in that: Set the target inverter to V / F control mode, and control the different voltages U output at 50Hz by modifying the upper limit frequency of the inverter. 输出 , carry out polarity verification of the generator-transformer group protection device; U 输出 =Un / f 上限 *f 交流 , where U n is the rated operating voltage of the inverter, f 交流 The standard frequency of alternating current is 50 Hz, f 上限 To set the upper limit frequency of the voltage regulator in real time.

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