Direct current voltage resistance and leakage test system and method for insulation diagnosis of hydro-generator

Abstract

The present application relates to a DC voltage resistance and leakage test system and method for water turbine generator insulation diagnosis, and belongs to the technical field of water turbine generator stator winding insulation state evaluation. The system comprises a control and data processing server, a signal acquisition and transmission module, a voltage boost control unit, a DC current measurement unit and a DC high voltage generation unit. The present application can meet the needs of various DC voltage boost leakage current tests, realize parameterization of the test process and structured storage of test data, ensure consistency and repeatability of the test process through parameterization of the test process, improve test data quality, and meet the needs of big data state analysis for condition-based maintenance.

Description

Technical Field

[0001] This invention belongs to the technical field of stator winding insulation condition assessment for hydro-generators, specifically relating to a DC withstand voltage and leakage test boost control system and digital method for assessing the insulation condition of stator windings in hydro-generators. Background Technology

[0002] With the development of industrial automation, digitalization, and big data and artificial intelligence, the power industry is gradually implementing intelligent operation and maintenance, with hydropower maintenance being a crucial component. Condition-based maintenance is a vital support for intelligent operation and maintenance, and a key element within it is condition analysis. The foundation of maintenance condition analysis lies in the quality and reliability of various offline and online testing data, and data quality depends on the accuracy of the testing instruments and the effectiveness of the testing methods.

[0003] Under DC voltage, the insulation structure of a hydro-generator generates a small DC current containing capacitive current, polarization current, conduction current, and leakage current components. These components change differently over time under voltage. As the voltage decreases over time, the remaining current consists of conduction current and surface leakage current. The conduction current is related to the insulation degradation state; it gradually increases under the same voltage as the insulation ages. Regularly measuring this current is crucial for monitoring and analyzing the insulation condition and guiding condition-based maintenance. Different generator insulation structures exhibit significant differences in the time characteristics of capacitive current, polarization current, conduction current, and leakage current, especially with polarization absorption times reaching tens of hours. Therefore, efficiently and accurately measuring conduction current is difficult. Theoretically, there are several testing methods, such as isochronous stepped voltage ramp testing, time-division stepped voltage ramp testing, and ramp voltage ramp testing. However, these methods require sophisticated testing equipment, and current DC withstand voltage and leakage current testing equipment does not meet the requirements of these three voltage ramp tests.

[0004] DC withstand voltage and leakage current testing are crucial offline tests for the insulation performance of hydroelectric generators. Traditional testing focuses on withstand voltage pass rate assessment while neglecting leakage current analysis. Driven by demand, testing equipment manufacturing has increasingly prioritized higher withstand voltage and capacity parameters, as well as system portability, miniaturization, and low cost. Functions are limited to manual DC voltage boosting / pull-down, leakage current measurement, and voltage / current display. However, the voltage / current and operation are not in a closed-loop control system, lacking automation. The equipment has low levels of automation and digitization, requiring technicians to manually boost voltage and record data as needed. Overall, the testing equipment is functionally simple, manual operation is inefficient, data reliability is poor, and the unstructured paper-based data is prone to creating data silos. Current DC withstand voltage and leakage testing equipment does not meet the requirements for withstand voltage and leakage testing in hydroelectric generator insulation condition analysis.

[0005] Current problems with DC withstand voltage and leakage current testing equipment in insulation testing of hydro-generators:

[0006] 1) There is no automatic function. The leakage current measurement is controlled by manual operation. The difference between the isochronous stepped voltage rise and the strict isochronous voltage rise is large. The reliability of leakage current data under each voltage step is low. The inconsistent voltage rise rate and the timing of segmented leakage current reading lead to large differences in the leakage current of the test results, and potential early defects are masked.

[0007] 2) Without automatic functions, the time-sharing step-up and ramp-up voltage boosting methods, which have higher efficiency and accuracy, cannot be implemented.

[0008] 3) The level of digitalization is low. The test equipment has no operating system and no automatic measurement and recording function. During the test, the instrument data is recorded manually. The data is discrete and the information is incomplete.

[0009] 4) The level of digitization is low. Test parameters such as boost rate, boost step, time interval, and test device parameters are not structured, which makes it difficult to reuse parameters and ensure that the parameters are consistent in multiple tests on the same device.

[0010] 5) The test results data records are not structured data with a unified standard, which makes them inconvenient for insulation condition analysis.

[0011] Therefore, overcoming the shortcomings of existing technologies is an urgent problem to be solved in the field of hydro-generator stator winding insulation condition assessment. Summary of the Invention

[0012] The purpose of this invention is to address the shortcomings of existing technologies and overcome the problems existing in current DC withstand voltage and leakage current testing equipment for hydro-generator insulation testing. It provides a DC withstand voltage and leakage current testing system and method for hydro-generator insulation diagnosis, meeting various DC boost leakage current testing needs, improving test data quality, enabling structured storage of test data, and meeting the needs of condition analysis for condition-based maintenance.

[0013] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0014] A DC withstand voltage and leakage test system for insulation diagnosis of hydro-generators includes: a control and data processing server, a signal acquisition and transmission module, a boost control unit, a DC current measurement unit, and a DC high voltage generation unit;

[0015] The boost control unit is connected to the signal acquisition and transmission module and the DC high voltage generator unit respectively, and is used to control the operation of the DC high voltage generator unit;

[0016] The DC high voltage generating unit is used to generate DC voltage and output it to the tested turbine generator.

[0017] The DC current measurement unit is connected to the test turbine generator and the DC high voltage generating unit respectively, and is used to measure the current output from the DC high voltage generating unit to the test turbine generator;

[0018] The signal acquisition and transmission module is also connected to the DC current measurement unit, the DC high voltage generation unit, and the control and data processing server, respectively. It is used to acquire the measurement results of the DC current measurement unit, the output information of the DC high voltage generation unit, and the control signals of the boost control unit, and then transmit them to the control and data processing server.

[0019] The control and data processing server is used to control the operation of the signal acquisition and transmission module, and to transmit control signals to the boost control unit through the signal acquisition and transmission module, thereby controlling the operation of the boost control unit; it is also used to process the data transmitted from the signal acquisition and transmission module to obtain the DC withstand voltage and leakage current test results of the tested hydro-generator.

[0020] This invention also provides a DC withstand voltage and leakage test method for insulation diagnosis of hydro-generators, using the aforementioned DC withstand voltage and leakage test system for insulation diagnosis of hydro-generators, comprising the following steps:

[0021] Step (1): Determine the DC leakage voltage boosting method and parameters based on the rated voltage of the hydro-generator insulation structure; the voltage boosting method includes the isochronous step voltage boosting method, the time-sharing step voltage boosting method, and the ramp voltage boosting method;

[0022] Among them, the isochronous stepped voltage boost test parameters are: parameter number CID, generator rated voltage UN, test voltage UT, stepped voltage ΔU, voltage accuracy requirement ±d%, fast rise ratio n, fast rise interval time T1, slow rise interval time T2, voltage stabilization time Td, fast voltage rise and fall parameter Kk, and slow voltage rise and fall parameter Km.

[0023] Time-sharing stepped voltage boosting parameters: Parameter number CID, generator rated voltage UN, test voltage UT, initial stepped voltage ΔU0, stepped voltage ΔU1~ΔUm, voltage accuracy ±d%, fast rise ratio n, fast rise interval time T1, slow rise interval time T2, fast voltage rise and fall parameter Kk, slow voltage rise and fall parameter Km;

[0024] Ramp-up parameters: Parameter number CID, Generator rated voltage UN, Initial step voltage ΔU0, Test voltage UT, Voltage accuracy ±d%, Fast ramp ratio n, Ramp-up slope K, Ramp-up control interval time T, Fast ramp interval time T1, Slow ramp interval time T2, Stabilization time Td, Fast voltage ramp-up parameter Kk, Slow voltage ramp-up parameter Km;

[0025] Step (2): Before each test, retrieve the corresponding test parameters by parameter number CID, confirm and start. The test system will automatically complete the test and record and store the test parameters and test data. When storing, the test data is stored under the corresponding number by the test data record number DID in sequence.

[0026] Step (3) retrieves the test data of the same equipment in the time dimension by using the DID test data record number, and then analyzes the insulation degradation trend through the test data.

[0027] Furthermore, preferably, in step (2), the stored content includes voltage, leakage current, time data, and current curves that change with time and voltage.

[0028] Furthermore, preferably, the isochronous stepped pressurization specifically includes the following steps:

[0029] S1. First, based on the isochronous stepped voltage boost test parameters, determine the voltage of each step: 1ΔU = 1*ΔU, 2ΔU = 2*ΔU, 3ΔU = 3*ΔU, and so on.

[0030] S2. Send a fast rise signal at a rate of Kk according to the fast rise interval T1, and continuously monitor the output voltage Uo. When the output voltage reaches n%1ΔU, switch to a slow rise signal at a rate of Km with a slow rise interval T2 to control the voltage rise until the output voltage Uo meets (1±d%)1ΔU. Start timing Td. During the process, continuously monitor the output voltage according to the ±d% accuracy requirement, and send a signal at a rate of Km with a slow rise interval T2 to adjust and maintain the voltage Uo at (1±d%)1ΔU.

[0031] S3. After the voltage stabilization time Td is reached, repeat the above 1ΔU voltage boosting process to perform 2ΔU step voltage boosting, 3ΔU step voltage boosting, and so on, until the required highest test voltage UT is reached.

[0032] Furthermore, preferably, the time-sharing stepped voltage boosting method specifically includes the following steps:

[0033] a1. Obtain the initial step voltage ΔU0;

[0034] a2. When the voltage rises, a fast rise signal with a rate of Kk is sent at the fast rise interval T1, and the output voltage Uo is continuously monitored. When the output voltage reaches n%ΔU0, the slow rise signal with a rate of Km at the slow rise interval T2 is switched to control the voltage rise until the output voltage Uo meets (1±d%)ΔU0. Then, the timer Td0 is started to stabilize the voltage. Td0 = 10 minutes. During the voltage stabilization process, the leakage current is continuously monitored, collected and recorded.

[0035] a3. Take the leakage current value I in the first minute of the Td0 timing process. 1m Leakage current I at minute 3.163.16m Leakage current value I at the 10th minute 10m The polarization absorption characteristic parameter N of the insulating medium is calculated using formulas (1) and (2).

[0036] I tc =(I1*I 10 )-I 3.16 2 / (I 1+ I 10 )-2*I 3.16 (1)

[0037] N=(I1-I tc ) / (I 10 -I tc (2)

[0038] Among them, I tc Indicates leakage current;

[0039] a4. Calculate the holding time Td1, Td2, ..., Tdm values ​​at each step voltage using the polarization absorption characteristic parameter N of the insulating medium and the step voltages ΔU1 to ΔUm.

[0040] a5.Td0 timeout immediately starts ΔU1 boost. When boosting begins, a fast boost signal is sent at a rate of Km according to the fast boost interval T1, and the output voltage Uo is continuously monitored. When the voltage reaches n%ΔU1, the slow boost signal with a rate of Km according to the slow boost interval T2 is switched to control the boost until the output voltage Uo = ΔU1 ± d%ΔU1.

[0041] a6. After the voltage reaches ΔU1, start timing Td1. During the process, continuously monitor the output voltage according to the ±d% accuracy requirement, and send a voltage regulation control signal with a slow rise interval T2 and a rate Km to adjust and maintain the voltage.

[0042] a7. After Td1 expires, immediately repeat the ΔU2 step voltage boost Td2 voltage hold, ΔU3 step voltage boost Td3 voltage hold, and so on, until the required highest test voltage UT is reached. Record the leakage current value during the process.

[0043] Furthermore, preferably, the ramp pressurization method specifically includes the following steps:

[0044] b1. Determine the initial step voltage ΔU0, and determine the initial voltage time Td0, where Td0 = 10 minutes;

[0045] b2. When the voltage boost begins, a fast boost signal at rate Kk is sent according to the fast boost interval T1, and the output voltage Uo is continuously monitored. When the output voltage Uo reaches n%ΔU0, a slow boost signal at rate Km with a slow boost interval T2 is switched to control the voltage boost until the output voltage U meets ΔU0±d%ΔU0. After the voltage reaches ΔU0, timing Td0 is started. During the process, the output voltage is continuously monitored according to the ±d% accuracy requirement, and a voltage regulation control signal at rate Km with a slow boost interval T2 is sent to adjust and maintain the voltage. During the voltage regulation process, leakage current is continuously detected, collected, and recorded.

[0046] b3. Take the leakage current value I at the 15th second during the Td0 timing process. 15S Leakage current I at 60 seconds 60S Leakage current value I at 600 seconds 600S Calculate the insulation resistance R, absorption ratio DAR, and polarization index PI; the calculation formula is: R = ΔU0 / I 60S DAR = I 60S / I 15S PI = I 600S / I60S ;

[0047] b4. Determine whether R, DAR, and PI meet the insulation requirements according to the system's set threshold. If all meet the insulation requirements, immediately start the ramp voltage rise with slope K; send a slow voltage rise signal according to the ramp voltage rise control interval T, and continuously monitor the output voltage Uo. When the output voltage Uo reaches n%UT, switch the slow voltage rise signal with a slow voltage rise interval T2 and a rate Km to control the voltage rise until the output voltage Uo = UT ± d%UT; start timing Td, and continuously monitor the output voltage according to the ±d% accuracy requirement during the process, and send a voltage regulation control signal with a slow voltage rise interval T2 and a rate Km to adjust and hold the voltage until the timing is completed.

[0048] In this invention, each voltage boosting method is parameterized and the parameters are stored in a structured manner. For each generator and each voltage boosting method, a set of test parameters is created and recorded under a unique parameter number. Subsequently, the same voltage boosting process is achieved by repeatedly calling the voltage boosting parameters using the parameter number. For example, when setting the isochronous stepped voltage boosting test parameters, firstly, the stepped voltage ΔU and the test voltage UT are determined based on the generator's rated voltage UN, and the gradient number UT / ΔU is determined. Further, the step voltages are determined as follows: 1ΔU = 1*ΔU, 2ΔU = 2*ΔU, 3ΔU = 3*ΔU, and 4ΔU = 4*ΔU.

[0049] During the isochronous stepped voltage boost test of this invention, voltage boost control is achieved by setting the fast boost interval T1, the slow boost interval T2, and the fast voltage rise / fall parameter Kk (kV / second) and the slow voltage rise / fall parameter Km (kV / second) after receiving the control signal; where ΔU is generally selected as 0.5UN; UT is generally 2UN, 2.5UN or 3UN;

[0050] In the time-sharing stepped voltage boosting parameters of this invention, the stepped voltage includes ΔU1, ΔU2, ..., ΔUm; m is a positive integer, and its value can be set as needed. For example, m = 5, i.e., stepped voltages ΔU1, ΔU2, ΔU3, ΔU4, ΔU5.

[0051] When setting the time-sharing stepped voltage boost test parameters, the initial stepped voltage ΔU0 is determined based on the generator's rated voltage UN and insulation structure, and is generally selected as 2.5kV or 5kV.

[0052] In this invention, the leakage current is collected and recorded through a DC current measurement unit. tc This indicates leakage current, including conductivity and surface leakage current.

[0053] The specific method for calculating the holding times Td1, Td2, Td3, Td4, and Td5 at each step voltage using the polarization absorption characteristic parameter N of the insulating medium and the step voltages ΔU1, ΔU2, ΔU3, ΔU4, and ΔU5 (i.e., m = 5 in ΔUm) is as follows:

[0054] Different voltage steps and the number of steps are selected according to the experimental requirements. The following example uses six voltage steps. Each step has a voltage holding time, and the holding time is different for each step voltage. The goal is to select a moment where the leakage current magnitude is proportional to the corresponding step voltage. By changing the recording time, the leakage current, which is related to both voltage and time, is transformed into a voltage-proportional relationship, thereby improving the sensitivity of leakage current in determining insulation status. Specifically, the holding times Td1, Td2, Td3, Td4, and Td5 at each step voltage are calculated using the insulation dielectric polarization absorption characteristic parameter N and the step voltages ΔU1, ΔU2, ΔU3, ΔU4, and ΔU5. The calculation formula is as follows:

[0055] I ΔU1 / I ΔU0 =ΔU1 / ΔU0 (3)

[0056] I ΔU2 / I ΔU0 =ΔU2 / ΔU0 (4)

[0057] I ΔU3 / I ΔU0 =ΔU3 / ΔU0 (5)

[0058] I ΔU4 / I ΔU0 =ΔU4 / ΔU0 (6)

[0059] I ΔU5 / I ΔU0 =ΔU5 / ΔU0 (7)

[0060] I ΔU0 =K*C*ΔU0*Td0 -N (8)

[0061] I ΔU1 =K*C*{ΔU0*(Td0+Td1) -N +(ΔU1-ΔU0)*Td1 -N } (9)

[0062] I ΔU2 =K*C*{ΔU0*(Td0+Td1+Td2) -N +(ΔU1-ΔU0)*(Td1+Td2) -N +(ΔU

[0063] 2-ΔU1)*Td2 -N }(10)

[0064] I ΔU3 =K*C*{ΔU0*(Td0+Td1+Td2+Td3) -N +(ΔU1-ΔU0)*(Td1+Td2+Td3)

[0065] -N +(ΔU2-ΔU1)*(Td2+Td3) -N +(ΔU3-ΔU2)*Td3 -N }(11)

[0066] I ΔU4 =K*C*{ΔU0*(Td0+Td1+Td2+Td3+Td4) -N +(ΔU1-ΔU0)*(Td1+Td2

[0067] +Td3+Td4) -N +(ΔU2-ΔU1)*(Td2+Td3+Td4) -N +(ΔU3-ΔU2)*(Td3+Td4) -N +(ΔU4-ΔU3)*Td4 -N }(12)

[0068] I ΔU5 =K*C*{ΔU0*(Td0+Td1+Td2+Td3+Td4+Td5)-N +(ΔU1-ΔU0)*(Td1

[0069] +Td2+Td3+Td4+Td5) -N +(ΔU2-ΔU1)*(Td2+Td3+Td4+Td5) -N +(ΔU3-ΔU2)*(Td3+Td4+Td5) -N +(ΔU4-ΔU3)*(Td4+Td5) -N +(ΔU5-ΔU4)*Td5 -N}

[0070] (13) The calculation equations for Td1, Td2, Td3, Td4, and Td5 can be derived from the above formulas:

[0071] (ΔU1-ΔU0)*Td1 -N +ΔU0*(Td0+Td1) -N -ΔU1*Td0 -N =0 (14)

[0072] (ΔU2-ΔU1)*Td2 -N +(ΔU1-ΔU0)*(Td2+Td1) -N +ΔU0*(Td2+Td1+Td0) -N -ΔU2*Td0 -N =0 (15)

[0073] (ΔU3-ΔU2)*Td3 -N +(ΔU2-ΔU1)*(Td3+Td2) -N +(ΔU1-ΔU0)*(Td3+Td2+Td1) -N +ΔU0*(Td3+Td2+Td1+Td0) -N -ΔU3*Td0 -N =0 (16)

[0074] (ΔU4-ΔU3)*Td4 -N +(ΔU3-ΔU2)*(Td4+Td3) -N +(ΔU2-ΔU1)*(Td4+Td3+Td2) -N +(ΔU1-ΔU0)*(Td4+Td3+Td2+Td1) -N +ΔU0*(Td4+Td3+Td2+Td1+Td0) -N -ΔU4*Td0 -N =0 (17)

[0075] (ΔU5-ΔU4)*Td5 -N+(ΔU4-ΔU3)*(Td5+Td4) -N +(ΔU3-ΔU2)*(Td5+Td4+Td3) -N +(ΔU2-ΔU1)*(Td5+Td4+Td3+Td2) -N +(ΔU1-ΔU0)*(Td5+Td4+Td3+Td2+Td1) -N +ΔU0*(Td5+Td4+Td3+Td2+Td1+Td0) -N -ΔU5*Td0 -N =0 (18)

[0076] In the above formula:

[0077] The K-winding absorption coefficient is determined by the winding insulation medium structure, the type of insulation material, and the temperature. For a specific generator, it remains constant at the same temperature. The derivation process parameters do not need to be considered in the time calculation. This is existing technology, and this invention does not improve upon it.

[0078] The parameters of the C winding capacitance are constant for a specific generator and can be measured by a capacitance testing instrument. The derivation process parameters do not need to be considered in the time calculation.

[0079] Polarization absorption characteristic parameters of N insulating dielectric;

[0080] The voltage steps are ΔU1, ΔU2, ΔU3, ΔU4, and ΔU5. Each voltage step must gradually increase, with the latter being greater than the former. The gradient can be arbitrary, and each voltage step value can be any value greater than the previous step.

[0081] The duration of holding at each of the following voltage steps: Td1, Td2, Td3, Td4, and Td5;

[0082] I ΔU1 I ΔU2 I ΔU3 I ΔU4 I ΔU5 Leakage current at the end of the holding time under each voltage step;

[0083] Detailed calculation steps:

[0084] Taking an 18kV hydro-generator as an example, time-sharing stepped DC withstand voltage and leakage current tests were conducted.

[0085] The first step is to determine the voltage boosting plan as 6 steps: ΔU0 = 5kV, ΔU1 = 9kV, ΔU2 = 18kV, ΔU3 = 27kV, ΔU4 = 36kV, ΔU5 = 45kV, and Td0 = 10 minutes.

[0086] The second step is to calculate N using formulas (1) and (2);

[0087] The third step is to calculate Td1 using N, ΔU0, ΔU1, Td0 and formula (14);

[0088] The fourth step is to calculate Td2 using N, ΔU0, ΔU1, ΔU2, Td0, Td1 and formula (15);

[0089] Fifth step, calculate Td3 using N, ΔU0, ΔU1, ΔU2, ΔU3, Td0, Td1, Td2 and formula (16);

[0090] Step 6: Calculate Td4 using N, ΔU0, ΔU1, ΔU2, ΔU3, ΔU4, Td0, Td1, Td2, Td3 and formula (17);

[0091] Step 7: Calculate Td5 using N, ΔU0, ΔU1, ΔU2, ΔU3, ΔU4, ΔU5, Td0, Td1, Td2, Td3, Td4 and formula (18).

[0092] Compared with the prior art, the beneficial effects of this invention are as follows:

[0093] This invention provides a DC withstand voltage and leakage test system and method for insulation diagnosis of hydro-generators. Through hardware innovation, it achieves equipment automation and proposes isochronous stepped voltage ramp control methods, time-sharing stepped voltage ramp control methods, and ramp stepped voltage ramp control methods for DC high-voltage insulation testing of hydro-generators, as well as parameterization and digitization of the voltage ramp process. The computer program controls the output of the isochronous stepped voltage, time-sharing stepped voltage, and ramp voltage using the aforementioned control methods and parameters. 1) Programmable isochronous stepped voltage testing ensures test consistency; 2) Time-sharing stepped voltage ensures that the polarization current in the leakage current is proportional to the voltage, thus ensuring that changes in conductivity current representing insulation aging are not masked; 3) Ramp voltage ensures that the capacitive current is a constant related to the voltage ramp rate, thus ensuring sensitive detection of conductivity current representing insulation aging.

[0094] This invention proposes a parameterized and structured method for the testing process to ensure repeatability and consistency, thereby improving the accuracy of leakage current measurement. Based on this method, software and hardware development enables the digitization and intelligentization of generator insulation DC high-voltage testing instruments, shortening testing time, increasing testing efficiency, eliminating the influence of manual operation differences, improving testing accuracy, and enhancing data quality. This, in turn, improves the reliability of time characteristic analysis, voltage characteristic analysis, and trend analysis of hydro-generator insulation leakage current, enabling generator insulation status analysis based on DC leakage current.

[0095] Building upon this system and methodology, further IoT development is undertaken on the structured basis of intelligent instruments and test information data (equipment information, test parameters, and test data). This enables interconnection and sharing among different test instruments and equipment, generator information from different plants and stations, test parameters, and test databases, promoting the intelligentization of electrical preventive testing. Structured test big data is realized, and diagnostic models are developed through data mining to achieve intelligent condition diagnosis based on tests. This paves the way for intelligent maintenance and condition-based maintenance, opening up key nodes for future intelligent maintenance. Attached Figure Description

[0096] Figure 1 This is a schematic diagram of the DC withstand voltage and leakage test boost control system for evaluating the insulation status of stator windings of hydro generators according to the present invention.

[0097] Figure 2 This is an isochronous step pressure rise diagram;

[0098] Figure 3 This is a boost control diagram;

[0099] Figure 4 This is a time-sharing stepped pressure increase chart;

[0100] Figure 5 This is a diagram showing the pressure increase of a sloping, stepped structure.

[0101] Figure 6 The UIT plot is a graph showing the voltage and current changes over time in an isochronous stepped boost test.

[0102] Figure 7 The UIT diagram for time-sharing stepped boost voltage test shows the voltage and current changing over time.

[0103] Figure 8 The UIT graph for the ramp-up test shows the voltage and current changing over time.

[0104] Figure 9 The diagram shows the UI characteristic of the ramp-up voltage and the current graph as a function of voltage. Detailed Implementation

[0105] The present invention will now be described in further detail with reference to the embodiments.

[0106] Those skilled in the art will understand that the following embodiments are for illustrative purposes only and should not be construed as limiting the scope of the invention. Where specific techniques or conditions are not specified in the embodiments, they are performed in accordance with the techniques or conditions described in the literature in the field or according to the product instructions. Materials or equipment whose manufacturers are not specified are all conventional products that can be obtained by purchase.

[0107] like Figure 1As shown, the DC withstand voltage and leakage test system for insulation diagnosis of hydro generator includes: a control and data processing server 101, a signal acquisition and transmission module 102, a boost control unit 103, a DC current measurement unit 104, and a DC high voltage generation unit 105.

[0108] The boost control unit 103 is connected to the signal acquisition and transmission module 102 and the DC high voltage generator unit 105 respectively, and is used to control the operation of the DC high voltage generator unit 105.

[0109] The DC high voltage generating unit 105 is used to generate DC voltage and output it to the test turbine generator;

[0110] The DC current measuring unit 104 is connected to the test turbine generator and the DC high voltage generating unit 105 respectively, and is used to measure the current output from the DC high voltage generating unit 105 to the test turbine generator.

[0111] The signal acquisition and transmission module 102 is also connected to the DC current measurement unit 104, the DC high voltage generation unit 105, and the control and data processing server 101, respectively, and is used to acquire the measurement results of the DC current measurement unit 104, the output information of the DC high voltage generation unit 105, and the control signals of the boost control unit 103, and then transmit them to the control and data processing server 101.

[0112] The control and data processing server 101 is used to control the operation of the signal acquisition and transmission module 102, and to transmit control signals to the boost control unit 103 through the signal acquisition and transmission module 102, thereby controlling the operation of the boost control unit 103; it is also used to process the data transmitted from the signal acquisition and transmission module 102 to obtain the DC withstand voltage and leakage current test results of the tested hydro turbine generator.

[0113] A DC withstand voltage and leakage test method for insulation diagnosis of hydro-generators, using the aforementioned DC withstand voltage and leakage test system for insulation diagnosis of hydro-generators, includes the following steps:

[0114] Step (1): Determine the DC leakage voltage boosting method and parameters based on the rated voltage of the hydro-generator insulation structure; the voltage boosting method includes the isochronous step voltage boosting method, the time-sharing step voltage boosting method, and the ramp voltage boosting method;

[0115] Among them, the isochronous stepped voltage boost test parameters are: parameter number CID, generator rated voltage UN, test voltage UT, stepped voltage ΔU, voltage accuracy requirement ±d%, fast rise ratio n, fast rise interval time T1, slow rise interval time T2, voltage stabilization time Td, fast voltage rise and fall parameter Kk, and slow voltage rise and fall parameter Km.

[0116] Time-sharing stepped voltage boosting parameters: Parameter number CID, generator rated voltage UN, test voltage UT, initial stepped voltage ΔU0, stepped voltage ΔU1~ΔUm, voltage accuracy ±d%, fast rise ratio n, fast rise interval time T1, slow rise interval time T2, fast voltage rise and fall parameter Kk, slow voltage rise and fall parameter Km;

[0117] Ramp-up parameters: Parameter number CID, Generator rated voltage UN, Initial step voltage ΔU0, Test voltage UT, Voltage accuracy ±d%, Fast ramp ratio n, Ramp-up slope K, Ramp-up control interval time T, Fast ramp interval time T1, Slow ramp interval time T2, Stabilization time Td, Fast voltage ramp-up parameter Kk, Slow voltage ramp-up parameter Km;

[0118] Step (2): Before each test, retrieve the corresponding test parameters by parameter number CID, confirm and start. The test system will automatically complete the test and record and store the test parameters and test data. When storing, the test data is stored under the corresponding number by the test data record number DID in sequence.

[0119] Step (3) retrieves the test data of the same equipment in the time dimension by using the DID test data record number, and then analyzes the insulation degradation trend through the test data.

[0120] In step (2), the stored content includes voltage, leakage current, time data, and current curves that change with time and voltage.

[0121] The isochronous stepped pressurization process specifically includes the following steps:

[0122] S1. First, based on the isochronous stepped voltage boost test parameters, determine the voltage of each step: 1ΔU = 1*ΔU, 2ΔU = 2*ΔU, 3ΔU = 3*ΔU, and so on.

[0123] S2. Send a fast rise signal at a rate of Kk according to the fast rise interval T1, and continuously monitor the output voltage Uo. When the output voltage reaches n%1ΔU, switch to a slow rise signal at a rate of Km with a slow rise interval T2 to control the voltage rise until the output voltage Uo meets (1±d%)1ΔU. Start timing Td. During the process, continuously monitor the output voltage according to the ±d% accuracy requirement, and send a signal at a rate of Km with a slow rise interval T2 to adjust and maintain the voltage Uo at (1±d%)1ΔU.

[0124] S3. After the voltage stabilization time Td is reached, repeat the above 1ΔU voltage boosting process to perform 2ΔU step voltage boosting, 3ΔU step voltage boosting, and so on, until the required highest test voltage UT is reached.

[0125] The time-sharing stepped voltage increase method specifically includes the following steps:

[0126] a1. Obtain the initial step voltage ΔU0;

[0127] a2. When the voltage rises, a fast rise signal with a rate of Kk is sent at the fast rise interval T1, and the output voltage Uo is continuously monitored. When the output voltage reaches n%ΔU0, the slow rise signal with a rate of Km at the slow rise interval T2 is switched to control the voltage rise until the output voltage Uo meets (1±d%)ΔU0. Then, the timer Td0 is started to stabilize the voltage. Td0 = 10 minutes. During the voltage stabilization process, the leakage current is continuously monitored, collected and recorded.

[0128] a3. Take the leakage current value I in the first minute of the Td0 timing process. 1m Leakage current I at minute 3.16 3.16m Leakage current value I at the 10th minute 10m The polarization absorption characteristic parameter N of the insulating medium is calculated using formulas (1) and (2).

[0129] I tc =(I1*I 10 )-I 3.16 2 / (I 1+ I 10 )-2*I 3.16 (1)

[0130] N=(I1-I tc ) / (I 10 -I tc (2)

[0131] Among them, I tc Indicates leakage current;

[0132] a4. Calculate the holding time Td1, Td2, ..., Tdm values ​​at each step voltage using the polarization absorption characteristic parameter N of the insulating medium and the step voltages ΔU1 to ΔUm.

[0133] a5.Td0 timeout immediately starts ΔU1 boost. When boosting begins, a fast boost signal is sent at a rate of Km according to the fast boost interval T1, and the output voltage Uo is continuously monitored. When the voltage reaches n%ΔU1, the slow boost signal with a rate of Km according to the slow boost interval T2 is switched to control the boost until the output voltage Uo = ΔU1 ± d%ΔU1.

[0134] a6. After the voltage reaches ΔU1, start timing Td1. During the process, continuously monitor the output voltage according to the ±d% accuracy requirement, and send a voltage regulation control signal with a slow rise interval T2 and a rate Km to adjust and maintain the voltage.

[0135] a7. After Td1 expires, immediately repeat the ΔU2 step voltage boost Td2 voltage hold, ΔU3 step voltage boost Td3 voltage hold, and so on, until the required highest test voltage UT is reached. Record the leakage current value during the process.

[0136] The ramp pressurization method specifically includes the following steps:

[0137] b1. Determine the initial step voltage ΔU0, and determine the initial voltage time Td0, where Td0 = 10 minutes;

[0138] b2. When the voltage boost begins, a fast boost signal at rate Kk is sent according to the fast boost interval T1, and the output voltage Uo is continuously monitored. When the output voltage Uo reaches n%ΔU0, a slow boost signal at rate Km with a slow boost interval T2 is switched to control the voltage boost until the output voltage U meets ΔU0±d%ΔU0. After the voltage reaches ΔU0, timing Td0 is started. During the process, the output voltage is continuously monitored according to the ±d% accuracy requirement, and a voltage regulation control signal at rate Km with a slow boost interval T2 is sent to adjust and maintain the voltage. During the voltage regulation process, leakage current is continuously detected, collected, and recorded.

[0139] b3. Take the leakage current value I at the 15th second during the Td0 timing process. 15S Leakage current I at 60 seconds 60S Leakage current value I at 600 seconds 600S Calculate the insulation resistance R, absorption ratio DAR, and polarization index PI; the calculation formula is: R = ΔU0 / I 60S DAR = I 60S / I 15S PI = I 600S / I60S ;

[0140] b4. Determine whether R, DAR, and PI meet the insulation requirements according to the system's set threshold. If all meet the insulation requirements, immediately start the ramp voltage rise with slope K; send a slow voltage rise signal according to the ramp voltage rise control interval T, and continuously monitor the output voltage Uo. When the output voltage Uo reaches n%UT, switch the slow voltage rise signal with a slow voltage rise interval T2 and a rate Km to control the voltage rise until the output voltage Uo = UT ± d%UT; start timing Td, and continuously monitor the output voltage according to the ±d% accuracy requirement during the process, and send a voltage regulation control signal with a slow voltage rise interval T2 and a rate Km to adjust and hold the voltage until the timing is completed.

[0141] like Figure 1As shown, the DC withstand voltage and leakage current testing system for hydro-generator insulation diagnosis includes: a control and data processing server 101, a signal acquisition and transmission module 102, a boost control unit 103, a DC current measurement unit 104, and a DC high voltage generation unit 105. Unlike traditional DC withstand voltage and leakage current testing equipment, this invention innovates on traditional hardware to adapt to the required boost method, proposes a voltage control strategy, and achieves control by executing the control strategy, thereby realizing the digitalization, Internet of Things, and intelligence of the DC withstand voltage and leakage current testing equipment.

[0142] In this invention, the signal acquisition and transmission module 102 is used for real-time output voltage signal sampling feedback, boost control pulse signal transmission, and real-time current signal sampling transmission, so as to realize closed-loop control of DC boost.

[0143] In the control and data processing server 101, when the target voltage is set, the boost control pulse signal is calculated by comparing the real-time voltage with the target voltage, and then the new boost control pulse signal is transmitted to the boost control unit 103 through the signal acquisition and transmission module 102 to control the boost.

[0144] The DC current measuring unit 104 of the present invention is a high-precision microammeter with shielding function connected in series at the output end of the DC high voltage generating unit 105 to measure the current flowing through the insulation structure, avoiding grounding system interference when measuring from the low voltage side. The measured current signal is transmitted through the optical fiber signal back-finding control and data processing server 101 for data processing.

[0145] The present invention relates to an isochronous stepped voltage boost control and digital method for insulation testing of stator windings of hydro-generators, as detailed below:

[0146] The required step voltage for the test is as follows: Figure 2 Boost control, such as Figure 3This method ensures both rapid response during voltage boosting and prevents the stepped voltage from overshooting within the required error range, while also ensuring that the error requirement is met throughout the voltage holding time. It is a control strategy implemented based on the aforementioned automatic control, achieving adjustable isochronous stepped voltage. Stepped voltage is achieved by proportionally sending controllable fast and slow boost commands. First, the target gradient voltage 1ΔU is determined. At the start of voltage boosting, a fast boost signal with a rate Kk is sent at a fast boost interval T1, and the output voltage Uo is continuously monitored. When the voltage reaches n%1ΔU, a slow boost signal with a rate Km at a slow boost interval T2 is switched to control the voltage boost until the output voltage Uo meets (1±d%)1ΔU. Timing Td is then started. During this process, the output voltage is continuously monitored according to the ±d% accuracy requirement, and a fast boost interval T1 signal with a rate Km is sent to adjust and maintain the voltage Uo at (1±d%)1ΔU. Immediately repeat the 2ΔU step voltage increase, 3ΔU step voltage increase, and 4ΔU step voltage increase until the required highest test voltage UT is reached. Under this control strategy, isochronous step voltages with different accuracy requirements can be achieved by adjusting T1, T2, Td, d, and ΔU, satisfying the testing of DC leakage current of generators with different capacities and insulation structures. This isochronous step voltage ensures that the test parameters are the same, thus ensuring higher reliability of the leakage current for insulation condition trend analysis.

[0147] The time-sharing stepped voltage boost control method and its digitalization for stator winding insulation testing of hydro generators are detailed below:

[0148] Unlike isochronous step voltage boosting, time-sharing step voltage boosting involves different holding times for each step. Taking six steps as an example, the general trend is that the holding time decreases as the step increases, but the specific time is determined by the polarization absorption characteristics of the insulating medium and the step voltage gradient. Figure 4 This method is a control strategy implemented based on the aforementioned automatic control of isochronous stepped voltage. The initial stepped voltage ΔU0 is determined according to the generator voltage level and insulation structure. At the start of voltage boosting, a fast-rise signal at rate Kk is sent according to the fast-rise interval T1, and the output voltage Uo is continuously monitored. When the voltage reaches n%ΔU0, the slow-rise signal at rate Km of the slow-rise interval T2 is switched to control the voltage boosting until the output voltage Uo satisfies (1±d%)ΔU0. The start-up timing Td0 = 10 minutes. During voltage stabilization, the leakage current is continuously monitored, collected, and recorded, and I is taken as the starting point. 1m I 3.16m I 10m The current value is calculated using formulas (1) and (2) to determine the polarization absorption characteristic parameter N of the insulating medium.

[0149] I tc =(I1*I 10 )-I 3.16 2 / (I1+ I 10 )-2*I 3.16 (1)

[0150] N=(I1-I tc ) / (I 10 -I tc (2)

[0151] Among them, I tc Leakage current includes conductivity and surface leakage current.

[0152] The holding times Td1, Td2, Td3, Td4, and Td5 at each step voltage are calculated using the polarization absorption characteristic parameter N of the insulating medium and the step voltages ΔU1, ΔU2, ΔU3, ΔU4, and ΔU5. The calculation formula is as follows:

[0153] I ΔU1 / I ΔU0 =ΔU1 / ΔU0 (3)

[0154] I ΔU2 / I ΔU0 =ΔU2 / ΔU0 (4)

[0155] I ΔU3 / I ΔU0 =ΔU3 / ΔU0 (5)

[0156] I ΔU4 / I ΔU0 =ΔU4 / ΔU0 (6)

[0157] I ΔU5 / I ΔU0 =ΔU5 / ΔU0 (7)

[0158] I ΔU0 =K*C*ΔU0*Td0 -N (8)

[0159] I ΔU1 =K*C*{ΔU0*(Td0+Td1) -N +(ΔU1-ΔU0)*Td1 -N} (9)

[0160] I ΔU2 =K*C*{ΔU0*(Td0+Td1+Td2) -N +(ΔU1-ΔU0)*(Td1+Td2) -N +(ΔU

[0161] 2-ΔU1)*Td2 -N}(10)

[0162] I ΔU3 = K * C * {ΔU0 * (Td0 + Td1 + Td2 + Td3) -N + (ΔU1 - ΔU0) * (Td1 + Td2 + Td3)

[0163] -N + (ΔU2 - ΔU1) * (Td2 + Td3) -N + (ΔU3 - ΔU2) * Td3 -N} (11)

[0164] I ΔU4 = K * C * {ΔU0 * (Td0 + Td1 + Td2 + Td3 + Td4) -N + (ΔU1 - ΔU0) * (Td1 + Td2 + Td3 + Td4) -N + (ΔU2 - ΔU1) * (Td2 + Td3 + Td4) -N + (ΔU3 - ΔU2) * (Td3 + Td4) -N + (ΔU4 - ΔU3) * Td4 -N} (12)

[0165] I ΔU5 = K * C * {ΔU0 * (Td0 + Td1 + Td2 + Td3 + Td4 + Td5) -N + (ΔU1 - ΔU0) * (Td1 + Td2 + Td3 + Td4 + Td5) -N + (ΔU2 - ΔU1) * (Td2 + Td3 + Td4 + Td5) -N + (ΔU3 - ΔU2) * (Td3 + Td4 + Td5) -N + (ΔU4 - ΔU3) * (Td4 + Td5) -N + (ΔU5 - ΔU4) * Td5 -N} (13) From the above formulas, the calculation equations for Td1, Td2, Td3, Td4, and Td5 can be derived:

[0166] (ΔU1 - ΔU0) * Td1 -N + ΔU0 * (Td0 + Td1) -N - ΔU1 * Td0 -N = 0 (14)

[0167] (ΔU2 - ΔU1) * Td2 -N + (ΔU1 - ΔU0) * (Td2 + Td1) -N + ΔU0 * (Td2 + Td1 + Td0) -N - ΔU2 * Td0 -N = 0 (15)

[0168] (ΔU3-ΔU2)*Td3 -N +(ΔU2-ΔU1)*(Td3+Td2) -N +(ΔU1-ΔU0)*(Td3+Td2+Td1) -N +ΔU0*(Td3+Td2+Td1+Td0) -N -ΔU3*Td0 -N =0 (16)

[0169] (ΔU4-ΔU3)*Td4 -N +(ΔU3-ΔU2)*(Td4+Td3) -N +(ΔU2-ΔU1)*(Td4+Td3+Td2) -N +(ΔU1-ΔU0)*(Td4+Td3+Td2+Td1) -N +ΔU0*(Td4+Td3+Td2+Td1+Td0) -N -ΔU4*Td0 -N =0 (17)

[0170] (ΔU5-ΔU4)*Td5 -N +(ΔU4-ΔU3)*(Td5+Td4) -N +(ΔU3-ΔU2)*(Td5+Td4+Td3) -N +(ΔU2-ΔU1)*(Td5+Td4+Td3+Td2) -N +(ΔU1-ΔU0)*(Td5+Td4+Td3+Td2+Td1) -N +ΔU0*(Td5+Td4+Td3+Td2+Td1+Td0) -N -ΔU5*Td0 -N =0 (18)

[0171] In the above formula:

[0172] The K-winding absorption coefficient is determined by the winding insulation medium structure, the type of insulation material and temperature. It remains constant for a specific generator at the same temperature. The derivation process parameters do not need to be considered in the time calculation.

[0173] The parameters of the C winding capacitance are constant for a specific generator and can be measured by a capacitance testing instrument. The derivation process parameters do not need to be considered in the time calculation.

[0174] Polarization absorption characteristic parameters of N insulating dielectric;

[0175] The voltage steps are ΔU1, ΔU2, ΔU3, ΔU4, and ΔU5. Each voltage step must gradually increase, with the latter being greater than the former. The gradient can be arbitrary, and each voltage step value can be any value greater than the previous step.

[0176] The duration of holding at each of the following voltage steps: Td1, Td2, Td3, Td4, and Td5;

[0177] I ΔU1 I ΔU2 I ΔU3 I ΔU4 I ΔU5 Leakage current at the end of the holding time under each voltage step;

[0178] Detailed calculation steps:

[0179] Taking an 18kV hydro-generator as an example, time-sharing stepped DC withstand voltage and leakage current tests were conducted.

[0180] The first step is to determine the voltage boosting plan as 6 steps: ΔU0 = 5kV, ΔU1 = 9kV, ΔU2 = 18kV, ΔU3 = 27kV, ΔU4 = 36kV, ΔU5 = 45kV, and Td0 = 10 minutes.

[0181] The second step is to calculate N using formulas (1) and (2);

[0182] The third step is to calculate Td1 using N, ΔU0, ΔU1, Td0 and formula (14);

[0183] The fourth step is to calculate Td2 using N, ΔU0, ΔU1, ΔU2, Td0, Td1 and formula (15);

[0184] Fifth step, calculate Td3 using N, ΔU0, ΔU1, ΔU2, ΔU3, Td0, Td1, Td2 and formula (16);

[0185] Step 6: Calculate Td4 using N, ΔU0, ΔU1, ΔU2, ΔU3, ΔU4, Td0, Td1, Td2, Td3 and formula (17);

[0186] Step 7: Calculate Td5 using N, ΔU0, ΔU1, ΔU2, ΔU3, ΔU4, ΔU5, Td0, Td1, Td2, Td3, Td4 and formula (18).

[0187] During the test, after the first step is completed, N, Td1, Td2, Td3, Td4, and Td5 are automatically calculated step by step by the system program. In the above example of the 18kV generator time-sharing step test, N=2, Td1=6.22 minutes, Td2=6.52 minutes, Td3=5.07 minutes, Td4=4.16 minutes, and Td5=3.54 minutes.

[0188] like Figure 4As shown, ΔU1 voltage boosting begins immediately after time Td0. During the initial boost, a fast-rise signal is sent at the fast-rise interval T1, and the output voltage Uo is continuously monitored. When the voltage reaches n%ΔU1, a slow-rise signal with a slow-rise interval T2 is switched to control the voltage boost until the output voltage Uo = ΔU1 ± d%ΔU1. After the voltage reaches ΔU1, timer Td1 is started. During this process, the output voltage is continuously monitored according to the ±d% accuracy requirement, and a voltage stabilization control signal with a slow-rise interval T2 is sent to adjust and hold the voltage. Immediately after time Td1, the following steps are repeated: ΔU2 step-rise voltage hold Td2, ΔU3 step-rise voltage hold Td3, ΔU4 step-rise voltage hold Td4, and ΔU5 step-rise voltage hold Td5 until the required highest test voltage UT is reached. The leakage current value is recorded during this process. This time-division stepped voltage method achieves the same-time stepped voltage test effect while significantly shortening the test time and improving test efficiency.

[0189] This invention relates to a slope voltage ramp control method for insulation testing of stator windings in hydro-generators. Details are as follows:

[0190] The required ramp voltage for the test is as follows: Figure 5 This ensures both rapid response during voltage boosting and a stable ramp voltage rise rate, while also meeting error requirements within the final voltage holding time. This is implemented based on the aforementioned automatic control. Ramp voltage is achieved by controlling a slow-rate voltage boost using a fast-cycle command. The initial ΔU0 and initial voltage time Td0 (10 minutes) are determined. At the start of voltage boosting, a fast-rise signal at rate Kk is sent according to the fast-rise interval T1, and the output voltage Uo is continuously monitored. When the voltage reaches n%ΔU0, a slow-rise signal at rate Km with a slow-rise interval T2 is switched to control the voltage boost until the output voltage U satisfies ΔU0 ± d%ΔU0. After the voltage reaches ΔU0, timing Td0 is started. During this process, the output voltage is continuously monitored according to accuracy requirements, and a voltage regulation control signal with a slow-rise interval T2 is sent to adjust the holding voltage. During voltage regulation, leakage current is continuously detected, collected, and recorded, and I is taken as the voltage. 15S I 60S I 600S The current value is obtained through the formula (R=ΔU0 / I) 60S DAR = I 60S / I 15S PI = I 600S / I60SCalculate the insulation resistance R, absorption ratio DAR, and polarization index PI. Once R, DAR, and PI meet the insulation requirements, immediately initiate a ramp-up voltage increase with a slope K. Send slow signals at fixed intervals T and continuously monitor the output voltage Uo. When the voltage reaches n%UT, switch to a slow-rise signal with a slow-rise interval T2 to control the voltage increase until the output voltage Uo = UT ± d%UT. Start timing Td = 60 seconds. During the process, continuously monitor the output voltage according to accuracy requirements and send slow-rise signals with a slow-rise interval T2 for adjustment. Under this control strategy, by adjusting ΔU0, UT, n, K, T1, T2, T, and Td, ramp voltages with different accuracy requirements can be achieved, satisfying the testing of DC leakage current of generators with different capacities and insulation structures. Stable absorption, polarization, and conduction currents can be obtained through this ramp voltage; at this point, the change in total current accurately reflects the change in conduction current due to insulation aging.

[0191] This invention addresses the issue of inconsistent leakage current data caused by factors such as manual voltage fluctuations during testing, reading timing errors, and differences in test parameter settings for the same device under test, which fail to reflect the generator's insulation status. This method parameterizes the testing process and uses a computer program to retrieve and control the test parameters. The program records and stores the test data in a structured format, enabling repeated testing of the same device throughout its lifecycle using the same set of parameters. This ensures consistent test control and guarantees accurate and reliable test data.

[0192] Application Examples

[0193] The DC leakage voltage boosting method and parameters are determined based on the rated voltage of the generator insulation structure: fast voltage rise / fall parameters Kk = 4.5kV / S, slow voltage rise / fall parameters Km = 0.1kV / S, isochronous stepped voltage boosting test parameters CID, UN, UT, ΔU, ±d%, n, T1, T2, Td, time-division stepped voltage boosting parameters CID, UN, UT, ΔU0, ΔU1, ΔU2, ±d%, n, T1, T2, ramp voltage boosting parameters CID, UN, ΔU0, UT, ±d%, n, K, T, T1, T2, Td. Before each test, the test parameters are retrieved and set using parameter number CID to start the test, record and store leakage current data and curves, and store them sequentially using record number DID. In the time dimension, the insulation degradation trend is analyzed by retrieving test data of the same equipment from previous tests using DID number. The structured test parameter table is shown in Table 1, taking an 18kV hydro-generator as an example.

[0194] Table 1. Structured Test Parameters

[0195]

[0196]

[0197] (1) Conduct insulation DC withstand voltage and leakage tests on an 18kV hydro-generator using an isochronous stepped method. Record the control parameters, the stepped voltage generated under these parameters, and the insulation leakage current under these voltage parameters. Figure 6 The leakage current variation trend of the insulation was tested three times consecutively at the same time using the same parameters. The test voltage and leakage current were consistent, showing good repeatability.

[0198] Table 2. Parameters for Isochronous Stepped Pressure Increase

[0199]

[0200] (2) Conduct insulation DC withstand voltage and leakage tests on an 18kV hydro-generator using a time-sharing stepped method. Record the control parameters, the time-sharing stepped voltage generated under these parameters, and the insulation leakage current under these voltage parameters. Figure 7 The leakage current variation trend of the insulation was tested three times consecutively using the same parameters at the same time. The test voltage and leakage current were consistent, demonstrating good repeatability. Compared with the isochronous step test, the leakage current was significantly reduced, approaching the conductivity current, and the test time of 40 minutes was much shorter than the theoretical several hours. This means that more accurate conductivity current can be measured in a shorter time while ensuring test repeatability.

[0201] Table 3. Time-of-use stepped pressurization parameters

[0202]

[0203] (3) An insulation DC withstand voltage and leakage test was conducted on an 18kV hydro-generator using a ramp-up voltage method. The control parameters, the ramp test voltage generated under these parameters, and the insulation leakage current curve under these voltage parameters are shown below. Figure 8 , Figure 9 The leakage current variation trend was tested three times consecutively using the same parameters. This method offers good consistency and repeatability of test voltage and leakage current, and requires a short time. Compared with time-division stepped voltage, this method only considers the slope of the curve change. The time interval between each small voltage increase is small, thus the current absorbed and polarized is constant. The nonlinear change of leakage current only reflects the conductivity current of insulation aging. The insulation state and its variation trend can be analyzed by measuring the current curve changes multiple times.

[0204] Table 4. Slope Pressure Parameters

[0205]

[0206] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the present invention as claimed. The scope of protection of this invention is defined by the appended claims and their equivalents.

Claims

1. A method for performing DC withstand voltage and leakage tests based on a DC withstand voltage and leakage test system for insulation diagnosis of hydro-generators, characterized in that: The DC withstand voltage and leakage test system for insulation diagnosis of hydro generators includes: a control and data processing server (101), a signal acquisition and transmission module (102), a boost control unit (103), a DC current measurement unit (104), and a DC high voltage generation unit (105). The boost control unit (103) is connected to the signal acquisition and transmission module (102) and the DC high voltage generator unit (105) respectively, and is used to control the operation of the DC high voltage generator unit (105); The DC high voltage generating unit (105) is used to generate DC voltage and output it to the test turbine generator; The DC current measurement unit (104) is connected to the test turbine generator and the DC high voltage generating unit (105) respectively. It is used to measure the current output from the DC high voltage generating unit (105) to the test turbine generator, and also to collect and record the leakage current of the test turbine generator. The signal acquisition and transmission module (102) is also connected to the DC current measurement unit (104), the DC high voltage generator unit (105), and the control and data processing server (101) respectively. It is used to acquire the measurement results of the DC current measurement unit (104), the output information of the DC high voltage generator unit (105), and the control signals of the boost control unit (103), and then transmit them to the control and data processing server (101). The control and data processing server (101) is used to control the operation of the signal acquisition and transmission module (102) and to transmit control signals to the boost control unit (103) through the signal acquisition and transmission module (102), thereby controlling the operation of the boost control unit (103); it is also used to process the data transmitted from the signal acquisition and transmission module (102) to obtain the DC withstand voltage and leakage current test results of the tested hydro turbine generator; The method for DC withstand voltage and leakage testing includes the following steps: Step (1): Determine the DC leakage voltage boosting method and parameters based on the rated voltage of the hydro-generator insulation structure; the voltage boosting method includes the isochronous step voltage boosting method, the time-sharing step voltage boosting method, and the ramp voltage boosting method; Among them, the isochronous stepped voltage boost test parameters are: parameter number CID, generator rated voltage UN, test voltage UT, stepped voltage ΔU, voltage accuracy requirement ±d%, fast rise ratio n, fast rise interval time T1, slow rise interval time T2, voltage stabilization time Td, fast voltage rise and fall parameter Kk, and slow voltage rise and fall parameter Km. Time-sharing stepped voltage boosting parameters: Parameter number CID, generator rated voltage UN, test voltage UT, initial stepped voltage ΔU0, stepped voltage ΔU1~ΔUm, voltage accuracy ±d%, fast rise ratio n, fast rise interval time T1, slow rise interval time T2, fast voltage rise / fall parameter Kk, slow voltage rise / fall parameter Km; Ramp-up parameters: Parameter number CID, generator rated voltage UN, initial step voltage ΔU0, test voltage UT, voltage accuracy ±d%, fast ramp ratio n, ramp slope K, ramp-up control interval time T, fast ramp interval time T1, slow ramp interval time T2, stabilization time Td, fast voltage ramp-up parameter Kk, slow voltage ramp-up parameter Km; Step (2): Before each test, retrieve the corresponding test parameters by parameter number CID, confirm and start. The test system will automatically complete the test and record and store the test parameters and test data. When storing, the test data is stored under the corresponding number by the test data record number DID in sequence. Step (3): In the time dimension, retrieve the test data of the same equipment through the DID test data record number, and then analyze the insulation degradation trend through the test data.

2. The method for performing DC withstand voltage and leakage tests based on the DC withstand voltage and leakage test system for insulation diagnosis of hydro-generators according to claim 1, characterized in that, In step (2), the stored content includes voltage, leakage current, time data, and current curves that change with time and voltage.

3. The method for performing DC withstand voltage and leakage testing based on the DC withstand voltage and leakage testing system for hydro-generator insulation diagnosis according to claim 1, characterized in that, The isochronous stepped pressurization process specifically includes the following steps: S1. First, based on the isochronous stepped voltage boost test parameters, determine the voltage of each step: 1ΔU=1*ΔU, 2ΔU=2*ΔU, 3ΔU=3*ΔU, and so on. S2. Send a fast rise signal at a rate of Kk according to the fast rise interval T1, and continuously monitor the output voltage Uo. When the output voltage reaches n%1ΔU, switch to a slow rise signal at a rate of Km with a slow rise interval T2 to control the voltage rise until the output voltage Uo meets (1±d%)1ΔU. Start timing Td. During the process, continuously monitor the output voltage according to the ±d% accuracy requirement, and send a signal at a rate of Km with a slow rise interval T2 to adjust and maintain the voltage Uo at (1±d%)1ΔU. S3. After the voltage stabilization time Td is reached, repeat the above 1ΔU voltage boosting process to perform 2ΔU step voltage boosting, 3ΔU step voltage boosting, and so on, until the required highest test voltage UT is reached.

4. The method for performing DC withstand voltage and leakage tests based on the DC withstand voltage and leakage test system for insulation diagnosis of hydro-generators according to claim 1, characterized in that, The time-sharing stepped voltage increase method specifically includes the following steps: a1. Obtain the initial step voltage ΔU0; a2. When the voltage rises, a fast rise signal with a rate of Kk is sent at the fast rise interval T1, and the output voltage Uo is continuously monitored. When the output voltage reaches n%ΔU0, the slow rise signal with a rate of Km at the slow rise interval T2 is switched to control the voltage rise until the output voltage Uo meets (1±d%)ΔU0. Then, the timer Td0 is started to stabilize the voltage. Td0=10 minutes. During the voltage stabilization process, the leakage current is continuously monitored, collected and recorded. a3. Take the leakage current value I in the first minute of the Td0 timing process. 1m Leakage current I at minute 3.16 3.16m Leakage current value I at the 10th minute 10m The polarization absorption characteristic parameter N of the insulating medium is calculated using formulas (1) and (2). I tc =(I1*I 10 )-I 3.16 2 / (I 1+ I 10 )-2*I 3.16 (1) N=(I1-I tc ) / (I 10 -I tc ) (2) Among them, I tc Indicates leakage current; a4. Calculate the holding time Td1, Td2, ..., Tdm values ​​at each step voltage using the polarization absorption characteristic parameter N of the insulating medium and the step voltages ΔU1~ΔUm; a5.Td0 timeout immediately starts ΔU1 boost. When boosting begins, a fast boost signal is sent at a rate of Km according to the fast boost interval T1, and the output voltage Uo is continuously monitored. When the voltage reaches n%ΔU1, the slow boost signal with a rate of Km according to the slow boost interval T2 is switched to control the boost until the output voltage Uo=ΔU1±d%ΔU1. a6. After the voltage reaches ΔU1, start timing Td1. During the process, continuously monitor the output voltage according to the ±d% accuracy requirement, and send a voltage regulation control signal with a slow rise interval T2 and a rate Km to adjust and maintain the voltage. a7. After Td1 expires, immediately repeat the ΔU2 step voltage boost Td2 voltage hold, ΔU3 step voltage boost Td3 voltage hold, and so on, until the required highest test voltage UT is reached. Record the leakage current value during the process.

5. The method for performing DC withstand voltage and leakage testing based on the DC withstand voltage and leakage testing system for hydro-generator insulation diagnosis according to claim 1, characterized in that, The ramp pressurization method specifically includes the following steps: b1. Determine the initial step voltage ΔU0, and determine the initial voltage time Td0, where Td0 = 10 minutes; b2. When the voltage boost begins, a fast boost signal with a rate of Kk is sent at a fast boost interval of T1, and the output voltage Uo is continuously monitored. When the output voltage Uo reaches n%ΔU0, a slow boost signal with a rate of Km at a slow boost interval of T2 is switched to control the voltage boost until the output voltage U meets ΔU0±d%ΔU0. After the voltage reaches ΔU0, timing Td0 is started. During the process, the output voltage is continuously monitored according to the ±d% accuracy requirement, and a voltage regulation control signal with a rate of Km at a slow boost interval of T2 is sent to adjust and maintain the voltage. During the voltage regulation process, leakage current is continuously detected, collected, and recorded. b3. Take the leakage current value I at the 15th second during the Td0 timing process. 15S Leakage current I at 60 seconds 60S Leakage current value I at 600 seconds 600S Calculate the insulation resistance R, absorption ratio DAR, and polarization index PI; The calculation formula is: R = ΔU0 / I 60S DAR=I 60S / I 15S PI=I 600S / I60S； b4. Determine whether R, DAR, and PI meet the insulation requirements according to the system's set threshold. If all meet the insulation requirements, immediately start the ramp voltage rise with slope K; send a slow voltage rise signal according to the ramp voltage rise control interval T, and continuously monitor the output voltage Uo. When the output voltage Uo reaches n%UT, switch the slow voltage rise signal with a slow voltage rise interval T2 and a rate Km to control the voltage rise until the output voltage Uo = UT ± d%UT; start timing Td, and continuously monitor the output voltage according to the ±d% accuracy requirement during the process, and send a voltage regulation control signal with a slow voltage rise interval T2 and a rate Km to adjust and hold the voltage until the timing is completed.

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