AC impedance testing device and method for detecting rotor winding inter-turn short circuit fault

Abstract

The present invention relates to an AC impedance testing device and method for detecting a short-circuit fault between turns of a rotor winding. An AC voltage regulator is used as a test power source, an ammeter is connected in series in the above-mentioned loop to measure the loop current, one end of a movable electrode is used to contact and connect the center point position between the poles of a generator rotor winding, a first voltmeter is connected between the positive pole of the generator rotor and the other end of the movable electrode, a second voltmeter is connected between the negative pole of the generator rotor and the other end of the movable electrode, and a third voltmeter is connected between the positive and negative poles of the generator rotor. The present invention does not require historical data, and utilizes the symmetrical characteristics of the two poles of the generator rotor to provide basic data for comparative analysis. During the test, the same test instrument is used, and the same test environment and test conditions are used. It is basically not affected by factors such as test equipment, test environment, test conditions, and test voltage, and can greatly improve the credibility of the basic data source during comparative analysis, and greatly reduce the system test error level.

Description

Technical Field

[0001] The invention relates to testing of inter-turn short-circuit faults in rotor windings of generators and phase-converting devices (hereinafter referred to as generators) in the power industry, and in particular to an improved testing method for rotor AC impedance testing using an industrial frequency power supply. Background Art

[0002] As generators in power systems participate in deep peak regulation more and more frequently, the load of generators will fluctuate within a large range, and the influence of electromagnetic force on their rotor windings will also increase. The inter-turn short-circuit fault of the generator rotor winding has become a frequent fault of the unit in recent years, seriously affecting the safe and stable operation of the unit. During the maintenance of the unit, it is crucial to detect and promptly discover the early faults of the inter-turn short-circuit of the rotor winding through electrical preventive tests, and to handle the defects during the maintenance of the unit to ensure the safe and stable operation of the generator after maintenance. At present, the electrical preventive test methods for generator rotor windings on site need to be greatly improved and enhanced in terms of the sensitivity and accuracy of defect detection.

[0003] In DL / T 596-2021 "Preventive Test Procedures for Power Equipment", the methods and cycles of electrical preventive test items for inter-turn short-circuit faults of generator rotor windings are specified as follows: 1) AC impedance test is a periodic routine test item, and its cycle is A-level maintenance or when necessary; 2) Repeated pulse method (RSO) test is a diagnostic test item, and its cycle is when necessary. At the same time, the technical criteria for the test method are specified as follows: 1) The AC impedance value should not change significantly compared with the data of previous years under the same test conditions; 2) The AC impedance value should be compared with the factory data or historical data, and a decrease of more than 10% should be noted; 3) Compared with the values ​​of previous years, if the change is large, dynamic inter-turn monitoring method, repeated pulse method and other methods can be used to find out whether there is an inter-turn short-circuit fault in the rotor winding.

[0004] From the above text description, it can be seen that the main technical route for detecting inter-turn short circuit of generator rotor winding through on-site preventive test is as follows: First, the AC impedance test of the periodic routine test items carried out in combination with the A-level maintenance of the unit is tested, and the test data is compared and analyzed with the factory data or historical data; secondly, if the comparison data changes significantly, when the impedance value decreases by more than 10%, attention should be paid, and it is judged that there is a high probability of inter-turn short circuit fault; if it is judged that there may be inter-turn short circuit fault, non-periodic diagnostic test items such as repeated pulse method or dynamic inter-turn monitoring method are used for further testing and confirmation. In fact, in addition to the repeated pulse method or dynamic inter-turn monitoring method, the diagnostic test item methods also include inter-pole voltage method, coil voltage method, inter-turn voltage distribution method, etc. These diagnostic test methods are stipulated and detailed in the power industry standard DL / T 1525-2016 "Guidelines for Diagnosis of Inter-turn Short Circuit Faults of Hidden Pole Synchronous Generator Rotors". The corresponding generator status and rotor position of different diagnostic methods are shown in Table 1.

[0005] Table 1 Generator status and rotor position corresponding to different diagnostic methods

[0006] Diagnostic Methods Generator status Rotor position Detection coil waveform method Generator rotation state and establish stable air gap flux inside the chamber AC impedance method Stationary or rotating state In or out of the chamber Repetitive Pulse Method Stationary or rotating state In or out of the chamber Interelectrode voltage method still Outside the chamber Coil voltage method still Outside the chamber Turn-to-turn voltage distribution method still Outside the chamber

[0007] As can be seen from Table 1, the detection coil waveform method is a monitoring method under the running state of the generator, and the other five methods are test methods for the generator in the rotating state without excitation or the static state of power failure. In actual field work, the AC impedance test is the most commonly used test method by grassroots power generation enterprises or maintenance test units as a periodic routine test, while the other methods are used as diagnostic test methods, mainly by technical supervision units such as manufacturers or scientific research institutes. Therefore, the AC impedance test can be said to be the first checkpoint for discovering problems, and its importance is self-evident. If the equipment failure is missed, the subsequent diagnostic test is no longer carried out, and the equipment defects are not discovered in time, it may lead to serious equipment failures or accidents in the future.

[0008] The AC impedance test and repeated pulse method test for detecting inter-turn short-circuit faults in generator rotor windings have the following methodological deficiencies:

[0009] 1) When using the AC impedance method for analysis and judgment, it must be compared with factory data or historical data, that is, there must be a reliable data source as the basic data. However, due to the many factors affecting the AC impedance test, such as different test equipment, test environment, test conditions, test voltage, etc., the test data has a large volatility. Using it as the basic data is likely to cause a large data deviation in comparative analysis;

[0010] 2) The existing standard sets a 10% attention value for changes in AC impedance data. This can prevent the possibility of a rotor inter-turn short circuit due to changes exceeding the attention value caused by systematic fluctuations in test data (deviations of about 5-8% often occur on site). However, at the same time, it is easy for the actual impedance value to change by less than 10% when there is indeed an inter-turn short circuit in the rotor winding, and the fault may be missed. According to real case data from multiple units that had inter-turn short circuits and were returned to the factory for processing, the change in the rotor AC impedance was only about 6%, which did not meet the 10% attention value requirement. In a sense, missed judgment is more terrible than misjudgment in defect discovery and prevention.

[0011] 3) When the AC impedance data is found to be out of standard, the repetitive pulse method can be used for detection. Objectively speaking, the repetitive pulse method utilizes the symmetrical characteristics of the generator rotor bipolar structure, and can judge the inter-turn short-circuit fault without historical data. It is an effective and sensitive method for detecting the inter-turn short-circuit of the rotor winding. However, to date, the generator manufacturers generally do not accept this method very much. When analyzing the inter-turn short-circuit fault of the rotor winding, the generator manufacturers prefer to use the inter-pole voltage method and coil voltage method with higher voltage (usually 200V). The reason is that the voltage applied to the rotor winding by the repetitive pulse method is relatively low, generally only a dozen volts, and the high-frequency and low-voltage waveform is easily interfered by the signal of the complex on-site environment. The application of this method to fault analysis and defect location is severely limited by the operator's personal experience level; at the same time, this method also has the inherent technical principle shortcomings of being insensitive to some defects (the fault point is located near the center of the rotor).

[0012] Therefore, improvement and innovation of generator rotor winding inter-turn short-circuit fault detection is imperative. Summary of the invention

[0013] In view of the above situation, in order to overcome the shortcomings of the prior art, the purpose of the present invention is to provide an AC impedance testing device and method for detecting short-circuit faults between turns of rotor windings, which can effectively solve the problem of efficient and accurate detection of short-circuit faults between turns of generator rotor windings.

[0014] The technical solution provided by the present invention is:

[0015] An AC impedance test device for detecting a short-circuit fault between turns of a rotor winding comprises a generator rotor, an AC voltage regulator, a first voltmeter, a second voltmeter, a third voltmeter, an ammeter and a movable electrode (a movable test contact electrode);

[0016] The AC voltage regulator is used as a test power source, and its two voltage output terminals are connected to the two poles of the generator rotor. The ammeter is connected in series to the above loop to measure the loop current. One end of the mobile electrode is connected to the center point between the poles of the generator rotor winding. The first voltmeter is connected between the positive pole of the generator rotor and the other end of the mobile electrode. The second voltmeter is connected between the negative pole of the generator rotor and the other end of the mobile electrode. The third voltmeter is connected between the positive and negative poles of the generator rotor, wherein:

[0017] AC voltage regulator: used to output a continuously adjustable sine wave AC voltage signal as the test power supply for the rotor winding of the generator to be tested;

[0018] The first voltmeter: used to measure the voltage V1 between the positive pole of the generator rotor and the moving electrode;

[0019] Second voltmeter: used to measure the voltage V2 between the negative pole of the generator rotor and the moving electrode;

[0020] The third voltmeter: used to measure the voltage V0 between the positive and negative poles of the generator rotor;

[0021] Ammeter: used to measure the current I applied by the AC voltage regulator to the two-pole circuit of the generator rotor winding;

[0022] Mobile electrode: used to contact the center point between the poles of the generator rotor winding to facilitate the measurement of the voltage between the positive and negative poles of the rotor to the mobile electrode.

[0023] An AC impedance testing method for detecting a rotor winding interturn short circuit fault comprises the following steps:

[0024] Step 1: Confirm that the generator rotor to be tested is outside the stator chamber and placed horizontally and still.

[0025] The generator rotor to be tested is pulled out from the stator chamber and placed horizontally outside the stator chamber, ensuring that there are no large metal objects around it, and that the carbon brush slip rings or conductive screws on the two poles of the rotor are not electrically connected to the outside world;

[0026] Step 2: Connect the electrical test circuit

[0027] Connect the two voltage output terminals of the AC voltage regulator to the carbon brush slip rings or conductive bolts of the two poles of the generator rotor through wires to form a measuring circuit. The ammeter is connected in series to the above circuit to measure the circuit current I. The movable electrode is in contact with the conductor at the center point of the rotor winding poles under the end guard ring on the excitation side of the generator rotor. The first voltmeter is connected between the positive pole of the generator rotor and the other end of the movable electrode to measure the voltage V1 between the positive pole of the generator rotor and the movable electrode; the second voltmeter is connected between the negative pole of the generator rotor and the other end of the movable electrode to measure the voltage V2 between the negative pole of the generator rotor and the movable electrode; the third voltmeter is connected between the positive and negative poles of the generator rotor to measure the voltage V0 between the positive and negative poles of the generator rotor; the voltage input terminal of the AC voltage regulator is connected to the on-site 220V AC power supply through an air switch to form the entire electrical test circuit;

[0028] Step 3: Boost Measurement and Data Recording

[0029] The voltage output end of the AC voltage regulator is first adjusted to zero, and the air switch is closed to supply power to the voltage input side of the AC voltage regulator. The voltage on the output side of the voltage regulator is slowly adjusted to increase. When the voltage V0 between the positive and negative poles of the rotor reaches 50V, 100V, 150V, 200V, and 250V, the voltage is stopped and the corresponding test data is recorded. The test data includes voltage V1, V2 and current I. After recording, the voltage is reduced to zero and the air switch is disconnected.

[0030] Step 4: Data processing

[0031] The recorded data are summarized and calculated, and the calculation formula is as follows:

[0032] Voltage V0 between the positive and negative poles of the rotor: record value, V0;

[0033] Total AC impedance Z0 between the positive and negative poles of the rotor: calculated value, Z0 = V0 / I;

[0034] Voltage V1 between the positive pole of the rotor and the center point: record value, V1;

[0035] AC impedance Z1 between the positive pole of the rotor and the center point: calculated value, Z1 = V1 / I;

[0036] Voltage V2 between the negative pole of the rotor and the center point: record value, V2;

[0037] AC impedance Z2 between the negative pole of the rotor and the center point: calculated value, Z2 = V2 / I;

[0038] Record and calculate the above voltage, current and impedance values ​​at different voltages;

[0039] Step 5: Data Analysis

[0040] Compare and calculate the impedance Z1 and Z2 under different voltages. If the impedance Z1 is less than Z2, calculate the deviation rate k1 = (Z1 / Z2-1) × 100%:

[0041] If k1 < 2%, it is determined that there is no inter-turn short circuit in the rotor winding;

[0042] If k1 ≥ 2%, it is judged that there is a turn-to-turn short circuit fault in the positive pole winding coil of the rotor on the Z1 side;

[0043] If the impedance Z1 is greater than Z2, then calculate the deviation rate k2 = (Z2 / Z1-1) × 100%:

[0044] If k2 < 2%, it is determined that there is no inter-turn short circuit in the rotor winding;

[0045] If k2≥2%, it is determined that there is a turn-to-turn short circuit fault in the negative pole winding coil of the rotor on the Z2 side.

[0046] If the step 5 determines that there is a turn-to-turn short circuit fault in the coil, then proceed to step 6, fault coil search:

[0047] The voltage output end of the AC voltage regulator is first adjusted to zero, and the air switch is closed to supply power to the voltage input side of the AC voltage regulator. The voltage on the output side of the AC voltage regulator is adjusted and increased to 200V and then stopped. The mobile electrode is contacted with the bottom coil positions of the rotor coils of the positive and negative poles under the end guard ring of the excitation side respectively. The voltage, current and impedance values ​​in this state are recorded and calculated. After recording, the voltage is reduced to zero and the air switch is disconnected. In the recorded data, if there is a large difference in the impedance of the coils at the corresponding positions of the positive and negative poles, it can be determined that there is an inter-turn short circuit fault in the coil winding with smaller impedance in the group.

[0048] The present invention utilizes the characteristics of symmetrical structure of the two poles of the generator rotor and basically consistent electrical parameters, and applies a voltage of 200V or higher for testing. Compared with the traditional AC impedance test method and the repetitive pulse method, the present invention has the following advantages:

[0049] 1) No historical data is required. The two-pole symmetry characteristics of the generator rotor are used to provide basic data for comparative analysis. The same test instrument, test environment and test conditions are used during the test. It is basically not affected by factors such as test equipment, test environment, test conditions and test voltage. The credibility of the basic data source during comparative analysis can be greatly improved, and the system test error level can be greatly reduced.

[0050] 2) Due to changes in the basic data source, the attention value of the test data change can be reduced from 10% to 2%, thereby greatly improving the sensitivity of defect detection.

[0051] 3) The test voltage retains the level of the traditional AC impedance test method and can reach a voltage level of 200V or higher, overcoming the shortcomings of the repetitive pulse method, such as low voltage and insensitivity in detecting some defects (the fault point is located near the center of the rotor). It is also less dependent on the operator's personal experience level, and manufacturers can recognize the test results under this test voltage.

[0052] 4) After finding that the data exceeds the standard, the impedance test of the separate coils can be further used to determine which set of coil windings the fault is located in, thereby locating the fault.

[0053] 5) This method combines the technical advantages of the existing AC impedance method, repetitive pulse method, inter-electrode voltage method, and coil voltage method. It can achieve the advantages of multiple test methods in one test. It can simultaneously and equivalently complete the AC impedance method test of routine tests and the inter-electrode voltage method test of diagnostic tests, greatly shortening the on-site testing time and improving on-site detection efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0054] Figure 1 Wiring diagram of the present invention.

[0055] Figure 2-1 This is the electrical schematic diagram of this method; Figure 2-2 This is the electrical schematic diagram of the traditional AC impedance method test.

[0056] Figure 3 This is a schematic diagram of the generator rotor coil connection.

[0057] Figure 4 This is a schematic diagram of the equivalent circuit of the generator rotor winding coil.

[0058] Figure 5 The following is the RSO test waveform diagram for the application example.

[0059] Figure 6 This is a physical schematic diagram of the location of the turn-to-turn short-circuit fault point in the application example.

[0060] Figure 7 This is a schematic diagram of the actual situation of inter-turn insulation ablation at the fault point in the application example. DETAILED DESCRIPTION

[0061] The specific implementation modes of the present invention are further described in detail below in conjunction with the specifications and examples.

[0062] The present invention discloses an AC impedance testing device for detecting a short-circuit fault between turns of a rotor winding, comprising a generator rotor, an AC voltage regulator, a first voltmeter, a second voltmeter, a third voltmeter, an ammeter and a movable electrode (a movable test contact electrode);

[0063] The AC voltage regulator is used as the test power supply, and its two voltage output terminals are connected through 15-20mm2 The wires are connected to the two poles of the generator rotor, and the ammeter is connected in series to the above loop to measure the loop current. One end of the mobile electrode is connected to the center point of the generator rotor winding poles. The first voltmeter is connected between the positive pole of the generator rotor and the other end of the mobile electrode. The second voltmeter is connected between the negative pole of the generator rotor and the other end of the mobile electrode. The third voltmeter is connected between the positive and negative poles of the generator rotor, where:

[0064] AC voltage regulator: used to output a continuously adjustable sine wave AC voltage signal as the test power supply for the rotor winding of the generator to be tested; its parameters can be 10kVA capacity and 0-380V output voltage;

[0065] The first voltmeter: used to measure the voltage V1 between the positive pole of the generator rotor and the moving electrode;

[0066] Second voltmeter: used to measure the voltage V2 between the negative pole of the generator rotor and the moving electrode;

[0067] The third voltmeter: used to measure the voltage V0 between the positive and negative poles of the generator rotor;

[0068] Ammeter: used to measure the current I applied by the AC voltage regulator to the two-pole circuit of the generator rotor winding;

[0069] Mobile electrode: used to contact the center point between the poles of the generator rotor winding to facilitate the measurement of the voltage between the positive and negative poles of the rotor to the mobile electrode.

[0070] Position of the inter-pole center point of the generator rotor winding: The inter-pole jumper wire between the positive and negative poles of the generator rotor winding is considered to be the inter-pole center point. The jumper wire crosses the inter-pole insulating partition and connects the 8th set of positive pole coils and the 8th set of negative pole coils.

[0071] The end of the movable electrode can be made into a probe that can be bent into a certain shape, so as to contact the rotor winding under the guard ring or at the rotor ventilation hole. During detection, the movable voltage can be changed to contact the position of different coils of the generator rotor winding to determine the specific faulty coil.

[0072] The voltmeter described in this embodiment is a high internal resistance voltmeter with an accuracy of 0.5 and a measuring range of 0 to 750V.

[0073] The ammeter described in this embodiment is a high-precision ammeter with an accuracy of 0.5 and a range of 0 to 50A.

[0074] An AC impedance testing method for detecting a rotor winding interturn short circuit fault comprises the following steps:

[0075] Step 1: Make sure the generator rotor to be tested is outside the stator chamber and placed horizontally and still.

[0076] The generator rotor to be tested is pulled out from the stator chamber and placed horizontally outside the stator chamber, ensuring that there are no large metal objects around it, and that the carbon brush slip rings or conductive screws on the two poles of the rotor are not electrically connected to the outside world;

[0077] Step 2: Connect the electrical test circuit

[0078] Connect the two voltage output terminals of the AC voltage regulator through 15-20mm 2 The conducting wire is connected to the carbon brush slip ring or conductive bolts at the two poles of the generator rotor to form a measuring circuit. The ammeter is connected in series to the above circuit to measure the circuit current I. The movable electrode is in contact with the conductor at the center point of the rotor winding poles under the end guard ring on the excitation side of the generator rotor. The first voltmeter is connected between the positive pole of the generator rotor and the other end of the movable electrode to measure the voltage V1 between the positive pole of the generator rotor and the movable electrode; the second voltmeter is connected between the negative pole of the generator rotor and the other end of the movable electrode to measure the voltage V2 between the negative pole of the generator rotor and the movable electrode; the third voltmeter is connected between the positive and negative poles of the generator rotor to measure the voltage V0 between the positive and negative poles of the generator rotor; the voltage input terminal of the AC voltage regulator is connected to the on-site 220V AC power supply through an air switch to form the entire electrical test circuit;

[0079] Position of the inter-pole center point of the generator rotor winding: The inter-pole jumper wire between the positive and negative poles of the generator rotor winding is considered to be the inter-pole center point. The jumper wire crosses the inter-pole insulating partition and connects the 8th set of coils at the positive pole and the 8th set of coils at the negative pole;

[0080] Step 3: Boost Measurement and Data Recording

[0081] The voltage output end of the AC voltage regulator is first adjusted to zero, and the air switch is closed to supply power to the voltage input side of the AC voltage regulator. The voltage on the output side of the voltage regulator is slowly adjusted to increase. When the voltage V0 between the positive and negative poles of the rotor reaches 50V, 100V, 150V, 200V, and 250V, the voltage is stopped and the corresponding test data is recorded. The test data includes voltage V1, V2 and current I. After recording, the voltage is reduced to zero and the air switch is disconnected.

[0082] Step 4: Data processing

[0083] The recorded data are summarized and calculated, and the calculation formula is as follows:

[0084] Voltage V0 between the positive and negative poles of the rotor: record value, V0;

[0085] Total AC impedance Z0 between the positive and negative poles of the rotor: calculated value, Z0 = V0 / I;

[0086] Voltage V1 between the positive pole of the rotor and the center point: record value, V1;

[0087] AC impedance Z1 between the positive pole of the rotor and the center point: calculated value, Z1 = V1 / I;

[0088] Voltage V2 between the negative pole of the rotor and the center point: record value, V2;

[0089] AC impedance Z2 between the negative pole of the rotor and the center point: calculated value, Z2 = V2 / I;

[0090] Record and calculate the above voltage, current and impedance values ​​at different voltages;

[0091] In practical application, the second voltmeter can be omitted, and the voltage V2=V0-V1 between the negative pole of the generator rotor and the moving electrode is obtained by calculation. The difference between the two is that one directly reads V2 and the other calculates V2. The technical solution of omitting the second voltmeter is an equivalent replacement technical solution with the technical solution of the present invention.

[0092] The record form can be found in Table 2

[0093] Table 2: Data Record Table

[0094] Parameter name V0 I V1 V2 Z0 Z1 Z2 Condition 1 Condition 2 Condition 3 ……

[0095] Step 5: Data Analysis

[0096] Compare and calculate the impedance Z1 and Z2 under different voltages. If the impedance Z1 is less than Z2, calculate the deviation rate k1 = (Z1 / Z2-1) × 100%:

[0097] If k1 < 2%, it is determined that there is no inter-turn short circuit in the rotor winding;

[0098] If k1 ≥ 2%, it is judged that there is a turn-to-turn short circuit fault in the positive pole winding coil of the rotor on the Z1 side;

[0099] If the impedance Z1 is greater than Z2, then calculate the deviation rate k2 = (Z2 / Z1-1) × 100%:

[0100] If k2 < 2%, it is determined that there is no inter-turn short circuit in the rotor winding;

[0101] If k2≥2%, it is determined that there is a turn-to-turn short circuit fault in the negative pole winding coil of the rotor on the Z2 side.

[0102] It should be noted that the above test process has actually completed the traditional AC impedance test and the inter-pole voltage test under the static state outside the rotor bore at the same time. The impedance Z0 is the rotor AC impedance value of the AC impedance method, and the voltages V1 and V2 are the two-pole voltage values ​​during the inter-pole voltage method test.

[0103] If the step 5 determines that there is a turn-to-turn short circuit fault in the coil, the process goes to step 6 to search for the faulty coil:

[0104] The voltage output end of the AC voltage regulator is first adjusted to zero, and the air switch is closed to supply power to the voltage input side of the AC voltage regulator. The voltage on the output side of the AC voltage regulator is adjusted to increase to 200V and stay there. The moving electrode is contacted with the bottom coil positions of the different rotor coils of the positive and negative poles under the end guard ring of the excitation side respectively. The voltage, current and impedance values ​​in this state are recorded and calculated. The recording table can be found in Table 3. After recording, the voltage is reduced to zero and the air switch is disconnected. Generally, each pole rotor has eight sets of coils, and each set of coils has 8 turns in most cases, and the first set of coils sometimes has 6 turns. It should be noted that when the moving electrode is within the positive winding range, the voltage V1 between the positive pole and the moving electrode is measured and recorded; when the moving electrode is within the negative winding range, the voltage V2 between the negative pole and the moving electrode is measured and recorded.

[0105] Since I and V0 remain unchanged at this time, the analysis focuses on calculating the impedances Z1 and Z2 corresponding to different positions of the moving electrodes, and calculating the impedance value Zmn between the coils. For example, the impedance Zmn of the first set of positive electrode coils only is recorded as Z01+, the impedance of the first and second sets of positive electrode coils and two sets of coils is recorded as Z12+, the impedance of the third and fourth sets of positive electrode coils and two sets of coils is recorded as Z34+, and so on; similar treatment is performed on the negative electrode coils, for example, the impedance of the first set of negative electrode coils only is recorded as Z01-, the impedance of the first and second sets of negative electrode coils and two sets of coils is recorded as Z12-, the impedance of the third and fourth sets of negative electrode coils and two sets of coils is recorded as Z34-, and so on.

[0106] Table 3: Fault coil search record table

[0107] Moving electrode position V0 I V1 Zn Positive coil 1 Positive coil 2 Positive coil 3 …… Moving electrode position V0 I V2 Zn Negative coil 1 Negative coil 2 Negative coil 3 ……

[0108] In the recorded data, if there is a large difference in the impedance of the coils at the corresponding positions of the positive and negative poles, it can be determined that there is an inter-turn short circuit fault in the coil winding with smaller impedance in the group.

[0109] Taking into full consideration the symmetry of the generator rotor structure, when there is no inter-turn short-circuit fault in the rotor, the electrical parameters of the corresponding coils at the positive and negative poles should be basically the same, as shown by Z01+=Z01-, Z12+=Z12-, Z34+=Z34-, and so on. When there is an inter-turn short-circuit fault in the rotor, the electrical parameters of the corresponding coils at the positive and negative poles will change significantly. When the impedance Z1 and Z2 deviation rate between the two poles is k, the impedance difference between a single set of coils or a double set of coils can reach 3-5 times the k value or higher. Therefore, when fault finding, when the impedance of a corresponding set of coils (including 1 or 2 sets of coils) is obviously different (the difference exceeds 6%), it can be determined that there is an inter-turn short-circuit fault in the coil winding with smaller impedance in the group.

[0110] The present invention has achieved good technical effects through practical application, and the application examples are as follows:

[0111] The test generator model is: QFSN-330-2-20, with a rated capacity of 300MW.

[0112] 1. Using traditional AC impedance test data

[0113] During the unit overhaul, electrical preventive tests were conducted, and the conventional AC impedance test method was used to conduct static AC impedance tests outside the chamber. The data were compared with the data during the historical overhaul period, as shown in Table 4:

[0114] Table 4 Test data of the traditional AC impedance method outside the chamber

[0115]

[0116] Under different voltages, the impedance change rate fluctuated greatly, ranging from 1.852% to 8.773%, with an average change rate of 5.240%, which was less than the 10% attention value required by the preventive test regulations. Initially, the site did not attach great importance to it, thinking that it was caused by the deviation of the system test, and did not consider the possibility of rotor winding inter-turn short circuit fault.

[0117] 2. Test data using the method of the present invention

[0118] Subsequently, the improved AC impedance test of the present invention was carried out, and the data are shown in Table 5:

[0119] Table 5 Test data of improved AC impedance method outside the chamber

[0120]

[0121] It can be seen from the above table that according to the improved AC impedance method of the present invention, the impedance change between poles 1 and 2 has exceeded 10%, with a small fluctuation between 10.190 and 10.450, and the numerical deviation has low stability, and no longer shows large fluctuations compared with the data of previous years. It is preliminarily judged that there is a short circuit fault between the winding turns of pole 2, which leads to a decrease in impedance.

[0122] At the same time, using the data from working conditions 2 and 5, when the voltage between the two poles is approximately 100V and 200V respectively, according to the judgment criteria of the traditional inter-pole voltage method, the inter-pole voltage difference also exceeds 10%, which is actually the voltage between the two poles corresponding to the impedance voltage divider of poles 1 and 2 under the corresponding working conditions.

[0123] At this point, let's summarize the advantages of the improved AC impedance test: 1) Without referring to historical data, the generator rotor bipolar symmetry characteristics are used as basic data for comparative analysis. The data deviation is very stable and has little fluctuation. Unlike the comparison of historical data, it will not be affected by the test instruments, test environment, test voltage and other conditions during the test, which greatly improves the credibility of the basic data source during comparative analysis. 2) Due to the change of the basic data source, the average deviation of the test data change increased from 5.24% to 10.357%, which is equivalent to amplifying the percentage of deviation, which is more conducive to finding problems. 3) Due to the significant improvement in the credibility and stability of the basic data source during comparative analysis, the test data change is very stable and does not change significantly with the test voltage, historical data, etc., so the attention value can be reduced from 10% to 2%, thereby greatly improving the sensitivity of finding defects. 4) The test voltage retains the level of the traditional AC impedance test method, which can reach 200V or higher voltage levels, and at the same time completes the diagnostic test items of the inter-electrode voltage method, greatly shortening the on-site test and diagnosis time and improving the efficiency of on-site detection.

[0124] 3. Further fault coil search

[0125] To further verify and locate the fault location, a repeated pulse short circuit test (RSO test) and an improved AC impedance test were performed on site. The RSO test waveform is as follows: Figure 5 shown.

[0126] From the graphical observation, the curves of pole 1 and pole 2 have good overlap for the most part, with only a certain deviation in some parts. The maximum value of the difference characteristic curve is about 0.1-0.2V, which may be ignored. However, after careful analysis, especially under the premise of the improved AC impedance judgment of the present invention that there is a turn-to-turn short-circuit fault, the analysis and judgment that although its absolute value is small, the waveform characteristics are close to the typical waveform data characteristics of the 8th set of coils of pole 2 of the rotor winding (the 8th set is closest to the center point between poles) when the turn-to-turn short-circuit occurs, and it is preliminarily judged that there is a certain degree of turn-to-turn short-circuit fault in the rotor winding, and it is located near the 8th set of coils of pole 2.

[0127] The improved AC impedance method test was performed using the test process of step 6 of the method of the present invention. To improve efficiency and facilitate on-site wiring, two sets of coils were measured each time, and 4 data were tested for each pole. The results of recording and analysis are shown in Tables 6 and 7:

[0128] Table 6 Fault finding record

[0129] Moving electrode position I V0 V1 Impedance Name Zm-n The dividing point between the second and third suites of Pole 1 25.966 200.7 21.3 Z12+ 0.8184 The dividing point between the 4th and 5th suites of Pole 1 48.6 Z34+ 1.0533 The dividing point between the 6th and 7th suites of Pole 1 76.9 Z56+ 1.0899 The center point of the two poles 105.8 Z78+ 1.1130 The dividing point between the 2nd and 3rd suites of Pole 2 21.1 Z12- 0.8087 The dividing point between the 4th and 5th suites of Pole 2 48.1 Z34- 1.0398 The dividing point between the 6th and 7th suites of Pole 2 76.4 Z56- 1.0899 negative electrode 94.0 Z78- 0.6778

[0130] Table 7: Calculation of impedance deviation at corresponding positions

[0131] Impedance Name Impedance Impedance Name Impedance Corresponding impedance deviation (%) Z12+ 0.8184 Z12- 0.8087 -1.176 Z34+ 1.0533 Z34- 1.0398 -1.280 Z56+ 1.0899 Z56- 1.0899 0 Z78+ 1.1130 Z78- 0.6778 -39.100

[0132] From the data in the table, we can see that the impedance deviation between the 7th and 8th coils Z78+ of pole 1 and the 7th and 8th coils Z78- of pole 2 is as high as 39.1%, which is very obvious that there is a turn-to-turn short circuit fault, and the data characteristic deviation is very obvious. The 7th and 8th sets were further tested on site, and it was finally determined that the 8th coil of pole 2 had a turn-to-turn short circuit fault. The specific process and data will not be described here.

[0133] According to the diagnosis results, the steam end guard ring was removed and checked, and it was found that there was an insulation burnt point between the turns of the steam end of the 8th coil of pole 2. Figure 6 When the inter-turn insulation was removed, a hole with a diameter of about 15 mm was found. Figure 7 , confirming that this is the turn-to-turn short-circuit fault point, indicating that the diagnostic results of the turn-to-turn short-circuit fault test and fault finding using the improved AC impedance method are accurate.

[0134] After confirming the inter-turn short-circuit fault point, the inter-turn short-circuit fault point was processed on site, and the ends of the steam excitation were cleaned and some insulating materials were replaced. After processing, all test results were retested and found to be normal.

Claims

1. An AC impedance test device for detecting a short circuit fault between turns of a rotor winding, comprising a generator rotor, characterized in that: It also includes an AC voltage regulator, a first voltmeter, a second voltmeter, a third voltmeter, an ammeter and a moving electrode; The AC voltage regulator is used as a test power source, and its two voltage output terminals are connected to the two poles of the generator rotor to form a measurement circuit. The ammeter is connected in series to the measurement circuit to measure the circuit current. One end of the mobile electrode is connected to the center point of the generator rotor winding poles. The first voltmeter is connected between the positive pole of the generator rotor and the other end of the mobile electrode. The second voltmeter is connected between the negative pole of the generator rotor and the other end of the mobile electrode. The third voltmeter is connected between the positive and negative poles of the generator rotor, wherein: AC voltage regulator: used to output a continuously adjustable sine wave AC voltage signal as the test power supply for the rotor winding of the generator to be tested; The first voltmeter: used to measure the voltage V1 between the positive pole of the generator rotor and the moving electrode; Second voltmeter: used to measure the voltage V2 between the negative pole of the generator rotor and the moving electrode; The third voltmeter: used to measure the voltage V0 between the positive and negative poles of the generator rotor; Ammeter: used to measure the current I applied by the AC voltage regulator to the two-pole circuit of the generator rotor winding; Mobile electrode: used to contact the center point between the poles of the generator rotor winding to facilitate the measurement of the voltage between the positive and negative poles of the rotor to the mobile electrode.

2. The AC impedance testing device for detecting rotor winding interturn short circuit fault according to claim 1, characterized in that: The first, second and third voltmeters are high internal resistance voltmeters with an accuracy of 0.5 and a measuring range of 0 to 750V.

3. The AC impedance testing device for detecting rotor winding interturn short circuit fault according to claim 1, characterized in that: The ammeter is a high-precision ammeter with an accuracy of 0.5 and a measuring range of 0 to 50A.

4. An AC impedance test method for detecting a rotor winding interturn short circuit fault, characterized in that: The following steps are involved: Step 1: Make sure the generator rotor to be tested is outside the stator chamber and placed horizontally and still. The generator rotor to be tested is pulled out from the stator chamber and placed horizontally outside the stator chamber, ensuring that there are no metal objects around it and that the carbon brush slip rings or conductive screws on the two poles of the rotor are not electrically connected to the outside world; Step 2: Connect the electrical test circuit Connect the two voltage output terminals of the AC voltage regulator to the carbon brush slip rings or conductive bolts of the two poles of the generator rotor through wires to form a measuring circuit. The ammeter is connected in series to the above circuit to measure the circuit current I. The movable electrode is in contact with the conductor at the center point of the rotor winding poles under the end guard ring on the excitation side of the generator rotor. The first voltmeter is connected between the positive pole of the generator rotor and the other end of the movable electrode to measure the voltage V1 between the positive pole of the generator rotor and the movable electrode; the second voltmeter is connected between the negative pole of the generator rotor and the other end of the movable electrode to measure the voltage V2 between the negative pole of the generator rotor and the movable electrode; the third voltmeter is connected between the positive and negative poles of the generator rotor to measure the voltage V0 between the positive and negative poles of the generator rotor; the voltage input terminal of the AC voltage regulator is connected to the on-site 220V AC power supply through an air switch to form the entire electrical test circuit; Step 3: Boost Measurement and Data Recording The voltage output end of the AC voltage regulator is first adjusted to zero, and the air switch is closed to supply power to the voltage input side of the AC voltage regulator. The voltage on the output side of the voltage regulator is slowly adjusted to increase. When the voltage V0 between the positive and negative poles of the rotor reaches 50V, 100V, 150V, 200V, and 250V, the voltage is stopped and the corresponding test data is recorded. The test data includes voltage V1, V2 and current I. After recording, the voltage is reduced to zero and the air switch is disconnected. Step 4: Data processing The recorded data are summarized and calculated, and the calculation formula is as follows: Voltage V0 between the positive and negative poles of the rotor: record value, V0; Total AC impedance Z0 between the positive and negative poles of the rotor: calculated value, Z0=V0 / I; Voltage V1 between the positive pole of the rotor and the center point: record value, V1; AC impedance Z1 between the positive pole of the rotor and the center point: calculated value, Z1=V1 / I; Voltage V2 between the negative pole of the rotor and the center point: record value, V2; AC impedance Z2 between the negative pole of the rotor and the center point: calculated value, Z2=V2 / I; Record and calculate the above voltage, current and impedance values ​​at different voltages; Step 5: Data Analysis Compare and calculate the impedance Z1 and Z2 under different voltages. If the impedance Z1 is less than Z2, calculate the deviation rate k1 = (Z1 / Z2-1) × 100%: If k1 < 2%, it is determined that there is no inter-turn short circuit in the rotor winding; If k1 ≥ 2%, it is judged that there is a turn-to-turn short circuit fault in the positive winding coil of the rotor on the Z1 side; If the impedance Z1 is greater than Z2, calculate the deviation rate k2 = (Z2 / Z1-1) × 100%: If k2 < 2%, it is determined that there is no inter-turn short circuit in the rotor winding; If k2≥2%, it is determined that there is a turn-to-turn short circuit fault in the negative pole winding coil of the rotor on the Z2 side.

5. The AC impedance testing method for detecting rotor winding interturn short circuit fault according to claim 4, characterized in that: If the step 5 determines that there is a turn-to-turn short circuit fault in the coil, then proceed to step 6, fault coil search: The voltage output end of the AC voltage regulator is first adjusted to zero, and the air switch is closed to supply power to the voltage input side of the AC voltage regulator. The voltage on the output side of the AC voltage regulator is adjusted and increased to 200V and then stays there. The mobile electrode is contacted with the bottom coil positions of the rotor positive pole and the rotor negative pole under the end guard ring of the excitation side respectively. The voltage, current and impedance values ​​in this state are recorded and calculated. After recording, the voltage is reduced to zero and the air switch is disconnected. In the recorded data, if there is a large difference in the impedance of the coils at the corresponding positions of the positive and negative poles of the rotor, it can be judged that there is an inter-turn short circuit fault in the coil winding with smaller impedance.

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