Insulation detection method for cable winding of phase modifier

Abstract

The invention discloses an insulation detection method for cable windings of a phase modifier, and relates to the field of phase modifiers, and the method comprises the following steps: S1, sequentially embedding an A-phase cable, a B-phase cable and a C-phase cable into iron core grooves of a stator iron core to respectively form a corresponding A-phase winding, a B-phase winding and a C-phase winding, and the insulating layer of each phase cable is made of a crosslinked polyethylene material; s2, cable terminal connectors are mounted at the wire outlet end and the neutral end of each phase of winding and are grounded; s3, respectively carrying out insulation resistance detection test on each phase of winding; s4, respectively carrying out an alternating current withstand voltage test on each phase of winding; and S5, respectively carrying out dielectric loss factor detection test on each phase of winding. The device can detect the insulation performance of the cable winding of the direct-hanging phase modifier, and has the advantages of comprehensive detection and high reliability.

Description

Technical Field

[0001] This invention relates to the field of synchronous condensers, and more specifically to a method for detecting the insulation of synchronous condenser cable windings. Background Technology

[0002] With the large-scale grid connection of intermittent renewable energy sources such as wind power and photovoltaics, the operating characteristics of the power system have changed significantly, posing a challenge to grid stability. Synchronous condensers, as key equipment for maintaining voltage stability, provide necessary voltage support and stability margin to the grid through rapid dynamic reactive power regulation. In ultra-high voltage direct current (UHVDC) transmission projects, synchronous condensers are even more crucial equipment in converter stations, effectively enhancing the system's immunity to disturbances, suppressing commutation failures, and ensuring the safe transmission of large-capacity electrical energy over long distances.

[0003] Direct-connected synchronous condensers can boost terminal voltage to 35kV, allowing direct connection to the high-voltage grid without transformers, thus eliminating transformer losses. They can also provide reactive power compensation and voltage support across the entire timescale, including transient, transient, and steady-state conditions. In the transient state, the condenser can rapidly release a large amount of reactive power during voltage drops caused by grid faults, reducing the magnitude and speed of the voltage drop. In the transient state, during fault recovery, the condenser provides reactive power support exceeding its rated capacity by 1.5 times or more, helping to restore grid voltage. In the steady-state state, the condenser can continuously regulate reactive power, providing short-circuit capacity and rotational inertia, improving grid stability.

[0004] In existing technologies, traditional synchronous condensers typically use mica-insulated strip stator bars as windings, and their manufacturing and testing processes are relatively mature. In contrast, direct-connected synchronous condensers generally use cross-linked polyethylene (XLPE) cables as stator windings, which have thicker insulation layers, higher withstand voltage levels, and are more suitable for high-voltage applications. However, China lacks mature experience in the manufacturing and installation of such cable windings. In particular, insulation damage is easily caused by mechanical stress during the winding unwinding process. If not detected in time, this can easily lead to ground faults or phase-to-phase breakdowns after commissioning, seriously affecting power grid safety and causing significant economic losses. Summary of the Invention

[0005] This invention aims to address one of the technical problems in related technologies to a certain extent. To this end, this invention provides an insulation testing method for synchronous condenser cable windings, capable of testing the insulation performance of directly connected synchronous condenser cable windings, and possessing the advantages of comprehensive testing and high reliability.

[0006] To achieve the above objectives, the present invention adopts the following technical solution: An insulation testing method for a synchronous condenser cable winding includes the following steps: S1, Phase A cable, Phase B cable and Phase C cable are sequentially embedded in the core slots of the stator core to form corresponding Phase A winding, Phase B winding and Phase C winding respectively. The insulation layer of each phase cable is cross-linked polyethylene material. S2, each phase winding has a cable terminal joint installed at the output end and neutral end and grounded; S3, Insulation resistance test is performed on each phase winding respectively; S4, each phase winding is subjected to an AC withstand voltage test; S5, conduct dielectric loss factor test on each phase winding respectively.

[0007] In this application, the insulation resistance test involves applying a DC voltage to the insulation layer, measuring the leakage current flowing through it, and calculating the insulation resistance value according to Ohm's law, reflecting the conductivity of the insulation layer under a DC electric field. The AC withstand voltage test involves applying a power frequency AC voltage much higher than the operating voltage to the insulation layer for a specified time. Its principle is to simulate overvoltage stress during operation, using a strong electric field to expose concentrated defects (such as bubbles, cracks, and impurities) that are not detectable at lower voltages. If such defects exist in the insulation layer, it will break down under high field strength. The dielectric loss factor test measures the energy loss of the insulation layer under AC voltage. When the insulation layer is aged, damp, or contains distributed impurities, its dielectric loss value will increase significantly; therefore, this test can determine the overall quality status of the insulation layer. Through insulation resistance testing, AC withstand voltage testing, and dielectric loss factor testing of each phase winding, a comprehensive evaluation of the cable winding insulation performance is achieved, thus offering advantages such as comprehensive testing and high reliability.

[0008] Optionally, in step S3, the insulation resistance test includes: applying a 5kV DC voltage between the output terminal and the neutral terminal of each phase winding after installation at room temperature; recording the insulation resistance value R1 after 15 seconds of voltage application and the insulation resistance value R2 after 60 seconds of voltage application, and calculating the absorption ratio R2 / R1; when the absorption ratio is ≥1.3 and the insulation resistance value after 60 seconds of voltage application is ≥600 MΩ, the insulation resistance test of that phase winding is deemed to have passed the standard.

[0009] A 5kV DC voltage is applied between the output terminal and the neutral terminal of each phase winding. The insulation resistance values ​​R1 and R2 are recorded after 15 seconds and 60 seconds of voltage application, respectively. The absorption ratio (R2 / R1) is calculated. When the absorption ratio is ≥1.3 and R2 is ≥600MΩ, the insulation resistance test is deemed to be up to standard. This overcomes the limitation of relying solely on a single insulation resistance value in traditional testing and avoids misjudgment caused by the difficulty in effectively detecting distributed defects such as insulation dampness and aging.

[0010] Optionally, step S3 further includes: when the insulation resistance test of a certain phase winding fails to meet the standard, the phase winding is dried; if the insulation resistance test of the phase winding still fails to meet the standard after drying, a DC high voltage is applied to the phase winding by DC impulse method, a pulse is generated by ball gap discharge, and the discharge sound of the fault point is listened to to determine the location of the fault point; after determining the fault point, the faulty section of cable containing the fault point is pulled out from the iron core slot and cut off, and a new section of cable is connected to the phase winding through a cable joint, and then the insulation resistance test of the phase winding is performed.

[0011] When the insulation resistance of a phase winding fails to meet the standard, a graded treatment process is implemented: First, the phase winding is dried; if it still fails to meet the standard, a DC high voltage is applied to the faulty phase using the DC impulse method, generating pulses through ball gap discharge, and the fault location is determined using the acoustic positioning principle; then, the faulty section of cable is pulled out of the iron core slot and cut off, and a new cable section is connected using a cable joint to complete the repair; finally, the insulation resistance test is repeated. This solves the technical problem in existing technologies where, after a failure in insulation resistance testing is detected, there is a lack of effective fault location and repair guidance, leading to low maintenance efficiency and incomplete fault elimination. It achieves rapid location and complete elimination of insulation layer faults, significantly improving maintenance efficiency and success rate, and ensuring that the insulation performance of the cable winding is fully restored to a qualified state after repair.

[0012] Optionally, in step S3, after the insulation resistance of each phase winding meets the standard, an AC withstand voltage test is performed on each phase winding. The AC withstand voltage test includes: applying a voltage of 57.5kV between the output terminal and the neutral terminal of a certain phase winding and maintaining the voltage for 1 minute; if no electrical breakdown occurs in the phase winding during the voltage application period, the AC withstand voltage test of the phase winding is deemed to have met the standard.

[0013] After the insulation resistance of each phase winding meets the standard, an AC withstand voltage test is performed on each phase winding. This involves applying a 57.5kV AC voltage at power frequency between the winding's output terminal and neutral terminal for one minute. If no electrical breakdown occurs during this period, the phase winding is considered to have passed the AC withstand voltage test. This method solves the problem that traditional testing methods cannot effectively detect concentrated defects (such as bubbles, cracks, and impurities) in the winding insulation, preventing sudden insulation breakdown accidents caused by these potential defects under operating voltage. By applying a test voltage higher than the rated voltage and maintaining it for a specific time, concentrated defects in the insulation system are effectively exposed, ensuring that the windings that pass the test have sufficient insulation strength margin, providing a crucial guarantee for the long-term safe operation of the equipment.

[0014] Optionally, in step S3, if an electrical breakdown occurs in the phase winding during the applied voltage, the cable with the electrical breakdown is pulled out of the iron core slot and cut off, and a new cable is connected to the phase winding through a cable connector. Then, the phase winding is subjected to an AC withstand voltage test.

[0015] If an electrical breakdown fault occurs during the AC withstand voltage test, the following repair procedure is performed: the broken-down cable segment is pulled out of the core slot and the faulty part is cut off. A new cable segment is connected through a cable joint to restore the winding integrity. Subsequently, a complete AC withstand voltage test is performed again on that phase winding. It is understood that if another electrical breakdown fault occurs, this repair procedure is repeated until no electrical breakdown fault occurs. Existing detection methods lack a repair procedure after a breakdown occurs during the AC withstand voltage test. The repair procedure in this application avoids the scrapping of the entire phase winding due to local insulation faults, while ensuring that the insulation performance of the repaired winding fully meets the standard requirements.

[0016] Optionally, the AC withstand voltage test also includes: when the voltage applied between the output terminal and the neutral terminal of a certain phase winding rises to 38.5kV, under anechoic conditions, visual observation is performed on the output terminal, neutral terminal, and cable terminal joints installed on both of the phase winding. If there are no visible, persistent golden bright spots, stable bright spots, or continuous halos in any of the observed parts, the visual observation of the phase winding is deemed to have met the standard.

[0017] During the AC withstand voltage test voltage ramp-up process, when the test voltage rises to 38.5kV (i.e., 1.1U), N In a darkroom environment, visual inspection is performed on the winding's output terminals, neutral terminal, and cable termination joints at both ends. If no continuous golden-yellow bright spots, stable bright spots, or continuous halos appear at any of the observed locations, the visual inspection of that phase winding is deemed to have met the standards. This avoids the problem of traditional insulation testing relying solely on "whether it has broken down" as the sole criterion, which makes it difficult to detect potential insulation defects such as early partial discharge or surface corona, and prevents the gradual deterioration of insulation materials due to the long-term development of corona discharge. Furthermore, by operating near the rated operating voltage (1.1U... N The introduction of visual corona detection in a darkroom can identify partial discharge phenomena caused by poor installation, shielding layer damage, or surface contamination, enabling a direct assessment of the surface condition of the insulation layer and improving the comprehensiveness of the detection and the ability to warn of potential hazards.

[0018] Optionally, in step S3, the AC withstand voltage test further includes: when the voltage value applied between the outgoing terminal and the neutral terminal of a certain phase winding rises to 38.5 kV, use an ultraviolet imager to perform corona detection on the winding at a distance of 2 m from the phase winding; if the measured number of photons ≤ 2000 / s, it is determined that the corona detection of this phase winding is qualified; when the corona detection of a certain phase winding is unqualified, repair the low-resistance shielding layer of the cable where corona appears until the corona detection is qualified.

[0019] During the AC withstand voltage test, when the test voltage rises to 38.5 kV (1.1U N ), use an ultraviolet imager to perform corona detection at a distance of 2 m from the measured phase winding. If the measured number of photons does not exceed 2000 / s, it is determined that the corona detection is qualified; if it is unqualified, repair the low-resistance shielding layer of the cable part where corona appears and repeat the detection until it is qualified. In the prior art, corona detection relies on subjective judgment, is difficult to quantitatively evaluate, and locate the corona source, while the detection method in this application can avoid local deterioration of the insulating layer material caused by the long-term existence of corona discharge and improve the long-term operation reliability of the equipment.

[0020] Optionally, in step S5, after the AC withstand voltage test of each phase winding is qualified, perform a dielectric loss factor detection test on each phase winding separately; the dielectric loss factor detection test includes: apply a voltage between the outgoing terminal and the neutral terminal of a certain phase winding, and the voltage value rises from 7 kV to 35 kV. Test the dielectric loss factor once every 7 kV of voltage increase. When the dielectric loss factor tanδ at 7 kV ≤ 1.0% and the dielectric loss factor tanδ at 35 kV ≤ 2.0%, it is determined that the dielectric loss factor detection test of this phase winding is qualified.

[0021] After the AC withstand voltage test is completed, perform a dielectric loss factor detection test on each phase winding separately: apply a stepped voltage increase from 7 kV to 35 kV between the winding outgoing terminal and the neutral terminal, with each 7 kV as a test point, and measure the dielectric loss factor tanδ at each voltage point. If tanδ ≤ 1.0% at 7 kV and tanδ ≤ 2.0% at 35 kV, it is determined that the dielectric loss detection of this phase winding is qualified. The dielectric loss factor detection test effectively evaluates problems such as the overall aging, moisture absorption, and distributed defects of the insulating layer within the operating voltage range. In addition, by measuring the dielectric loss factor at multiple voltage points, the change in the loss characteristics of the insulating material under different electric field strengths can be systematically evaluated, and the early insulation deterioration trend can be sensitively identified, providing data support for evaluating the long-term operation reliability of the cable winding and ultimately preventing operation failures caused by insulation aging.

[0022] Optionally, surge protectors are installed at the outgoing terminals of the A-phase winding, B-phase winding, and C-phase winding.

[0023] Sheath protectors are installed at the outgoing terminals of phase A, phase B, and phase C windings, forming an overvoltage protection system for the cable. During testing and operation, this system prevents insulation damage caused by induced high voltages on the shielding layer due to lightning or switching voltages. In other words, by configuring sheath protectors at each phase outgoing terminal, the overvoltage amplitude on the cable shielding layer is limited, providing overvoltage protection for the cable insulation layer. This reduces the risk of insulation damage due to voltage surges during testing and operation, thereby improving the overall safety and service life of the equipment.

[0024] Optionally, each phase cable includes multiple branches, the outgoing ends of which are connected by cable termination connectors, and the neutral ends of which are connected by cable termination connectors.

[0025] High-capacity synchronous condensers, due to their large operating current and limited current carrying capacity of a single cable, require a multi-branch parallel structure. Therefore, each phase cable winding consists of multiple parallel branches. The outgoing terminals of each branch are electrically connected through cable termination joints, and the neutral terminals of each branch are also electrically connected through cable termination joints, forming a complete winding for each phase. The use of cable termination joints ensures uniform electric field distribution and reliable insulation strength at the multi-branch connection points, guaranteeing the safety and stability of the electrical connection.

[0026] These features and advantages of the present invention will be disclosed in detail in the following specific embodiments and accompanying drawings. The preferred embodiments or means of the present invention will be shown in detail in conjunction with the accompanying drawings, but are not intended to limit the technical solutions of the present invention. In addition, each of these features, elements and components appearing in the following text and drawings is a plurality of, and different symbols or numbers are used for convenience of representation, but all represent parts with the same or similar construction or function. Attached Figure Description

[0027] The present invention will be further described below with reference to the accompanying drawings: Figure 1 This is a schematic diagram of the structure of the camera cable winding in this invention.

[0028] Among them, 1. Phase A winding; 2. Phase B winding; 3. Phase C winding; 4. Cable terminal joint; 5. Sheath protector. Detailed Implementation

[0029] Embodiments of the present invention are described in detail below, examples of which are illustrated in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described are intended to explain the present invention and should not be construed as limiting the invention.

[0030] The terms "an embodiment," "example," or "trademark" used in this specification refer to a particular feature, structure, or characteristic described in connection with the embodiment itself that may be included in at least one embodiment disclosed in this patent. The phrase "in an embodiment" appearing in various places throughout the specification does not necessarily refer to the same embodiment.

[0031] Example: This embodiment provides an insulation detection method for a synchronous condenser cable winding, including the following steps: S1, as Figure 1 As shown, phase A cable, phase B cable and phase C cable are sequentially embedded in the core slots of the stator core to form corresponding phase A winding 1, phase B winding 2 and phase C winding 3, respectively. The insulation layer of each phase cable is cross-linked polyethylene material. S2, each phase winding has a cable terminal connector 4 installed at the output end and neutral end and grounded; S3, Insulation resistance test is performed on each phase winding respectively; S4, each phase winding is subjected to an AC withstand voltage test; S5, conduct dielectric loss factor test on each phase winding respectively.

[0032] Cross-linked polyethylene (XLPE) possesses excellent electrical properties, but existing technologies lack methods for testing the insulation performance of XLPE cables during installation. Therefore, this embodiment provides an insulation testing method to detect potential damage to the cable winding insulation layer during installation of cables with XLPE insulation. In this embodiment, the insulation layer of each phase cable is made of XLPE. Phase A, Phase B, and Phase C cables are sequentially embedded into the core slots of the stator core of a direct-mounted synchronous condenser to form corresponding Phase A winding 1, Phase B winding 2, and Phase C winding 3, respectively. These three windings together constitute the stator coil of the synchronous condenser. The surface of the cable winding insulation layer is covered with a low-resistance shielding layer and a metal protective layer, which effectively balances the electric field distribution and prevents corona discharge on the winding surface under reliable grounding conditions. However, after the cable winding is installed, the distance between the conductors at both ends and the low-resistance shielding layer on the insulation surface is too close, forming a concentrated electric field area. Directly applying high voltage will cause surface flashover at the ends, thus making effective testing of the cable insulation layer impossible. Therefore, in this embodiment, cable termination connectors 4 are installed at the output and neutral ends of each phase winding (cable). These cable termination connectors 4 increase the creepage distance, extend the insulation path between the conductors at both ends of the cable and the low-resistance shielding layer, and also reduce the potential difference at the end surfaces. The installation of cable termination connectors 4 creates the necessary and safe testing conditions for subsequent high-voltage tests such as AC withstand voltage tests and dielectric loss factor detection tests.

[0033] Insulation resistance testing involves applying a DC voltage to the insulation layer, measuring the leakage current, and calculating the insulation resistance value using Ohm's law. This reflects the conductivity of the insulation layer under a DC electric field. AC withstand voltage testing involves applying a power frequency AC voltage, much higher than the operating voltage, to the insulation layer for a specified time. Its principle is to simulate overvoltage stress during operation, using a strong electric field to expose concentrated defects (such as bubbles, cracks, and impurities) that are not visible at lower voltages. If such defects exist in the insulation layer, it will break down under high field strength. Dielectric loss factor testing measures the energy loss of the insulation layer under AC voltage. When the insulation layer is aged, damp, or contains distributed impurities, its dielectric loss value increases significantly; therefore, this test can determine the overall quality condition of the insulation layer.

[0034] This embodiment achieves a comprehensive evaluation of the cable winding insulation performance through insulation resistance testing and AC withstand voltage testing of each phase winding, as well as dielectric loss factor testing. Therefore, it offers the advantages of comprehensive testing and high reliability. Furthermore, this testing method is specifically designed for the structural characteristics of cable windings with XLPE insulation (such as the need for end-joint treatment of the electric field) and the risk of damage during the winding process (such as mechanical stress damage). Compared to traditional bar-based testing methods, it is more targeted and applicable, thus ensuring high reliability of the test results.

[0035] The detection method in this embodiment can also be applied to stator cable windings of synchronous condensers, thermal power plants, and hydropower plants with higher withstand voltage levels of 35kV and above, laying a reliable technical foundation for the research and application of cable windings of synchronous condensers, thermal power plants, and hydropower plants with higher voltage levels.

[0036] In step S3, the insulation resistance test includes: applying a 5kV DC voltage between the output terminal and the neutral terminal of each phase winding after installation at room temperature; recording the insulation resistance value R1 after 15 seconds of voltage application and the insulation resistance value R2 after 60 seconds of voltage application, and calculating the absorption ratio R2 / R1; when the absorption ratio is ≥1.3 and the insulation resistance value after 60 seconds of voltage application is ≥600 MΩ, the insulation resistance test of that phase winding is deemed to have passed the standard.

[0037] In this embodiment, a 5kV DC voltage is applied between the output terminal and the neutral terminal of each phase winding, and the insulation resistance values ​​R1 and R2 are recorded after 15 seconds and 60 seconds of voltage application, respectively. The absorption ratio (R2 / R1) is calculated. When the absorption ratio is ≥1.3 and R2≥600MΩ, the insulation resistance test is deemed to be up to standard. This overcomes the limitation of relying solely on a single insulation resistance value in traditional testing and avoids misjudgment caused by the difficulty in effectively detecting distributed defects such as insulation dampness and aging.

[0038] Step S3 further includes: when the insulation resistance test of a certain phase winding fails to meet the standard, the phase winding is dried; if the insulation resistance test of the phase winding still fails to meet the standard after drying, a DC high voltage is applied to the phase winding by DC impulse method, a pulse is generated by ball gap discharge, and the discharge sound of the fault point is listened to to determine the location of the fault point; after determining the fault point, the fault section of cable containing the fault point is pulled out from the iron core slot and cut off, and a new section of cable is connected to the phase winding through a cable joint, and then the insulation resistance test of the phase winding is performed.

[0039] In this embodiment, when the insulation resistance of a certain phase winding fails to meet the standard, a graded processing procedure is performed: First, the phase winding is dried; if it still fails to meet the standard, a DC high voltage is applied to the faulty phase using the DC impulse method, generating pulses through ball gap discharge, and the location of the fault point is determined using the acoustic positioning principle; then, the faulty section of cable is pulled out of the iron core slot and cut off, and a new cable section is connected using a cable joint to complete the repair; finally, the insulation resistance test is performed again. This solves the technical problem in the prior art where, after the insulation resistance test finds a non-compliance, there is a lack of effective fault location and repair guidance, resulting in low maintenance efficiency and incomplete fault elimination. It achieves rapid location and complete elimination of insulation layer faults, significantly improving maintenance efficiency and success rate, and ensuring that the insulation performance of the cable winding is fully restored to a qualified state after repair.

[0040] In step S3, after the insulation resistance of each phase winding meets the standard, an AC withstand voltage test is performed on each phase winding. The AC withstand voltage test includes: applying a voltage of 57.5kV between the output terminal and the neutral terminal of a certain phase winding and maintaining the voltage for 1 minute; if no electrical breakdown occurs in the phase winding during the voltage application period, the AC withstand voltage test of the phase winding is deemed to have met the standard.

[0041] In this embodiment, after the insulation resistance of each phase winding meets the standard, an AC withstand voltage test is performed on each phase winding. This involves applying a 57.5kV power frequency AC voltage between the winding's output terminal and neutral terminal for one minute. If no electrical breakdown occurs during this period, the phase winding is considered to have passed the AC withstand voltage test. This solves the problem that traditional testing methods cannot effectively detect concentrated defects (such as bubbles, cracks, impurities, etc.) in the winding insulation, preventing sudden insulation breakdown accidents caused by these potential defects under operating voltage. By applying a test voltage higher than the rated voltage and maintaining it for a specific time, concentrated defects in the insulation system are effectively exposed, ensuring that the windings that pass the test have sufficient insulation strength margin, providing a crucial guarantee for the long-term safe operation of the equipment.

[0042] The formula for calculating the value of the power frequency AC voltage applied between the winding output terminal and the neutral terminal is: 1.5U N +5 Among them, U N This refers to the rated operating voltage of the synchronous condenser. In this embodiment, the rated operating voltage of the synchronous condenser is 35V, therefore the applied AC voltage at power frequency between the winding output terminal and the neutral terminal is 57.5kV. It is understood that when testing synchronous condensers with other rated operating voltages, the applied AC voltage should also change.

[0043] It should be noted that after performing the AC withstand voltage test on each phase winding, the aforementioned insulation resistance test needs to be repeated on each phase winding at room temperature. A 5kV DC voltage is applied between the output terminal and the neutral terminal of each phase winding, and the insulation resistance values ​​R1 and R2 are recorded after 15 seconds and 60 seconds of voltage application, respectively. The absorption ratio (R2 / R1) is calculated. When the absorption ratio is ≥1.3 and R2 is ≥600MΩ, the insulation resistance test is deemed to be up to standard.

[0044] In step S3, if an electrical breakdown occurs in the phase winding during the applied voltage, the cable with the electrical breakdown is pulled out of the iron core slot and cut off. A new cable is then connected to the phase winding through a cable connector, and the phase winding is then subjected to an AC withstand voltage test.

[0045] In this embodiment, if an electrical breakdown fault occurs during the AC withstand voltage test, the following repair procedure is performed: the broken cable segment is pulled out of the core slot and the faulty part is cut off. A new cable segment is connected through a cable joint to restore the winding integrity. Subsequently, a complete AC withstand voltage test is performed again on that phase winding. It is understood that if another electrical breakdown fault occurs, this repair procedure is repeated until no electrical breakdown fault occurs. Existing detection methods lack a repair procedure after a breakdown occurs during the AC withstand voltage test. The repair procedure in this embodiment avoids the scrapping of the entire phase winding due to local insulation faults, while ensuring that the insulation performance of the repaired winding fully meets the standard requirements.

[0046] The AC withstand voltage test also includes: when the voltage applied between the output terminal and the neutral terminal of a certain phase winding rises to 38.5kV, under anechoic conditions, visual observation is performed on the output terminal, neutral terminal, and cable terminal joint 4 installed on both of the phase winding. When there are no visible, persistent golden bright spots, stable bright spots, or continuous halos in all observed parts, the visual observation of the phase winding is deemed to have met the standard.

[0047] In this embodiment, during the AC withstand voltage test voltage boosting process, when the test voltage rises to 38.5kV (i.e., 1.1U), NIn a darkroom environment, visual inspection is performed on the winding's output terminals, neutral terminals, and cable terminal joints 4 at both ends. If no continuous golden-yellow bright spots, stable bright spots, or continuous halos appear at any of the observed locations, the visual inspection of that phase winding is deemed to have met the standards. This avoids the problem of traditional insulation testing relying solely on "whether it has broken down" as the sole criterion, which makes it difficult to detect potential insulation defects such as early partial discharge or surface corona, and prevents the gradual deterioration of insulation materials due to the long-term development of corona discharge. Furthermore, by operating near the rated operating voltage (1.1U... N The introduction of visual corona detection in a darkroom can identify partial discharge phenomena caused by poor installation, shielding layer damage, or surface contamination, enabling a direct assessment of the surface condition of the insulation layer and improving the comprehensiveness of the detection and the ability to warn of potential hazards.

[0048] In step S3, the AC withstand voltage test also includes: when the voltage applied between the output terminal and the neutral terminal of a certain phase winding rises to 38.5kV, an ultraviolet imager is used to perform corona detection on the phase winding at a distance of 2m; if the measured photon count is ≤2000 / s, the corona detection of the phase winding is deemed to meet the standard; when the corona detection of a certain phase winding fails to meet the standard, the cable with corona is repaired with a low-resistance shielding layer until the corona detection meets the standard.

[0049] In this embodiment, during the AC withstand voltage test, when the test voltage rises to 38.5kV (1.1U) N When the test is performed, an ultraviolet imager is used to detect corona discharge at a distance of 2m from the winding of the phase being tested. If the number of photons measured does not exceed 2000 / s, the corona discharge test is considered to be up to standard; if it is not up to standard, the cable section where corona discharge occurs is repaired with a low-resistance shielding layer, and the test is repeated until it meets the standard. In the prior art, corona discharge detection relies on subjective judgment, is difficult to quantify and assess, and is difficult to locate the corona source. However, the detection method in this embodiment can avoid localized deterioration of the insulation material caused by long-term corona discharge, thereby improving the long-term operational reliability of the equipment.

[0050] In step S5, after the AC withstand voltage test of each phase winding meets the standard, a dielectric loss factor test is performed on each phase winding. The dielectric loss factor test includes: applying voltage between the output terminal and the neutral terminal of a certain phase winding, with the voltage value increasing from 7kV to 35kV, and testing the dielectric loss factor every 7kV increase. When the dielectric loss factor tanδ at 7kV is ≤1.0% and the dielectric loss factor tanδ at 35kV is ≤2.0%, the dielectric loss factor test of that phase winding is deemed to have met the standard.

[0051] In this embodiment, after completing the AC withstand voltage test, a dielectric loss factor test is performed on each phase winding: a stepped voltage increase from 7kV to 35kV is applied between the winding's output terminal and neutral terminal, with each 7kV point serving as a test point, and the dielectric loss factor tanδ is measured at each voltage point. If tanδ ≤ 1.0% at 7kV and tanδ ≤ 2.0% at 35kV, then the dielectric loss test for that phase winding is deemed to have passed the standard. The dielectric loss factor test effectively assesses issues such as overall aging, moisture absorption, and distributed defects of the insulation layer within the operating voltage range. Furthermore, by measuring the dielectric loss factor at multiple voltage points, the changes in the loss characteristics of the insulation material under different electric field strengths can be systematically evaluated, allowing for sensitive identification of early insulation degradation trends. This provides data support for assessing the long-term operational reliability of the cable winding, ultimately preventing operational failures caused by insulation aging.

[0052] Sheath protectors 5 are installed at the output terminals of phase A winding 1, phase B winding 2, and phase C winding 3.

[0053] In this embodiment, sheath protectors 5 are installed at the output terminals of phase A winding 1, phase B winding 2, and phase C winding 3, forming an overvoltage protection system for the cable. This system prevents insulation damage caused by induced high voltage on the shielding layer due to lightning or switching voltage during testing and operation. In other words, by configuring sheath protectors 5 at each phase output terminal, the overvoltage amplitude on the cable shielding layer is limited, providing overvoltage protection for the cable insulation layer. This reduces the risk of insulation layer damage due to voltage surges during testing and operation, improving the overall safety and service life of the equipment.

[0054] Each phase cable includes multiple branches, and the outgoing ends of the multiple branches are connected through cable terminal joint 4. The neutral ends of the multiple branches are also connected through cable terminal joint 4.

[0055] In this embodiment, due to the large operating current and limited current carrying capacity of a single cable, a multi-branch parallel structure is required for high-capacity synchronous condensers. Therefore, each phase cable winding consists of multiple parallel branches. The outgoing terminals of each branch are electrically connected via cable termination connectors 4, and the neutral terminals of each branch are also electrically connected via cable termination connectors 4, forming a complete winding for each phase. The application of cable termination connectors 4 ensures uniform electric field distribution and reliable insulation strength at the multi-branch connection points, guaranteeing the safety and stability of the electrical connection.

[0056] In addition, if any abnormality is found in the cable terminal joint 4 during insulation resistance testing, AC withstand voltage testing, or dielectric loss factor testing, the cable terminal joint 4 needs to be replaced first, and the testing should be carried out again after the replacement is completed.

[0057] The above are merely specific embodiments of the present invention, but the scope of protection of the present invention is not limited thereto. Those skilled in the art should understand that the present invention includes, but is not limited to, the contents described in the accompanying drawings and the specific embodiments above. Any modifications that do not depart from the functional and structural principles of the present invention will be included within the scope of the claims.

Claims

1. A method for insulation testing of a phase-shifting cable winding, characterized in that, Includes the following steps: S1, Phase A cable, Phase B cable and Phase C cable are sequentially embedded in the core slots of the stator core to form corresponding Phase A winding, Phase B winding and Phase C winding respectively. The insulation layer of each phase cable is cross-linked polyethylene material. S2, each phase winding has a cable terminal joint installed at the output end and neutral end and grounded; S3, Insulation resistance test is performed on each phase winding respectively; S4, each phase winding is subjected to an AC withstand voltage test; S5, conduct dielectric loss factor test on each phase winding respectively.

2. The insulation testing method according to claim 1, characterized in that, In step S3, the insulation resistance test includes: applying a 5kV DC voltage between the output terminal and the neutral terminal of each phase winding after installation at room temperature; recording the insulation resistance value R1 after 15 seconds of voltage application and the insulation resistance value R2 after 60 seconds of voltage application, and calculating the absorption ratio R2 / R1; when the absorption ratio is ≥1.3 and the insulation resistance value after 60 seconds of voltage application is ≥600 MΩ, the insulation resistance test of that phase winding is deemed to have passed the standard.

3. The insulation testing method according to claim 2, characterized in that, Step S3 further includes: when the insulation resistance test of a certain phase winding fails to meet the standard, the phase winding is dried; if the insulation resistance test of the phase winding still fails to meet the standard after drying, a DC high voltage is applied to the phase winding by DC impulse method, a pulse is generated by ball gap discharge, and the discharge sound of the fault point is listened to to determine the location of the fault point; after determining the fault point, the fault section of cable containing the fault point is pulled out from the iron core slot and cut off, and a new section of cable is connected to the phase winding through a cable joint, and then the insulation resistance test of the phase winding is performed.

4. The insulation testing method according to claim 1, characterized in that, In step S3, after the insulation resistance of each phase winding meets the standard, an AC withstand voltage test is performed on each phase winding. The AC withstand voltage test includes: applying a voltage of 57.5kV between the output terminal and the neutral terminal of a certain phase winding and maintaining the voltage for 1 minute; if no electrical breakdown occurs in the phase winding during the voltage application period, the AC withstand voltage test of the phase winding is deemed to have met the standard.

5. The insulation testing method according to claim 4, characterized in that, In step S3, if an electrical breakdown occurs in the phase winding during the applied voltage, the cable with the electrical breakdown is pulled out of the iron core slot and cut off. A new cable is then connected to the phase winding through a cable connector, and the phase winding is then subjected to an AC withstand voltage test.

6. The insulation testing method according to claim 4, characterized in that, The AC withstand voltage test also includes: when the voltage applied between the output terminal and the neutral terminal of a certain phase winding rises to 38.5kV, under anechoic conditions, visual observation is performed on the output terminal, neutral terminal, and cable terminal joints installed on both of the phase winding. When there are no visible, persistent golden bright spots, stable bright spots, or continuous halos in any of the observed parts, the visual observation of the phase winding is deemed to have met the standard.

7. The insulation testing method according to claim 4, characterized in that, In step S3, the AC withstand voltage test also includes: when the voltage applied between the output terminal and the neutral terminal of a certain phase winding rises to 38.5kV, an ultraviolet imager is used to perform corona detection on the phase winding at a distance of 2m; if the measured photon count is ≤2000 / s, the corona detection of the phase winding is deemed to meet the standard; when the corona detection of a certain phase winding fails to meet the standard, the cable with corona is repaired with a low-resistance shielding layer until the corona detection meets the standard.

8. The insulation testing method according to claim 1, characterized in that, In step S5, after the AC withstand voltage test of each phase winding meets the standard, a dielectric loss factor test is performed on each phase winding. The dielectric loss factor test includes: applying voltage between the output terminal and the neutral terminal of a certain phase winding, with the voltage value increasing from 7kV to 35kV, and testing the dielectric loss factor every 7kV increase. When the dielectric loss factor tanδ at 7kV is ≤1.0% and the dielectric loss factor tanδ at 35kV is ≤2.0%, the dielectric loss factor test of that phase winding is deemed to have met the standard.

9. The insulation testing method according to claim 1, characterized in that, Sheath protectors are installed at the output terminals of phase A winding, phase B winding, and phase C winding.

10. The insulation testing method according to claim 1, characterized in that, Each phase cable includes multiple branches, the outgoing ends of which are connected by cable termination joints, and the neutral ends of which are connected by cable termination joints.

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