Analis sa pagproseso sa 550 kV GIS Withstand Voltage test
Ang gas - insulated metal - enclosed switchgear (GIS) mao ang usa ka switching device gisulod sa mga switching appliances sama sa circuit breakers (GCB), disconnectors (DS), earthing switches (ES), ug mga unit sama sa voltage transformers, current transformers, surge arresters, ug enclosed busbars. Ang tanang high - potential components gibutang sulod sa grounded enclosed metal shell, nga gipuno sa SF₆ gas nga may maayo nga insulating ug arc - extinguishing properties isip insulating medium. Ang GIS adunay compact structure, small footprint, low maintenance requirements, easy installation, good interrupting performance, ug walay interference, ug kasagaran na gamiton sa power systems.
Ang 550 kV GIS sa 500 kV step - up substation sa usa ka kompanya nag-adopt og double - busbar wiring arrangement structure, uban 2 main transformer incoming lines, 1 starting and standby transformer incoming line, 2 outgoing lines, ug 1 bus - tie, total 6 circuit breakers. Kada 1M ug 2M gisulod og 1 PT bay. Gitimo kini sa October 28, 2022, ug natapos ang on - site assembly sa December 10, 2022. Sa panahon sa handover withstand voltage test, ang supporting insulator naka - experience og abnormal breakdown.
Gibuhat ang mga analysis gikan sa mga aspeto sama sa location sa anomaly, on - site assembly quality, material compliance, factory manufacturing history, X - ray flaw detection, resin dissolution, ug electric field simulation. Nakuha ang cause sa fracture sa supporting insulator, ug gihatagan og suggestions para sa pag - strengthen sa supervision ug quality control sa panahon sa GIS manufacturing process.Ang on - site withstand voltage ug insulation test guidelines alang sa gas - insulated metal - enclosed switchgear, ug ang approved test plan.
Test Voltage
Ang 80% sa rated short - time power - frequency withstand voltage value sa 740 kV gihatagan sa manufacturer, nga 592 kV, ug ang duration mao ang 1 minute.
Conditions that the Tested Equipment Should Meet
Test Method and Criteria
Ang test voltage sa tested GIS dapat i - increase gikan sa 0 V hangtod 318 kV unang, gi - hold sa 5 minutes, pagkatapos i - increase hangtod 473 kV ug gi - hold sa 3 minutes. Sa dili pa matapos, ang test voltage dapat i - increase hangtod sa rated withstand voltage value sa 592 kV ug gi - hold sa 1 minute. Kon walay breakdown, consider qualified.
Searching for and Handling of Abnormal Points
Overview of the Breakdown Abnormality
Sa 14:03 sa December 11, 2022, gibuhat ang insulation handover withstand voltage test sa main circuit sa 550 kV GIS sa substation sa construction site. Sa panahon sa testing sa phases B ug C, ang voltage gi - increase hangtod 318 kV ug gi - hold sa 5 minutes, passing the test. Sa panahon sa voltage gi - increase hangtod 473 kV ug gi - hold sa 2 minutes, nangyari ang breakdown. Ang voltage nagsabot sa 0 V, ug narinig ang loud abnormal sound sa substation, interrupting the test. Pagkahuman sa pag - implement sa safety measures, ang insulation resistance to ground sa 1M - C phase main circuit gisukod sa 400 MΩ, ug ang remaining part sa 200 GΩ. Gi - determine nga may fault sa certain device carried by the 1M - C phase. Ang wiring for the withstand voltage test ug abnormal area makita sa Figure 1. Ang blackened part sa figure indicates the voltage - applying range.
Makita gikan sa Figure 1 nga ang voltage - applying range includes: 6 circuit breakers carried by bus 1M, 6 bus disconnectors, 2 line - side disconnectors, 5 sets of air bushings, 1 bus disconnector of the PT carried by 1M, ug 6 bus disconnectors of 2M. Ang voltage - applying point gisulod sa riser sa incoming line sa Main Transformer No. 2 sa labas.
Process of Searching for Abnormal Points
Ang GIS adunay fully - enclosed structure, uban multiple independent components forming an integrated whole. Ang equipment associated with 1M adunay 83 independent gas compartments, making it rather challenging to locate abnormal points. Pagkahuman sa research, gi - adopt ang point - by - point elimination method aron mapalitbiti ang scope sa abnormal equipment.
Konsekwensiya sa fully - enclosed structure sa GIS, ang insulation mahimo lang masukod sa exposed parts, ug ang insulation measurement points tanan sa 15 - meter - high riser seats sa labas. Sa panahon sa measurement sa insulation, adunay daghan nga restrictive factors. Bisag hain, ang mga tawo gigamit og crane aron maka - get on ug off, ug communication tools required for liaison, ug test leads mahimo mosusog sa panahon sa measurement. Pinaagi sa analysis, nakita nga closing the PT disconnecting switch associated with 1M ug removing the secondary ground wire of the PT mahimo ra convenient aron gamiton ang PT isip insulation measurement point, allowing inspectors to communicate in real - time without relying on communication tools.
Gitangtang ang tanang disconnecting switches connected to GIS 1M, ug gitigom ang tanang circuit breakers. Pagkatapos, pagsugod sa interval sa voltage - applying point, ang disconnecting switches connected to 1M (excluding the 1M VT disconnecting switch) gitigom one by one, ug gi - measure ang insulation every time ang disconnecting switch gitigom. Sa dili pa matapos, sa outgoing line interval 5W11 sa 1M - C bus, ang insulation sa main circuit gisukod sa 400 M&Ω;. Further opening the circuit breaker of this interval, finally determined ang abnormal point sa area from the line - side disconnecting switch of this circuit breaker to the outdoor GIS bushing.
Gi - isolate ang abnormal area sa Figure 1, ug gi - carry out ang second voltage application sa non - abnormal parts based sa main insulation withstand voltage test procedure. Ang resulta showed compliance. Power - frequency withstand voltage tests conducted sa remaining equipment, all of which passed smoothly.
Handling of Abnormal Points
Adunay 5 independent gas compartments sa abnormal area. Aron accurately locate ang abnormal point, kinahanglan buhata ang inspection sa bawat gas compartment one by one.Bisag hain, ang SF₆ gas inside the GIS naging toxic after the test, sa December 12, 2022, pagkahuman sa gas recovery ug disassembly sa equipment, natukod nga ang supporting insulator sa three - way busbar sa lower section sa vertical busbar sa 02 - 5 gas compartment sa 1M - C bus fractured. Ang busbar conductor, casing, ug adjacent insulators all met the product technical requirements.
Ang manufacturer replaced ang abnormal insulator sa December 13, reinstalled the busbar, ug completed gas treatment, leak detection, moisture measurement, ug main - circuit resistance measurement. After the results were found to be qualified, sa December 14, gi - carry out ang power - frequency withstand voltage test again using the above - mentioned test wiring method ug following the main - circuit insulation withstand voltage test procedure. The test results were qualified (592 kV held for 1 minute).
Analysis of the Causes of Supporting Insulator Fracture
Adunay total 145 supporting insulators sa GIS. Kon ang fractured supporting insulator isolated case o part of a batch - wide problem crucial importance for the safe and reliable commissioning of the step - up substation. Therefore, to identify the root cause of the fault insulator's fracture, investigations are carried out from the following aspects.
Inspection of Busbar On - site Assembly Quality
Ang CX1 - 1C (factory number, the same below) busbar assembled on - site sa December 3, 2022. Sa panahon sa assembly process, ang on - site representative sa manufacturer verified each item against the "On - site Docking Confirmation Operation Item Card". The owner and the supervisor witnessed the process jointly, ug assembly mahimo ra proceed after the three parties completed the signing formalities. After the assembly was completed, on - site verification tests such as gas moisture content, leak detection, ug loop resistance gibuhat. This basically rules out the possibility that the insulator fracture caused by on - site assembly quality, process, ug other factors.
Inspection of the Material Compliance of Supporting Insulators for Busbars
Ang fractured supporting insulator adunay factory - out number Z220704 - 1G1, manufactured by a subsidiary company of the manufacturer sa July 2022. Before leaving the factory, this supporting insulator underwent inspections ug tests including visual inspection, dimensional measurement, vitrification temperature testing, X - ray flaw detection, ug electrical testing, all of which showed compliance.
Ang factory - out inspection reports ug incoming - inspection records of the insulators indicate that both the factory - out ug incoming - inspection results meet the requirements.
Inspection of Busbar Manufacturing History
An inquiry into the assembly history of the CX1 - 1C busbar unit shows that the manufacturer started production ug assembly sa September 20, 2022, ug completed the work sa October 12, 2022. The records in the assembly history table indicate that both the internal ug external assembly processes met the technical requirements ug process standards specified in the drawings, with no abnormalities found. Therefore, it can be excluded that the processes listed in the manufacturing history table caused the fracture of the supporting insulator.
Inspection of Busbar Factory - out Tests
The CX1 - 1C busbar underwent lightning impulse, power - frequency withstand voltage, ug partial discharge tests in the manufacturer's factory sa October 6, 2022, all of which were passed on the first attempt, ug the test results were qualified. This indicates that the busbar ug insulators normal when they left the factory.
Inspection of Abnormal Supporting Insulators
Inspections are carried out from aspects such as the failure nature of the abnormal supporting insulators ug verification tests (including dimensional inspection, flaw detection, material analysis, etc.).
Failure Nature
Analysis of the surface discharge path of this insulator shows that there is an appearance of through - damage in the insulating part between the high - voltage electrode ug low - voltage electrode. Generally, the through - damage of an insulator occurs due to the presence of certain defects inside the insulating part, or due to additional mechanical stress, which causes cracks inside the insulating part, ug then through - breakdown occurs along the cracks.
Verification Tests
Dimensional re - inspection. The dimensional re - inspection of the abnormal supporting insulator was qualified. The re - inspection results are shown in Table 1.
X - ray flaw detection. X - ray flaw detection was carried out on the abnormal supporting insulator, ug no external defects other than fracture cracks were found.Resin material re - inspection. Samples were taken from the abnormal specimens for re - inspection of density, filler content rate, ug glass transition temperature, ug the results were qualified. The resin material detection results are shown in Table 2.
Re - inspection of the resin - to - electrode bonding interface. The non - discharged area of the insulator was cut, ug the resin - to - metal bonding surface of the insulator was dyed for flaw detection. Except for the local slight penetration of the coloring agent at the fracture, the rest of the area was normal, proving that there were no defects inside the resin ug that the resin was well - bonded to the electrode.
Re - inspection of resin melting. After the resin of the abnormal supporting insulator was melted at high temperature, the electrode was re - inspected. There was local abnormal deformation at the position of the discharge point on the arc - shaped surface of the high - voltage electrode. In conclusion, during the manufacturing process of the supporting insulator, improper operation caused abnormal deformation of the arc - shaped surface of the high - voltage electrode. Since the deformation was minor, the operators failed to detect it in a timely manner, allowing defective components to enter the next process ug eventually leading to the pouring of the insulator.
This failure was caused by non - standard operation of the operators, which led to abnormal deformation of the electrode ug subsequent fracture of the insulator. The structure of this supporting insulator is an insulation structure that the manufacturer has been using. Since 2003, more than 36,000 insulators have been manufactured ug are operating reliably in the field. Therefore, the fracture of this supporting insulator is an isolated case.
Simulation Verification
For safety reasons, simulation verification was carried out on the busbar with this insulator structure.Voltage application: The central conductor ug the high - voltage electrode of the insulator are at 1675 kV, while the casing, support base, ug low - voltage electrode of the insulator are at 0 potential.
Judgment criteria: Under the minimum functional gas pressure of 0.45 MPa, the surface - flashover electric field strength of the insulator should not exceed 12 kV/mm, ug the electric field strength of the high - voltage electrode of the insulator should not exceed 50 kV/mm.
The simulation results show that the maximum surface - flashover electric field strength of the insulator is 10.5 kV/mm, which is less than 12 kV/mm, ug the result is qualified. The maximum electric field strength on the surface of the high - voltage electrode is 21.2 kV/mm. Converted to the condition of a power - frequency voltage of 318 kV, the maximum electric field strength is 40.2 kV/cm, which is less than 50 kV/cm, ug the result is also qualified.
The 550 kV GIS of the 500 kV step - up substation was successfully energized for the first time sa December 28, 2022. Unit 2 was connected to the grid for the first time sa November 29, 2023. All equipment in the substation has withstood the pressure test ug is operating normally.
Conclusion
For important high - voltage equipment of 110 kV and above, it is necessary to strictly follow the relevant requirements of DL/T 586—2008 "Technical Guidelines for Supervision of Power Equipment Manufacturing" to strengthen the factory - based supervision of equipment ug control the manufacturing quality of equipment from the source. GIS manufacturers must enhance their quality control awareness, comprehensively sort out the quality - related risk points at each post, ug improve documents such as operation specifications, operation standards, ug operation procedures for product assembly at all voltage levels. Comprehensive control should be carried out over links such as component procurement, product design, component processing technology, incoming inspection, product assembly, testing, ug on - site installation to ensure the safety, stability, ug reliability of products.
