Transformer Bushings: Ginahan, Mga Tipo & Guide sa Paghimo Function: Ginahan Types: Mga Tipo Installation Guide: Guide sa Paghimo

Transformer Bushings: External Insulation and Current-Carrying Components

Ang mga transformer bushings mao ang primaryong mga external insulation devices nga gipasangay sa tank sa transformer. Ang mga leads gikan sa mga winding sa transformer kinahanglan mopasar sa ubos niining mga insulating bushings, nga naghatag og insulation tali sa mga leads ug tali sa mga leads ug ang tank sa transformer, samtang nagserbisyo usab isip mechanical support sa mga leads.

Depende sa voltage level, ang mga transformer bushings mahimong makita sa daghang klase: porcelain bushings, oil-filled bushings, ug capacitor-type bushings.

• Ang mga porcelain bushings kasagaran gigamit sa mga transformers nga rated 10 kV o mas lawas. Kini nagsangpot sa usa ka conductive copper rod nga mopasar sa usa ka porcelain housing, uban ang hangin nga naghatag sa internal insulation.

• Ang mga oil-filled bushings kasagaran gigamit sa 35 kV-class transformers. Kini nga mga bushings adunay insulating oil nga gipuno sa interior sa porcelain housing, diin usa ka copper conductor mopasar, insulated ngadto sa oil-impregnated paper.

• Ang mga capacitor-type bushings gigamit sa high-voltage transformers nga mas taas sa 100 kV. Kini nagsangpot sa usa ka main insulation unit (capacitor core), upper ug lower porcelain housings, connecting sleeve, oil reservoir (conservator), spring assembly, base, grading ring (corona shield), measuring terminal, line terminal, rubber gaskets, ug insulating oil.

Ang mga transformer bushings nagserbisyo aron mapalit sa labaw ang mga internal high-voltage ug low-voltage winding leads gikan sa oil tank. Kini wala ra naghatag og insulation tali sa mga leads ug ground, apan nagdumala usab og critical role sa pag-secure sa mga leads. Isip usa sa mga current-carrying components sa transformer, ang mga bushings magdala sa load current continuously sa normal operation ug kinahanglan molihok sa short-circuit current sa panahon sa external faults.

Kaya, ang sumusunod nga mga requirements giaplikar sa mga transformer bushings:

• Kinahanglan adunay naka-specify nga electrical insulation strength ug sufficient mechanical strength.

• Kinahanglan ipakita ang maayo nga thermal stability ug capable sa pagtubag sa momentary overheating sa panahon sa short-circuit conditions.

• Dapat kompakto ang size, light weight, excellent sealing performance, high interchangeability, ug easy to maintain.

Ang bushing mahimong gisangpot sa usa ka capacitor core, oil reservoir, flange, ug upper/lower porcelain housings. Ang main insulation mao ang capacitor core, gihatag sa concentric capacitive layers nga giconnect sa series. Kini nga assemblage giputli sa usa ka sealed chamber nga gihatag sa upper ug lower porcelain housings, oil reservoir, flange, ug base. Ang chamber gipuno sa treated transformer oil, resulta sa usa ka oil-paper insulation structure. Ang oil-resistant rubber gaskets gigamit sa contact surfaces tali sa major components. Tanang components gipigda sama sa usa ka central preloading force nga gihatag pinaagi sa usa ka set sa strong springs nga nahimutang sa oil reservoir, sigurado nga ang tanang bushing magpadayon nga hermetically sealed.

Ang flange adunay air vent plug, oil sampling device, ug terminals para sa measurement sa dielectric loss (tan δ) ug partial discharge (PD). Sa panahon sa operation, ang protective cover sa measuring terminal kinahanglan i-install aron sigurado nga grounded ang screen (test tap); open-circuit conditions stricto prohibito.

Adunay duha ka main connection methods tali sa bushing ug ang high-voltage leads sa transformer:

• Cable-penetration type

• Conductor-rod current-carrying type

Pre-Installation Inspection of Transformer Bushings:

Bago ang installation, ang sumusunod nga checks dapat ibuhat:

• Check the porcelain surface for cracks or damage.

• Ensure the inner surfaces of the flange neck and grading ring are thoroughly cleaned.

• Confirm the bushing has passed all required tests.

• For oil-filled bushings, verify the oil level indication is normal and check for any oil leakage.

Ang mga bushings kinahanglan gamiton sa conditions nga naka-specify sa ilang model designation, ug ang sumusunod nga precautions dapat gi-obserba:

• Sealing Integrity: Ensuring the bushing remains sealed is key to achieving long service life. Any seal points disturbed during installation or maintenance must be carefully restored to their original sealed condition.

• Oil Level Control and Adjustment: The oil level inside the bushing should be periodically monitored during operation. If the oil level is too high or too low, adjustment is required.

• If the oil level is too high, excess oil can be drained slowly through the oil drain plug on the flange.

• If the oil level is too low, qualified transformer oil of the same grade specified on the nameplate must be added through the filling port of the oil reservoir.

• For bushings with consistently normal oil test results in annual preventive tests, the interval between preventive tests may be appropriately extended to reduce the frequency of oil sampling. Any issues should be referred to the manufacturer. The bushing must not be disassembled by the user.

Correct Oil Sampling Procedure:
Clean the area around the oil drain plug on the flange. Open the plug and slowly screw in a dedicated oil sampling nozzle into the center threaded hole of the plug until it contacts the internal seal. Tighten the nozzle to compress the sealing gasket, allowing the transformer oil inside the bushing to flow out through the nozzle. After sampling, reverse the above steps to restore the original sealed condition.

Note: When removing the nozzle, do not loosen the oil drain plug. If loosening occurs, immediately tighten the plug using the appropriate spanner.

Measuring Terminal Grounding:
A measuring terminal is provided on the flange of the bushing. When measuring dielectric loss or partial discharge, remove the terminal cover and connect the test lead—the terminal stud is insulated from the flange. After testing, the terminal cover must be securely replaced to ensure reliable grounding. The measuring terminal must never be left open-circuited during operation.

Dielectric Loss Measurement Note:
The dielectric loss value measured on-site at 10 kV may differ from factory test data due to influences such as the measuring instrument, bushing position, and environmental conditions. It is recommended to use a high-voltage Schering bridge for measurement, and data obtained under high-voltage conditions should be considered authoritative.