12KV‑36KV / 250‑630A DIN Threaded‑connection Bushing

Overview

In oil‑immersed power and distribution transformer systems across European and global markets, high‑quality insulation accessories are indispensable for long‑term, fault‑free grid operation. Among these core components, the DIN threaded‑connection bushing serves as a critical insulated feed‑through part, designed to conduct electric current safely from the internal transformer winding out through the earthed metal tank wall.

The 12KV‑36KV / 250‑630A DIN threaded‑connection bushing is manufactured in full compliance with German DIN industrial standards, widely adopted for medium‑voltage oil‑filled transformers, compact substations and renewable‑energy transformer stations. Unlike flange‑mounted or cable‑type transformer bushings, this threaded‑connection variant features a male‑thread terminal at the top conductor end, allowing fast, secure bolt‑on connection with overhead cables, bus‑bars and external wiring terminals without extra clamping accessories. Its ceramic porcelain insulator body delivers excellent hydrophobicity, anti‑pollution performance and dielectric strength under harsh outdoor operating environments.

For distribution network engineers, transformer OEM manufacturers and electrical contractors, selecting a DIN‑standard threaded‑connection bushing guarantees mechanical interchangeability, simplified spare‑part replacement and full compatibility with European‑specification transformer tanks. Voltage coverage from 12 kV up to 36 kV, paired with continuous current ratings ranging from 250 A to 630 A, makes this bushing series flexible enough to cover most common medium‑voltage distribution‑transformer projects.

Definition of DIN Threaded‑connection Transformer Bushing

A threaded‑connection DIN bushing is a type of oil‑immersed transformer bushing that follows DIN dimensional specifications. It consists of a glazed porcelain insulating shell, a central conductive copper rod, threaded top connection terminal, internal sealing gaskets, tank‑mounting flange assembly and earth‑link accessories.

The “threaded‑connection” feature refers to the exposed top‑end conductor fitted with standard metric external threads (such as M12, M16, M20), enabling technicians to fasten cable lugs directly onto the bushing by tightening matching nuts. This connection method provides strong mechanical pull‑out resistance, reliable electrical contact and convenient on‑site assembly work.

Inside the transformer tank, the lower conductor section of the bushing is submerged in transformer mineral oil. The porcelain barrier isolates the live central conductor from the grounded steel tank, preventing short‑circuit faults and leakage current. Porcelain sheds (umbrella‑shaped ribs) on the outer surface increase the creepage distance, lowering the risk of surface flash‑over in humid, dusty or coastal salt‑fog environments.

Core Advantages of 12‑36KV, 250‑630A DIN Threaded‑connection Bushings

1. DIN‑Standard InterchangeabilityAll main mounting dimensions, thread specifications and creepage distances follow widely‑recognized DIN requirements. End‑users can replace old bushings from different manufacturers without modifying transformer tank opening holes, which drastically cuts maintenance downtime and spare‑part management costs.
2. Robust Threaded Terminal ConnectionMetric threaded top terminals deliver stable mechanical clamping force. After proper torque tightening, the joint maintains low contact resistance, avoiding overheating risks under long‑term full‑load current from 250 A to 630 A. Compared to clamp‑on terminals, threaded connections show better anti‑vibration performance for transformers installed near railways, industrial workshops or locations with frequent mechanical shaking.
3. High‑Performance Porcelain InsulationHigh‑grade glazed porcelain material provides outstanding dielectric strength, thermal shock resistance and surface hydrophobic property. Multi‑shed umbrella designs extend creepage paths, making these bushings suitable for medium‑pollution and heavy‑pollution outdoor districts. No cracks or insulation failure will happen under normal cyclic temperature changes between summer heat and winter frost.
4. Excellent Oil‑Sealing PerformanceMulti‑layer rubber gasket sets are installed between the bushing body and transformer tank flange. When correctly assembled, the sealing system prevents transformer‑oil leakage and stops outside moisture, dust and air from entering the oil chamber. Good sealing protects transformer‑oil quality and slows down internal winding insulation ageing.
5. Wide‑Range Parameter CoverageThis product family covers the medium‑voltage spectrum from 12 kV, 24 kV up to 36 kV, and ampere ratings: 250 A, 315 A, 400 A, 500 A, 630 A. Such broad selection helps transformer producers pick one‑to‑one matched bushings for different power‑rating oil‑immersed distribution transformers. Custom‑built non‑standard dimensions can also be manufactured for special transformer‑tank layouts.
6. Simple Installation and Maintenance‑Friendly StructureThreaded‑connection bushings adopt top‑down tank‑mounted installation. Field workers can complete cable connection, inspection, disassembly and replacement without lifting the heavy transformer tank cover. Visible porcelain sheds make routine visual inspection very convenient; operators can quickly spot surface dirt, glaze cracks or flash‑over marks during regular grid maintenance rounds.

Main Application Fields

• Oil‑immersed distribution transformers for European‑style urban and rural power‑distribution networks
• Medium‑voltage transformers inside compact package substations
• Step‑up transformers for solar photovoltaic farms and on‑shore wind‑power stations
• Industrial‑plant power transformers for factories, mining facilities and water‑treatment stations
• Transformer retrofit and spare‑part replacement projects for old DIN‑spec transformers
• Indoor and outdoor medium‑voltage power‑supply equipment requiring threaded conductor terminals

Technical Specification Table for Reference 

Note: Above figures represent common industry reference values. Exact dimensions are subject to official DIN specification documents and manufacturer drawings. Custom creepage distances and thread specifications are available on request for special‑pollution‑area projects.

Installation Guidelines

Before mounting a DIN threaded‑connection bushing, technicians must confirm three critical matching parameters: rated voltage, rated continuous current and tank‑opening dimension. Never fit a bushing whose voltage or current rating is lower than the transformer’s operating requirement.

Clean all contact surfaces of the transformer tank flange, remove old gasket residue, metal burrs and dust. Place brand‑new rubber sealing gasket evenly, avoid twisting or squeezing the gasket. Lower the bushing slowly through the tank opening hole, then fasten the flange mounting bolts in diagonal sequence with recommended torque value, to guarantee uniform gasket compression and eliminate oil‑leak risks.

When connecting external cables onto the top threaded terminal: place cable lug, flat washer and spring washer onto the threaded rod, then tighten the nut to specified torque. Excessively high torque may deform the copper conductor or crack porcelain insulation, while insufficient torque will cause loose joints, contact over‑heating and potential safety hazards.

After installation, carry out visual inspection, oil‑leakage check and high‑voltage withstand test before energizing the transformer.

Operation & Maintenance Recommendations

Carry out visual inspections every 6‑12 months. Check porcelain surfaces for dirt deposits, glaze scratches, flash‑over traces and cracks. Clean polluted porcelain sheds by dry cloth or approved insulator‑cleaning detergent, do not use sharp hard tools which can scratch the glazed protective layer.

Regularly inspect the top threaded connection joint for over‑heating discoloration marks. If the transformer has experienced heavy short‑circuit‑current impact, re‑check nut tightness of the threaded terminal. Whenever oil leakage appears at the tank‑flange sealing area, shut down transformer power supply, remove the bushing and replace old sealing gaskets.

Selection Checklist for Buyers

When sourcing a suitable 12‑36KV / 250‑630A DIN threaded‑connection bushing, buyers should confirm these key points:

1. Rated voltage class (12kV / 24kV / 36kV) matching transformer voltage level
2. Rated continuous current (250 A‑630 A)
3. Top‑end metric thread dimension
4. Tank‑opening mounting hole diameter
5. Required creepage distance according to site pollution grade
6. Shed / umbrella quantity
7. Oil‑immersion service compatibility for mineral transformer‑oil

Conclusion

The 12KV‑36KV / 250‑630A DIN threaded‑connection bushing remains a mature, reliable medium‑voltage insulation solution for DIN‑standard oil‑immersed transformers. Its threaded‑terminal design, interchangeable DIN dimensions, durable porcelain insulation and wide parameter range make it a popular choice for new transformer manufacturing and aftermarket maintenance projects all over European and international power markets. Proper product selection, standardized installation and periodic maintenance will extend its service life and secure stable, safe operation of the whole distribution‑transformer system.