24‑36KV/250A EN Bushing: Definition, Specifications, Advantages, Application & Selection Guide
Introduction
24‑36KV/250A EN bushing is a type of high‑voltage transformer bushing manufactured in compliance with European EN power‑equipment standards, designed for 24 kV to 36 kV voltage class transformers and associated distribution equipment. As critical wall‑penetrating insulating components, EN‑standard bushings enable live high‑voltage conductors to pass through the earthed metal tank wall of oil‑immersed transformers, providing reliable electrical insulation and stable current transmission at a rated current of 250 A.
These EN‑compliant bushings adopt outdoor‑optimized shed profiles to realize sufficient creepage distance and dry‑arc distance, making them well‑suited for European‑style power projects and export‑oriented transformer assemblies. The product portfolio covers EN‑24/250 and EN‑36/250 variants with multiple dimension options, covering 24 kV and 36 kV system voltage levels. Even though the EN bushing is treated as an auxiliary transformer accessory, its dielectric performance and mechanical integrity directly influence transformer operational safety. Defects such as surface tracking, partial discharge, mechanical deformation or insufficient creepage distance may trigger flashover faults and unplanned transformer shutdowns. This technical article explains core definitions, structural features, key benefits, detailed technical specifications, application scenarios, selection points and field maintenance best practices for 24‑36KV/250A EN bushings, serving as practical reference material for substation engineers, procurement specialists and field maintenance technicians.
Working Principle & Structural Features of 24‑36KV/250A EN Bushing
A 24‑36KV/250A EN bushing creates a controlled insulated passage for live conductors crossing grounded transformer tank housings. The main insulating body bears high‑voltage dielectric stress between live conductive parts and the earthed tank structure, while the internal conductive rod carries continuous 250 A rated load current.
The outer surface is molded with multiple sheds (shield). Different shed configurations including 6‑unit sheds, 8‑unit sheds and 9‑unit sheds are available to boost creepage distance, improving resistance against pollution flashover for outdoor service environments. The top end is equipped with standardized Md external thread connection for terminal hardware fitting assembly; different terminal connector styles can be matched according to site wiring requirements.
The bottom mounting section is designed for transformer tank‑cover installation. The tank cover opening dimension d0 defines the required cut‑out size on transformer tank plates, with 4‑M10*58 mounting hole layout for fastening. Key dimension parameters cover overall height H, installation‑related dimensions h2, h3, h4, conductor thread Md, and diameter parameters d1, d2, d3, d4. Additional dimension E and C support customized height adjustment for special project conditions. According to general industry specifications, non‑standard variant dimensions can be machined upon project request, and C‑series height can be customized to satisfy special transformer structural constraints.
Main Product Variants
The 24‑36KV/250A EN bushing family contains three mainstream standard models for 24 kV and 36 kV system voltage grades:
EN‑24/250: 24 kV system voltage, rated current 250 A
This is the base 24 kV EN‑standard bushing version. It features 6‑unit shed configuration, compact overall height, moderate creepage and dry‑arc distance. Suitable for 24 kV class oil‑immersed transformers, general‑pollution indoor and outdoor distribution applications.
EN‑36/250 (Version 1): 36 kV system voltage, rated current 250 A
Rated for 36 kV system voltage level, adopting 8‑unit shed structure. Increased overall height and extended creepage & dry‑arc distance compared with 24 kV model. Targeted for 36 kV distribution transformers under normal pollution‑grade outdoor conditions.
EN‑36/250 (Version 2): 36 kV system voltage, rated current 250 A
36 kV high‑performance variant with 9‑unit shed design. It delivers the maximum creepage distance among this product series, oriented for heavy‑pollution outdoor sites, coastal regions and harsh atmospheric environments where higher anti‑flashover performance is demanded.
Core Advantages of 24‑36KV/250A EN Bushing
Typical Application Scenarios
‑ 24 kV and 36 kV oil‑immersed distribution transformers following European EN standards
‑ Export‑oriented transformer manufacturing projects for European and international markets
‑ Outdoor distribution substations with light, moderate and heavy atmospheric pollution
‑ Industrial‑plant internal power‑supply transformer equipment
‑ Renewable‑energy wind farm and photovoltaic station step‑up transformers adopting EN specifications
‑ Retrofitting and spare‑part replacement for existing EN‑standard transformer assets
Technical Specifications Table
Table: 24‑36KV/250A EN Bushing Technical & External Dimensions
| Code | Model | H | h2 | h3 | h4 | Md | d1 | d2 | d3 | d4 | E | C | d0 Tank‑cover opening | h1 arcing distance | creep distance | shield shed configuration | weight (kg) |
|---|
| XD.0250.24.EN | EN‑24/250 | 430 | 310 | 323 | 74 | M12×1.75 | 115 | 6.5 | 74 | 50 | 175 | 100 | 78 | 217 | 500 | 6 single sheds | 3.9 |
| XD.0250.33.EN.01 | EN‑36/250 | 559 | 444 | 457 | 74 | M12×1.75 | 170 | 6.5 | 74 | 50 | 150 | 200 | 78 | 350 | 995 | 8 single sheds | 9.5 |
| XD.0250.33.EN.02 | EN‑36/250 | 591 | 476 | 489 | 74 | M12×1.75 | 170 | 6.5 | 74 | 50 | 150 | 220 | 78 | 382 | 1116 | 9 single sheds | 12 |
- Above data represents standard industry reference dimensions.
- Special non‑standard sizes can be customized upon customer request; dimension C height can be adjusted as required by project.
Selection Guide for 24‑36KV/250A EN Bushing
- System Voltage Confirmation: Select EN‑24/250 for 24 kV power‑system applications; choose EN‑36/250 series for 36 kV system voltage scenarios. All models carry 250 A rated continuous current.
- Pollution Grade Evaluation: For general‑pollution environments, select 6‑shed or 8‑shed variants. For coastal, industrial heavy‑dust and high‑humidity locations, specify 9‑shed configuration to obtain larger creepage distance.
- Mechanical Mounting Compatibility: Verify tank‑cover opening dimension d0, 4‑M10*58 mounting hole layout, top‑end Md thread specification, and overall height H to reserve sufficient internal and external clearance space around transformer tanks.
- Custom Dimension Requirements: For retrofit projects or special transformer structures, confirm whether customized C‑height or other modified dimensions are needed.
Standard Compliance: Confirm conformance with relevant EN transformer bushing standards for export‑targeted projects.
Installation & Routine Maintenance Guidance
Pre‑installation Check
Installation Notes
‑ Tighten mounting bolts evenly following recommended torque values. Over‑torque may cause insulation damage; insufficient torque will lead to sealing gaps.
‑ Avoid heavy mechanical impact against shed sections during lifting and assembly. Maintain adequate phase‑to‑phase and phase‑to‑ground electrical clearances.
‑ Fasten top terminal connector properly to prevent over‑heating points caused by poor contact resistance.
Routine Maintenance
‑ Carry out visual inspection every 6‑12 months. For heavily‑polluted outdoor locations, shorten inspection intervals. Check insulation surface contamination status, shed integrity and connection fastener conditions.
‑ Clean accumulated dust and contaminants on shed surfaces on a regular schedule to preserve effective creepage performance.
‑ Complete all inspection and maintenance operations only after the transformer is fully de‑energized. Do not disassemble internal bushing components on‑site.
Conclusion
24‑36KV/250A EN bushings are essential EN‑standard high‑voltage insulating through‑wall components for 24 kV‑36 kV European‑specification transformers. With three mainstream model options and multiple shed configurations, this series balances compact structure, flexible creepage‑distance selection and customizable dimensional capability. It can satisfy general‑pollution to heavy‑pollution outdoor operating‑site demands, and is widely adopted for export transformers, European‑market power‑distribution projects and energy‑generation step‑up equipment. Correct model selection, standardized installation and periodic visual inspection will minimize bushing‑related faults and guarantee long‑term safe operation of transformer systems.
