CNC Metal Spun 5052 Aluminum Shielding Enclosure for 1100kV Ultra High Voltage (UHV) Transmission Systems

1. Industry Background and Technical Challenges

The Ultra High Voltage (UHV) power transmission sector represents a strategic national energy infrastructure domain. Equipment installed on 1100kV transmission lines must meet extremely stringent requirements in:

• Electrical insulation protection
  
• Electromagnetic shielding performance
  
• Structural reliability
  
• Outdoor weather resistance
  
• Long-term operational stability
  

The client is a leading manufacturer of UHV transmission equipment. The shielding enclosure is installed at both ends of transmission tower insulator strings and performs critical functions:

• Electromagnetic interference (EMI) shielding
  
• Arc discharge suppression
  
• Environmental protection of insulators
  

Previous Manufacturing Limitations

The original shielding covers were fabricated using:

• Stainless steel material
  
• Multi-piece welded assembly
  

This resulted in the following issues:

• Excessive weight: 28 kg per unit
  
• Difficult on-site installation
  
• Outdoor corrosion over time
  
• Weld seams causing shielding discontinuity
  
• Risk of arc discharge under UHV conditions
  

A material upgrade combined with advanced seamless forming technology was required.

2. Selected Solution: Custom CNC Metal Spun 5052 Aluminum Alloy UHV Shielding Enclosure

KMS developed a seamless monolithic shielding enclosure using large-diameter CNC metal spinning technology.

Geometric Specifications

• Diameter: Ø800 mm
  
• Height: 450 mm
  
• Structure: Hemispherical dome + cylindrical body integrated design
  

Wall Thickness

• Main body: 2.5 ± 0.1 mm
  
• Reinforced top and mounting area: 5.0 mm
  

Material Specification

• Alloy: 5052 Aluminum Alloy (Al-Mg series)
  
• Tensile strength ≥ 230 MPa
  
• Yield strength ≥ 190 MPa
  
• Excellent corrosion resistance
  
• Good electrical conductivity
  

Material compliant with GB/T 3880.1-2012 and equivalent international standards.

Surface Treatment Options

• Brushed finish
  
• Mirror polishing (6K level)
  
• Anodizing with chromate sealing
  
• Oxide film thickness: 15–20 μm
  

3. Core Manufacturing Process

3.1 Raw Material Selection and Pre-Treatment

• 6 mm thick certified 5052 aluminum plate
  
• Ultrasonic testing (UT) for internal defect inspection
  
• CNC plasma blank cutting with ±0.1 mm tolerance
  
• Stress-relief annealing:
  300°C heat treatment, 1-hour holding time
  

Purpose: eliminate residual stress prior to forming.

3.2 Large-Diameter CNC Metal Spinning Forming

Manufactured using a vertical heavy-duty CNC spinning machine.

Process parameters:

• Roller feed rate: 3 mm/s
  
• Spinning force: 120 kN
  
• Multi-pass progressive forming (5 passes)
  

Forming sequence:

1. Hemispherical dome formation
   
2. Cylindrical body formation
   
3. Integrated seamless shaping
   

Wall thickness uniformity controlled within:

≤ 0.1 mm deviation

Result: Seamless monolithic enclosure without weld joints.

3.3 Finishing and Mounting Machining

Post-forming processes include:

• Edge curling (R3 mm radius) for operator safety
  
• CNC machining of mounting flange
  
• 8 × M16 mounting holes
  
• Hole position tolerance: ±0.05 mm
  

Ensures precise integration with insulator string assemblies.

3.4 Surface Treatment

Depending on customer requirements:

• Uniform brushed finish
  
• 6K mirror polishing
  

Followed by:

• Anodizing treatment
  
• Chromate sealing process to improve adhesion and corrosion resistance
  

Final cleaning performed prior to high-voltage testing.

3.5 Final Inspection and Performance Testing

Comprehensive quality verification includes:

3D Laser Scanning

• Full geometric dimensional inspection
  

High-Voltage Withstand Test

• 1100 kV voltage
  
• 1-minute holding time
  
• No arc discharge
  
• No dielectric breakdown
  

Salt Spray Test

• 720 hours
  
• No corrosion
  

Ingress Protection Test

• IP65 rating
  
• Dust-tight and water-resistant
  

4. Core Technical Advantages

Lightweight Engineering Advantage

Replacing stainless steel with 5052 aluminum reduced weight:

From 28 kg → 17 kg
Weight reduction: 40%

Benefits:

• Reduced transmission tower load
  
• 50% increase in installation efficiency
  
• 30% reduction in installation cost
  

Superior Shielding Performance

Seamless CNC spun construction eliminates:

• Weld seams
  
• Shielding discontinuity
  

Measured shielding effectiveness:

99.8%

Exceeds customer requirement of 99%.

Effectively prevents:

• Electromagnetic leakage
  
• Arc discharge under UHV conditions
  

Exceptional Weather Resistance

Anodizing + chromate sealing dual protection.

Validated by:

• 720-hour salt spray resistance
  
• High/low temperature cycling (-40°C to 70°C, 100 cycles)
  
• No cracking or deformation
  

Service life:

Up to 15 years

1.5× longer than traditional stainless welded covers.

Large-Diameter Precision Forming Capability

• Diameter capacity ≥ Ø800 mm
  
• Dimensional tolerance: ±0.2 mm
  
• Installation clearance ≤ 0.5 mm
  

Ensures precise integration with UHV insulator systems.

5. Quality Validation

Shielding Performance Verification

Tested at National High Voltage Electrical Equipment Testing Center.

Results:

• 1100 kV test passed
  
• 99.8% shielding efficiency
  
• Compliant with GB/T 22072-2021
  (General Technical Requirements for UHV Power Equipment)
  

Environmental Durability Testing

• 720-hour salt spray test passed
  
• IP65 ingress protection verified
  
• Temperature cycling test passed
  

Structural Strength Validation

• Mounting pull-out test ≥ 50 kN
  
• Suitable for high wind and seismic conditions
  
• 1.5 m drop test passed without deformation
  

Material and Dimensional Verification

• Spectrographic analysis confirms 5052 alloy compliance
  
• 3D laser scanning:
  Dimensional deviation ≤ 0.18 mm
  Mounting hole tolerance ±0.03 mm
  

6. Customer Problems Successfully Solved

Electrical Safety Risk Eliminated

Seamless spun design prevents shielding failure and arc discharge.

Accident rate reduced to zero.

Ensures safe and stable operation of 1100 kV transmission lines.

Reduced Installation Complexity and Structural Load

40% weight reduction significantly decreases:

• Tower load
  
• Lifting requirements
  
• On-site installation time
  

Extended Service Life and Reduced Maintenance Cost

15-year service life vs. 10 years for welded stainless covers.

Lower replacement frequency
Lower maintenance cost

Perfect Dimensional Compatibility

100% fit with insulator string assemblies.
Installation clearance ≤ 0.5 mm.

Improved overall system reliability.