Copper Busbar Overlap Rules: Key Insights for Optimal Performance
Copper busbars are crucial conductors in power systems, and the quality of their connections directly impacts the operational efficiency and safety of electrical equipment. The connection between copper bus bars must consider electrical principles, physical properties, and manufacturing requirements to ensure excellent conductivity, reliable mechanical strength, and long-term stability. Below is a detailed explanation of copper bar overlap rules:
1. Basic Principles of Overlap
The purpose of overlapping power busbars is to ensure low-loss current transmission while maintaining mechanical stability at the joint. Specific principles include:
Low Contact Resistance: The resistance at the overlap area should be minimized to reduce energy loss and heating.
Strong Mechanical Connection: The joint must have sufficient mechanical strength to withstand electromagnetic forces and vibrations.
Prevention of Oxidation and Corrosion: Protective measures must be applied to contact surfaces to prevent increased contact resistance due to environmental factors.
Thermal Stability: The joint should withstand thermal expansion and large current surges during operation.
2. Preparatory Work Before Overlap
2.1 Surface Preparation
Oxide Layer Removal: The surface of copper busbars is prone to oxidation. Before overlapping, clean the contact surfaces with sandpaper or a wire brush to expose the metal.
Application of Conductive Paste: Apply conductive paste (e.g., anti-oxidation conductive grease) on the contact surfaces to reduce contact resistance and prevent oxidation.
2.2 Grounding Requirements
Grounding Marking: For grounding copper busbars, yellow-green paint should be applied as a marking, but the contact area must remain exposed.
Grounding Reliability: Grounding overlaps require extremely low resistance, typically achieved with large overlap areas.
3. Structural Requirements for Overlap
3.1 Overlap Length
Overlap length is key to ensuring both electrical and mechanical performance:
Standard Overlap Length: Generally, the overlap length should be 2-3 times the width of the copper bus bar. For example, a 100mm-wide copper bar requires an overlap length of 200-300mm.
High Current Applications: For high-current scenarios, increase the overlap length based on current density and temperature rise requirements.
3.2 Bolt Arrangement
Number of Bolts: The overlap area should have at least 2-4 bolts, depending on the size and current requirements of the electrical busbars.
Bolt Spacing: Bolt spacing should be uniform, typically 2-3 times the bolt diameter.
Tightening Torque: Bolts must be tightened to the specified torque to prevent loosening or damage to the copper busbar. Common torque ranges are 40-70Nm (depending on bolt specifications).
4. Electrical Performance Requirements for Overlap
4.1 Contact Resistance
Contact resistance at the overlap area is critical for electrical performance:
Industry Standard: Contact resistance should be less than 0.1mΩ to ensure good electrical connectivity.
Testing Method: Use a micro-ohmmeter to test contact resistance.
4.2 Temperature Rise Requirements
The temperature rise at the overlap area must be within acceptable limits:
General Requirement: The temperature rise should not exceed 30-65°C above ambient temperature.
High-Temperature Scenarios: For special applications (e.g., high-voltage or new energy systems), use high-temperature-resistant materials, allowing a temperature rise of up to 85°C or higher.
5. Environmental Protection for Overlap
5.1 Corrosion Prevention
Protective measures are essential for the long-term stability of the overlap area:
Protective Coating: Apply anti-oxidation coatings or electroplating (e.g., tin or nickel plating) to the overlap area.
Environmental Requirements: In humid or corrosive environments, add additional sealing protection, such as protective covers or insulated sleeves.
5.2 Insulation Protection
Exposed Areas: Insulate exposed overlap areas with heat-shrink tubing or insulating tape.
High-Voltage Environments: Add insulating barriers to improve safety in high-voltage scenarios.
6. Thermal Expansion and Mechanical Performance Considerations
6.1 Thermal Expansion Compensation
Copper's thermal expansion coefficient is relatively high (~16.5×10^-6/K). Consider thermal expansion effects under high-temperature or large-current conditions:
Gap Reservation: Reserve proper thermal expansion gaps during overlap to prevent loosening or deformation during long-term operation.
Flexible Design: Use expansion joints or flexible copper busbars for long-distance connections to compensate for thermal expansion.
6.2 Mechanical Strength
The overlap area must withstand mechanical vibrations, electromagnetic forces, and environmental stress:
Tensile Strength: Bolts should have sufficient tensile strength to meet load requirements. Use high-strength bolts (e.g., grade 8.8 or higher).
Electromagnetic Force Resistance: Design the overlap area to withstand electromagnetic forces caused by short-circuit currents in high-current scenarios.
7. Overlap Requirements for Different Materials
7.1 Copper-to-Copper Overlap
Copper-to-copper connections have excellent conductivity. The main focus is on surface cleanliness and mechanical strength.
7.2 Copper-to-Aluminum Overlap
Preventing Galvanic Corrosion: Direct contact between copper and aluminum can cause corrosion due to potential differences. Use transition joints (e.g., copper-aluminum composite plates).
Protective Measures: Apply anti-oxidation agents or use tin-plated surfaces to prevent galvanic reactions.
8. Maintenance and Inspection
8.1 Regular Inspection
Check bolt tightness to prevent loosening.
Inspect for signs of corrosion or oxidation on the surface.
8.2 Temperature Monitoring
Use infrared thermometers or temperature sensors to monitor temperature changes at the overlap area and promptly address abnormal heating.
9. Practical Summary
The rules for copper bar overlap involve electrical theory, manufacturing techniques, and physical properties. In applications such as distribution cabinets, high-voltage cabinets, or new energy battery systems, proper overlap design significantly improves system efficiency and reliability. By strictly adhering to the above rules, engineers can ensure excellent performance at overlap areas, providing long-term stability for electrical equipment.